Post on 10-Apr-2020
GDAŃSK UNIVERSITY OF TECHNOLOGY
FACULTY OF CHEMISTRY
DEPARTMENT OF PROCESS ENGINEERING
AND CHEMICAL TECHNOLOGY
ENVIRONMENTAL REMEDIATION TECHNOLOGIES
CHEMICAL METHODS FOR WASTEWATER TREATMENT
FROM LANDFILLS - FENTON, OZONATION
AND PHOTOCATALYTIC REACTIONS
GDAŃSK 2018/2019
1. INTRODUCTION
Leachates can be defined as seepage waters from municipal waste landfills. They are characterized by
reduction properties and significantly increased parameters of biological and chemical oxygen demand
(BOD5 and COD), high concentrations of solutes, chlorides, sulphates and ammonium nitrogen compounds.
In contrast to municipal sewage, leachate from landfills is difficult to purify with biological methods.
In the last decade, intensive research has been undertaken to find effective methods of removing toxic
impurities that occur in water, sewage and leachates both in trace amounts and in relatively high
concentrations. One of the currently available technologies is Advanced Oxidation Processes (AOPs), based
on reactions involving hydroxyl ·OH radicals. Hydroxyl radicals are the strongest oxidant that can be used
for water and wastewater treatment (the oxidation potential is 2.80 V). They are generated, inter alia, during
the decomposition of ozone in the aquatic environment during chain radical reactions, as well as during
photolysis of hydrogen peroxide, chlorine, Fe(III) aqueous solutions, during Fenton reaction, or under the
influence of ionizing radiation.
The hydroxyl radicals are not selective and react with most of the dissolved organic and inorganic
compounds at a high degradation rate constant of the reaction. To increase efficiency in many oxidation
processes, several different oxidants are used, and reactions with the use of OH· radicals are only one of the
stages of the wastewater treatment process [Hoigne 1996]. AOPs are important for the treatment of sewage,
leachate, contaminated surface and groundwater as well as for the production of ultrapure water [Braun,
1996].
2. OVERVIEW OF OXIDATION METHODS
Among advanced oxidation technologies there are chemical and photochemical processes (light-
induced oxidation processes). In principle, they can be divided into two groups: technologies running at
atmospheric pressure and at ambient temperature (e.g. ozonolysis and photooxidation) and technologies
requiring the use of elevated temperatures and pressures (wet oxidation and supercritical water oxidation).
Chemical degradation methods:
• wet air oxidation (WAO),
• supercritical water oxidation (SCWO),
• electrochemical oxidation,
• oxidation with ozone and hydrogen peroxide,
• Fenton reaction
Photochemical processes:
• UV photolysis,
• processes using UV/H2O2,
• processes using UV/O3,
• processes using UV/H2O2/O3,
• photocatalytic degradation in aqueous semiconductor suspensions,
• photo-Fenton reaction,
• processes using ultrasounds [Prousek 1996].
Common features of NPU methods include:
• Organic pollutants are decomposed to carbon dioxide, water and ammonia (or nitrogen) and to
simple compounds such as low molecular weight organic acids (acetic and formic acid),
• In reaction systems, an oxidizer with high oxidation potential is generated. The free radical
mechanism dominates, and one of the most important reagents is the hydroxyl radical
• high oxidation potentials cause that AOPs belong to non-selective methods - all groups of organic
compounds and non-oxidized forms of inorganic compounds undergo oxidation.
Particular AOPs methods differ mainly in the method of generating the hydroxyl radical.
Oxidation of organic compounds proceeds through to one of three mechanisms:
• the hydroxyl radical accepts the electron from the organic substance to form a new radical, while
simultaneously reducing itself to the hydroxyl ion - it is the electron transfer reaction,
• splitting off the hydrogen atom from the molecule. This process creates an organic radical and water
- it is a hydrogen transfer reaction,
• addition of a hydroxyl radical to a double bond in alkenes and aromatic compounds, which leads to
the formation of a radical on the carbon atom - this is the addition reaction of the hydroxyl radical.
2.1. Wet oxidation with air
The process of wet oxidation is carried out in the liquid phase, at elevated temperature (from 100 to 300 °
C) and under increased pressure (from 0.5 to 20 MPa). During the process, air or oxygen is pressed into
the reaction medium. Organic carbon is oxidized to CO2, organic nitrogen to ammonia or free nitrogen,
and organic chlorides and sulphides are converted into inorganic chlorides and sulphates. The
effectiveness of the method is based on two beneficial features of this reaction system:
• with the increase of temperature above 393K, the solubility of oxygen in aqueous solutions
increases significantly.
