UNIVERSITY OF CINCINNATIsorialga/Rajesh's Thesis .pdf · Rajesh Babu Doppalapudi B.Tech., Civil...

UNIVERSITY OF CINCINNATI DATE: 10/24/2001

I, Rajesh Doppalapudi ,

hereby submit this as part of the requirements for the degree of: Master of Science

in: Environmental Engineering

It is entitled: Electrochemical Reduction of Munitions Wastewater: Bench Scale and Pilot Scale Studies

Approved by: Dr. George Sorial Dr. Dionysios Dionysiou Dr. Makram Suidan

ELECTROCHEMICAL REDUCTION OF MUNITIONS WASTEWATER-

BENCH SCALE AND PILOT SCALE STUDIES

A thesis submitted to the

Division of Research and Advanced Studies

of the University of Cincinnati

in partial fulfillment of the

requirements for the degree of

MASTER OF SCIENCE

in the Department of Civil and Environmental Engineering

of the College of Engineering

2001

by

Rajesh Babu Doppalapudi

B.Tech., Civil Engineering, I.I.T. Bombay, 1998

Committee Chair: Dr. George Sorial

ABSTRACT

The munitions wastewater is observed to be mainly of two kinds: (1) 2,4-dinitrotoluene

(DNT) in the presence of ethanol and (2) a mixture of 2,4,6-trinitrotoluene (TNT) and

hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). This research evaluates the performance of

electrochemical processes in reducing these nitroaromatics. Experiments were conducted by

using simulated wastewater. Initially experiments were conducted on a bench scale batch reactor

to study the effect of various parameters including the applied current, stir rate, and dissolved

oxygen on the reduction of nitroaromatics. Based on the results obtained from the bench scale

experiments, a continuous flow pilot scale reactor was designed and developed. Experiments

simulating batch conditions were first conducted on the pilot scale reactor to study the effect of

current, type of electrolyte, and the ionic strength of the feed solution. Experiments were then

conducted on the reactor to study the reduction of DNT in a continuous flow mode.

Results obtained from the bench scale experiments showed an increase in reduction of

nitroaromatics with an increase in current. But at higher currents (53mA & 65mA) the rates of

reduction stabilized indicating that at such higher currents mass transfer governs the rates of

reduction. The rates of reduction also increased with an increase in stir rate. Batch simulation

experiments conducted on the pilot scale reactor showed that the rates of reduction of DNT

increase with an increase in current or concentration of electrolyte. Again the rates of reduction

at higher currents (150 and 200mA) stabilized, further confirming the effect of mass transfer

limitations at higher currents. Based on the results obtained from the batch simulation

experiments, continuous flow experiments were conducted at three different currents ( 150, 200

and 300mA). 200 mA was observed to be the optimal value of the applied current for the

reduction of DNT. For an applied current of 200mA, 80% reduction of DNT was obtained.

At the end of each experiment end products were analyzed to identify and quantify the

various intermediates formed during the electrochemical reduction of nitroaromatics. End

products determined for all the experiments showed 60-100% molar balance conversion. Most of

the intermediates were observed in the solid phase probably due to the polymerization of

intermediates during the reduction of nitroaromatics.

ACKNOWLEDGMENTS

I would like to thank my advisor, Dr. George Sorial for his constant guidance, support and many

valuable suggestion, without which this research would have been an exercise in futility. I

would also like to thank Dr. Makram Suidan and Dr. Dionysios Dionysiou for serving on my

committee and for their insights and suggestions.

I would also like to thank the members of my research group, Manish Mehta and Dinesh

Palaniswamy for their help, suggestions and friendship. I would also like to thank Roopsingh

Guruswamy and Bharadwaj Karthik for their suggestions.

i

TABLE OF CONTENTS

TABLE OF CONTENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

1. INTRODUCTION AND LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3.1 Biological Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3.2 Chemical Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.3.3 Electrochemical Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2. ELECTROCHEMICAL REDUCTION OF SIMULATED MUNITIONS

WASTEWATER IN A BENCH SCALE BATCH REACTOR . . . . . . . . . . . . . 17

2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.3 Degradation Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.4 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3. ELECTROCHEMICAL REDUCTION OF 2,4-DINITROTOLUENE IN A

ii

CONTINUOUS FLOW PILOT SCALE REACTOR . . . . . . . . . . . . . . . . . . . . . 53

3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

3.3 Degradation pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

3.4 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

3.5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

3.6 A Preliminary Operating Cost Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

3.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

3.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

4. RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1

DNT Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A2

TNT and RDX Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A9

Batch Simulation Experiments for Reduction of DNT . . . . . . . . . . . . . . . . . . A16

Continuous Flow Experiments for Reduction of DNT . . . . . . . . . . . . . . . . . . A29

iii

LIST OF TABLES

2.1 Summary of Experimental Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

2.2 Electrochemical Reduction of DNT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2.3 Electrochemical Reduction of TNT in a Combined Mixture of TNT and RDX. . . . . . . 37

2.4 Electrochemical Reduction of RDX in a Combined Mixture of TNT and RDX. . . . . . . 38

2.5 Mole Balance of DNT in a Open Batch Reactor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2.6 Mole Balance of TNT in a Open Batch Reactor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

2.7 Mole Balance of TNT under Anoxic Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.1 Observed First Rate Constants for the Reduction of DNT. . . . . . . . . . . . . . . . . . . . . . . 78

3.2 Mole Balance of DNT for Batch Simulation Experiments. . . . . . . . . . . . . . . . . . . . . . . .79

3.3 Mole Balance of DNT for Continuous Flow Experiments. . . . . . . . . . . . . . . . . . . . . . . . 80

iv

LIST OF FIGURES

1.1 Reductive Biodegradation Pathway Identified for DNT. . . . . . . . . . . . . . . . . . . . . . . . . 15

1.2 Reductive Biodegradation Pathway Identified for TNT . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.1 Experimental Setup of Batch Reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.2 Reduction of DNT under Various Conditions (C0 = 100 mg/L) . . . . . . . . . . . . . . . . . . . 46

2.3 Reduction of TNT under Various Conditions (C0 = 70 mg/L) . . . . . . . . . . . . . . . . . . . . 47

2.4 Reduction of RDX under Various Conditions (C0 = 10 mg/L) . . . . . . . . . . . . . . . . . . . 48

2.5 Product Distribution in the Aqueous Phase for Reduction of DNT with an

Applied Current of 65 mA and Stir Rate of 2040 rpm under Anoxic Conditions . . . . . .49

2.6 Product Distribution in the Aqueous Phase for Reduction of DNT with an

Applied Current of 45 mA and Stir Rate of 2040 rpm under Anoxic Conditions . . . . . .50

2.7 Proposed Mechanism for Reduction of DNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

2.8 Proposed Mechanism for Reduction of TNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

3.1 Setup of Pilot Scale Electrochemical Reactor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

3.2 Reduction of DNT Using NaCl as Electrolyte in Batch Simulation Experiments. . . . . . 83

3.3 Reduction of DNT Using Na2SO4 as Electrolyte in Batch Simulation Experiments. . . . 84

3.4 Performance of the Reactor with Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 85

3.5 Performance of the Reactor Immediately after Reactor Cleaning. . . . . . . . . . . . . . . . . . .86

3.6 Variation of Concentration of Solids with Time During Reactor Cleaning. . . . . . . . . . ..87

3.7 Variation of Concentration of DNT with Time for 200mA Current as

Determined from Batch Simulation Experiment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

3.8 Proposed Mechanism for Reduction of DNT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

v

4.1 Reduction of DNT with Time for Various Systems of Reactors. . . . . . . . . . . . . . . . . . . 93

1

1. INTRODUCTION AND LITERATURE REVIEW

2

1.1 Introduction

Contamination of water with hazardous and toxic chemicals is one of the major problems

facing the world today. The contamination of soil and water with residues of explosives has been

observed at many large military complexes. The manufacture, processing, and packaging of

explosives at military ammunition sites over several decades have resulted in high concentrations

of explosives in munitions waste. 2,4-Dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) and

hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are observed to be the main components of the

munitions generated wastewater. TNT is the most common contaminant found in both soil and

ground water samples at most of the munitions contaminated sites (Jenkins and Walsh 1993).

2,4-Dinitrotoluene and 2,6-dinitrotoluene are the products of incomplete nitration of toluene

during the synthesis of TNT, and hence find their way to munitions wastewater. RDX enters

waste stream since TNT is often used in binary mixtures with RDX by the US Armed forces.

There are six different isomers of DNT, but only 2,4-DNT and 2,6-DNT are the most

commonly found ones. DNT is mainly used as a plasticizer and burn-rate modifier in single base

propellants for military purposes. Commercially DNT is used as an intermediate in the

manufacture of toluene di-isocyanate, used in the production of polyurethane foams. The

manufacture of polyurethane accounts for 99% of DNT use. DNT enters waste stream mainly

during water-dry, wet screening and solvent recovery processes. DNT is highly toxic to both

humans and animals. DNT is a potent liver carcinogen and based on its carcinogenicity, the

estimated cancer risk from lifetime consumption of the maximum allowable dose of DNT is

0.002 mg/Kg/day (Palmer et al. 1996). The LD50 value in rats for DNT is 268mg/Kg (Sax and

Lewis 1989).

3

TNT is the most widely used explosive. It is used as a military explosive in bombs and in

grenades. It has been widely used for filling shells and airborne demolition bombs (Kline 1990).

In addition to military use, small amounts of TNT is also used for industrial explosive

applications, such as deep well and under water blasting. TNT is prepared by the nitration of

toluene with a mixture of nitric acid and sulphuric acid (Sax and Lewis 1989). TNT enters waste

soil and water ecosystems mainly by military activities like the manufacture, loading and disposal

of explosives and propellants.TNT is reported to be toxic to both humans and animals. TNT can

enter the body via inhalation, ingestion or skin contact. The USEPA set the Drinking Water

Equivalent Level (DWEL), a lifetime exposure at which health effects would not occur, for TNT

at 20 µg/L (EPA 1989).

RDX, Royal Demolition Explosive, is one of the most commonly used military explosive.

Because of its sensitivity to shock detonation, RDX is commonly used in conjunction with other

explosives such as TNT and cyclotols and hence finds its way into waste streams. RDX also

enters wastewater during manufacture and munitions loading processes. RDX is reported to be

slightly toxic to humans but highly toxic to invertebrates and fish. Exposure to RDX has been

reported to cause nausea, irritability, confusion and convulsions in humans (Palmer et al. 1996).

Based on its status as a Class C possible human carcinogen, the USEPA has published a water

quality criterion of 0.3 µg/L for RDX.

1.2 Objectives

The main objectives of this research are to (1) study the electrochemical reduction of

simulated munitions waste water on a bench scale batch reactor (2) design and develop a pilot

scale continuous flow reactor for the reduction of nitroaromatics (3) test the pilot scale reactor

4

using simulated munitions waste water and (4) determine the various intermediates and end

products formed during the reduction of nitroaromatics.

To achieve the above objectives the following tasks were performed

1. Bench scale batch experiments were conducted to study the electrochemical reduction of

munitions waste water. The munitions wastewater was observed to be of two kinds (1)

100 mg/L DNT and 300 mg/L ethanol and (2) 70 mg/L TNT and 10 mg/L RDX.

Experiments were conducted for various currents (23 - 65 mA), two different stir rates

(630 and 2040 rpm) and presence and absence of dissolved oxygen.

2. A pilot scale continuous flow reactor was designed and developed based on the results

obtained from the bench scale experiments.

3. Batch simulation experiments were conducted on the pilot scale reactor to study the effect

of current density, ionic strength of feed solution and type of electrolyte on the reduction

of DNT. All experiments were conducted under anoxic conditions.

4. Continuous flow experiments were conducted on the pilot scale reactor to study the

reduction of DNT based on the results obtained from the batch simulation experiments.

The current was varied between 150 mA and 300 mA to optimize the value of applied

current.

During all the experiments samples were collected and analyzed to determine the various

intermediates and end products formed.

1.3 Literature Review

1.3.1 Biological Pathways

Most of the biodegradation pathways identified to date for the nitroaromatics often

5

require cometabolites (alternate carbon for metabolic energy for cells) for the biological process

to proceed. This implies that the biodegradation of these compounds is due to secondary effects

and not the direct utilization of the compounds for microbial metabolic activity. Reductive

pathways and reduction-oxidation pathways have been identified in biological systems and are

capable of carrying out the transformation of these compounds. Three moles of hydrogen are

required for the reduction of each nitro group to the corresponding amino group in the reductive

pathway.

Parrish (1977) observed that DNT was biotransformed by fungi when supplemental

glucose was provided as the carbon source under aerobic conditions. A biological transformation

pathway for DNT has been described, shown in Figure 1.1, which involves the enzymatic

reduction of both nitro groups to the corresponding amino groups. The biotransformation

intermediates include 4,4'-dinitro-2,2'-azoxytoluene, 2,2'-dinitro-4,4'-azoxytoluene, 4-

hydroxylamino-2-nitrotoluene, 4-acetamido-2-nitrotoluene and 2-acetamido-4-nitrotoluene.

Under aerobic conditions 2,4-diaminotoluene was not detected, while under anaerobic conditions

the reduction of both nitro groups was observed (McCormick et al. 1978). The 4-nitro group was

preferentially reduced in comparison to the 2-nitro group.

Valli et al. (1992) studied the reduction-oxidation process capable of leading to the

mineralization of DNT by the fungus, P. chrysosporium, under nitrogen limiting conditions. One

of the nitro groups is first reduced to form aminonitrotoluene. The mono-amino intermediate is

then oxidized to 4-nitro-1,2-benzoquinone and subsequently reduced to 4-nitro-1,2-

hydroquinone. Further reduction of this intermediate results in the formation of 1,2,4-

trihydroxybenzene, which undergoes ring cleavage leading to mineralization.

6

Vanderloop et al. (1999) studied the effect of an anaerobic/anoxic fluidized-bed granular

activated carbon (GAC) bioreactor in series with an activated sludge rector for the treatment of

DNT. Ethanol was supplied as the primary substrate during methanogenic operation. DNT was

observed to be completely transformed to DAT under anaerobic conditions in the fuidized bed

GAC reactor. The DAT was further mineralized in the activated sludge reactor, with complete

recovery of DAT nitrogen.

Pseudomonas species, under aerobic conditions biotransformed TNT and a variety of

nitroaromatic compounds to the corresponding amines and in some instances acetylated

intermediates (Schackmann and Muller 1991). Studies done by Boopathy et al. (1993) observed

the performance of anaerobic soil consortium to remove TNT in the presence of various electron

acceptors. A significant amount of TNT was observed to be removed in the enrichment culture

that used nitrate as the electron acceptor. They also showed that the main intermediates of TNT

degradation are 2-amino-4,6-dinitrotoluene and its isomer 4-amino-2,6-dinitrotoluene. The

biotransformation of TNT to a diamino-mononitro reduction product was catalyzed by a sulfate

reducing bacterium under anaerobic conditions with and without alternate carbon (Boopathy and

Kulpa 1992).

Parrish (1977) found that certain fungal isolates were capable of the transformation of

TNT at 100 mg/L with supplemental carbon source. A series of reduction products were

identified and no evidence for mineralization was found. The scheme shown in Figure 1.2

represents a sequential set of reduction steps leading to the diamino derivatives (McCormick et

al. 1976). The azoxy compounds shown in the scheme apparently result from a nonenzymatic

oxidation of the reactive 4-hydroxylamino-2,6-dinitrotoluene. The 4-nitro group on TNT is

7

preferentially reduced compared to the 2-nitro group.

RDX and the related N-acetylated derivative, AcRDX, were studied in aqueous systems

and found to be biotransformed by mixed populations of microorganisms under anaerobic

conditions when supplemental carbon was provided (McCormick et al. 1981; Sikka et al. 1980).

Intermediates in this pathway included mono-, di-, and trinitroso- derivatives formed during the

sequential reduction of the nitro groups on the parent compound. Young et al. (1996) observed

biotransformation of RDX in liquid culture by a consortium of bacteria found in horse manure.

Five types of bacteria were found to be predominant in the consortium and the most effective

bacteria at transforming RDX was observed to be Serratia marcescens.

Jackson et al. (1976) reported the anaerobic degradation of RDX in aqueous solutions and

in wastewaters from a nitramine manufacturing facility. RDX was present in the wastewater at

around 12 mg/L. In the follow on studies with wastewater derived from nitramine manufacture,

complete removal of RDX was reported in anaerobic biological treatment systems with

supplemental carbon in the form of hydroxyethyl cellulose.

1.3.2 Chemical Pathways

The adsorption of nitroaromatics on activated carbon (GAC) is most commonly used for

the treatment of munitions wastewater. Ho and Daw (1988) studied GAC adsorption of DNT

under ambient conditions. At least six other compounds other than DNT were detected in high

performance liquid chromatography (HPLC) analyses of solven extracts from the spent activated

carbon. Some of these compounds were observed to be the result of oxidation of DNT. These

products are likely the result of abiotic GAC surface catalyzed reactions with molecular oxygen.

The spent GAC is classified as a K045 hazardous waste and must be further treated (Levsen et al.

8

1993). Options include disposal in a secure hazardous landfill, incineration, or regeneration by

partial oxidation of the GAC. However, while incineration has been demonstrated as an effective

technology, issues such as safety concerns, noise, air emissions, costs etc. motivated research in

alternative technology. The other adsorption technologies include resin adsorption, surfactant

complexing, liquid-liquid extraction, ultrafiltration and reverse osmosis (Rodgers and Bunce

2001). All of these technologies concentrate the nitroaromatic into other media, but do not

modify them into non-hazardous compounds.