• increasing the temperature increases the rate of chemical reactions and improves the efficiency of
free radical formation.
Wet air oxidation is carried out in a heterogeneous gas-liquid system in the following stages:
a) transfer of oxygen from the gas phase to the gas-liquid interface,
b) transfer of dissolved oxygen from the gas-liquid interface to the liquid mass
c) chemical reaction between dissolved oxygen and substrates.
These features of wet oxidation make it a highly unselective process and the high temperature of the
process allows to achieve significant conversion rates of substrates and intermediate products ranging
from 70 to 100%. The wet oxidation process is considered to be effective when the concentration of
impurities in liquid or semi-liquid waste does not exceed 1.5 % -20 % by weight, and the amount of
treated wastewater is not less than 15-20 m3/day.
Over the years, the process of wet air oxidation has found application in:
• removing glycols, detergents, phenols, napholes and their derivatives, pesticides as well as synthetic oils
and resins from sewage,
• treatment of waste water streams that are too diluted for combustion and too concentrated for biological
treatment,
• the treatment of wastewater from the spirit industry (mainly from the distillation of fermentation broth),
• the oxidation of sewage containing cyanides and nitriles derived from galvanizing processes, from coke
ovens and from pharmaceutical synthesis processes,
• the oxidation of polyethylene glycols and surfactants,
• the regeneration of activated carbons used for the treatment of wastewater containing toxic and waste
organic compounds (Zarzycki, 2002).
At present, there are around 400 industrial wet
oxidation installations in the world. The most
popular installation is ZIMPRO® (USA) operating
on the basis of a flow tower reactor, which consists
of a vertical tank fed from the bottom with liquid
and gas. The flow in the reactor is laminar and the
products are discharged from the top of the reactor.
The ZIMPRO® installation diagram is shown in
Fig. 1
Fig. 1. Scheme of ZIMPRO® installation
Wastewater containing easily settling suspensions can be purified using the WETOX® method.
The oxidation process runs in a high-pressure reactor consisting of a horizontal tank, divided into sections,
each of which has an independent air supply and a stirrer. The device works based on the idea of a cascade
of reactors with perfect mixing. The advantage of the reactor is the possibility of wastewater treatment
containing easily sedimenting suspensions, and the disadvantage - the use of agitators, whose drive shafts
are led through the reactor wall to the outside, which requires expensive seals and special bearing.
2.2. Supercritical oxidation
In recent years, a number of applications have been developed for the long-known thermodynamic state of
the substance which is supercritical fluid. A special role as a medium alongside carbon dioxide plays
water, especially in the area oriented to environmental protection, because it turned out to be a very
promising environment for the oxidation of pollutants and organic waste. Oxidation in supercritical water
is carried out above the critical point of water (> 22 MPa and 374°C). The similarity of oxidation in the
supercritical condition is only formal for other wet oxidation processes, because above the critical point in
the reaction mixture we have a one-phase process, and thus the kinetics of the process lies solely in the
area of chemical kinetics.
Water in the supercritical state changes its properties as a solvent - from ionic to non-ionic. Oxidation in
supercritical water in relation to classical thermal methods provides practically complete mineralization.
That creates the possibility of running a process in a closed circuit, in a more concentrated environment, at
a lower temperature, and in particular it eliminates the effect of secondary gas emissions. At the supercritical
point the water volume is 3 times higher than in normal conditions (d = 0.322 g·cm-3), and the dielectric
constant ε is only 5.3. As a result, under the conditions of the oxidation process, at a temperature of about
400°C and for a pressure between 23-26 MPa, the water occurs in the form of a dense gas. Organic
substances, including hydrocarbons, and molecular oxygen become mutually soluble with water, while
inorganic salts precipitate out of solution. These unique properties of supercritical water allow the contact
of oxygen and organic compounds in one phase, in which rapid and complete oxidation of organic
substances occurs at temperatures of 550-650°C. Under these conditions, the conversion rate can be over
99.99% for a one-minute residence time.