Bolton and Cater (1993) researched the effect of advanced oxidation technologies (AOT)

for the treatment of nitroaromatics using oxidizing agents such as hydrogen peroxide or ozone,

with or without the addition of catalysts or photolysis. The hydroxyl radicals generated during

this process initiate ring opening and ultimately mineralize the nitroaromatic to CO2 and H2O. Li

et al. (1998) used Fenton’s reagent, alone or in combination with UV (254nm), for remediating

aqueous waste contaminated with nitroaromatic explosives. UV assistance increased the rate of

oxidation and the extent of mineralization of the contaminants. The reaction rate depended on the

number and position of the nitro groups on the aromatic ring. Schmelling and Gray (1995)

demonstrated that TiO2 photocatalysis using near UV radiation may be highly effective in the

remediation of TNT. Photocatalytic tranformation included both oxidation and reduction.

Trinitrobenzoic acid, trinitrobenzene, and trinitrophenol were observed to be the oxidative

intermediates and 3,5-dinitroaniline was identified as the reduction intermediate.

Hydrothermal technologies, which include wet air oxidation and supercritical water

oxidation, are oxidation technologies that involve mineralization of organics by oxygen or H2O2

at higher temperatures and pressures. Hao et al. (1993) demonstrated the effective use of wet air

9

oxidation (WAO) of TNT at temperatures ranging from 200o to 320o C, and PO2 from 0.13 to

1.31. The WAO removal efficiency was observed to be a function primarily of temperature and ,

to a lesser extent, of PO2. Acetic acid and 1,3-dinitrobenzene were oberved to be accumulating at

lower temperatures.

Aromatic nitro compounds are catalytically hydrogenated to amines in acidic solution.

Rajashekharam et al. (1998) hydrogenated DNT on 5% Pd/Al2O3 catalyst, using a trickle-bed

reactor at 45-55o C, and developed a model to predict hydrogenation rates at different particle

sizes and gas/liquid velocities.

1.3.3 Electrochemical Pathways

Electrochemistry with its unique ability to oxidize or reduce compounds at a well-

controlled electrode potential and by just adding or removing electrons, offers many interesting

possibilities in environmental engineering. Electrochemical treatment is a fairly new technology

in the field of environmental engineering and hence only limited research was done on this

subject. Electrochemistry is increasingly being used for the degradation of hazardous chemicals

and in the production of energy by more environmentally friendly methods. Simonsson (1997)

described the use of electrochemical processes for treatment of wastewater solutions, flue gases

and contaminated water and soil. He observed that treatment of waste using electrochemical

processes can be achieved using either anodic oxidation or cathodic reduction.

Electrochemical processes were reportedly effective in the destruction of aromatic

organochlorine wastes (Bunce et al. 1997). Both, oxidative and reductive approaches were

carried out using either direct electrolysis at the surface of an electrode, or by generating a

reactive intermediate that attacks the substrate in a subsequent step. Though the complete

10

combustion of organochlorines to CO2 was unlikely to be economical, the compound could be

oxidized to an unsaturated aliphatic compound, which could be more easily oxidized than the

starting compound.

Electrochemical processes were studied for the treatment of industrial non-biodegradable

effluents originated from a flavor manufacturing facility (Ribordy et al. 1997). The values of

temperature, pH, electrode characteristics and other parameters affecting the electrochemical

treatment were optimized and the TOC was observed to be reduced by 52% in the wastewater.

The effluents obtained after the electrochemical treatment were observed to be non toxic and

easily biodegradable. Polcaro and Palmas (1997) investigated the effectiveness of

electrochemical oxidation for the removal of chlorophenols from aqueous solutions. The

chlorophenols were effectively removed as well as their reaction intermediates, which are still

toxic.

Hintze and Wagner (1992) reduced nitroaromatic explosives to amines in the cathode

compartment of an electrochemical cell. Rodgers and Bunce (2001b) reduced TNT and related

compounds at modest potentials at a variety of cathodes, with high current efficiencies and

essentially quantitative material balance and suggested subsequent electrochemical oxidation to

polymerize the amines to insoluble byproducts. Aminotoluenes were observed as the

intermediates during the reduction of DNT, with 2,4-diaminotoluene being the major product.

For the reduction of TNT, triaminotoluene was observed to be never more than a minor product

and aminonitrotoluenes consisted of most of the intermediates. About 70% of the aminotoluenes

could be polymerized in the subsequent electrochemical oxidation.

Electrochemical degradation of DNT in a bench scale reactor was studied and a number

11

of parameters including dissolved oxygen, current, voltage and electrode shape and material were

investigated (Jolas et al. 2000). Electrochemical experiments using graphite rod were observed to

be mass transfer limited, whereas degradation studies using titanium mesh wire were not.

Products of degradation were identified as DAT, aminotoluenes and azoxydimers.

12

1.4 References

Bolton, J. R., and Cater, S. R. (1993). "Aquatic and surface photochemistry: Chp. 33."

Homogenous Photodegradation of Pollutants in Contaminated Water: An Introduction, R.

Zepp, Crosby, D., ed., CRC Press, Boca Raton, FL, 467-490.

Boopathy, R., and Kulpa, C. F. (1992). "Trinitrotoluene bacterium desulfovibrio sp. (B strain)

isolated from an anaerobic digester." Curr. Microbiol., 25, 235-241.

Boopathy, R., Wilson, M., and Kulpa, C. F. (1993). "Anaerobic removal of TNT under different

electron accepting conditions: lab study." Water Environment Research, 55, 271-275.

Bunce, N. J., Merica, S. G., and Lipkowski, J. (1997). "Prospects for the use of electrochemical

methods for the destruction of aromatic organochlorine wastes." Chemosphere, 35(11),

2719-2726.

EPA. (1989). "Health advisory on 2,4,6-trinitrotoluene." ISS order no. PB90-273566, U.S.

Environmental Protection Agency, Office of Drinking Water, Washington, D.C.

Hao, O. J., Phull, K. K., Davis, A. P., Chen, J. M., and Maloney, S. W. (1993). "Wet air

oxidation of trinitrotoluene manufacturing red water." Water Environment Research, 65,

213-220.

Hintze, J. L., and Wagner, P. J. (1992). "TNT waste water feasibility study: phase 1 laboratory

study." DAAH01-91-C-0738, Gencorp Aerojet Propulsion Division, US Army Missile

Command, Production Base Modernization Activity.

Ho, P. C., and Daw, C. S. (1988). "Adsorption and desorption of dinitrotoluene on activated

carbon." Environ. Sci. Technol.(22), 919-924.

Jackson, R. A., Green, J. M., and Hash, R. L. (1976). "Nitamine removal study." DAAA09-73-C-

0079, Holston Defense Corporation, Dover.

Jenkins, T. F., and Walsh, M. E. (1993). "Field screening methods for munitions residues in

soils, semiaron technologies for remediating sites contaminated with explosive and

radioactive wastes." EPA/625/K-93/001, Office of Research and Development,

Washington, D.C.

Jolas, J. L., Pehkonen, S. O., and Maloney, S. W. (2000). "Reduction of 2,4-dinitrotoluene with

graphite and titanium mesh cathodes." Water Environment Research, 72(2), 179-188.

13

Kline, C. (1990). Kline guide to the U.S. chemical industry., Kline and Complany, Inc., Fairfield,

NJ.

Levsen, K., Mussmann, E., Berger-Preiss, E., Priess, A., Volmer, D., and Wunsch, G. (1993).

"Analysis of nitroaromatics and nitramines in ammunition waste water and in aqueous

samples from former ammunition plants and other military sites." Acta Hydrochim.

Hydrobiolog., 21, 153-156.

Li, Z. M., Shea, P. J., and Comfort, S. D. (1998). "Nitrotoluene destruction by UV catalyzed

Fenton reagent oxidation." Chemosphere, 36(8), 1849-1865.

McCormick, N. G., Cornell, J. H., and Kaplan, A. M. (1978). "Identification of biotransformation

products from 2,4-dinitrotoluene." App. Environ. Microbiol.(35), 945-948.

McCormick, N. G., Cornell, J. H., and Kaplan, A. M. (1981). "Biodegradation of hexahydro-

1,3,5-trinito-1,3,5-triazine." Appl. Environ. Microbiol., 42, 817-823.

McCormick, N. G., Feeherry, F. E., and Levinson, H. S. (1976). "Microbial transformation of

2,4,6-trinitrotoluene and other nitroaromatic compounds." App. Environ. Microbiol.(31),

949-958.

Palmer, W. G., Small, M. J., Jack, C. D., and James, C. E. (1996). "Toxicology and

environmental hazards." Organic Energetic Comcpounds, P. L. Marinkas, ed., Nova

Science Publishers, Inc., New York, 289-372.

Parrish, F. W. (1977). "Fungal transformation of 2,4-dinitrotoluene and 2,4,6-trinitrotoluene."

App.Environ.Micro.Biol, 47, 1295-98.

Polcaro, A. M., and Palmas, S. (1997). "Electrochemical oxidation of chlorophenols." Ind. Eng.

Chem. Res.(36), 1791-1798.

Rajashekharam, M. V., Jagannathan, R., and Chaudhari, R. V. (1998). "A trickle bed reactor for

the hydrogenation of 2,4-DNT: experimental verification." Chem. Eng. Sci. Res., 36, 592-

595.

Ribordy, P., Pulgarin, C., Kiwi, J., and Peringer, P. (1997). "Electrochemical versus

photochemical pretreatment of industrial wastewaters." Water Sci. Tech., 35(5), 293-302.

Rodgers, J. D., and Bunce, N. J. (2001). "Treatment methods for the remediation of nitroaromatic

explosives." Water Research, 35(9), 2101-2111.

14

Rodgers, J. D., and Bunce, N. J. (2001b). "Electrochemical treatment of 2,4,6-trinitrotoluene and

related compounds." Environ. Sci. Technol., 35(2), 406-410.

Sax, N. I., and Lewis, R. J. (1989). Dangerous Properties of Industrial Materials, Van Nostrand

Reinhold, New York.

Schackmann, A., and Muller, P. (1991). "Reduction of nitroaromatic compounds by different

Pseudomonas species under aerobic conditions." Appl. Microbiol. Biotechnol.(34), 809-

813.

Schmelling, D. C., and Gray, A. K. (1995). "Photocatalytic transformation and mineralization of

2,4,6-trinitrotoluene in titanium dioxide slurries." Water Research, 29(12), 2651-2662.

Sikka, H. C., Banerjee, S., Pack, E. J., and Appleton, H. T. (1980). "Environmental fate of RDX

and TNT." Report DSMD 17-77-C-7026, U.S. Army Medical and Research Development

Command, Fort Detrick.

Simonsson, D. (1997). "Electrochemistry for a cleaner environment." Chemical Society Reviews,

26, 181-189.

Valli, K., Brock, B. J., Joshi, D. K., and Gold, M. H. (1992). "Degradation of 2,4-dinitrotoluene

by the lignin-degrading fungus Phanerochaete Chrysosporium." App. Environ.

Microbiol.(58), 221-228.

Vanderloop, S. L., Suidan, M. T., Moteleb, M. A., and Maloney, S. W. (1999).

"Biotransformation of 2,4-dinitrotoluene under different electron acceptor conditions."

Water Research, 33(5), 1287-1295.

Young, D. M., Kitts, C. L., Unkefer, P. L., and Ogden, K. L. (1996). "Biological breakdown of

RDX in slurry reactors." Biotechnol. Bioeng., 56, 258-267.

15

CH3

NO2

NO2

CH3

NO2

NHOH

CH3

NO2

NH2

CH3

NHOH

NO2

CH3

NH2

NO2

CH3

NH2

NH2

N

NO2 NO2

NO

CH3

N

NO2

CH3

NO2

NO

H3CCH3

CH3

NO

NO2

CH3

NO2

NOCH3

N

NO2 NO2

NO

4-nitroso-2-nitrotoluene 4-amino-2-nitrotoluene

2-nitroso-4-nitrotoluene

4,4'-dinitro-2,2'-azoxytoluene

DAT


DNT

2-amino-4-nitrotoluene

Figure 1.1. Reductive Biodegradation Pathway Identified for DNT

CH3


4-hydroxylamino-2-nitrotoluene

2-hydroxylamino-4-nitrotoluene

16

NO2

NO2O2N

NO2

NHOHO2N NO2

NH2O2N

NH2

NH2O2N

NO2

NH2H2N

NHOH

NO2O2N

NH2

NO2O2N

NO2

NO2N

O

N

CH3

NO2

CH3

NO2

NO2

NO2N

O

N NO2

NO2

CH3CH3

2,4-diamino-6-nitrotolene

CH3

4,2',6,6'-tetranitro-2,4'-azoxytoluene


CH3


NO2

NO2N

O

N NO2

NO2

H3C CH3

4-amino-2,6-dinitrotoluene

CH3



CH3

CH3

CH3

TNT

CH3

4-hydroxyalmino-2,6-dinitrotoluene

2-hydroxylamino-4,6-dinitrotoluene

Figure 1.2. Reductive Biodegradation Pathway Identified for TNT

1 Paper Submitted for Publication in Environmental Engineering Science

17

2. ELECTROCHEMICAL REDUCTION OF SIMULATED MUNITIONS

WASTEWATER IN A BENCH SCALE BATCH REACTOR1

18

2.1 Abstract

2,4,6- trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and hexahydro-1,3,5– trinitro-

1,3,5- triazine (RDX) are major constituents of munitions production wastewater discharged

from explosive manufacturing units and munitions load, assembly and pack operations.

Experiments were carried out to study the electrochemical reduction of DNT and a mixture of

TNT and RDX. The effect of various parameters including current, stir rate and presence and

absence of dissolved oxygen was investigated. Experiments were conducted using glassy carbon

rods as the cathode and platinum wire as the anode. End products were also analyzed for the

experiments to obtain molar balance closure for the conversion of the nitroaromatic to

intermediates. The experimental results showed that the electrochemical reduction of

nitroaromatics follow pseudo first order rate kinetics. The first order rate constants for the

reduction of nitroaromatics were observed to increase with an increase in current or stir rate. The

rate of reduction of the nitroaromatic was observed to be significantly higher under anoxic

conditions than under open batch conditions. A molar balance closure of 60-90% could be

obtained for all the experiments.

Keywords: Electrochemical reduction, trinitrotoluene, dinitrotoluene, RDX, nitro-aromatics,

munitions waste water.

19

2.2 Introduction

Explosives contamination problem has been found at many U.S. Department of Energy

and Department of Defense sites. 2,4,6 – trinitrotoluene (TNT), 2,4 – dinitrotoluene (DNT) and

hexahydro – 1,3,5 – trinitro – triazine (RDX) are major constituents of munitions production

wastewater. The United States Department of Defense (DoD) has identified more than 1000 sites

with explosives contamination of which more than 95% were contaminated with TNT and 87%

exceeded permissible ground water contaminant levels (Walsh et al. 1993). Most of the sites

have been found to contain significant amounts of explosives in soil and water samples generated

by demilitarization operations that were conducted in the 1970s. Wastewater containing TNT

and RDX is still generated from demilitarization, and load, assemble, and pack operations. This

wastewater is currently treated by adsorption onto activated carbon. Although effective, it is an

expensive method and generates a by-product hazardous waste in the spent activated carbon.

As per the OSHA assessment of LD50, both TNT and DNT have been classified as

“slightly toxic” to humans. TNT has been found to be toxic to a number of organisms and

aquatic life (Burrows et al. 1989). TNT has been determined to be mutagenic to humans (Kaplan

and Kaplan 1982). The United States Environmental Protection Agency (U.S. EPA) lists TNT

and DNT as priority pollutants because of their toxicological properties. RDX has been shown to

be acutely and chronically toxic to fish (Burton et al. 1994). The U.S. EPA has set a final acute

value of 5.18 mg/L for RDX.

2.3 Degradation Pathways

Biological Pathways: The biological pathways could be broadly classified into aerobic and

anaerobic degradation. Pseudomonas species have been shown to degrade both DNT and TNT

20

aerobically with supplemented glucose as carbon source (Parrish 1977). Under anaerobic

conditions, the sulfate reducing bacteria Desulfovibrio sp (B Strain) transformed TNT into many

reduction products (Boopathy and Kulpa 1992; Boopathy et al. 1993; Preuss et al. 1993; Preuss

and Rieger 1995). Berchtold et al. (1995) designed a fluidized-bed anaerobic granular activated

carbon reactor, which effectively transformed DNT to 2,4-diaminotoluene (DAT). They also

showed that conversion of DNT is unaffected by influent ethanol concentration, though 200

mg/L of ethanol was determined to be the minimum concentration of ethanol needed to affect the

reduction of DNT to DAT. McCormick et al. (1985a) studied 2,4-DNT under continuous culture

conditions in a nutrient rich medium under aerobic and anaerobic conditions. RDX and related

N-acetylated derivative AcRDX were studied in aqueous systems and found to be bio

transformed by mixed populations of microorganisms under aerobic conditions when

supplemental carbon was provided. Intermediates in this pathway included mono, di and tri

amino compounds formed during the sequential reduction of the nitro groups on the parent

compound (McCormick et al. 1981; McCormick et al. 1985b; McCormick et al. 1985c; Sikka et

al. 1980).

Chemical Pathways: Many commonly used chemical remediation technologies for the removal

of nitroaromatics are separation processes rather than destruction processes, all of which

concentrate the nitroaromatic explosives for further treatment (Rodgers and Bunce 2001).

Incineration and GAC, though used extensively in the degradation of nitro-aromatics, have some

serious environmental concerns. The most promising areas of research are the photochemical

and electro-chemical reduction. TNT strongly absorbs UV radiation between 200 and 280 nm.

Exposure of TNT to sunlight or near UV radiation results in the rapid conversion of TNT into a

21

variety of aromatic photolysis products, including the nitroamines and azoxytoluenes, which are

also formed during bio degradation (Burlinson et al. 1973). Photo catalytic transformation of

TNT was shown to include both oxidative and reductive steps. Trinitrobenzoic acid, trinitro

benzene, and trinitro phenol were observed as oxidative intermediate species and 3,5

dinitroaniline was identified as a stable reduction product (Schmelling et al. 1998).

Electrochemical Pathways: Though bio-degradation and other conventional methods are quiet

efficient in the degradation of nitro-aromatics, they have some distinct disadvantages.

Anaerobic biodegradation is shown to be very effective in the degradation of nitroaromatics. But

it has been observed that the munitions wastewater do not always contain the nitroaromatic,

during which time anaerobic conditions must be maintained in the reactor by the addition of

other organic compounds. This process involves high costs for the maintenance of the reactor.

Hence, electrochemical methods have attracted a great deal of attention in recent years.

Electrochemistry with its unique ability to oxidize or reduce compounds at a well-controlled

electrode potential and by just adding or withdrawing electrons offers many interesting

possibilities in environmental engineering (Simonsson 1997).

Rodgers and Bunce (2001b) reduced TNT and DNT isomers to aminotoluenes with high

current efficiencies at a variety of cathodes. They further suggested subsequent electrochemical

oxidation to polymerize the aminotoluenes to insoluble byproducts. Jolas et al. (2000) conducted

experiments for the electrochemical reduction of DNT with graphite and titanium mesh cathodes

under open and anoxic conditions. Mass transfer limitations were observed to effect the

reduction of DNT with the graphite rod, whereas reduction using titanium mesh cathode showed

almost no effect of mass transfer limitations. 2,4-DAT, 4-amino-2-nitrotoluene and one of the

22

dinitro-azoxytoluene dimers were identified as the intermediates formed during the reduction of

DNT. Lessard and Velin Prikidanovics (1990) carried out the synthesis of DAT by the electro

reduction of DNT in a basic solution of pH 13 . The proposed possible mechanism is the

reduction of the nitro group to the hydroxyl amino group by a combination of electronation-

protonation(EP) and electro catalytic hydrogenation (ECH). This is followed by the reduction of

hydroxyl amino group to the amino group, an ECH mechanism.

The overall conversion of DNT to DAT may occur by an ECH mechanism summarized

by equations 1, 2, 3 and 4, where M is the surface of the electrode, M(H) represents the

chemisorbed hydrogen generated at the surface of the electrode by the reduction of water and

M(DNT) and M(DAT) are the adsorbed starting material and product, respectively.

M + H2O + e- � M(H) + OH- (1)

M + DNT � M(DNT) (2)

M(DNT) + 12M(H) � M(DAT) + 4H2O (3)

M(DAT) � M + DAT (4)

Objectives: The main objectives of this research were to provide information regarding: (1) the

kinetics of electrochemical reduction of simulated propellant wastewater (DNT 100 mg/L and

ethanol 300 mg/L) and pinkwater (TNT 70 mg/L and RDX 10 mg/L) at various currents, and

stir-rates; (2) the impact of the presence and absence of dissolved oxygen on the electrochemical

reduction rates; and (3) the intermediates and end products formed during the electrochemical

reduction of the nitroaromatics.

23

2.4 Materials and Methods

Experimental Setup: The experimental setup of the batch reactor is shown in Figure 1. The

main reactor is a 2.5 liter glass cylinder with an ‘L’ shaped tube attached on one side of the

reactor. The glass cylinder acts as the cathode compartment and the ‘L’ shaped tube is used as

the anode compartment. The cathode and the anode compartments are separated by a nafion

membrane # 117 (Solution Technology/C.G Processing, Rockland, DE) which prevents the

anodic and cathode solutions from mixing and only allows the transfer of ions. Two glassy

carbon rods, 7mm in diameter and 150 mm in length, obtained form SGL Carbon Corporation

(St.Mary’s, PA), were used as the cathode. A six-inch long platinum wire (Fisher scientific,

Pittsburgh, PA) was used as the anode. The glass reactor has a lid, as shown in Figure 1, for

maintaining anoxic conditions in the reactor when necessary. A Honey well UDC 3000

Universal Digital Controller (Honeywell, Philadelphia, PA) was used as a constant source of

current. A Fisher Scientific Thermix Stirrer (Model 120s), along with a two-inch teflon coated

bar, was used to mix the contents in the reactor.

Chemicals: DNT was obtained from Aldrich (Milwaukee, WI) at 97% purity and was used as

such. Sodium phosphate obtained from Fisher Scientific (Pittsburgh, PA) was used as the buffer.

Anhydrous sodium sulfate from Fisher Scientific was used to maintain constant ionic strength in

the anodic and cathode solutions. For quantification of the various intermediates formed during

the reduction of DNT the following compounds were obtained. 2,4-diaminotoluene was obtained

from Aldrich and was used as received. 2-amino-4-nitrotoluene and 4-amino-2-nitrotoluene

were also obtained from Aldrich and were used as received. Previous studies also reported the

formation of nitrosotoluenes and dimers during the reduction of DNT (Jolas et al. 2000). Since

24

these intermediates were not available commercially, they were synthesized in the laboratory

using the synthesis methods reported by Pehkonen (1999).

TNT and RDX were obtained from the U.S. Army and were used as received. For the

quantification of TNT intermediates, the following chemicals were purchased from

AccuStandard Inc. (New Haven, CT):

2,4-diamino-6-nitrotoluene, obtained at a concentration of 0.1 mg/mL in acetonitrile; 2,6-

diamino-4-nitrotoluene, obtained at a concentration of 0.1 mg/mL in acetonitrile; 2,2’,6,6’-

tetranitro-4,4’-azoxytoluene, obtained at a concentration of 0.1 mg/mL in acetonitrile: methanol

(1:1); 4,4’,6,6’-tetranitro-2,2’-azoxytoluene, obtained at a concentration of 0.1 mg/mL in

acetonitrile: methanol (1:1); 4-amino-2,6-dinitrotoluene, obtained at a concentration of 1 mg/mL

in acetonitrile: methanol (1:1); and 2-amino-4,6-dinitrotoluene, obtained at a concentration of 1

mg/mL in acetonitrile: methanol (1:1).

Experimental Procedure: All experiments were conducted at room temperature in a 2.5 liter

pyrex glass reactor (see Figure 1). Munitions wastewater was of two kinds (1) 100 mg/L of DNT

in the presence of 300 mg/L of ethanol and (2) a mixture of 70 mg/L of TNT and 10 mg/L of

RDX. To simulate the munitions wastewater in the laboratory required amounts of DNT/ethanol

or TNT /RDX were allowed to mix in 2 liters of water in the glass reactor for a period of two

days to ensure complete solubility. On the day of the experiment, required amounts of Na2SO4

(36 g/L) and sodium phosphate buffer (0.02 M) were added to the solution and allowed to mix

for one hour. For anoxic experiments, the sodium phosphate and sodium sulfate were first

added to 2 liters of deionized (DI) water. The solution was then purged with nitrogen gas untill

the dissolved oxygen (DO) level dropped to 1.4 mg/L. DNT/ethanol or TNT/RDX were then

25

added to the solution and the reactor sealed with a lid and kept under a blanket of nitrogen. The

solution was then allowed to mix for a period of two days. Experiments were carried out at five

different current settings of 23, 34, 45, 53 and 65 mA. The Honeywell UDC is capable of

providing a constant current input to the electrodes. Two different speed settings on the stirrer

were used for a given applied current. Stir rates of 630 rpm and 2040 rpm were used. Six to

eight samples were taken at regular time intervals for each experimental run. The pH of the

solution was also regularly monitored using an Oakton WD-35615-Series pH/mV/temperature

meter with a pH probe and maintained at a pH of 8 ± 0.2. A summary of the reactor conditions

is shown in Table 1. Experiments with high currents (53 and 65 mA) were run for 6 hours and

experiments with low currents (23, 34, and 45 mA) were allowed to run for 12 hours.

Analytical Procedure: The degradation of DNT was monitored by extracting 2.5mL of the

reaction mixture from the cathode compartment with 0.5 mL of dichloromethane, followed by a

rigorous shaking for 90 seconds. The dichloromethane contained 2.56 x 10-4 M quinoline as an

internal gas chromatography standard. The samples were analyzed by an Agilent 6890 plus

series gas chromatography equipment (GC), (Agilent Technologies, Wilmington, DE) with a

flame ionization detector, a 30m x 0.32mm inside diameter fused silica capillary column with a

0.25 �m film thickness( HP-5, Agilent Technologies, Wilmington, DE), and a carrier gas of

nitrogen (550kPa (80psi)). The flow rate of the carrier gas was maintained at 6.0 mL/min. The

injector and the detector were maintained at 250oC. The GC oven temperature was maintained at

110 oC for the first 1.5 minutes and then ramped to 300 oC at a rate of 17 oC/min and kept at 300

oC for 3 minutes. Quinoline and DNT were observed at retention times of 2.59 and 4.82 minutes,

respectively. The above procedure was also used to quantify the intermediates formed in the

26

aqueous phase. The retention time of DAT was 3.65 min. The retention times of 4-amino-2-

nitrotoluene and 2-amino-4-nitrotoluene were 4.93 and 5.25 minutes, respectively. The other two

isomers 4-nitro-2-nitrosotoluene and 2-nitro-4-nitrosotoluene had retention times of 4.89 and

4.90 minutes, respectively. However, many intermediates were also observed in the solid phase.

To quantify the solids, the solution was filtered and the residue dried in a vacuum desiccator.

The dried solids were then weighed and dissolved in a known volume of dichloromethane. This

solution was then analyzed for intermediates using the GC. The solution was also injected in gas

chromatography-mass spectroscopy (GC/MS) equipment for analysis of the azoxytoluenes

(dimers). The GC/MS used was an Agilent 6890 GC plus series and MS Engine 5973 (Agilent

Technologies, Wilmington, DE) equipped with a selective mass ion detector, a 30m x 0.25mm

inside diameter fused silica capillary column with a 0.25�m film thickness (HP-5ms, Agilent

Technologies, Wilmington, DE), and a carrier gas of helium (50 psi). The flow rate of the carrier

gas was maintained at 2mL/min. The injection temperature was maintained at 250oC. The GC

oven temperature was maintained at 110 oC for the first 1.5 minutes and then ramped to 300 oC at

a rate of 17 oC/min and kept at 300 oC for 3 minutes. The two azoxytoluenes, 2,2'-dinitronitro-

4,4'-azoxytoluene (dimer 1) and 4,4'-dinitro-2,2'-azoxytoluene (dimer 2) had retention times of

12.86 and 13.11 minutes, respectively. Both the azoxytoluenes have been quantified against

specific ions of 316 atomic mass units.

TNT, RDX and their intermediates were analyzed using high pressure liquid

chromatography (HPLC) equipped with diode array detector. The reduction of TNT and RDX

was monitored by taking 4 mL of sample from the reaction mixture and directly injecting in the

HPLC. The HPLC instrument used in the analysis was an Agilent 1100 with a quartenary pump

27

and a UV diode array detector (Agilent Technologies, Wilmington, DE). A 15 cm x 4.6mm ID

SUPELCOSILtm LC-18-DB 5µm column was used for the analysis. The mobile phase solvent

contained 50% HPLC grade water and 50% high purity acetonitrile. The flow rate of the mobile

phase was 0.7 mL/min. All the compounds were quantified and calculated using absorbence at

205nm. TNT and RDX were observed at retention times of 6.526 and 4.059 minutes,

respectively. 2,6-diamino-4-nitrotoluene and 2,4-diamino-6-nitrotoluene were observed at 3.167

and 3.174 minutes, respecively. 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene were

observed at 5.275 and 5.312 minutes, respectively. The two azoxytoluenes, 2,2’,4,4’-tetranitro-

6,6’-azoxytoluene and 4,2’,6,6’-tetranitro-2,4’-azoxytoluene were observed at 30.039 and 30.604

minutes, respectively. The solids formed during the experiment were collected by filtering the

solution at the end of each experiment and drying in a vacuum desiccator. The dried solids were

then weighed and dissolved in known volume of acetonitrile. This solution was then analyzed for

intermediates using the HPLC.

28

2.5 Results and Discussion

The concentrations of the nitro-aromatic compounds obtained at different times for each

experiment were plotted on a semi logarithmic plot of C/Co versus time, where C represents the

concentration at a specific time t and Co represents the initial concentration. Linear regression

analyses were conducted to obtain the pseudo first order rate constants for the experiments

conducted under various currents and stir rates. At the end of each experimental run the solution

was filtered and analyzed for various solids. The various end products observed were then

reported as percentage conversion of the nitroaromatic to the respective compound.

Reduction of DNT: Electrochemical reduction experiments were conducted with the current

varied between 23mA and 65mA and two stir rate settings (630 & 2040rpm). The initial

concentration of DNT was 100 mg/L with 300mg/L ethanol. Figure 2 shows the semi

logarithmic plots for reduction of DNT with time under the various conditions studied. The rate

constants obtained through linear regression analysis for the reduction of DNT under open and

anoxic conditions for the various conditions are shown in Table 2. As can be seen from Table 2

the rate of reduction increases with the initial increase in current, and levels off at higher values

of current. It is speculated that the solids formed during the experiment get accumulated on the

surface of the cathode thus preventing proper transfer of nitroaromatic from the bulk solution to

the surface of the cathode. This clearly shows that at higher current values (e.g.65mA) mass

transfer limitations govern the reduction kinetics. The nitroaromatic at such high currents is not

able to reach the cathode surface at the same rate as the production of electrons is occurring. As

a result the efficiency of the nitroaromatic reduction would decrease and more hydrogen gas

would evolve instead. The mass transfer rate at higher currents thus effectively becomes the

29

overall reduction rate. At lower currents it is the intrinsic chemical reduction rate along with the

mass transfer that is governing the reaction process. A detailed explanation is given below.

At the surface of the anode the oxidation half reaction given by equation 5 takes place.

2H2O � 4H+ + 4e- + O2 (5)

The hydrogen protons formed at the surface of the anode move through the nafion membrane to

the main bulk solution towards the cathode where the reduction half reaction given by equation 6

occurs.

2H+ + 2e-� 2H (6)

There are three distinct steps (phases) that determine the reduction kinetics of a nitroaromatic

molecule. First is the bulk movement of the nitroaromatic in the solution toward the electrode

surface. Because the nitroaromatic solution is well mixed, this can be safely assumed to be

extremely fast. On the other hand, at the cathode surface because of the solid liquid interface

convective mixing does not take place. Hence the protons from the bulk move to the cathode

surface to undergo reaction 2 by diffusing from bulk to the surface. This mechanism (step 2) is

extremely slow and usually is the rate governing step in the mass transfer limited reactions. The

hydrogen radicals formed are extremely reactive and instead of undergoing the reactions given by

equations 7 through 9 that result in the reduction of the nitroaromatic, they readily combine with

each other to form hydrogen gas given by equation 10.

C7H5NO2NO2 + 2H � C7H5NO2NO + H2O (7)

C7H5NO2NO + 2H � C7H5NO2NHOH (8)

C7H5NO2NHOH + 2H � C7H5NO2NH2 + H2O (9)

2H � H2 (10)

30

Thus the nitroaromatic has to move through the diffusion layer formed by the protons and

hydrogen radicals to undergo the reduction reaction. The third step is the intrinsic chemical

reaction between the nitroaromatic compound and the hydrogen radical (equations 7 through 9).

Without any mixing (or stirring), the cathode region would get depleted of protons (because of

conversion of hydrogen radicals by equation 10), and the anode region would get richer in

protons because of the production of protons (equation 5). The stirring causes good mixing and

hence convective diffusion of the nitroaromatic to the cathode surface takes place. The

magnitude of stirring will determine the diffusion layer thickness. Higher stirring results in a

smaller diffusion layer thickness. The smaller the diffusion layer, the faster would be the

movement of the nitroaromatic towards the electrode and the larger would be the reduction rate.

This explains the higher rate constants observed at higher stir rate settings in experiments

performed with nitroaromatics in the current study.

Similar reasoning can be applied to current density. An increase in current causes more

rapid release of electrons (or a more rapid conversion of H+ to H), and steeper concentration

gradient of protons from bulk to the electrode surface. This would in turn lead to a lower proton

concentration in the diffusion layer, which would again yield higher transfer rates of

nitroaromatics and therefore higher reduction rates are observed at higher currents. But at very

high currents (65mA) there is a very rapid formation of hydrogen radicals at the surface of the

electrode and the nitroaromatic cannot diffuse to the surface of the cathode at the same rate as

the production of hydrogen radicals. As a result the efficiency of the nitroaromatic reduction

would decrease and more hydrogen gas would evolve instead.

Reduction of TNT and RDX: Electrochemical reduction experiments were conducted on a

31

mixture of TNT and RDX under both open and anoxic conditions. The initial concentrations of

TNT and RDX were 70 mg/L and 10 mg/L, respectively. The current was varied between 23 mA

and 65 mA. Two stir rate settings were used (630 & 2040 rpm). Figure 3 shows the semi

logarithmic plots for the reduction of TNT with time under the various conditions studied.

Figure 4 shows the semi logarithmic plots for the reduction of RDX with time under the various

conditions studied. The reduction first order rate constants obtained through linear regression

analysis are shown in Table 3 for TNT and in Table 4 for RDX. From Tables 3 and 4 it can be

observed that the rate constants increase with increase in current for low currents (25 & 34 mA),

but at higher currents the rate constant stabilizes. Mass transfer limitations are speculated to be

the reasons for the stabilization of rate constants at higher current values. The same reasoning

stated for DNT is also applicable for the reduction of TNT.