Oxidation in the supercritical state has found application in:
• oxidation of substances considered to be particularly dangerous or burdensome for the environment
due to its toxicity while being resistant to oxidation (nitrophenols, aliphatic and aromatic halogen
derivatives, polychlorinated biphenyls and dioxins),
• disposal of toxic and dangerous substances related to national defense,
• in oxidation processes, e.g. carbon monoxide, hydrogen, ammonia, methane or acetic acid,
• oxidation of wastewater from the paper industry and excess active sludge from municipal and
industrial treatment plants.
The schematic of the installation of the supercritical water oxidation process (MODEC® method)
is shown in Figure 2.
Fig. 2 Scheme of installation for supercritical oxidation
In general, the process proceeds as follows: the feed prepared in the tank (F) is a solution or a suspension
of fine particles of an organic substance. Liquid oxygen is used as the oxidant, which is pumped from the
tank (T) through a high-pressure pump through the evaporator (P). The feed and the oxidant meet in the
reactor (R). The reactor, as the most important part of the installation, must meet four basic conditions:
• the residence time must guarantee sufficiently deep oxidation,
• must be resistant to corrosive reaction environments and hydrodynamic conditions also a precipitation
of some reaction products,
• have an ability to utilize the heat of reaction.
The post-reaction stream, after leaving the reactor, gives off heat to the stream in the heat exchange system
(W).The system components are also the final cooling system (Ch) and the separation of reaction products
S1, S2
2.3. Oxidation with ozone and hydrogen peroxide
In many countries, ozone is the most widely used substance used to purify drinking water. It is
also used for the oxidation of pollutants in the case of industrial wastewater. One of the main advantages of
using ozone is its beneficial effect on the environment. The reaction products of ozone with chemical
compounds that are water contaminants are mostly non-toxic and biodegradable, and ozone itself transform
to form oxygen.
Ozone is known as the most selective oxidant. The oxidation reactions initiated by ozone in aqueous
solutions are mainly complex reactions. Ozone can react with organic substances in two ways: directly or
through radicals (secondary oxidant). The presence of solutes affects the oxidation process and thus the end
products obtained. The ozone can react with organic substances by various mechanisms. The simplest of
them is the basic reaction of ozone with an organic molecule. However, most of the reactions probably
occur between organic matter and hydroxyl radicals.The ozone oxidation potential is 2.07 V, while the
oxidation potential of hydrogen peroxide is 1.77 V. Therefore, hydrogen peroxide is also used as an oxidant
in wastewater treatment processes. Both oxidants are often used together. The use of hydrogen peroxide
significantly reduces the costs of wastewater treatment compared to the use of ozone alone. The probable
reaction mechanism is shown below:
𝐻2𝑂2 → 𝐻𝑂𝑂− +𝐻+
𝐻𝑂𝑂− + 𝑂3 → 𝐻𝑂𝑂∙ + 𝑂3
∙−
Ozonation is used, among others:
• for drinking water treatment (oxidation and precipitation of iron and manganese compounds,
improvement of taste, oxidation of organic compounds, etc.),
• for water treatment in swimming pools,
• for the treatment of process water (in cooling circuits, process water in the semiconductor materials
industry, in laundry facilities)
• for the treatment of municipal and industrial wastewater and leachate (disinfection of municipal
sewage, oxidation of organic compounds, improvement of biofilters)
2.4. Fenton's reaction
Over one hundred years ago, J.H. Fenton (1884) discovered that Fe2+ ions strongly catalyze the
oxidation reaction with hydrogen peroxide of some organic acids. Subsequent studies have shown that a
mixture of H2O2 and Fe2+ is able to oxidize many other organic substances at moderate temperatures and
under normal pressure. The reaction has become one of the most effective AOP techniques. Currently, AOP
processes using hydrogen peroxide, in addition to the classic Fenton reaction, also include reactions in
H2O2/Fe2+, H2O2/Fe2+/UV and H2O2/Fe3+/UV systems. Research on the mechanism of oxidation showed the
formation of hydroxyl radicals by catalytic decomposition of hydrogen peroxide in acidic solution. The
Fenton reaction produces an iron ion, a hydroxyl radical (OH·) and a hydroxyl ion (OH-).
Fe2+ + H2O2 → Fe3+ + OH− + OH•
OH• + H2O2 → HO2 • +H2O
Fe3+ + • HO2 → Fe2+ + H+ + O2
Fe2+ + • HO2 → Fe3+ + HO2–
Fe2+ + OH• → Fe3+ + OH−
The oxidative effect of Fenton's reagents strongly depends on:
• pH of the solution,
• the ratio of H2O2 and Fe2+ concentrations,
• temperature
• amount of hydrogen peroxide in relation to the load of pollutants initial concentration of iron ions.
With the increase in the concentration of iron ions and hydrogen peroxide, the efficiency of the oxidation
reaction increases, however, too high concentrations of both reagents may cause a decrease in the reaction
rate. The pH range in which the oxidation occurs is from 3 to 5, but the optimum pH value for the Fenton
reaction is between 3 and 4. In contrast, the weight ratio of catalyst to hydrogen peroxide is 1:5 [Bigda
1995].
Fenton reagent is an effective oxidant of many organic substances and almost all organic compounds
containing hydrogen can be oxidized by hydroxyl radicals produced by the Fenton reaction. The group of
chemical compounds for which the Fenton reaction cannot be effectively used include, for example, acetic
acid, acetone, chloroform, methylene chloride, n-paraffin.
The main advantage of the Fenton process, as compared to other methods of wastewater treatment, is
the lack of H2O2 residues in the post-reaction system and catalytic only amounts of Fe2+ used in the reaction.
In addition, the Fenton reaction is carried out at ambient or slightly higher temperature (293-303 K) using
the heat of reaction to warm the mixture. This is an important advantage of this process, because it does not
require installation of a heat exchanger in the reactor, and energy is used to mix and dose reagents. The
Fenton reaction is used both for pre-treatment as well as for lowering COD before further biological
treatment of wastewater, or for the mineralization of toxic and difficult to biodegrade contaminants.
The Fenton process has been applied to several types of wastewater:
• process waters generated during the synthesis of chemicals, drugs, insecticides, dyes, explosives (TNT,
RDX);
• sewage from refineries;
• wastewater from the production of polymers containing phenol or formaldehyde;
• wastewater generated in the wood industry containing, among others cresols and copper compounds;
• sewage generated as a result of soil cleaning [Bigda 1995].
Waste water oxidation under industrial conditions is carried out in non-pressurized batch reactors.
A typical reactor is a non-pressurized tank with a stirrer. Process control is based on the sensors' indications,
which continuously measure temperature, pH and oxidation-reducing potential. The diagram of the reactor
for wastewater oxidation using the Fenton reagent is shown in Fig. 3.
Fig. 4 Scheme for Fenton reaction system
The dosing of reagents is carried out using dosing pumps. The tank is first filled with sewage and then the
pH is corrected (before adding the catalyst) with dilute sulfuric acid.
2.5. UV photolysis
Direct UV photolysis involves the excitation of a molecule by photon absorption, resulting in a
chemical reaction. The direct effect of UV radiation can be:
• conversion of organic compounds into other,
• breaking of chemical bonds,
• complete degradation of organic compounds
UV radiation causes the dissociation of oxidizing compounds and the formation of highly reactive
radicals capable of degrading organic pollutants. Direct photochemical degradation with UV radiation is
only in the case where the incident light is absorbed by the contamination. Highly fluorinated or chlorinated
saturated aliphatic compounds can be effective eliminated by homolysis of carbon-halogen bonds.
UV photolysis is used to eliminate:
• chlorinated and nitrated aromatic compounds,
• phenols,
• halogenated aliphatic compounds.
2.6. Processes using UV/H2O2
In the process of in-depth oxidation with the participation of hydrogen peroxide and UV radiation,
hydroxyl radicals are generated in the photolysis results of hydrogen peroxide. The widely accepted
mechanism of H2O2 photolysis is the homolysis of oxygen-oxygen bonds with the formation of two
hydroxyl radicals.
The advantages of using H2O2 in comparison to other methods of chemical or photochemical wastewater
treatment are: widespread availability, thermal stability, total solubility in water, and much lower cost than
when using, for example, ozone. In degradation processes in the H2O2/UV system, the most commonly used
light source is a low-pressure mercury lamp. It emits mainly radiation with a wavelength of 253,7 nm, which
is about 70% of the light energy emitted by the lamp. If hydrogen is introduced into the hydrogen peroxide
aqueous solution exposed to UV radiation, they will be included in the H2O2 chain reaction cycle (Fig.4).