Intermediates and End Products

DNT Experiments: Intermediates and end products were identified for the experiments

conducted. End product studies conducted for three experiments were used to calculate the

molar conversion of DNT to other products. The results obtained are shown in Table 5. An

approximate 90-100% molar balance was achieved for experiments conducted with DNT. An

important finding from this study is that about 70% of the products are present in the solid phase,

which is formed during the experiment. Only DAT (about 20%) is found in the aqueous phase.

Figures 5 and 6 show the variation of intermediates observed in the aqueous phase with time for

two experiments under anoxic conditions. From Figures 5 and 6 it can be observed that initially

the concentration of aminotoluenes is higher than the concentration of DAT and as the

experiment proceeds the concentration of aminotoluenes stabilizes whereas the concentration of

32

DAT is increasing. Figure 7 shows the possible mechanism for the electrochemical reduction

pathway of DNT (Kaplan 1996). From Figure 7 it can be observed that DNT is first reduced to

aminonitrotoluenes which are further reduced to DAT. This explains the stabilization of the

concentration of aminonitrotoluenes and the increase in concentration of DAT after some time.

Figure 7 also shows the possible mechanism for the formation of azoxytoluene dimers which

were not detected in this study.

TNT and RDX Experiments: End product analysis conducted for four experiments (under

open conditions) were used to calculate the molar conversion of TNT to other products. The

results are shown in Table 6. From Table 6 it can be seen that approximately 60-100% molar

balance could be attained for all the experiments. Most of the end products are observed to be in

the solid phase. The products formed during the reduction of TNT were mainly amino

substitutes of nitro groups of TNT and azoxytoluenes. The possible mechanism for the reduction

pathway of TNT is shown in Figure 8 (Kaplan 1996). As shown in Figure 8, azoxytoluene

dimers are formed due to the polymerization of the unstable intermediates (in braces). RDX was

expected to yield mono, di and tri-nitroso substitutes of nitro groups in RDX commonly called

MNX, DNX and TNX, respectively (Kaplan 1996). Since these compounds are not

commercially available and no published methods of synthesis could be obtained, the

intermediates of RDX could not be confirmed or quantified.

End products were also analyzed for the experiments conducted for the reduction of TNT and

RDX under anoxic conditions. Table 7 lists the various intermediates obtained. About 90 mg of

solids were collected at the end of each experiment. A known amount of solids was allowed to

mix in acetonitrile for a day. The solution was then filtered and the filtrate weighed to calculate

33

the amount of solids that were dissolved. It was observed that only about 20% of the solids could

be dissolved. The filtered solution was analyzed on HPLC and only about 20% of the dissolved

solids could be accounted for. Table 7 also lists some unknown peaks that were observed on the

HPLC. These peaks were calibrated using the calibration of the closest calibrated compound

based on retention time. It was observed that more unidentified intermediates were formed in the

aqueous phase under anoxic conditions than in the experiments conducted under open systems.

However the amount of these intermediates were low as seen in Table 7. No closure of molar

balance could be obtained because over 80% of solids formed did not go into solution.

34

2.6 Conclusions

The current study showed that electrochemical processes can successfully be used for the

reduction of nitroaromatics: 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) and

hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Electrochemical reduction of nitroaromatics was

shown to be readily taking place under both open and anoxic conditions. The rates of reduction

were observed to be increasing with an increase in current, but at higher currents (53 & 65 mA)

mass transfer rates govern the rates of reduction under both open and anoxic conditions. The

rates of reduction were also observed to increase with an increase in stir rate. The reduction of

the nitroaromatic under anoxic conditions is observed to be higher than reduction under open

conditions.

End products determined for the reduction of DNT showed about 90 -100% molar

balance conversion. The products formed due to electrochemical reduction of DNT were

primarily 2,4 diaminotoluene (DAT) and the amino substitutes of nitro groups. An approximate

60 -100% molar balance conversion could be attained for the reduction of TNT under open

conditions. The products formed due to electrochemical reduction of TNT were two kinds of

azoxy dimmers and various amino-substitutes of the nitro groups. In general, under both

conditions (open and anoxic) the solids formed amounted to about 50-65% by weight of the TNT

or DNT added to the system.

35

2.7 References

Berchtold, S. R., Vanderloop, S. L., Suidan, M. T., and Maloney, S. W. (1995). "Treatment of

2,4-dinitrotoluene using a two-stage system: fluidized bed anaerobic granular activated

carbon reactors and aerobic activated sludge reactors." Water Environment Research, 67,

1081-1091.

Boopathy, R., and Kulpa, C. F. (1992). "Trinitrotoluene bacterium desulfovibrio sp. (B strain)

isolated from an anaerobic digester." Curr. Microbiol., 25, 235-241.

Boopathy, R., Wilson, M., and Kulpa, C. F. (1993). "Anaerobic removal of TNT under different

electron accepting conditions: lab study." Water Environment Research, 55, 271-275.

Burlinson, N. E., Kaplan, L. A., and Adams, C. E. (1973). "Photochemistry of TNT:

investigation of the pink water problem." Rep. AD-769 670, Naval Ordinance Laboratory,

White Oak, Md.

Burrows, W. D., Paulson, E. T., and Carnahan, R. P. (1989). "Biological treatment composition

of B waste waters. II. Analysis of perfomance of Holston Army Ammunition Plant waste

water treatment facility." Technical report 8806, U.S.Army Biomedical Research and

Development Laboratory, Frewderick.

Burton, D. T., Turley, S. D., and Peter, G. T. (1994). "Toxicity of RDX to the freshwater green

algae." Water Air and Soil Pollution., 76(449-457).



Kaplan, D. L. (1996). "Biotechnology and Bioremediation for Organic Energetic Compounds."

Organic Energetic Compounds, P. L. Marinkas, ed., Nova Science Publishers, Inc.,

Commack, New York.

Kaplan, D. L., and Kaplan, A. M. (1982). "Mutagenecity of 2,4,6-trinitrotoluene surfactant

complexes." Biol. Environ. Contam. Toxicol., 28(33).

Lessard, J., and Velin Prikidanovics, A. (1990). "An efficient electrosynthesis of 2,4- and 2,6-

diaminotoluenes." J. App. Electrochem., 20, 527-529.

McCormick, N. G., Cornell, J. H., and Kaplan, A. M. (1981). "Biodegradation of hexahydro-

1,3,5-trinito-1,3,5-triazine." Appl. Environ. Microbiol., 42, 817-823.

36

McCormick, N. G., Cornell, J. H., and Kaplan, A. M. (1985b). "The fate of hexahydro-1,3,5-

trinitro-1,3,5-triazine (RDX) and related compounds in anaerobic denitrifying continuous

culture systems using simulated waste water." Technical Report 85-008, U.S. Army

Natick Research, Development and Engineering, Natick, MA.

McCormick, N. G., Cornell, J. H., and Kaplan, A. M. (1985c). "The anaerobic biotransformation

of RDX, HMX and their acetylated derivatives." Technical Report 85-007, U.S. Army

Natick Research, Development and Engineering Center, Natick, MA.

McCormick, N. G., Peltonen, T. D., and Kaplan, A. M. (1985a). "Biotransformation of waste

water constituents from ball powder production." Report 85/050, U.S Army Natick

Research,Development and Engineering Center, Natick.



Pehkonen, S. O. (1999). "Electrochemical reduction of nitro-aromatics: 2,4,6-trinitrotoluene

(TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4-dinitrotoluene (DNT)."

Technical Report 99/89, CERL.

Preuss, A., Fimpel, J., and Diekert, G. (1993). "Anaerobic transformation of 2,4,6-trinitrotoluene

(TNT)." Arch. Microbiol., 159, 345-353.

Preuss, A., and Rieger, P. G. (1995). "Anaerobic transformation of 2,4,6-trinitrotoluene (TNT)

and other nitroaromatic compounds." Biodegradation of Nitroaromatic Compounds, J. C.

Spain, ed., Plenum Press, New York, 69-85.





Schmelling, D. C., Gray, A. K., and P.V., K. (1998). "Radiation induced reactions of 2,4,6-

trinitrotoluene in aqueous solutions." Environ. Sci. Technol., 32, 971-974.

Sikka, H. C., Banerjee, S., Pack, E. J., and Appleton, H. T. (1980). "Environmental fate of RDX

and TNT." Report DSMD 17-77-C-7026, U.S. Army Medical and Research Development

Command, Fort Detrick.

37

Simonsson, D. (1997). "Electrochemistry for a cleaner environment." Chemical Society Reviews,

26, 181-189.

Walsh, M. E., Jenkins, T. F., Schnitker, P. S., Elwell, J. W., and Stutz, M. H. (1993). “USA Cold

Regions Research and Engineering Laboratory CRREL Special Report 93-5". Hanover,

N.H., pp. 1-17.

38

Table 2.1- Summary of Experimental Conditions

Parameters Values

Reactor Volume 2000 mL

Salt Concentration 36 g/L

Initial Nitroaromatic Concentration 10-100 mg/L

pH 8.0 ± 0.2

Applied Current 23 mA - 65 mA

Stir rate 630, 2040 rpm

Electrodes Glassy Carbon (Sigradur G)

Surface Area 67.5 sq.cm (Glassy Carbon)

Porosity 0%

Dissolved Oxygen 0.2 mg/L (anoxic)

8.4 mg/L (Open system)

39

Table 2.2- Electrochemical Reduction of DNT

NitroaromaticExperimental

condition

Current

(in mA)

Stirrate

(in rpm)

Rate

Constant(min-1)

R2

Coefficient of

Correlation

DNT Open system 65 2040 0.0057 0.9914

DNT Open system 53 2040 0.0063 0.9932

DNT Open system 45 2040 0.0058 0.9786

DNT Open system 34 2040 0.0056 0.9823

DNT Open system 23 2040 0.0028 0.9696

DNT Open system 65 630 0.0062 0.9986

DNT Open system 53 630 0.0061 0.9957

DNT Open system 45 630 0.0060 0.9965

DNT Open system 34 630 0.0057 0.994

DNT Open system 23 630 0.0026 0.9797

DNT Anoxic 65 2040 0.0072 0.9993

DNT Anoxic 45 2040 0.0074 0.9958

DNT Anoxic 25 2040 0.0043 0.9931

40

Table 2.3 - Electrochemical Reduction of TNT in a Combined Mixture of TNT and RDX


Condition

Current

(in mA)

Stirrate

(in rpm)

Rate Constant

(min-1)

R2

Coefficient of

Correlation

TNT Open system 65 2040 0.0061 0.9942

TNT Open system 53 2040 0.0075 0.99575

TNT Open system 45 2040 0.0067 0.9995

TNT Open system 34 2040 0.0058 0.9972

TNT Open system 23 2040 0.0018 0.9833

TNT Open system 65 630 0.0059 0.9975

TNT Open system 53 630 0.0061 0.9985

TNT Open system 45 630 0.0054 0.9948

TNT Open system 34 630 0.0053 0.9925

TNT Open system 23 630 0.0017 0.9858

TNT Anoxic 65 2040 0.012 0.9942

TNT Anoxic 45 2040 0.011 0.9978

TNT Anoxic 25 2040 0.0096 0.9958

41

Table 2.4 - Electrochemical reduction of RDX in a Combined Mixture of TNT and RDX.


ConditionCurrent(in mA)

Stir rate(in rpm)

rate constant(min-1)

R2

Coefficient ofCorrelation

RDX Open 65 2040 0.0059 0.9977

RDX Open 53 2040 0.0064 0.9892

RDX Open 45 2040 0.0053 0.9882

RDX Open 34 2040 0.0048 0.9912

RDX Open 23 2040 0.0014 0.988

RDX Open 65 630 0.0042 0.9912

RDX Open 53 630 0.0049 0.9878

RDX Open 45 630 0.0044 0.995

RDX Open 34 630 0.0034 0.9828

RDX Open 23 630 0.0014 0.9858

RDX Anoxic 65 2040 0.0102 0.9921

RDX Anoxic 45 2040 0.0085 0.9646

RDX Anoxic 25 2040 0.0035 0.969

42

Table 2.5 - Mole Balance of DNT in a Open Batch Reactor

Current

(mA)

Stir- rate

(rpm)Compounds

Solid Phase (% molar

conversion of DNT)

Aqueous phase (% molar

conversion of DNT)

65 2040

4-nitro, 2-

nitrosotoluene

2-nitro, 4-

aminotoluene

4-nitro,2-

aminotoluene

DAT

35.8

34.0

2.6

---

---

---

---

21.2

53 2040

4-nitro, 2-

nitrosotoluene

2-nitro, 4-

aminotoluene

4-nitro, 2-

aminotoluene

2-nitro, 4-

nitrosotoluene

DAT

14.9

72.7

3.12

0.1

---

---

---

---

---

21.2

25 630

4-nitro, 2-nitroso

toluene

2-nitro, 4-

aminotoluene

DAT

52.8

48.0

---

---

---

20.7

43

Table 2.6. Mole Balance of TNT in a Open Batch Reactor

Current

(mA)

Stir-rate

(rpm)Compounds

% molar

conversion of TNT

to the compound

(solid phase)

% molar

conversion of TNT

to the compound

(Aqueous phase)

45 2040

2-Amino-4,6-

dinitrotoluene

Dimer 1

Dimer 2

TNT

2.5

35.4

19.1

---

---

---

---

5.2

45 630

Dimer 1

Dimer 2

TNT

30.1

29.3

---

---

---

6.7

34 630

2-Amino-4,6-

dinitrotoluene

Dimer 1

Dimer 2

TNT

3.7

77.7

17.0

---

---

---

---

4.2

25 630

2-Amino-4,6-

dinitrotoluene

4-Amino-2,6-

dinitrotoluene

Dimer 1

Dimer 2

TNT

7.4

---

20.9

37.4

---

---

2.3

---

---

26.2

Dimer 1: 2,2’,4,4’-tetranitro-6,6’-azoxytoluene

Dimer 2: 4,2’,6,6’-tetranitro-2,4’-azoxytoluene

44

Table 2.7. Mole Balance of TNT under Anoxic Conditions

Current(mA)

Stir-rate

(rpm)Compounds

Conc ofcompoundin liquid

phase(mg/L)

Conc ofcompound

in solidphase

(mg/L)

% molarconversionof TNT tocompound

(solidphase)

% molarconversion of

TNT to thecompound

(Aqueousphase)

65 2040

2,6-Diamino-4-nitrotoluene


4-Amino-2,6-nitrotoluene

Peak1(RT:2.88)Peak2(RT:2.37)Peak3(RT:2.65)Peak4(RT:2.79)Peak5(RT:26.3)

1.6

1.7

---4.24.41.33.4---

---

---

2.6------------3.4

4.0

4.4

------------------

---

---

5.6---------------

45 2040




Peak1(RT:2.23)Peak2(RT:2.61)Peak5(RT:26.5)

4.9

9.1

---13.36.7---

---

---

2.9------

14.0

10.7

19.6

------------

---

---

5.4---------

25 2040




Dimer1Dimer2

Peak1(RT:2.23)Peak2(RT:2.62)Peak3(RT:2.73)Peak4(RT:4.33)Peak5(RT:26.5)

6.2

2.3

---------6.74.86.51.3---

---

---

0.22.32.8------------2.0

13.8

5.8

------------------------

---

---

0.44.04.9---------------

45

Figure 2.1 Experimental Setup of Batch Reactor.

Power Supply

+ -Glass reactor

Cathode

Stir bar

Nafion membrane

Anode

Lid

46

Figure 2.2. Reduction of DNT under Various Conditions (C0 = 100 mg/L).

Time, min

0 200 400 600

ln (C

/C0)

-5

-4

-3

-2

-1

0

45mA, 2040rpm, open34mA, 2040rpm, open23mA, 2040rpm, open65mA, 2040rpm, open53mA, 2040rpm, open65mA, 630rpm, open45mA, 630rpm, open34mA, 630rpm, open23mA, 630rpm, open65mA, 2040rpm, anoxic45mA, 2040rpm, anoxic25mA, 2040rpm, anoxic53mA, 630rpm, openRegression lines

47

Figure 2.3. Reduction of TNT under Various Conditions (C0 = 70 mg/L)Time, min

0 200 400 600

ln (C

/C0)

-3

-2

-1

0

65mA, 2040rpm, open53mA, 2040rpm, open45mA, 2040rpm, open34mA, 2040rpm, open23mA, 2040rpm, open65mA, 630rpm, open53mA, 630rpm, open45mA, 630rpm, open34mA, 630rpm, open23mA, 630rpm, open65mA, 2040rpm, anoxic45mA, 630rpm, anoxic25mA, 2040rpm, anoxicRegression lines

48

Figure 2.4. Reduction of RDX under Various Conditions (C0 = 10 mg/L)Time, min

0 200 400 600

ln (C

/C0)

-3

-2

-1

0

Regression lines

65mA, 2040rpm, open53mA, 2040rpm, open25mA, 2040rpm, open34mA, 2040rpm, open23mA, 2040rpm, open65mA, 630rpm, open53mA, 630rpm, open45mA, 630rpm, open34mA, 630rpm, open23mA, 630rpm, open65mA, 2040rpm, anoxic45mA, 2040rpm, anoxic25mA, 2040rpm, anoxic

49

Figure 2.5. Product Distribution in the Aqueous Phase for Reduction of DNT with an Applied Current of 65 mA and Stir Rate of 2040 rpm under Anoxic Conditions

Time, min

0 100 200 300 400

Con

cent

ratio

n, m

M

0

100

200

300

400

500DNTDAT4-Amino-2-nitrotoluene2-Amino-4-nitrotoluene

50

Time, min

0 100 200 300 400 500

Con

cent

ratio

n, m

M

0

100

200

300

400

500

600

DNTDAT4-Amino-2-nitrotoluene2-Amino-4-nitrotoluene

Figure 2.6. Product Distribution in the Aqueous Phase for Reduction of DNT with an Applied Current of 45 mA and Stir Rate of 2040 rpm under Anoxic Conditions

51

CH3

NO2

NO2

CH3

NO2

NHOH

CH3

NO2

NH2

CH3

NHOH

NO2

CH3

NH2

NO2

CH3

NH2

NH2

N

NO2 NO2

NO

CH3

N

NO2

CH3

NO2

NO

H3C CH3

CH3

NO

NO2

CH3

NO2

NO

Figure 2.7. Proposed Mechanism for the Reduction of DNT

DNT

4-nitroso-2-nitrotoluene 4-amino-2-nitrotoluen

2-amino-4-nitrotoluene2-nitroso-4-nitrotoluene

DAT4,4'-dinitro-2,2'-azoxytoluene 2,2'-dinitro-4,4'-azoxytoluene

52

NO2

NO2O2N

NO2

NHOHO2N

NO2

NH2O2N

NH2

NH2O2N

NO2

NH2H2N

NHOH

NO2O2N

NH2

NO2O2N

NO2

NO2N

O

N

CH3

NO2

CH3

NO2


2,4-diamino-6-nitrotole

TNT

CH3

CH3

NO2

NO2N

O

N NO2

NO2

CH3CH3

Figure 2.8. Proposed Mechanism for the Reduction of TNT




CH3


CH3CH3

CH3CH3

1 Paper Submitted for Publication in ASCE Journal of Environmental Engineering

53

3. ELECTROCHEMICAL REDUCTION OF 2,4-DINITROTOLUENE IN

A CONTINUOUS FLOW PILOT SCALE REACTOR1

54

3.1 Abstract

An electrochemical pilot scale reactor was used to treat 2,4-dinitrotoluene (DNT).