Fig. 4 Oxidation Mechanism in H2O2/UV.
2.7. Processes in O3/UV system
Oxidation of compounds by means of ozone assisted by UV radiation is one of the most commonly used
processes of oxidation of various types of pollutants. The combined action of ozone and UV radiation is
also one of the most advanced techniques in the technological aspect. The essence of processes using ozone
and UV is ozolonolysis causing the formation of H2O2. In this way, the combination of UV and ozonation
is more effective than the sum of these two individual processes (synergistic effect). This method is used
for compounds that are resistant to ozonation. It is the most commonly used AOP method for a wide range
of pollutants. The process is used in the I or II-stage system. In a one-stage system, wastewater is
simultaneously treated with ozone and irradiated with UV radiation. In the II-stage system, the wastewater
is ozonized in the first reactor and then partially oxidized, along with the residual ozone, they pass into the
second reactor, where they are irradiated with UV radiation.
The disadvantage of the method, as in all methods using ozone, is the low solubility of ozone in water
and the associated poor mass exchange, high cost of ozone generation and its corrosiveness. Tests on real
waste water from industry textile (both general and chemical dry cleaners) showed that the combined use
of ozone and UV radiation allows to obtain better results in the distribution of pollutants. It depends on the
type of sewage and the parameter analyzed (Kos, 1998, Perkowski, 200).
2.9. Photocatalytic degradation in aqueous semiconductor suspensions
Heterogeneous photocatalysis using semiconductor suspensions is a method that is becoming more
and more popular. Most of the data on photocatalytic reactions using semiconductor suspensions concern
metal oxides (TiO2, ZnO, SnO2, WO3), sulphides (CdS, ZnS), selenides (CdSe) and tellurides (CdTe).
TiO2 is characterized by a number of advantages, including: a relatively low price, high oxidation potential,
non-toxicity, high chemical stability, high oxidation potential of photogenerated charge carriers, moreover,
it is not soluble in most reaction environments. Due to its photocatalytic properties it is used for: production
of self-cleaning coatings on the surface of panels, fabrics, glass, foils, car mirrors, soundproofing panels,
cement, paints, pigments, materials used in the process of deodorization of rooms. In addition, it is used in
the processes of wastewater treatment, water from organic contaminants and microorganisms.
The photoactivation of TiO2 is possible when the incident radiation energy is equal to or greater
than the bandgap energy (see Figure 5). The value of TiO2 bandgap energy, i.e. the energy that separates
the valence band from the conduction band, is in the range of 3.0-3.2 eV depending on the crystal structure.
It corresponds to a radiation of wavelength below 388 nm, hence TiO2 is activated by light from the UV
range. The first stage of the photocatalytic reaction mechanism is the absorption of photon, which involves
the transfer of the electron from the valence band to the conduction band.
Fig. 5. Scheme of TiO2 particle photoexcitation, CB- conduction band, VB- valence band
In the valence band of the photocatalyst, an electron gap (called hole) is created. Generated charge carriers:
holes and electrons can be recombined in the crystal lattice or cause fluorescence or heat generation. They
can also migrate to the photocatalyst surface and participate in redox chemical reactions with H2O, OH-, O2
molecules adsorbed from the aqueous solution and organic compounds. Hydroxyl radicals are formed as a
result of the oxidation reaction between holes and a water molecules or a hydroxyl anions. On the other
hand, the oxygen anion radical is formed during the reaction of electrons with adsorbed oxygen. The oxygen
anion radical can generate a hydrogen peroxide molecule and a hydroxyl radical. The reaction of
photocatalytic oxidation of organic compounds can be expressed in a general way:
𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒 + 𝑂2 𝑇𝑖𝑂2,ℎ𝑣→ 𝐶𝑂2 + 𝐻2𝑂 +𝑚𝑖𝑛𝑒𝑟𝑎𝑙 𝑎𝑐𝑖𝑑𝑠
The above equation indicates the total mineralization of organic compounds. During the photocatalytic
reaction the mineralization step is the last stage of an oxidation. The intermediate stage of the photocatalytic
reaction is the formation of intermediate degradation products.
Many factors influence the photocatalytic degradation process. Among them the most important are:
• type of semiconductor,
• proper preparation of its surface,
• intensity of incident light,
• solvent,
• temperature,
Natural organic matter (NOM),
• pH of the solution (in the case of aqueous solutions) [Zarzycki, 2002].