Experiments were conducted by using a glassy carbon (zero perosity) coated graphite cylinder as

the cathode and a platinum wire as the anode. All experiments were conducted under anoxic

conditions. Initially, experiments simulating batch conditions were conducted to obtain the

optimum operating conditions for the reactor. During this batch-mode study, the effect of various

parameters such as applied current, electrolyte concentration, and type of electrolyte on the

reduction of DNT were evaluated. Results obtained showed that the rates of reduction of DNT

increased with an increase in current or concentration of electrolyte. Based on the results

obtained from the batch simulation experiments, continuous flow experiments were conducted at

three different currents. The ionic strength of the feed solution was maintained at 0.027 M. A

current density of 200mA was found to provide a stable reduction of DNT at the 80 % level for a

period of 14 days after which reactor cleaning is necessary for removal of solids that were formed

within the reactor. End products determined for the experiments showed 80-100% molar balance

conversion.

Keywords: Electrochemical reduction, dinitrotoluene, DNT, nitro-aromatics, munitions waste

water, continuous flow reactor.

55

3.2 Introduction

Environmental contamination of 2,4-dinitrotoluene (DNT) mainly occurs due to the

release of DNT into air, water and soil from munitions manufacturing and processing plants. For

military purposes, DNT is primarily used as a plasticizer and burn rate modifier in single base

propellants. Commercially, DNT is used in the manufacture of toluene diisocyanate, which is

then used in the production of polyurethane foams. DNT is prepared by the nitration of toluene

and nitrotoluene in the presence of nitric and sulfuric acid. In military applications, it enters

waste streams mainly during propellant production. DNT is highly toxic to both humans and

animals. The 50% lethal dose (LD50) value for rates for DNT is 268 mg/kg (Sax and Lewis

1989). It is rapidly absorbed in the lungs and through the skin and is considered a probable

human carcinogen by the USEPA (Palmer et al. 1996). Based on carcinogenicity, the estimated

excess cancer risk from lifetime consumption of the maximum allowable dose of DNT is 2 ×10-3

mg/kg/day. The waters containing DNT have been classified as a RCRA regulated waste

3.3 Degradation pathways

Biological Pathways: The biological degradation of DNT can be divided into two main

categories – aerobic and anaerobic degradations. Pseudomonas species is shown to degrade

DNT aerobically with supplemental glucose as the carbon source (Parrish 1977). Bradley et al.

(1997) carried out a lab study of DNT using aerobic microorganisms. It was noted that 22% of

the substrate was reduced to 4-amino-2-nitrotoluene (4A2NT), 6% was reduced to 2-amino-4-

nitrotoluene (2A4NT), 28% was mineralized and 20% remained unchanged. DNT was shown to

be completely transformed to 2,4-diaminotoluene (DAT) using a mixed culture, obtained from

municipal activated sludge, under anaerobic conditions (Berchtold et al. 1995). Vanderloop et al.

56

(1999) used an anaerobic/anoxic fluidized bed granular activated carbon bioreactor in series with

an activated sludge reactor to treat DNT. Influent DNT was completely transformed to DAT in

the anaerobic stage and the DAT was subsequently mineralized in the activated sludge reactor,

with complete recovery of DAT nitrogen. DNT was also shown to be completely mineralized by

an oxidative pathway with a Pseudomonas species using DNT as the sole carbon source

(Spanggord et al. 1991).

Chemical Pathways: DNT wastewater is typically treated by activated carbon adsorption

followed by incineration of the spent carbon (Ho 1986). The other chemical techniques for the

removal of DNT include resin adsorption, surfactant complexing, liquid-liquid extraction,

ultrafiltration and reverse osmosis (Rodgers and Bunce 2001). These technologies are non-

destructive and expensive, and further the spent GAC is classified as a K045 hazardous waste

and must be further treated (Levsen et al. 1993). Also the incineration of the spent carbon poses

air quality concerns due to NOx emissions (Sax and Lewis 1989). Cheng et al. (1996) observed

that DNT was abiotically reduced to 4A2NT and 2A4NT in the presence of high concentration of

sulfide. The other major technique, widely reported in literature, is the catalytic hydrogenation of

DNT over a Pd/C catalyst. Palladium-catalyzed hydrogenation has been found to completely

reduce DNT to DAT (Janssen et al. 1996). The intermediates were observed to be

hydroxylamino-2-nitrotoluene, 4A2NT and 2A4NT.

Electrochemical Pathways: Most of the present day technologies used in the degradation of

nitroaromatics are either highly inefficient or fail to work in an actual treatment plant. Many

commonly used chemical pathways are only separation processes, which concentrate the

nitroaromatic explosives for further treatment. Incineration is the most commonly used

57

secondary treatment, which has many drawbacks such as safety concerns, noise, air emissions,

costs, regulatory requirements etc. Anaerobic fluidized bed granular activated carbon bioreactor

has been shown to be very effective in the degradation of DNT waste water at the pilot scale

(Vanderloop et al. 1999). But it has been observed that the munitions wastewater do not always

contain the nitroaromatic, during which time anaerobic conditions must be maintained in the

bioreactor by the addition of other organic compounds. This process involves high costs for the

maintenance of the reactor, which has motivated research in alternative technologies. One such

technology is electrochemistry.

Willberg et al. (1996) explored the oxidation of nitroaromatics in an electrohydraulic

discharge reactor. They also observed that the addition of ozone to the electrohydraulic

discharge reactor dramatically increased the degradation rate and caused greater than 99%

degradation. This enhancement was attributed to the reaction of nitroaromatic with the hydroxyl

radicals produced by the photolysis of ozone since the dark reaction of nitroaromatic with ozone

is very low. Electrochemical methods of dechlorinating chlorinated aromatic compounds were

shown to offer promise because of their high energy efficiency and relative simplicity of the

equipment (Bunce et al. 1997). Electrochemical techniques have also been explored on the

treatment of industrial waste waters. Ribordy et al. (1997) studied the effect of electrochemical

treatment on industrial non-biodegradable effluents from a flavor manufacturing facility. The

optimal values of temperature, pH, electrode characteristics, initial concentration of effluents and

amount of NaCl used were determined.

The nitrogen in the nitro group of the DNT is at a high oxidation state of +3 and can be

easily reduced. Rodgers and Bunce (2001b) reduced DNT isomers to aminotoluenes with high

58

current efficiencies at a variety of cathodes. They further suggested subsequent electrochemical

oxidation to polymerize the aminotoluenes to insoluble byproducts. Jolas et al. (2000) conducted

experiments for the electrochemical reduction of DNT with graphite and titanium mesh cathodes

under open and de-oxygenated conditions. Mass transfer limitations were observed to effect the

reduction of DNT with graphite rod, whereas reduction using titanium mesh cathode showed

almost no effect of mass transfer limitations. DAT, 4A2NT and one of the dinitro-azoxytoluene

dimers were identified as the intermediates formed during the reduction of DNT. Lessard and

Velin Prikidanovics (1990) carried out the synthesis of DAT by the electro reduction of DNT in a

basic solution of pH 13 . The possible mechanism proposed for the reduction of DNT to DAT is

the reduction of the nitro group to the hydroxyl amino group by a combination of electronation-

protonation(EP) and electro catalytic hydrogenation (ECH).

Objectives: The main objectives for this research are (1) to study the influence of various

parameters (applied current, ionic strength, type of electrolyte and effective length) on the

reduction of DNT by conducting batch simulation experiments in a pilot scale reactor (2) to test

the pilot scale reactor for the reduction of DNT in a continuous flow mode and (3) to determine

the various end products formed during the electrochemical reduction of DNT.

59

3.4 Materials and Methods

Experimental Setup: Figure 1 shows the experimental setup for the pilot scale continuous flow

reactor. The pilot scale reactor consists of two concentric cylinders. The outer cylinder, the

cathode compartment of the reactor, is graphite carbon with surface impregnation of vitreous

carbon (glassy carbon of zero porosity). It has an internal diameter of 12cm (4.72”) and a height

of 60cm (23.62”). The carbon cylinder was fabricated by M.G.P., Inc (Robesonia, PA). The

inner cylinder is a Nafion membrane tube N424 (C.G. Processing, Rockland, DE) supported by

teflon flanges. The diameter of the membrane is 8.3185cm (3.275”). A 24-inch platinum wire

(Fisher Scientific, Pittsburgh, PA), spans through the length of the inner cylinder and acts as the

anode. The two feed tanks are made of stainless steel and have a capacity of 75 L. The effluent

and salt tanks are 7 gallon Polyethylene tanks (Fisher Scientific, Pittsburgh, PA). Three pumps,

with a pumping capacity of 6-20 L/day are used in the experimental setup. One pump is used for

pumping the feed solution, one is used as a recirculating pump, and the third pump is used for

pumping the salt solution in the anode compartment. All three pumps are positive displacement

pumps (Barnant company, Barrington, IL), HD-MA type 01-10 with a maximum capacity of 1

L/hour. The maximum number of strokes is 100/min. and has a maximum pressure of 142 psig,

with a suction height of 1.5m. Two 500-mL holding stainless steel tanks are used for pH

adjustment. One is used for adjusting the pH in the recycle stream and the other for the salt

solution stream. These tanks are with secure lids that have two ports. One port is used for the

pH probe and the other port is fitted with a septum for injection of acid for pH adjustment. Two

AP50 pH/ATC combination electrodes with silver/silver chloride reference (Fisher scientific,

Pittsburgh, PA) were used as the pH probes. The feed tanks are of capacity 75 L each and are

60

fabricated of stainless steel. The mixing of feed solution was done by using high power magnetic

stirrers (Thermix Stirrer Models), obtained from Fisher Scientific (Pittsburgh, PA). A Honeywell

UDC 3000 Universal Digital Controller (Honeywell, Philadelphia, PA) was used as a constant

source of current. All piping connections are made of either Teflon or stainless steel.

Chemicals: 2,4-Dinitrotoluene was obtained from Aldrich (Milwaukee, WI) at 97% purity and

was used as received. Sodium phosphate obtained from Fisher Scientific (Pittsburgh, PA) was

used as the buffer. Anhydrous sodium sulfate or sodium chloride (Fisher Scientific, Pittsburgh,

PA) were as used as electrolytes. For quantification of the various intermediates formed during

the reduction of DNT the following compounds were obtained. 2,4-diaminotoluene, 2-amino-4-

nitrotoluene, and 4-amino-2-nitrotoluene were obtained from Aldrich, Milwaukee, WI and were

used as received. Previous studies (Jolas et al. 2000) also reported the formation of

nitrosotoluenes and dimers during the reduction of DNT. Since these intermediates were not

available commercially, they were synthesized in the laboratory using the synthesis methods

reported by Pehkonen (1999).

Experimental Procedure: One of the feed tanks was initially filled with deionized (DI) water

and the required amount of sodium phosphate buffer (0.02M) was then added. The pH was then

adjusted to 8.00 ± 0.2 by adding 1N sulfuric acid and the water was purged with nitrogen for

twelve hours. In order to simulate munitions DNT wastewater which has an average

concentration of 100 mg/L DNT and 300 mg/L ethanol, the required amounts of DNT and

ethanol were then added to the purged water in the tank. The lid of the tank was then securely

tightened and the tank was kept under a head pressure of nitrogen gas and left to mix for at least

2 days. After two days, the solution was then pumped into the reactor using one of the positive

61

displacement pumps at the desired flow rate. For the continuous flow experiments, the feed

solution was allowed to continuously flow through the reactor for about ½ hour and then the

recycle pump was started for recycling part of the effluent into the reactor at a specific recycle

ratio. In the anode compartment section of the reactor, a 0.25M sodium sulfate solution was used

as the electrolyte solution. The salt solution was continuously pumped inside the Nafion

membrane tube in the reactor in a closed loop and was changed when the conductivity of the

solution dropped below 30 mS/cm. The rate of pumping of the electrolyte solution was

maintained constant at 20 L/day.

The batch simulation studies were conducted by pumping the feed solution to the reactor

to a required volume, the feed pump was then turned off, and the recycle pump was then turned

on at full speed to ensure good mixing within the reactor. The anodic solution was allowed to

continuously flow through the anode compartment. Samples were collected at regular time

intervals to monitor the reduction of DNT. At the end of each experiment the effluent solution

was collected from the reactor, filtered, and analyzed for the various intermediates in both the

liquid and solid phases.

Analytical procedure: For continuous flow experiments, the reactor was monitored daily for

feed flow rate, recycle flow, and the flow rate of the salt solution. The pH of the solution,

conductivity of salt solution and dissolved oxygen of influent and effluent streams were

monitored at least three times a day. An Accumet AP63 handheld pH meter (Fisher Scientific,

Pittsburgh, PA) was used to measure the pH. The pH was maintained at 8.0 ± 0.2 by adding the

required amount of 0.1M H2SO4. A Corning model 311 portable conductivity meter (Fisher

Scientific, Pittsburgh, PA) was used to measure the conductivity of the salt solution. Effluent

62

samples were withdrawn from the pilot scale reactor daily to monitor the dissolved oxygen

content and the effluent concentration of DNT. A Hanna HI 9143 portable waterproof dissolved

oxygen meter (Fisher Scientific) was used to measure the dissolved oxygen content. The

degradation of DNT was monitored by extracting 2.5 mL of the reaction mixture from the

cathode compartment with 0.5 mL of dichloromethane, followed by a rigorous shaking for 90

seconds. The dichloromethane contained 2.56 x 10-4 M quinoline as an internal gas

chromatography standard. The samples were analyzed using Agilent 6890 series gas

chromatography equipment (GC) (Agilent Technologies, Wilmington, DE) with a flame

ionization detector, a 30m x 0.32mm inside diameter fused silica capillary column with a 0.25

�m film thickness(HP-5, Agilent Technologies, Wilmington, DE), and a carrier gas of nitrogen

(550kPa (80psi)). The flow rate of the carrier gas was maintained at 6.0 mL/min. The injector

and the detector were maintained at 250oC. The GC oven temperature was maintained at 110 oC

for the first 1.5 minutes and then ramped to 300 oC at a rate of 17 oC/min and kept at 300 oC for 3

minutes. Quinoline and DNT were observed at retention times of 2.59 and 4.82 minutes,

respectively. The above procedure was also used to quantify the intermediates formed in the

aqueous phase. The retention time of DAT was 3.65 min. The retention times of 4A2NT and

2A4NT were 4.93 and 5.25 minutes, respectively. The other two isomers 4-nitro-2-nitrosotoluene

and 2-nitro-4nitrosotoluene had retention times of 4.89 and 4.90 minutes, respectively. However,

many intermediates were also observed in the solid phase. To quantify the solids, the solution

was filtered and the residue dried in a vacuum desiccator. The dried solids were then weighed

and dissolved in known volume of dichloromethane. This solution was then analyzed for

intermediates using the GC. The solution was also injected into a gas chromatography-mass

63

spectroscopy equipment(GC/MS) for analysis of the azoxytoluenes (dimers). The GC/MS used

was an Agilent 6890 GC and MS Engine 5973 (Agilent Technologies, Wilmington, DE)

equipped with a selective mass ion detector, a 30m x 0.25mm inside diameter fused silica

capillary column with a 0.25�m film thickness (HP-5MS, Agilent Technologies, Wilmington,

DE), and a carrier gas of helium (345 KPa (50 psi)). The flow rate of the carrier gas was

maintained at 2mL/min. The injection temperature was maintained at 250oC. The GC oven

temperature was maintained at 110 oC for the first 1.5 minutes and then ramped to 300 oC at a

rate of 17 oC/min and kept at 300 oC for 3 minutes. The two azoxytoluenes, 2,2'-dinitronitro-4,4'-

azoxytoluene (dimer 1) and 4,4'-dinitro-2,2'-azoxytoluene (dimer 2) had retention times of 12.86

and 13.11 minutes, respectively. Both the azoxytoluenes have been quantified against specific

ions of 316 atomic mass units.