Reduction
Oxidation
3. REFERENCES
Barrat P.A., Baumgartl A., Hannay N., Vetter M., Xiong F. (1996), CHEMOX™ Advanced Waste
Water Treatment with the Impinging Zone Reactor, „Oxidation Technologies for Water and
Wastewater Treatment" Goslar, Germany, May 12-15 1996 Bigda R.J., Consider Fenton's chemistry for wastewater treatment, Chemical Engineering Progress 12,
62-66, 1995 Braun A.M., Oliveros E. (1996), How to evaluate photochemical methods for water treatment
Intemational Conference „Oxidation Technologies for Water and Wastewater Treatment" Goslar,
Germany, May 12-15 1996 Fox M.A., Dulay M.T., Heterogeneous photocatalysis, Chem. Rev. 93, 341-
357, 1993 Hoigne J., Intercalibration of OH radical sources and water quality parameters. Intemational
Conference „Oxidation Technologies for Water and Wastewater Treatment" Goslar, Germany, May
12-15 J996 Goslar, Germany, May 12-15 1996 Guha AK., Shanbhag P. V., Sirkar K.K., Multiphase ozonołysiis oforganics m wastewater by a novel
membranę reactor, AlChE Joumal 41 (8), (1995) Kowal AL., Świderska-Bróż M., Oczyszczanie wody, PWN Warszawa (1996) Langlais B, Reckhow D.A., Brink D.R., Ozone in water treatment. Application and Engineering,
AWWA Research Foundation & Lewis Publisher (1991) Legrini O., Oliveros E., Braun A. M., Photochemical Processes for Water Treatment, Chem. Rev. 93,
671-698, 1993, Luck F., A review ofindustrial catałytic wet air Oxidation processes, Catalysis Today 27, 195 -202 (1996)
Prousek J. (1996), Advanced Oxidation process for water treatment. Chemical process, Chem. Listy 90,
229-23 Prousek J. (1996), Advanced Oxidation process for water treatment. Photochemical process,
Chem. Listy 90, 307-315 Roche P., Volk C., Carbonnier F., Paillard H., Ozone Science & Engineering 16, 135-55 (1994) Trapido M., Yaressinina Y., Munter R., Ozonation of phenols in wastewater from oil shale chemical
treatment, Environmental Technology 16 (30), 233-241 (1995) Zarzycki R., Imbierowicz M., Rogacki G., Filipiak T., Nowoczesne metody unieszkodliwiania
odpadów. Mat. seminarium naukowego "Ochrona środowiska w przemyśle - techniki i technologie".
Łódź, (1996) „Zaawansowane techniki utleniania w ochronie środowiska” pod redakcją Romana
Zarzyckiego Łódź, (2002)
THE AIM OF THE EXCERCISE
The aim of the exercise is to evaluate an efficiency of phenol oxidation reaction using three AOP
systems: a) photocatalytic oxidation in TiO2 suspension, b) Fenton reaction and c) ozonation and
comparison of these three methods.
CALIBRATION CURVE OF PHENOL CONCENTRATION
Phenol concentration will be determined spectrophotometrically. For quantitative analysis, it is
necessary to make a calibration curve. In the flasks with a capacity of 50 cm3 prepare standard solutions (5
cm3 each) of phenol at a concentration of 10, 20, 30, 40 and 50 mg/dm3 and add successively 7.5 cm3 of p-
nitroaniline (PNA) and 2 cm3 of sodium nitrite solution. Then, shake and cool 10 min in an ice bath. Next,
add 15 cm3 of sodium carbonate solution, fill up to required volume with water. Measure absorbance of
colored solution at λ= 480 nm.
FENTON’S REACTION The measurement of phenol oxidation using the Fenton method is carried out according to the following
procedure: a) Fill the glass reactor with 1dm3 of model phenol solution at a concentration of 50 mg/dm3 and 0.5 dm3
of distilled water. The pH of the solution should be adjusted to pH 3-4 with a sulfuric acid solution. The
acidic reaction of the solution prevents the precipitation of iron hydroxide after the addition of the catalyst, b)turn on the magnetic stirrer and set the required speed of rotation at 500 rpm,
c) Prepare a solution of iron(II) sulphate. Dissolve 3 g of FeSO4x7H2O in distilled water, adjust the pH with
sulfuric acid to a value of 3-4 and dilute to 100 cm3 with distilled water,
d) Collect a "0'-sample into a 25 cm3 flask, basify with NaOH solution to pH=10.
e) Add to reaction solution 1.5 cm3 of 30% hydrogen peroxide solution and 15 cm3 of previously prepared
catalyst solution,
f) Reaction should be carried out for 20 minutes. Samples of volume 25 cm3 should be taken every 5 min, of which 10 cm3 should be designated for determination of phenol, and the remaining 15 cm3 for possible repetition of the assay - note: after collection the samples should be alkalinized (using NaOH solution) to stop the reaction.