64

3.5 Results and Discussion

Batch Simulation Experiments: Experiments simulating batch conditions were conducted to

study the impact of applied current (53mA-200mA), ionic strength of feed (0-0.027M), type of

electrolyte (NaCl and Na2SO4), and the effective length of the reactor (1.9L = ½ full and 3.8L =

completely full). To simulate batch conditions, the feed solution was pumped into the reactor

until it was either full or ½ full depending on the condition of the experimental run and the feed

pump was then turned off. The recycle pump was then turned on at full speed and the

experiment was conducted with a recycle of 160 L/day to ensure mixing. Samples were taken

from the reactor at regular time intervals. At the end of each experimental run the reactor was

emptied and the collected solution filtered and the filtrate and the residue analyzed for

intermediate reduction products. The dissolved oxygen in all the experimental runs was

maintained at 1.2 – 1.4 mg/L.

The concentrations of DNT obtained at different times for the various experiments

conducted were plotted on a semi logarithmic plot of C/C0 versus time, where C represents the

concentration at a specific time t and C0 represents the initial concentration. Figure 2 represents

the data collected when NaCl was used as the electrolyte and Figure 3 represents the data

collected when Na2SO4 was used as the electrolyte. Linear regression analysis were conducted

to obtain the pseudo first order rate constants which are presented in Table 1. The first section in

Table 1 (first 4 rows) shows the impact of ionic strength on the rate constant for a 53 mA current

and NaCl used as the electrolyte. The remaining section shows a comparison between the two

electrolytes (NaCl and Na2SO4) for different currents and two reactor volumes. From Table 1 the

following observations are evident: 1) For a current of 53 mA and NaCl used as the electrolyte,

65

the rate constant increased sharply with ionic strength. 2) For a constant ionic strength of 0.027

M, there was no significant difference between the two electrolytes for the various currents and

reactor volumes studied. 3) For both electrolytes, the rate constants determined for ½ reactor

volume (1.9 L) compared very well to full reactor volume (3.8 L) when the current is doubled. 4)

For 150 and 200 mA currents, the rate constants were practically the same.

Continuous Flow Experiments: Theoretically, if one performs an electron balance in a system,

say for 90% reduction of DNT to DAT over a certain fixed time, the minimum current to be

applied can be determined. For a given time and applied current, the number of electrons

released into the system can be calculated from Faraday’s Law.

(1)N um ber o f m o les o f e lec trons re leasedIt

F=

Where I = current applied in Amperes

t = time for which current is applied in seconds

F = Faraday’s constant �96500 Coulombs/mol

At the surface of the anode the oxidation half reaction given by equation 2 takes place.

2H2O � 4H+ + 4e- + O2 (2)

The hydrogen protons formed at the surface of the anode move through the Nafion membrane to

the main bulk solution towards the cathode where the reduction half reaction represented by

equation 3 occurs.

2H+ + 2e-� 2H (3)

66

The hydrogen radicals formed at the surface of the cathode are used in the reduction of DNT as

shown by equations 4 through 6.

C7H5NO2NO2 + 2H � C7H5NO2NO + H2O (4)

C7H5NO2NO + 2H � C7H5NO2NHOH (5)

C7H5NO2NHOH + 2H � C7H5NO2NH2 + H2O (6)

Hence for complete reduction of one nitro group to amino group 6 hydrogen radicals are

required, thus requiring six electrons (see equation 2). Since there are two nitro groups on DNT,

for reduction of each molecule of DNT to DAT, 12 electrons are required. If one considers a

concentration of DNT of 100mg/L and a volume of the cathode compartment equivalent to 3.8

L, the mass of DNT within the reactor is 380 mg. Therefore, the number of moles of DNT is

2.09 x 10-3 moles. For 90% reduction, the number of moles of DNT reduced is 1.88 x 10-3 moles.

Therefore, the number of moles of electrons required will be 22.54 x 10-3 moles. If a flow-rate of

8.5 L/ day is used, the retention time is 11 hr within a reactor with a cathode compartment

volume of 3.8 L. Using equation (1), the amount of current required for 90% reduction is thus

54.93 mA. But the above calculations are based on the assumption that there is 100% efficiency

of the usage of electrons for the reduction of DNT. In reality the hydrogen radicals released at

the cathode are not only used for the reduction of DNT but also react with each other to form

hydrogen gas.

2H � H2 (6)

Furthermore, it is noticed from the batch simulation experiments that the rate of reduction at a

current of 53 mA was low. The results obtained from the batch simulation experiments have

shown that the rate of reduction of DNT leveled off at higher currents (150 & 200mA).

67

Continuous flow experiments were then conducted on the pilot scale reactor to determine

the reduction of DNT in the reactor. The ionic strength of the feed solution was maintained at

0.027M using Na2SO4 as the electrolyte. The pH of the solution in the reactor was maintained at

8.00 ± 0.2. The DO level of the feed was maintained at 1.3-1.5 mg/L. The flow rate of the feed

was maintained at 8.5 ± 0.5 L/day with a recycle ratio of 20:1.

The feed solution was first pumped into the reactor and allowed to flow in a continuous

mode for 10 minutes for stabilizing the flow in the reactor and the current supply was then turned

on. Samples were first collected every hour for the first three hours and then once everyday for

determining the performance of the reactor with respect to the reduction of DNT.

The first experimental run was started by applying 200mA current across the electrodes.

Samples collected after one day of operation showed 80.9 % reduction of DNT. Figure 4 shows

the performance of the reactor with time. The current was maintained at 200 mA for a period of

13 days and the average reduction of DNT was 80.5 ± 1.93 %. On day 14, the reduction of DNT

dropped to 77.6 %, probably due to the accumulation of solids on the surface of the membrane

and the cathode. At this time, the experiment was stopped. The reactor was emptied and the

sample collected was analyzed for the various intermediates formed in the liquid and solid

phases.

The reactor was then cleaned for removing any solids accumulated on the surface of the cathode

and the membrane. The following steps were followed for reactor cleaning.

• De-ionized water was pumped into the reactor until the reactor was full. The feed pump

was then turned off and the recycle pump turned on at maximum recycle rate for five

68

minutes. The reactor was then emptied and 500mL sample was collected to measure the

amount of solids.

• De-ionized water was then continuously pumped in the reactor and allowed to run

through the reactor at a flow rate of 50 L/day and with the recycle pump at the maximum

recycle rate to remove any solids accumulated on the surface of the membrane and the

cathode. This was done for a time period of 18-20 hours and 500mL samples were

collected at selected time intervals.

On day 15, following reactor cleaning, another experimental run was conducted using a

current of 200mA to determine the reproducibility of the results collected previously. Samples

were taken hourly for the first three hours for determining the time required for the reduction of

DNT to reach the average value. Figure 5 shows the performance of the reactor for the first 26

hours during an experimental run. From the figure it can be seen that the reduction of DNT

increases rapidly with time and the reduction of DNT is 60% after three hours which corresponds

to 75% of the maximum reduction previously attained before reactor cleaning. The sample

collected after 24 hours which corresponds to day 16 in Figure 4, showed a DNT reduction of

79.14%. The experimental run was conducted for a period of 14 days, up to day 29, during which

period the reduction of DNT was 80.1 ± 1 %. This is in good agreement with the results obtained

in the previous experimental run. On day 29, the reduction of DNT was 77.0%. The experiment

was stopped at this time, the reactor was emptied, the sample collected was analyzed for the

various intermediates, and the reactor was cleaned as mentioned previously.

On day 30, an experimental run was started by using a current of 300 mA. Again samples

were collected for the first three hours and the results have shown a reduction of DNT of 62.6 %

69

after 3 hours (see Figure 5). The reduction of DNT on day 31, was 79.8% (see Figure 4). The

experiment was conducted for a period of 13 days up to day 42. During this period the reduction

of DNT was 81.5 ± 1.3 %. The sample collected on day 42 has shown a DNT reduction of only

73.8%. The reason for deterioration of DNT reduction after only 13 days could be due to more

conversion of DNT and hence faster accumulation of solids on the cathode and the membrane.

The experiment was stopped at this time, the reactor emptied, the sample collected was analyzed

for the various intermediates, and the reactor was then cleaned.

Following reactor cleaning, an experimental run was conducted using 150mA current

(day 43 in Figure 4). Again samples were collected for the first three hours and a reduction of

53.9% was achieved within 3 hours (see Figure 5). The experiment was conducted for 14 days

from day 43 to day 57, during which period the reduction of DNT was 75.6 ± 2.2 % (see Figure

4). On day 57, the reduction of DNT was 73.1 % and hence the experiment was stopped, the

reactor emptied, the sample collected was analyzed for the various intermediates, and the reactor

was then cleaned.

From the above experiments it can be seen that there is no significant increase in

efficiency as the current was increased from 200mA to 300mA. But when the current was

reduced to 150mA there was about 5% reduction in efficiency. Hence 200mA can be assumed to

be the current at which optimum DNT reduction could be attained.

On day 58, a final experimental run was conducted at 200mA current to observe whether

the previous results could be reproduced. Samples were collected for the first three hours and it

can be seen that 61.5 % reduction of DNT could be attained within 3 hours (see Figure 5). The

sample collected on day 59 which corresponds to 24 hr from start up has shown a reduction of

70

80.1 % (see Figure 4). The experiment was continued for 14 days, which corresponds from day

58 to day 72 in Figure 4. During this period the reduction of DNT was 80.2 ± 1.2 %, which

compares well with the results obtained for the first two experiments (80.5% & 80.1%). On day

72, the reduction of DNT was 76.7% and hence the experiment was stopped and the reactor was

cleaned.

The samples collected during the cleaning of the reactor after each experimental run were

analyzed for solids concentration for determining the effectiveness of the cleaning mechanism.

Figure 6 shows the plot of concentration of solids with time for reactor cleaning conducted after

two experimental runs. It can be seen that over 80% of the solids are removed within one hour

and by conducting 18 hours of cleaning 95% of the solids are removed.

Continuous Versus Batch Simulation: A plot of the variation of DNT concentration obtained

from the batch simulations experiment for a 200 mA current and ionic strength of 0.0027 M

using sodium sulfate as the electrolyte is shown in Figure 7. In order to compare the reduction of

DNT in the continuous flow experiments to the reduction in the batch simulation experiments the

following calculations were conducted. The continuous flow experiments were conducted for a

flow rate of 8.2 �0.67 L/day in a reactor volume of 3.8 L which gives a retention time of 685

min. Since an average of 80% reduction of DNT was observed, the rate of reduction of DNT in

the continuous flow can be then determined.

Rate of reduction = (C0 – Ceff)/retention time = (100 – 20)/685 = 0.117 mg/L-min

From the batch simulation experiment conducted at the same conditions, the rate of reduction is

determined by the slope of the curve at 80% reduction of DNT or C/C0 = 0.2 (shown by the

71

dotted line in Figure 7). The rate determined is 0.09 mg/L-min which compares very closely with

that obtained from the continuous flow experiment.

Intermediates and End Products: The collected samples at the end of each batch simulation

experiment were analyzed for the various end products in the liquid and solid phases. Table 2

shows the percent molar conversion of DNT to various compounds obtained for six experimental

runs. From Table 2 it can be seen that about 60-80% molar balance closure could be attained.

70-80% of the intermediates are observed to be in the solid phase. 2,2’-dinitro-4,4’-azoxytoluene

(dimer 1) is observed to be the major intermediate in the solid phase, whereas DAT is the only

intermediate observed in the liquid phase. Aminotoluenes formed during the experiment are

observed only in the form of solids. Figure 8 shows the possible mechanism for the formation of

the various end products during the reduction of DNT (Kaplan 1996). From Figure 8 it can be

seen that DNT is first reduced to aminotoluenes which are further reduced to DAT. Figure 8 also

shows the possible mechanism for the formation of azoxytoluene dimers due to the

polymerization of the unstable intermediates (in braces).

At the end of each continuous flow experiment, the liquid volume collected from the

reactor was analyzed for the various intermediates formed during the experiment. Table 3 shows

the various intermediates obtained during these experiments. A molar balance closure could be

attained for all the experiments within 5-10% error. On average 80% of the intermediates are in

the solid phase, consisting only of 2,2’-dinitro-4,4’-azoxytoluene (dimer 1) and 4,4’-dinitro-2,2’-

azoxytoluene (dimer 2). In the liquid phase, DAT is about 15% and the aminotoluenes consist

about 5% of the intermediates.

72

3.6 A Preliminary Operating Cost Analysis

An operating cost analysis for a continuous flow electrochemical reactor was conducted.

The operating cost involves the cost of pumping and the cost of power supply for the reduction of

DNT. Three pumps were used in the reactor. One to pump the feed solution into the reactor, one

to recycle the effluent into the reactor and the third to pump salt solution into the anode

compartment. The feed pump and the salt solution pump were of the same capacity and had a

power consumption of 70W each. The recycle pump was of higher capacity and had a power

consumption of 150W. Thus, the total power consumption for pumping is 290W. Considering a

cost of 0.02 dollars/ kWh (Cincinnati Gas and Electrical Company), the total cost for pumping is

given by

Pumping cost = 0.02 x290x10-3 dollars/hour

= 0.0058 dollars/hour

= 0.14 dollars/day

For 80% reduction of DNT, 200mA current had to applied across the electrodes. The voltage

across the electrodes was 3.18 ± 0.22 V. Hence the total power consumed during this period can

be calculated as

Power consumed = Current x Voltage

= 200 x 10-3 x 3.18

= 0.636 W

Therefore,

Power supply cost = 0.02 x 0.636 x 10-3 dollars/hour

= 1.272 x 10-5 dollars/hour

73

= 3.053 x 10-4 dollars/day

Hence the total cost of operation is 0.14 dollars/day. Since 8.5 L of waste water is treated per

day, the total cost for treating 8.5 L of 100 mg/L of DNT is $0.14, with about 99.8% consumed in

the cost of pumping.

At this rate, the treatment cost for propellent wastewater would be $5/kgal. This

compares quite favorably to other processes such as activated carbon adsorption, which has been

estimated in the $10-100/kgal range for munitions watewater. These costs for munitions

wastewater treatment are derived from Maloney et al. (2001) in which a yearly cost of $36,000

was estimated to treat 7.5 gpm of pink water (contaminated with TNT and RDX) using the

anaerobic fluidized bed (~ $10/kgal), and from IT Corporation (1996) in which activated carbon

adsorption for propllent wastewater containing 100 mg/L of DNT was estimated to cost

$1000/kgal for production rate of 4 M lb propellent/year (Note: the total range for activated

carbon was $85/kgal at 6 M lb/year, to $190/kgal for 1 M lb/year).

74

3.7 Conclusions

Batch simulation experiments were conducted to investigate the effect of applied current,

ionic strength and type of electrolyte on the electrochemical reduction of 2,4-dinitrotoluene

(DNT). The results indicated that the rate of reduction increased sharply with ionic strength of

the feed. The rate of reduction was found to be also dependant on the current applied. It

increased with current density and leveled off at a current of 150 mA. The results also indicated

that no significant differences were noticed between using NaCl or Na2SO4 as an electrolyte.

End product studies conducted for the batch simulation experiments showed a mole balance

closure of 60-90% and most of the intermediates were observed in the solid phase.

Based on the results obtained from batch simulation experiments, continuous flow

experiments were conducted in the pilot scale reactor for three different currents (150, 200 and

300 mA) using Na2SO4 as the electrolyte (I = 0.027 M) . From the results, it was observed that

200 mA can be considered to be the optimum value of the applied current for the reduction of

DNT. On average, 80% reduction of DNT could be attained for an applied current of 200mA.

Stable performance of the reactor could be maintained for a period of 14 days after which reactor

cleaning is deemed necessary for removal of solids adhering to the membrane surface or the

glassy carbon surface. Complete recovery of reactor performance after cleaning was attained.

This behavior is important to envision because during the period when there is no DNT in the

munitions waste water, the reactor can be shut off and the waste water passed directly to the

activated sludge system. End product studies conducted on the continuous flow experiments

showed a complete mole balance closure with an error of 5 - 10 %. On average, 80% of the

intermediates were observed in the solid phase.

75

Previous studies by Vanerloop et al. (1999) showed that complete mineralization of DAT

could be attained in an activated sludge reactor. Based on the findings in the current study, using

a continuous flow electrochemical reactor followed by an activated sludge reactor, a complete

removal of DAT, which was the main constituent in the aqueous phase, could be attained.

A preliminary operating cost analysis was conducted for the electrochemical reactor. The

operating cost for a reactor with a flow rate of 8.5 L/day is $0.14/day. The pumping system

provided the major contribution of the cost which is about 99.8%.

76

3.8 References

Berchtold, S. R., Vanderloop, S. L., Suidan, M. T., and Maloney, S. W. (1995). "Treatment of

2,4-dinitrotoluene using a two-stage system: fluidized bed anaerobic granular activated

carbon reactors and aerobic activated sludge reactors." Water Environment Research, 67,

1081-1091.

Bradley, P. M., Chapelle, F. H., and Landmeyer, J. E. (1997). "Potential for intrinsic

bioremediation of a DNT-contaminated aquifer." Groundwater, 35(1), 12-17.

Bunce, N. J., Merica, S. G., and Lipkowski, J. (1997). "Prospects for the use of electrochemical

methods for the destruction of aromatic organochlorine wastes." Chemosphere, 35(11),

2719-2726.

Cheng, J., Suidan, M. T., and Venosa, A. D. (1996). "Abiotic Reduction of 2,4-Dinotrotoluene in

the presence of sulfide minerals under anoxic conditions." Water Sci. Tech., 34(10), 25-

33.