Determination of phenol concentration
Determination of phenol involves the coupling of phenol with diazoated p-nitroaniline in an alkaline
solution. The resulting colored compound is determined colorimetrically (480 nm wavelength).
Procedure:
1. Transfer 10 cm3 of the phenol solution to a 100 cm3 flask. Add 15 cm3 of paranitroaniline and 4 cm3 of
sodium nitrite, then cool down in an ice bath for 10 minutes.
2. After cooling, add 30 cm3 of sodium carbonate and fill with water up to required volume.
3. The concentration of phenol should be determined spectrophotometrically via measurements of
absorbance at 480 nm.
OZONATION
Apparatus:
To measure the efficiency of phenol oxidation the apparatus presented schematically in Figure 6 is
used. Ozone is generated in a generator / 4 / based on electrical discharges. The efficiency of the generator
is regulated by changing the gas flow rate. The source of air or oxygen supplied to the ozonator is gas
cylinder /1/. The gas flow rate is regulated using rotameter /2/ and gas cylinder valves. The ozonator is
connected to the autotransformer and the voltage and the primary current are measured using a voltmeter
/6/ and ammeter /5/. Secondary voltage data is a dependence (transformer ratio): Uw = 36 Up. Oxidation
of the phenol solution is carried out in the reactor /7/.
Figure 6 Scheme of the ozonization system. 1 - a cylinder with compressed air, 2 – rotameter, 3 - gas dryer, 4 - ozone generator,
5 – ammeter, 6 – voltmeter, 7 – reactor, 8 - scrubber for absorbing unreacted O3, 9 - scrubbers with KI solution, 10 - gas meter
The method of carrying out the measurements is as follows:
1. Fill the column with a model phenol solution of concentration 50 mg/dm3 to a volume of 2 dm3.
2. Adjust the pH of the solution in the column with NaOH to 10-12.
3. Take a "0" sample into the bottle made of amber glass.
4. Open the ozone supply valve to the column /7/ and simultaneously close the valve to the hood.
5. Adjust the gas flow rate due to the change in flow resistance,
6. Ozonation should be carried out for 20 minutes (from the moment ozone bubbles appear in the
column 7 /). Take samples of the solution into amber-glass bottles every 5 min, of which 10 cm3
should be used to determine phenol concentration,
7. In order to terminate the ozonization process:
- open the valve to the hood and at the same time close the valve supplying ozone to the reactor,
- turn off the power supply of the ozone generator to high voltage,
- after 2 minutes, stop the air flow (oxygen),
Determination of phenol concentration
Determination of phenol involves the coupling of phenol with diazoated p-nitroaniline in an alkaline
solution. The resulting colored compound is determined colorimetrically (480 nm wavelength).
Procedure:
1. Transfer 10 cm3 of the phenol solution to a 100 cm3 flask. Add 15 cm3 of paranitroaniline and 4 cm3 of
sodium nitrite, then cool down in an ice bath for 10 minutes.
2. After cooling, add 30 cm3 of sodium carbonate and fill with water up to required volume.
3. The concentration of phenol should be determined spectrophotometrically via measurements of
absorbance at 480 nm.
PHOTOCATALYTIC PHENOL DEGRADATION IN THE UV/TiO2 SYSTEM
1. 1 dm3 reactor fill with 1dm3 ml of phenol solution (Co = 50 mg/dm3) and 2 g of the photocatalyst,
2. Place the reactor in a holder and cover with alumina foil,
3. In order to reach the state of equilibrium, leave the reactor for 10 minutes.
4. Then take a zero sample and turn on the UV lamp,
5. Reaction should be carried out for 20 minutes. Take samples of the solution into amber-glass bottles
every 5 min, of which 10 cm3 should be used to determine phenol. The collected solution should be
separated from the photocatalyst by means of a syringe filter (PLEASE REMEMBER TO
REGENERATE THE FILTERS)
6. Turn off the lamp after 20 minutes.
Determination of phenol concentration
Determination of phenol involves the coupling of phenol with diazoated p-nitroaniline in an alkaline
solution. The resulting colored compound is determined colorimetrically (480 nm wavelength).