Ho, P. C. (1986). "Photooxidation of 2,4-Dinitrotoluene in aqueous solution in the presence of

hydrogen peroxide." Environ. Sci. Technol., 20(1), 260-265.

IT Corporation (1996), “Treatment of Propellent Production Wastewaters Containing 2,4-

Dinitrotoluene,” Report Number SFIM-AEC-ETD-CR-95048, U.S. Army Environmental

Center, Aberdeen, MD.

Janssen, H. J., Kruithof, A. J., Steghniuis, G. J., and Westerterp. (1996). "Kinetics of the

Catalyitc Hydrogenation of 2,4-Dinitrotoluene." Ind. Eng. Chem. Res., 29, 754-766.



77

Kaplan, D. L. (1996). "Biotechnology and Bioremediation for Organic Energetic Compounds."

Organic Energetic Compounds, P. L. Marinkas, ed., Nova Science Publishers, Inc.,

Commack, New York.

Lessard, J., and Velin Prikidanovics, A. (1990). "An efficient electrosynthesis of 2,4- and 2,6-

diaminotoluenes." J. App. Electrochem., 20, 527-529.

Levsen, K., Mussmann, E., Berger-Preiss, E., Priess, A., Volmer, D., and Wunsch, G. (1993).

"Analysis of nitroaromatics and nitramines in ammunition waste water and in aqueous

samples from former ammunition plants and other military sites." Acta Hydrochim.

Hydrobiolog., 21, 153-156.

Maloney, S.W., Achison, N.R., Hickey, R.F., and Haine, R.L (2001). “Anaerobic Treatment of

Pinkwater in a Fluidized Bed Reactor Containing GAC,” AIChE Journal (in Press).

Palmer, W. G., Small, M. J., Dacre, J. C., and Eaton, J. C. (1996). "Toxicology and

Environmental Hazards." Organic Energetic Compounds, P. L. Marinkas, ed., Nova

Science Publishers Inc., Commack, New York.



Pehkonen, S. O. (1999). "Electrochemical reduction of nitro-aromatics: 2,4,6-trinitrotoluene

(TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4-dinitrotoluene (DNT)."

Technical Report 99/89, CERL.

Ribordy, P., Pulgarin, C., Kiwi, J., and Peringer, P. (1997). "Electrochemical versus

photochemical pretreatment of industrial wastewaters." Water Sci. Tech., 35(5), 293-302.

78





Sax, N. I., and Lewis, R. J. (1989). Dangerous Properties of Industrial Materials, Van Nostrand

Reinhold, New York.

Spanggord, R. J., Spain, J. C., Nishino, S. F., and Mortelmans, K. E. (1991). "Biodegradation of

2,4-dinitrotoluene by a Pseudomonas sp." Appl. Environ. Microbiol., 57, 5700.



Water Research, 33(5), 1287-1295.

Willberg, D. M., Lang, P. S., Hochemer, R. H., Kratel, A., and Hoffmann, M. R. (1996).

"Degradation of 4-chlorophenol, 3,4-dichloroaniline and 2,4,6-trinitrotoluene in an

electrohydraulic discharge reactor." Environ. Sci. Technol., 30, 2526-2534.

79

Table 3.1. Observed First Rate Constants for the Reduction of DNT

Current (mA)Volume ofReactor (L)

ElectrolyteIonic strengthof feed (M)

Rate constant(min-1)

R2

Coefficient ofCorrelation

53 1.9 NaCl 0 0.00067 0.9874

53 1.9 NaCl 0.009 0.00077 0.9756

53 1.9 NaCl 0.018 0.0018 0.9785

53 1.9 NaCl 0.027 0.0036 0.9726

53 1.9 Na2SO4 0.027 0.0039 0.9782

100 3.8 NaCl 0.027 0.0041 0.9967

100 3.8 Na2SO4 0.027 0.0044 0.9883

100 1.9 NaCl 0.027 0.0054 0.9688

100 1.9 Na2SO4 0.027 0.0052 0.9672

150 3.8 NaCl 0.027 0.0056 0.9653

150 3.8 Na2SO4 0.027 0.0057 0.9645

200 3.8 NaCl 0.027 0.0057 0.9634

200 3.8 Na2SO4 0.027 0.0059 0.9712

80

Table 3.2. Mole Balance of DNT for Batch Simulation Experiments

Current

(mA)

Volume

of

Reactor

(L)

Electrolyte

Ionic

Strength

(M)

Compound

% Molar

Conversion to

DNT (solid

phase)

% Molar

Conversion to

DNT (aqueous

phase)

53 1.9 NaCl 0

DNT

DAT

4A2NT

2A4NT

Dimer 1

--

--

0.4

0.4

9.1

53.7

4.5

--

--

--

53 1.9 NaCl 0.009

DNT

DAT

4A2NT

2A4NT

Dimer 1

--

--

1.1

0.9

12.4

39.9

4.8

--

--

--

100 1.9 NaCl 0.027

DNT

DAT

4A2NT

2A4NT

Dimer 1

--

--

6.3

4.6

40.5

3.1

8.4

--

--

--

100 3.8 NaCl 0.027

DNT

DAT

4A2NT

2A4NT

Dimer 1

--

--

3.3

2.4

24.6

11.1

9.8

--

--

--

100 1.9 Na2SO4 0.027

DNT

DAT

4A2NT

2A4NT

Dimer 1

--

--

4.3

3.8

38.7

2.2

8.8

--

--

--

200 3.8 Na2SO4 0.027

DNT

DAT

4A2NT

2A4NT

Dimer 1

--

--

3.4

3.2

38.0

2.4

7.7

--

--

--

81

Table 3.3. Mole Balance of DNT for Continuous Flow Experiments

Experiment Current Compound% Molar

Conversion ofDNT (solid phase)

% MolarConversion ofDNT (aqueous

phase)

Exp 1 200 mA

DNTDAT

4A2NT2A4NTDimer 1Dimer 2

--------

34.629.5

22.410.62.92.8----

Exp 2 200 mA

DNTDAT


--------

27.234.0

21.47.162.82.7----

Exp 3 150 mA

DNTDAT


--------

36.432.0

26.89.43.23.1----

Exp 5 200 mA

DNTDAT


--------

35.431.1

20.412.53.12.9----

82

feed tank 1

feed tank 2

effluenttank

feed pump

salt tank

anodic solution pump

nafion membraneplatinum wire(anode)

carbon cathode coated with glassy carbon

recycle pump

constant current supply

Figure 3.1. Setup of the Pilot Scale Electrochemical Reactor

holding tank

holding tank

83

Figure 3.2. Reduction of DNT Using NaCl as Electrolyte in Batch Simulation Experiments

Time, min

0 200 400 600

Ln(C

/C0)

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

53 1.9 053 1.9 0.00953 1.9 0.01853 1.9 0.027100 3.8 0.027100 1.9 0.027150 3.8 0.027200 3.8 0.027

Current Volume Ionic strength mA L M

84

Figure 3.3. Reduction of DNT Using Na2SO4 as Electrolyte in Batch Simulation

Experiments

Time, min

0 200 400 600

Ln(C

/C0)

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

53 1.9 0.027100 3.8 0.027100 1.9 0.027150 3.8 0.027200 3.8 0.027

Current Volume Ionic Strength mA L M

85

Figure 3.4. Performance of the Reactor with Time

Time, days

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Efflu

ent C

once

ntra

tion

of D

NT

0

10

20

30

40

50

60

70

80

90

100

DN

T R

educ

tion,

%

0

10

20

30

40

50

60

70

80

90

100

Effluent concentration of DNTDNT Reduction

Current = 200mA Current=200mA Current=300mA Current=150mA Current=200mA

86

Figure 3.5. Performance of the Reactor Immediately after Reactor Cleaning

Time, hrs

0 1 2 3 4 22 23 24 25 26 27

DN

T R

educ

tion,

%

0

10

20

30

40

50

60

70

80

90

100

Current = 200mACurrent = 300mACurrent = 150mACurrent = 200mA (repeat)

87

Figure 3.6. Variation of Concentration of Solids with Time During Reactor Cleaning

Time, min

0 200 400 600 800 1000 1200

C/C

0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Current = 300mACurrent = 150mA

88

Figure 3.7. Variation of Concentration of DNT with Time for 200mA Current as Determined from Batch Simulation Experiment

Time, min

0 200 400 600 800 1000 1200 1400 1600 1800

C/C

0

0.0

0.2

0.4

0.6

0.8

1.0

89

CH3

NO2

NO2

CH3

NO2

NHOH

CH3

NO2

NH2

CH3

NHOH

NO2

CH3

NH2

NO2

CH3

NH2

NH2

N

NO2 NO2

NO

CH3

N

NO2

CH3

NO2

NO

H3C CH3

CH3

NO

NO2

CH3

NO2

NO

Figure 3.8. Proposed Mechanism for the Reduction of DNT

DNT

4-nitroso-2-nitrotoluene 4-amino-2-nitrotoluen

2-amino-4-nitrotoluene2-nitroso-4-nitrotoluene

DAT4,4'-dinitro-2,2'-azoxytoluene 2,2'-dinitro-4,4'-azoxytoluene

90

4. RECOMMENDATIONS

91

In the previous chapters, electrochemistry was shown to be effective in the reduction of

nitroaromatics. Batch experiments were conducted to study the kinetics of reduction and a pilot

scale reactor was developed to study the reduction of nitroaromatics in a continuous flow mode.

This chapter deals with the further work that need to be performed and also some

recommendations to improve the system.

The results obtained from the pilot scale reactor studies showed 80% reduction of DNT.

Experiments for the reduction of DNT were conducted at a very high recycle ratio of 20:1. At

such high recycle ratios the reactor acts as a completely mixed reactor (CSTR) for all practical

purposes. In a CSTR the concentration of the reducing compound in the reactor is same as the

concentration of the compound in the effluent. Hence the concentration of DNT in the reactor

will be about 20mg/L, whereas the concentration of DNT in the feed is 100mg/L. Since the rate

of reduction is directly proportional to concentration of DNT, the rate will be very low when

compared to the rate if the concentration was 100mg/L. In a plug flow reactor, the concentration

of DNT decreases progressively through the system. Hence a plug flow reactor is more efficient

than a CSTR. It is shown that by using a number of CSTRs connected in series, the efficiency of

the system could be increased (Levenspiel 1999). Though the concentration is uniform in each

reactor, there is a change in concentration as fluid moves from reactor to reactor. This stepwise

drop in concentration, shown in Figure 4.1, suggests that the larger the number of units in series,

the closer should the behavior of the system approach plug flow. This will optimize the rate of

reduction and hence high efficiencies could be attained. The above experimental setup could be

tested by first using two reactors in series and further increasing the number of reactors to obtain

the desired efficiency.

Experiments were conducted using simulated munitions waste water. The feed solution

92

contained 1.23g/L of Na2SO4 as the electrolyte to increase the conductivity of the solution. But in

reality there is no electrolyte present in the munitions wastewater. Batch simulation experiments

conducted using feed solution without any electrolyte showed very low reduction of DNT. To get

better reduction using lower salt concentrations in the feed solution the distance between the

nafion membrane and the carbon cathode must be reduced. This can be achieved either by using a

nafion membrane of larger diameter or by decreasing the inner diameter of the cathode.

Experiments may be conducted using the above experimental setup.

The various intermediates and end products formed during the electrochemical reduction

of nitroaromatics were identified and quantified. DAT and dimers are observed to be the main

intermediates formed during the reduction of DNT. DAT is easily biologically degraded in an

activated sludge reactor (Vanderloop et al. 1999). A coupled treatment scheme of

electrochemical reactor followed by an aerobic activated sludge reactor could be studied.

All the experiments were conducted using simulated munitions wastewater. The

wastewater was prepared by adding the required amounts of chemicals to de-ionized water.

Experiments may now be conducted on site using the actual wastewater generated from the

munitions plant. The other organic and inorganic compounds present in the munitions

wastewater could have a significant effect on the reduction of nitroaromatics.

References

Levenspiel, O. (1999). Chemical Reaction Engineer, John Wiley & Sons, Inc., New York.



Water Research, 33(5), 1287-1295.

93

Figure 4.1. Reduction of DNT with Time for Various Systems of Reactors

Time (min)

0 100 200 300 400 500 600 700 800 900 1000

C/C

0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Col 1 vs Col 2 Col 4 vs Col 5 Col 7 vs Col 8

A1

APPENDIX

Experimental Data

A2

DNT Experiments

Experiment 1

C0 = 100 mg/L Current = 65 mA

Stir rate = 2040 rpm Open system

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 7.98 13.6 95.75

60 7.99 12.2 62.76

120 7.95 11.3 41.91

180 7.98 10.9 32.21

240 7.99 10.5 22.19

300 7.98 9.6 17.14

360 8.00 9.2 12.33

Experiment 2

C0 = 100 mg/L Current = 53mA

Stir rate = 2040rpm Open system

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 7.98 9.4 99.6

60 7.99 8.8 75.82

120 8.00 8.2 49.03

180 8.00 7.8 34.86

240 7.97 7.4 23.75

300 7.98 7.2 16.16

360 8.00 7.0 10.88

A3

Experiment 3

C0 = 100mg/L Current = 45mA


Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 8.00 12.5 90.01

96 7.98 10.5 70.54

180 7.96 9.3 29.76

270 7.98 8.8 19.78

360 7.95 8.5 10.65

450 8.01 8.2 4.99

540 8.00 8.1 1.81

Experiment 4

C0 = 100mg/L Current = 34 mA


Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 8.02 8.9 92.53

120 7.94 7.3 66.84

240 9.96 7.6 34.36

360 9.95 7.6 16.43

480 8.00 8.0 6.99

600 8.01 8.0 4.26

690 7.98 8.0 2.29

A4

Experiment 5

C0 = 100 mg/L Current = 25 mA


Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 8.00 6.1 95.53

120 7.96 6.3 69.01

240 8.00 4.4 47.89

360 7.97 4.9 39.64

480 7.99 4.8 26.89

600 7.99 4.6 21.95

720 8.03 5.0 11.50

Experiment 6



Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 7.93 13.3 95.85

60 7.97 11.7 72.29

120 8.00 11.1 48.36

180 7.94 10.3 34.41

240 7.97 9.6 23.83

300 7.98 9.3 16.73

360 8.00 8.9 10.54

A5

Experiment 7



Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 7.94 10.9 94.85

60 7.97 9.7 67.52

120 7.96 9.1 47.25

180 7.98 8.7 33.70

240 7.97 8.2 20.83

300 7.98 8.1 15.28

360 7.95 7.8 11.77

Experiment 8



Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

13 7.97 14.3 90.41

90 7.98 14.1 64.14

180 7.99 14.6 39.70

270 7.97 14.0 22.96

360 7.97 13.6 11.78

450 7.96 8.2 7.01

510 7.99 7.5 5.09

A6

Experiment 9



Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 7.95 7.4 94.32

90 7.99 6.9 68.59

180 7.97 6.4 46.33

270 7.97 6.6 26.35

360 7.97 6.2 15.32

450 7.98 6.2 8.69

540 7.96 6.2 4.98

Experiment 10



Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

10 7.95 5.4 96.59

120 8.00 5.4 69.47

240 7.96 5.0 61.60

360 7.98 4.8 46.91

480 7.99 4.6 33.25

600 7.97 4.5 21.12

720 7.99 4.5 14.90

A7

Experiment 11


Stir rate = 2040 rpm Anoxic system

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.90 19.8 91.52

15 7.94 17.8 84.01

60 7.93 14.3 58.63

120 7.95 13.4 37.32

180 7.90 13.2 25.49

240 7.98 13.0 16.10

300 7.94 13.0 10.22

360 7.95 12.8 7.02

Experiment 12



Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.98 19.8 97.74

15 7.95 15.4 89.92

90 7.98 13.1 54.12

180 7.97 12.2 25.41

270 7.91 11.9 12.49

360 7.92 11.5 6.32

420 7.93 11.4 3.90

460 7.95 11.0 2.95

A8

Experiment 13



Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.96 19.1 96.34

15 7.93 8.3 90.04

120 7.98 7.7 59.97

240 7.98 7.2 31.55

360 7.99 7.0 17.53

420 7.92 6.9 15.49

480 7.98 6.8 11.77

540 7.95 6.7 8.21

A9

TNT and RDX Experiments

Experiment 14

C0 = 70mg/L TNT & 10mg/L RDX Current = 65mA


Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.98 19.8 66.27 10.64

10 7.99 11.0 56.43 9.87

60 7.98 10.5 39.70 7.87

120 7.99 10.0 25.99 5.18

180 7.99 9.5 16.77 3.41

240 7.95 8.7 13.52 2.65

300 8.00 8.3 9.33 1.84

360 8.00 8.2 6.31 1.30

A10

Experiment 15



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.96 19.8 65.52 9.11

10 7.98 10.5 55.84 8.54

60 7.97 9.5 37.20 8.26

120 7.99 9.0 22.15 5.46

184 7.99 8.7 13.87 3.39

240 7.96 7.8 9.36 2.35

300 7.98 7.5 5.91 1.43

360 7.99 7.3 4.08 0.98

Experiment 16



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.98 19.8 64.92 8.21

10 7.99 10.5 56.36 7.94

100 7.97 9.5 28.94 6.52

185 7.95 9.0 16.48 3.82

300 7.96 8.7 7.80 2.05

364 7.98 7.8 4.95 1.34

426 7.99 7.6 3.37 0.91

A11

Experiment 17



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.97 19.8 61.6 8.50

10 7.95 8.9 57.45 8.35

123 7.98 7.5 22.77 7.55

236 7.95 6.9 9.08 4.13

360 7.96 6.3 4.10 1.80

477 7.97 5.9 2.65 0.93

546 7.99 5.6 2.30 0.71

A12

Experiment 18



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.96 19.1 63.71 8.21

10 7.93 8.3 54.32 6.98

120 7.98 7.7 37.97 7.95

240 7.98 7.2 34.42 7.63

360 7.99 7.0 34.31 7.36

487 7.92 6.9 33.14 7.25

600 7.98 6.8 32.4 7.11

720 7.95 6.7 30.6 6.90

Experiment 19



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.96 19.7 59.65 8.30

10 7.98 13.6 53.75 7.85

60 7.99 12.2 38.56 6.71

123 7.95 11.3 25.71 4.99

180 7.97 10.9 18.29 3.65

240 7.99 10.5 13.22 2.80

300 7.98 9.6 9.01 2.41

353 8.00 9.2 7.22 1.97

A13

Experiment 20



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.97 19.7 55.35 9.35

10 7.98 12.4 50.56 9.14

60 7.97 11.5 36.68 8.06

121 7.99 10.8 24.39 6.33

180 7.98 10.2 16.66 3.95

243 7.95 9.5 11.62 2.96

300 7.96 9.2 8.12 2.25

366 7.99 8.9 5.81 1.77

Experiment 21



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.98 19.7 70.02 9.52

10 7.96 10.6 60.54 9.07

90 7.97 9.2 37.58 7.58

165 7.98 8.3 22.23 5.05

255 7.99 7.8 13.48 3.27

347 7.97 7.5 9.35 2.28

425 7.97 7.1 6.14 1.57

474 7.96 6.9 4.69 1.23

A14

Experiment 22



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.96 19.7 68.62 9.07

10 7.97 8.9 45.54 8.53

100 7.96 8.3 30.38 7.49

185 7.93 7.8 16.36 6.30

275 7.98 7.5 9.55 4.30

363 7.99 7.3 6.17 2.78

450 7.97 7.1 3.96 2.25

543 8.00 7.0 2.85 1.48

Experiment 23



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 7.98 19.7 63.40 7.68

10 7.99 11.6 58.63 7.32

120 7.97 10.2 45.18 5.34

240 7.95 9.3 40.74 4.86

360 7.97 8.9 33.1 4.21

488 7.98 8.7 26.0 3.55

600 7.98 8.2 23.34 3.21

720 8.00 7.8 16.61 2.80

A15

Experiment 24



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 8.00 19.3 53.56 9.33

15 7.93 15 51.09 9.23

60 7.93 13.8 33.42 6.94

120 7.88 12.3 15.99 3.73

180 7.89 11.1 8.38 1.89

240 7.90 10.4 3.93 1.03

300 7.95 10.0 1.62 0.53

Experiment 25



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 8.01 19.3 62.65 9.57

15 7.95 11.2 53.48 9.07

90 7.95 9.8 26.38 6.51

180 7.92 9.1 8.87 3.81

240 7.92 8.5 4.87 2.17

300 7.91 8.1 2.63 0.95

330 7.95 7.9 1.58 0.62

A16

Experiment 26



Time

(min)

pH Voltage

(V)

TNT Concentration

(mg/L)

RDX

Concentration

(mg/L)

0 8.00 19.3 61.11 9.95

15 7.94 7.8 56.38 9.26

90 7.93 6.9 30.38 7.13

180 7.90 5.9 13.38 6.23

240 7.95 6.2 7.87 4.95

300 7.98 6.0 3.62 3.63

370 7.95 6.0 1.96 2.53

A17

Batch Simulation Experiments for Reduction of DNT

Experiment 27

C0 = 100mg/L Feed DO = 1.32 mg/L

Electrolyte = NaCl Feed Conductivity = 3.3 mS/cm

Inonic Strength = 0 M Volume = 1.9 L

Current = 53mA

Time

(Min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.98 2.0 91.73

60 7.86 1.9 87.77

180 7.89 2.0 80.26

240 7.93 2.0 76.57

300 7.97 2.1 74.33

450 7.84 2.0 68.83

800 7.89 2.0 63.66

1260 7.86 2.1 55.66

1620 7.84 2.1 51.80

2640 7.93 2.1 39.64

A18

Experiment 28



Inonic Strength = 0.009 M Volume = 1.9 L

Current = 53mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.91 2.1 84.64

20 7.78 2.2 58.96

40 7.81 2.1 56.96

60 7.83 2.0 54.79

120 7.82 2.3 52.29

180 7.85 2.2 48.65

240 7.90 2.2 45.65

300 7.87 2.2 43.33

570 7.91 2.1 38.66

830 7.82 1.9 35.98

1410 7.85 2.0 31.17

1830 7.82 2.2 26.00

2830 8.15 2.1 23.77

A19

Experiment 29




Current = 53mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.93 1.9 84.56

30 7.89 1.9 60.15

40 7.95 2.0 56.43

60 7.89 2.1 54.43

90 7.94 2.0 49.49

120 7.91 2.0 46.72

180 7.92 2.0 40.52

240 7.90 2.1 37.96

300 7.80 2.1 35.69

655 7.81 2.0 20.54

1210 7.82 1.9 10.10

1620 7.84 2.0 7.72

2677 7.84 2.2 4.95

A20

Experiment 30




Current = 53mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.93 1.8 105.83

5 7.90 1.9 101.97

10 7.92 2.0 90.70

15 7.96 2.1 87.54

20 7.94 2.1 83.15

30 7.93 2.1 78.91

60 7.92 2.2 70.70

90 7.95 2.1 58.50

120 7.96 2.1 53.84

180 7.99 2.2 42.53

240 7.90 2.1 37.07

300 7.94 2.2 29.35

510 7.95 2.2 19.59

840 7.93 2.1 8.85

1410 7.91 2.2 6.09

1800 7.93 2.1 2.61

2793 8.02 2.2 1.43

A21

Experiment 31




Current = 100mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.96 2.0 84.56

5 7.91 2.2 74.94

10 7.94 2.2 73.62

20 7.97 2.3 70.77

43 7.99 2.2 65.16

70 7.90 2.3 58.35

90 7.90 2.4 55.74

120 7.97 2.4 49.92

180 7.99 2.4 40.30

245 7.98 2.5 31.28

560 8.00 2.5 9.69

700 7.94 2.5 6.93

1500 7.94 2.4 3.83

A22

Experiment 32




Current = 100mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 8.03 2.4 74.87

5 7.95 2.4 66.67

10 7.96 2.5 60.96

15 7.95 2.5 58.54

20 7.95 2.5 54.44

40 7.97 2.5 48.37

60 8.00 2.6 42.33

93 7.82 2.6 34.99

115 7.85 2.7 31.36

175 7.89 2.7 22.54

237 7.93 2.8 18.43

300 7.96 2.9 14.36

583 7.92 2.9 6.01

730 7.82 2.8 3.98

1806 7.89 2.8 2.63

A23

Experiment 33




Current = 150mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 8.00 2.2 96.55

5 7.97 2.4 83.08

10 7.97 2.5 81.79

20 7.99 2.5 77.17

40 7.98 2.6 68.99

60 8.00 2.4 62.49

120 8.00 2.5 43.27

180 7.88 2.7 30.07

240 7.95 2.8 21.57

300 7.90 2.9 16.46

540 7.93 2.9 7.35

740 7.98 2.8 4.79

1890 8.26 2.9 3.49

A24

Experiment 34




Current = 200mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 8.00 2.6 95.13

5 8.00 2.7 83.66

10 7.97 2.7 76.42

20 7.94 2.8 73.15

40 7.96 2.8 63.51

60 7.99 2.9 59.98

85 8.00 3.0 50.85

155 7.90 3.0 32.33

180 7.90 3.1 28.19

240 7.90 3.1 19.81

320 7.90 3.1 13.50

560 7.90 3.1 6.59

720 7.90 3.1 4.61

1830 8.23 3.2 3.73

A25

Experiment 35


Electrolyte = Na2SO4 Feed Conductivity = 5.3 mS/cm


Current = 53mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 8.10 2.2 103.503

5 8.01 2.2 85.16

10 8.00 2.2 80.61

16 8.00 2.2 78.56

22 8.00 2.2 76.97

40 7.90 2.3 72.20

71 7.96 2.3 61.13

100 7.97 2.3 53.14

120 7.97 2.3 47.75

180 7.99 2.4 34.15

242 7.92 2.4 26.79

302 7.93 2.4 19.23

570 8.00 2.5 8.12

750 7.90 2.5 4.75

1820 7.90 2.5 3.64

1770 7.97 2.5 2.07

3005 7.88 2.5 1.35

A26

Experiment 36




Current = 100mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.98 2.3 101.11

5 7.97 2.2 88.02

10 7.98 2.3 82.57

20 7.98 2.3 83.59

30 7.93 2.3 76.82

54 7.95 2.4 70.08

100 7.91 2.4 65.05

120 7.90 2.4 60.04

195 7.93 2.4 47.58

240 7.88 2.5 44.96

300 7.85 2.5 37.74

540 7.80 2.5 21.79

850 7.87 2.4 12.53

1385 7.93 2.4 10.02

1730 7.89 2.5 9.30

3000 7.99 2.4 7.75

A27

Experiment 37




Current = 100mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.90 2.90 101.84

5 7.91 2.90 71.85

10 7.93 3.10 64.53

15 7.91 3.10 61.28

20 7.94 3.30 57.90

40 7.92 3.50 47.52

60 7.95 3.50 40.61

90 7.94 3.60 31.68

120 7.95 3.60 25.34

180 7.83 3.60 17.78

252 7.80 3.60 15.13

545 7.83 3.60 4.46

710 7.84 3.60 3.71

1500 7.85 3.60 2.50

1595 8.16 3.60 2.32

A28

Experiment 38




Current = 150mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 7.91 2.30 99.54

5 7.96 2.50 73.22

11 8.00 2.50 70.09

17 8.00 2.50 67.96

22 8.00 2.50 62.33

40 8.00 2.60 59.11

60 8.00 2.50 49.45

95 7.83 2.70 34.38

122 7.91 2.70 23.86

187 7.97 2.70 17.37

247 7.93 2.80 14.46

551 7.85 2.80 5.93

795 7.85 2.70 3.76

1440 7.80 2.70 2.14

1690 7.90 2.60 1.69

3000 7.98 2.60 1.49

A29

Experiment 39




Current = 200mA

Time

(min)

pH Voltage

(V)

Concentration

(mg/L)

0 8.02 2.70 99.88

5 7.98 2.70 83.62

10 8.01 2.70 81.43

15 8.01 2.80 77.39

20 8.01 2.90 74.57

40 7.98 2.90 66.39

63 7.90 2.90 56.61

90 7.98 3.00 48.80

120 7.97 3.00 41.42

183 7.90 3.00 28.52

255 7.91 3.00 21.46

315 7.89 2.90 15.14

580 7.80 2.90 6.73

720 7.85 2.80 4.53

1702 8.15 2.80 2.49

A30

Continuous Flow Experiments for Reduction of DNT

Experiment 40

C0 = 100mg/L Ionic Strength = 0.027M

Current = 200mA Electrolyte = Na2SO4

Time

(days)

pH of

Feed

DO of Feed

(mg/L)

Salt Solution

Conductivity

Voltage

(V)

Influent

Concentration

mg/L

Effluent

Concentration

(mg/L)

0 7.91 1.36 31.4 3.2 93.35 ---

1 7.85 1.24 30.3 3.4 95.69 18.242

2 7.83 1.29 30.0 3.5 94.09 17.69

3 7.85 1.23 30.6 3.5 90.09 17.52

4 7.84 1.35 30.1 3.9 90.97 16.07

5 7.89 1.27 30.5 3.8 90.64 16.37

6 7.85 1.32 31.2 3.4 86.56 14.69

7 7.85 1.34 33.4 3.2 87.69 14.90

8 7.87 1.40 33.4 3.2 102.45 16.22

9 7.85 1.38 33.0 3.3 102.07 15.43

10 7.80 1.41 32.8 3.2 104.87 17.42

11 7.84 1.39 32.8 3.2 89.252 17.56

12 7.85 1.44 32.6 3.2 86.27 16.66

13 7.85 1.46 32.6 3.3 87.19 17.43

14 7.85 1.43 32.5 3.3 90.92 20.41

A31

Experiment 41



Time

(days)

pH of

Feed

DO of Feed

(mg/L)

Salt Solution

Conductivity

Voltage

(V)

Influent

Concentration

mg/L

Effluent

Concentration

(mg/L)

0 7.85 1.42 32.5 2.6 88.61 ---

1 hr 7.91 1.45 32.5 3.1 88.61 64.07

2 hrs 7.89 1.41 32.5 3.1 88.61 43.54

3 hrs 7.89 1.39 32.6 3.2 88.61 33.69

1 7.91 1.40 32.4 3.1 87.53 18.26

2 7.85 1.46 32.4 3.0 88.20 17.64

3 7.80 1.30 32.2 3.0 87.63 16.59

4 7.80 1.32 32.2 3.2 88.92 18.28

5 7.78 1.40 32.1 3.2 97.57 21.46

6 7.90 1.39 32.0 3.0 106.47 19.37

7 7.80 1.44 31.9 3.1 101.81 21.48

8 7.73 1.39 31.9 3.1 103.03 21.49

9 7.84 1.38 31.7 3.1 99.08 20.64

10 7.81 1.44 31.7 3.2 100.78 20.31

11 7.89 1.39 31.6 3.0 90.15 18.81

12 7.93 1.33 31.6 2.8 87.02 15.60

13 7.91 1.43 31.6 3.1 86.00 17.47

14 7.86 1.49 31.5 3.2 101.58 21.71

A32

Experiment 42



Time

(days)

pH of

Feed

DO of Feed

(mg/L)

Salt Solution

Conductivity

Voltage

(V)

Influent

Concentration

mg/L

Effluent

Concentration

(mg/L)

0 7.84 1.42 32.9 2.5 93.26 ---

1 hr 7.86 1.46 32.9 3.4 93.26 64.06

2 hrs 7.81 1.41 32.9 3.5 93.26 46.13

3 hrs 7.95 1.44 32.9 3.5 93.26 34.85

1 7.79 1.36 33.0 3.4 97.91 19.79

2 7.89 1.40 32.8 3.5 107.43 22.75

3 7.82 1.30 32.8 3.4 103.28 20.08

4 7.79 1.38 32.9 3.6 97.71 17.55

5 7.75 1.28 33.0 3.4 99.24 17.86

6 7.85 1.36 33.0 3.4 113.06 20.52

7 7.96 1.40 33.0 3.5 112.26 20.12

8 7.85 1.29 33.0 3.5 105.97 20.38

9 7.80 1.25 33.0 3.5 98.04 18.09

10 7.90 1.35 33.0 3.6 95.46 17.18

11 7.89 1.33 32.9 3.5 93.99 24.21

12 7.93 1.32 32.9 3.6 96.54 25.28

A33

Experiment 43



Time

(days)

pH of

Feed

DO of Feed

(mg/L)

Salt Solution

Conductivity

Voltage

(V)

Influent

Concentration

mg/L

Effluent

Concentration

(mg/L)

0 7.80 1.35 33.0 2.3 104.03 ---

1 hr 7.86 1.48 33.0 2.6 104.03 67.72

2 hrs 7.87 1.42 33.0 2.3 104.03 55.05

3 hrs 7.98 1.46 32.9 2.5 104.03 47.94

1 7.85 1.40 33.0 2.9 105.39 20.02

2 7.79 1.40 32.8 2.9 103.41 22.55

3 7.94 1.40 32.8 3.0 97.46 26.82

4 7.85 1.48 32.8 3.0 93.39 20.91

5 7.95 1.44 32.7 3.0 92.89 21.90

6 7.87 1.43 32.6 3.1 97.36 24.21

7 7.79 1.48 32.5 3.0 100.25 24.15

8 7.81 1.44 32.4 2.7 96.12 24.30

9 7.85 1.36 32.4 3.1 95.57 24.40

10 7.79 1.42 32.4 3.1 96.38 24.38

11 7.80 1.44 32.3 3.0 97.74 24.45

12 7.87 1.36 32.2 2.9 91.91 23.82

13 7.95 1.45 32.2 3.0 93.00 23.42

14 8.03 1.41 32.1 3.0 88.10 23.69

A34

Experiment 44



Time

(days)

pH of

Feed

DO of Feed

(mg/L)

Salt Solution

Conductivity

Voltage

(V)

Influent

Concentration

mg/L

Effluent

Concentration

(mg/L)

0 7.91 1.45 32.1 2.5 88.91 ---

1 hr 7.90 1.46 32.1 3.0 88.91 62.08

2 hrs 7.86 1.41 32.0 3.0 88.91 46.11

3hrs 7.93 1.29 31.9 3.1 88.91 34.86

1 7.81 1.45 31.9 3.0 90.78 19.06

2 7.80 1.39 31.9 3.1 110.37 21.53

3 7.80 1.42 31.9 3.1 104.65 21.64

4 7.91 1.49 32.0 3.2 102.57 21.49

5 7.85 1.42 31.9 3.0 91.26 17.30

6 7.80 1.45 31.8 3.3 96.76 19.94

7 7.90 1.40 31.8 3.1 103.28 19.2

8 7.85 1.35 31.8 3.1 102.49 20.43

9 7.83 1.42 31.7 3.0 102.62 20.79

10 7.90 1.42 31.7 3.2 98.83 19.96

11 7.87 1.41 31.6 3.3 96.48 19.14

12 7.79 1.45 31.6 3.3 98.06 19.78

13 7.93 1.43 31.6 3.3 98.56 21.57

14 8.05 1.45 31.5 3.2 87.71 20.40

UNIVERSITY OF CINCINNATIsorialga/Rajesh's Thesis .pdf · Rajesh Babu Doppalapudi B.Tech., Civil...

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