Procedure:
1. Transfer 10 cm3 of the phenol solution to a 100 cm3 flask. Add 15 cm3 of paranitroaniline and 4 cm3 of
sodium nitrite, then cool down in an ice bath for 10 minutes.
2. After cooling, add 30 cm3 of sodium carbonate and fill with water up to required volume.
3. The concentration of phenol should be determined spectrophotometrically via measurements of
absorbance at 480 nm.
REPORT:
1. The purpose and scope of the exercise, a precise description of the apparatus.
2. Measurement results.
3. Determination of the calibration curve of the phenol solution (graph, necessary calculations).
4. Determination of phenol degradation kinetics - necessary graphs and calculations.
5. In the case of the report on the last classes, the exercise should compare the efficiency of phenol
oxidation in individual processes.
FENTON REACTION – REPORT
Date of the exercise ..............................
L.p. Name and Surname
1
2
3
4
5
Table 1. The results of measurements of standard solutions
Phenol concentration [mg/l] Absorbance
10
20
30
40
50
Table 2. Results of measurements and observations of phenol oxidation.
Time Phenol
concentration
Visual
assessment
Absorbance Solutions
(color)
[min] [mg/dm3]
0
5
10
15
20
X – absorbance Y – concentration of phenol [mg/dm3]
OZONATION - REPORT
Date of the exercise ..............................
L.p. Name and Surname
1
2
3
4
5
Gas flow rate:
Table 1. Results of measurements and observations of the process
Table 2. Measurement results of standard solutions
Phenol concentration [mg/l] Absorbance
10
20
30
40
50
Time
[min] Absorbance
Phenol
concentration
[mg/dm3]
Visual assessment of the process
Color of
the solution
The size
of the bubbles Foam formation
0
5
10
15
20
PHOTOCATALITIC DEGRADATION IN TiO2 SUSPENSION - REPORT
Date of the exercise ..............................
L.p. Name and Surname
1
2
3
4
5
Photocatalyst used: ...................................................
Tabela 1. The results of measurements of standard solutions
Table 2. Results of measurements and observations of phenol oxidation.
Time Phenol
concentration
Visual
assessment
Absorbance of olutions
(color)
[min] [mg/dm3]
0
5
10
15
20
Phenol concentration [mg / l] Absorbance
10
20
30
40
50
GDAŃSK UNIVERSITY OF TECHNOLOGY
FACULTY OF CHEMISTRY
DEPARTMENT OF PROCESS ENGINEERING
AND CHEMICAL TECHNOLOGY
ENVIRONMENTAL REMEDIATION TECHNOLOGIES
PHOTOCATALITIC DEGRADATION OF PHENOL
IN TiO2 SUSPENSION
TEACHER: dr inż. Izabela Wysocka
STUDENTS:
1
2
3
4
5
GROUP:
DATE OF PERFORMING
THE EXERCISE:
REPORT SUBMISSION
DATE:
GDAŃSK UNIVERSITY OF TECHNOLOGY
FACULTY OF CHEMISTRY
DEPARTMENT OF PROCESS ENGINEERING
AND CHEMICAL TECHNOLOGY
ENVIRONMENTAL REMEDIATION TECHNOLOGIES
FENTON REACTION
TEACHER: dr inż. Izabela Wysocka
STUDENTS:
1
2
3
4
5
GROUP:
DATA OF PERFORMING
THE EXERCISE:
REPORT SUBMISSION
DATE:
GDAŃSK UNIVERSITY OF TECHNOLOGY
FACULTY OF CHEMISTRY
DEPARTMENT OF PROCESS ENGINEERING
AND CHEMICAL TECHNOLOGY
ENVIRONMENTAL REMEDIATION TECHNOLOGIES
OZONATION
TEACHER: dr inż. Izabela Wysocka
STUDENTS:
1
2
3
4
5
GROUP:
DATA OF PERFORMING
THE EXERCISE:
REPORT SUBMISSION
DATE: