Optimization for Disinfection Byproducts_11!15!2008

8/14/2019 Optimization for Disinfection Byproducts_11!15!2008

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Optimization of Treatment for Disinfection Byproducts Control 1

Optimization of Treatment for Disinfection Byproducts Control

Optimization of Treatment for Disinfection Byproducts Control

Jeffery L. Droll

[email protected]

Warren National University

FPPE490: Final Paper

Dr. Magdy Girgis PhD

November 12, 2008


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Abstract

In January, 2002 modifications to the Clean Water Act went into effect that lowered the

maximum level of specific contaminants associated with the disinfection of drinking

water with chlorine referred to as disinfection byproducts (DBPs). This rule had the

greatest impact on purveyors that treat water from surface sources such as rivers, lakes

and reservoirs

The reason for this impact is the presence of naturally occurring organic matter (NOM)

produced by the organisms living in the water or within the water shed from which the

water is collected. The NOM then reacts with the chlorine being applied for disinfection

producing undesirable byproducts. This essay will present a case study of one facility

where conventional treatment methods and each unit process was successfully optimized

to yield a finished water that met both the regulatory requirements and the aesthetic

demands of the customers.


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Table of ContentsI) Introduction 7

A) The Ottawa Ohio Water Treatment Plant Case Study 7

B) What is Optimization 11

C) Disinfection Byproducts 12

1) What Are Disinfection Byproducts? 12

2) What is Naturally Occurring Organic Matter? 14

II) Optimization 16

A) Examination of Historical Records 16

1) Water Quality for the Previous Two Years 16

a) Raw Water Source and Raw Water Characteristics 18b) Water Quality after Treatment in the Clarifiers 17

c) Water Quality after Recarbonation 19

d) Water Quality after Filtration 21

e) Water Quality at the Plant Tap 22

2) Evaluation of Individual Unit Processes 24

a) Existing Pretreatment Capabilities 24

b) Raw Water Supply and Low Service Pumping 25

c) Rapid Mixing 26

d) Clarifiers (Coagulation, Flocculation,

Sedimentation)28

i) Coagulation 28

ii) Flocculation 29

iii) Sedimentation 31

e) Recarbonation Basins 34

f) Filtration 36

g) Transfer Pumping (Intermediate Pumping) 44

h) Clear Well Storage (Finished Water Storage) and

Disinfection44

i) High Service Pumping 46

3) Chemical Feed Systems 47

a) Potassium Permanganate 47b) Powdered Activated Carbon 48

c) Coagulant Feed System 49

d) Lime Feed System 50

e) Soda Ash Feed System 51

f) Carbon Dioxide Feed System 52

g) Phosphate Feed System 53

h) Chlorine Feed System 54


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III) Jar Testing 56A) Initial Phase (Establishing a Baseline) 56

1) Verification of Present Conditions and Treatment 56

a) Establish Rapid Mixer Energy Transfer Values 57

b) Establish Flocculation Detention Time 58

c) Establish Sedimentation Time 59

2) Pretreatment Chemical Dosages 60

3) Coagulant Dosages 61

4) Softening Chemical Dosages 61

5) Simulated Recarbonation (pH Adjustment) 63

6) Phosphate Dosages 63

7) Disinfection and Simulated Distribution System Testing 64B) Experimental Phase (Chemical) 64

1) Modification to Chemical Dosages 64

a) Pretreatment Chemical Dosages 65

i) Sequencing of Chemical Additions 66

b) Coagulant Dosages 67

i) Single Basin Treatment 68

ii) Split Treatment 68

c) Softening Chemical Dosages 70

d) Disinfection, Simulated Distribution System Testing 71

2) Compilation and Comparison 72

3) Modifications to Unit Processes 72

a) Addition of Reaction (Contact) Basins 72

b) Modifications to Rapid Mix Basins Required 73

c) Separation of Treatment between Clarifiers 74

d) Modifications to Sludge Recirculation Piping on

Clarifiers75

e) Control of Solids in the Clarifier Slurry Pool and

Reaction Zone76

IV) The Human Factor 77

V) Summary 79

A) Results of Optimization 79

1) Summary of Changes 79

a) Unit processes 79

b) Chemical Treatments 81

VI) Looking Forward 83

References 84


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Appendices 89

Abbreviations and Acronyms 90Tables 92

Figures 107


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I) Introduction

A) The Ottawa Water Treatment Plant Case Study

I chose the Ottawa Water Treatment Plant for this paper for several reasons, but primarily

because the success achieved demonstrates the effectiveness of process optimization on

obtaining compliance with the recently promulgated limits for specific contaminants in

drinking water.

The Ottawa Water Treatment Plant and its water source are typical of most surface water

treatment plants constructed during the 1960s and 1970s in Ohio. However, extra

thought was given to specific details of this treatment plants design by the engineers that

allowed it to be adapted and the treatment optimized with minimal physical modifications

during this process.

The water source for the Village of Ottawa is the Blanchard River. This source was

chosen when the demands for water within the village exceeded the capacity of the

aquifer in the region. According to the United States Geologic Survey (USGS)* the river

has an estimated drainage area (water shed) of approximately 350 square miles and an

average daily discharge of approximately 271 cubic feet per second (2,027 gallons per

second) (gps). This average daily flow combined with the 121 million gallon reservoir

along the north bank of the river which was constructed at the same time as the treatment

plant was, allows for an abundant supply of water at all times. Additionally, the reservoir

capacity allows the treatment plant operators to monitor the quality of the water in the

river and to be selective when impounding water from the river.


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The Ottawa Water Treatment Plant is what is generally considered a conventional

treatment plant using chemical precipitation of suspended contaminants and excess

hardness. However, this particular treatment plant was designed with solids contact

clarification units installed at different elevations allowing for both series and parallel

operation of the units. The importance of this feature will be expanded upon later.

A general overview of the unit processes used and their purpose is as follows. Processes

added or found to need substantial modification as a result of this optimization are

denoted with an asterisk.

Low service pumping:

Low service pumping is used to supply the energy required to lift the raw water

into the treatment plant when the water elevation in the reservoir is not at a

sufficient height to accomplish this.

Pretreatment Basins:*

The pretreatment basins are used to provide contact time for the addition of

potassium permanganate (KMnO4) and powdered activated carbon (PAC) that are

used to condition and adsorb organic contaminants, respectively. Each basin

provides 30 minutes of residence time with mixing to assure that the chemicals

have been brought into contact with all of the water present and to allow adequate

time for the chemicals to fully react.

Rapid mixing:*

A rapid mixer is a small chamber in the influent channel equipped with a high

intensity mechanical mixer that is used to thoroughly disperse chemical

coagulants throughout the raw water before the chemicals can fully react with the

alkalinity in the water.

Clarification:


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Filtration is in essence the final polishing of the water before it is disinfected and

delivered to the distribution system. Here beds of sand particles of nearly uniform

size (approx. 0.5 mm) trap the small particles that would not settle in the clarifier

are removed along with a substantial number of bacteria and bacterial cysts.

Disinfection:

Disinfection is usually performed by injecting a solution carrying dissolved

chlorine gas or sodium hypochlorite (bleach) into the filtered water. The normal

dosage is approximately 4 milligram per liter (mg/L)

Clearwell Storage:The clearwell is the storage tank used to hold the filtered and disinfected water.

Here sufficient time is provided to allow the chlorine to subdue the disease

causing microorganisms. Additionally, the volume of the clearwell provides a

reserve for high demand periods and storage during low demand periods to reduce

variations in plant production. It may be likened to a warehouse. However, the

clearwell and the storage time it provides are both a blessing and a curse for

surface water treatment plants. This point will be expanded on in later sections.

High Service Pumping:

These pumps provide the energy required to move the treated water out into the

distribution system at the volume and the pressure required.

Distribution system storage:

Distribution system storage is a means of storing water at different locations out

in the community to provide the ability to maintain both pressure and volume in

locations where such could not be reliably accomplished by the high service

pumps at the treatment plant. This storage can be in the form of elevated tanks

commonly seen around communities or in the form of underground storage tanks

where the water is transferred back to the distribution system by pumps when

needed.


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Each of these unit processes were looked at in detail during this study and a method was

developed to optimize the performance of each to reduce the production of disinfection

byproducts in the water without adding substantially to the operational complexity of the

facility.

B) What is Optimization?

One dictionary definition of optimization is to make something function at its best.

Another definition of optimization is to accomplish a task with the smallest amount ofeffort. The later definition is often confused with the concept of minimization. By either

definition, something must be given up.

In the past, disinfection byproducts (DBPs) were not considered when treating water.

Chemical dosages and process unit sizes were determined base on what would produce

an acceptable product for the smallest investment. When DBPs were found and

determined to pose a significant health risk to those consuming the water, (Chloral

Hydrate in Drinking Water (2007)) many previous treatment strategies and treatment

plants proved to be, for the most part, inadequate. (Hill, Fred (2007)), (World Health

Organization (2004)).

In optimizing a water treatment plant for DBP control it was found that there were

optimum chemical dosages and optimum methods of operating individual treatment units.

I some cases a study of the chemical dosages produced a Bell Curve while others reached

a point of diminishing return (Periio, M. (2006)). When studying the physical treatment

unit sizes, most often the principle of diminishing return was the determining factor.

However, the strategy for operating the treatment units often produced a Bell Curve

(Heinonen, Pekka and Pisto, Sannimaria -Lopez (2007)).


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In this study we will examine what was done to optimize chemical dosages and the

operation of the treatment units for DBP control.

C) Disinfection Byproducts

1) What Are Disinfection Byproducts?

Disinfection byproducts are produced when the chlorine that is added to the water for

disinfection reacts with the small amounts of organic matter that is left in the water aftertreatment. The terms applied to these contaminants are THMs and HAA5s (Weeks,

Daniel P., PhD (2003)). These terms are acronyms for Trihalomethane and the five Halo-

acetic acid compounds presently being tested for.

On the periodic table of elements, the elements in the column in which chlorine resides

are referred to as halogens. Therefore the term halo is applied to these compounds.

The chlorine compound most commonly used for disinfection is Hypochlorite. It is

produced when chlorine gas reacts with water. The hypochlorite molecule acts as an

anion with a charge of negative one (1-). The molecule consists of one chlorine atom, one

oxygen atom and depending upon the pH, a hydrogen atom or an alkali metal (as found in

bleach, sodium hypochlorite). The effectiveness of this molecule comes from the fact that

it contains two of the most highly active, negatively charged elements, oxygen and

chlorine (Weeks, Daniel P., PhD (2003), pg. 36). This combination disinfects by

disrupting the structure of the molecules that make up the outer membranes of

microorganisms and viruses, and then by upsetting metabolic activities within the cells.

Organic molecules can be generally classified as saturated and unsaturated. Saturated

organic molecules have hydrogen atoms at all locations on the carbon atom or carbon


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atom chain where substitution can take place. Unsaturated organic molecules have

something other than hydrogen at one or more of the available sites. (Basuray, Sagnik and

Chia Chang, Hsueh, (2007))

In the study of biology you will find that the molecules making up the membranes of

microorganisms are unsaturated organic molecules, therefore a reaction with hypochlorite

is possible. In the concentrations used for disinfection, hypochlorite will seldom react

with saturated organic molecules. The unsaturated organic molecules already have one

of the hydrogen atoms substituted by an oxygen atom or carbon atoms that are doublebonded to other carbon atoms. These substitutions upset the balance of charges

(electrons) around the carbon atom or carbon atom chain allowing the highly negatively

charged components of the hypochlorite molecule to remove the remaining hydrogen

atoms and substitute for them.

These molecules that are not fully saturated with hydrogen come from the metabolic

activities of other living things or from the remains of those living things that have died.

Since these substituted molecules tend to be slightly polar in nature because of the

presence of the oxygen or the double bond, they tend to be highly soluble in water. An

example of these molecules would be methanol alcohol, acetic acid (vinegar) and ethanol

alcohol. All of which are common precursors for disinfection byproducts.

Chlorine is not the only halogen element found in these DBP compounds. Small amounts

of bromine will be commonly found in natural waters with trace amounts of iodine being

occasionally found. These two elements are not normally found in a state that will allow

them to engage in substitution reactions. They are oxidized to hypobromite and

hypoiodite by the hypochlorite allowing them to engage in these reactions in the same

manner as the hypochlorite (Pascal Roche, Benanou, David. (2006)).


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Although it is said that several hundred halogenated organic compounds have been

identified, the compounds tested for in these two groups are produced in the largest

quantities and have been identified as posing a threat to the health of those who consume

the water.

The THM compounds tested for are Chloroform, Bromo-dichloro-methane, Dibromo-

chloro-methane and Bromoform. The HAA5 compounds tested for are Monochloroacetic

acid, Monobromoacetic acid, Dichloroacetic acid, Trichloroacetic acid, Bromo-

chloroacetic acid and Dibromoacetic acid.

2) What is Naturally Occurring Organic Matter?

Naturally occurring organic matter (NOM) consists of soluble and semi-soluble organic

(carbon based) molecules. The molecules are the remnants of organisms that have died,

were eaten, or were produced from the metabolic activities of the organisms that inhabit

the water and the surrounding water shed that provides the source of the water to be

treated. These molecules vary in size from single carbon (methyl) alcohols and

aldehydes, to massive humic acid molecules that may contain more that 10,000 carbon

atoms. These larger molecules are the ones that give healthy river and pond water its

characteristic earthy or musty smell (Prashant, Kumar (2003)).

In most natural systems the tendency is for the organisms to utilize the organic molecules

as food and successively break them down into ever smaller parts. Often these remaining

small molecules are utilized by bacteria as food and converted to a final mineral

(inorganic) state. However, small quantities of them often remain. These remaining

molecules are the molecules that provide the substrates (precursors) for THM and HAA5

compounds.


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Often during treatment strong acidic, alkaline or oxidizing chemicals are applied to the

water. Some of these chemicals have been found to increase the number of precursors in

the water by breaking pieces off of the very large molecules during the treatment process.

These are some of the concerns we will be addressing during the optimization process.

Those are; how to remove the larger molecules without creating more precursors and to

utilize the chemical conditioning and adsorptive characteristics of certain treatment

chemicals to remove as many of the precursors already present as possible.


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II) Optimization

A) Examination of Historical Records

The examination of historical operating records is a critical part of any optimization

work. This should include any information the plant operators have compiled over the

years. Most of the records will be the results of standardized laboratory tests. This type of

information is the most useful when comparing the performance of the processes toindustry benchmark standards. It allows for trending of critical parameters and the

building of relationships between operation of the plant and finished water quality.

However, the most often overlooked information is notes made by the operators

expressing subjective opinions about the performance of a piece of equipment, some

attribute of the water that is not tested for regularly such as the color or odor of the raw

water, weather conditions or an opinion pertaining to the quality of a treatment chemical.

Any of these personal insights have the potential to help direct energy in the most useful

direction. Many times this information is only available through lengthy conversations

with the staff or from operators logs that do not contain test data. Often these notes are

about events within the plant or the water shed. Although these notes may not directly

affect the data, they may explain anomalies and allow parsing of the data that would

otherwise tend to skew the analyses of the data.

1) Water Quality for the Previous Two Years

Because the amount of data collected on a daily basis at most water treatment plants can

be immense, it is necessary to limit it to a range that will provide the most useful

information for the work at hand. Experience has shown that the overall source water


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quality will change very little over time if there have been no major changes within the

watershed. Therefore two years of data will allow the observation and trending of both

seasonal and weather related changes along with changes in the process units

Table 1 is a listing of the average water quality data for the two years prior to this study.

a) Raw Water Source and Raw Water Characteristics

Initially the raw water source is looked at to determine if it is capable of supplyingenough water to meet the needs of the community. This is an important consideration

because the quality of the water in the stream will vary over the course of the year and if

the amount of water available in the stream at any given time is sufficient to allow

impounding; the plant operators can be selective and impound only when the water

quality is determined to be acceptable.

The basic parameters used to determine water quality are:

Turbidity

Organic content (determined by UV254 scan)

Alkalinity

Hardness

The first parameter directly affects the longevity of the reservoir since the turbidity in a

river is primarily composed of small suspended particles that will become sediment in the

reservoir. The other three parameters directly impact the economics of treating the water

by dictating the amounts of treatment chemicals required to achieve an acceptable

finished product.

The raw water source is the Blanchard River. According to the USGS the Blanchard

River serves a water shed of approximately 350 square miles (USGS 04189000


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Blanchard River) and the river has an average monthly flow of 271 cubic feet per second

(2,027 gallons per second), which equates to 175 million gallons per day. From the data

indicating an average flow past the treatment plant of this magnitude and the

communitys average need being less than 3 million gallons per day, the treatment plant

operators can be selective. Conversations with the operators indicated they were using

this to their advantage.

b) Water Quality after Treatment in the Clarifiers

The quality of treatment obtained through the clarifiers is probably the most critical stage

of the treatment process. The clarifiers are in essence large high rate chemical reaction

vessels. As with any chemical process there are several factors which will determine the

overall efficiency of the process.

The basic characteristics of the clarifiers and their average effluent water quality are

detailed in Table 2.

The operators perform laboratory tests on the clarified water to determine the

effectiveness of treatment. Although these tests are not mandated by any regulatory

agency, they are considered necessary by the operators to control the process. These tests

are:

Turbidity

Alkalinity

Hardness

pH

UV254

Turbidity on clarified water is an indicator of the effectiveness of treatment as it relates to

the removal of suspended and precipitated matter from the water. The largest portion of


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these vessels is designed to provide quiescent conditions with a decreasing flow velocity

as the waster rises through the outer portion.

The alkalinity of the water is a measure of the amounts of calcium and magnesium

present that is associated with a carbonate or hydroxide anion. Often times this is referred

to as the buffer capacity of the water.

The hardness of the water allows the operators to determine the total amount of calcium

and magnesium in the water and differentiate between the amount of calcium andmagnesium that is alkalinity (carbonate) and the amount of calcium and magnesium that

is associated with non-carbonate anions.

The pH of the water allows the operators to determine the species of the carbonate anions

present since the balance of carbonate and bicarbonate anions is critical to the stability

(corrosiveness) of the water; this allows them to determine the amount of adjustment that

is required in the recarbonation process.

The results of the UV254 analysis performed on the clarified water is compared to the

results of the UV254 analysis performed on the raw water to determine the processs

efficiency at removing organic material from the water.

As with the raw water, laboratory analyses records from the previous two year was

examined. The information shown in Table 2 reflects the averages of the clarified water

quality for the two years prior to this study.

c) Water Quality after Recarbonation


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During precipitative softening in the clarifier the pH of the water is raised by the addition

of calcium hydroxide (lime) to a level where all of the alkalinity is converted to either

carbonate or hydroxide species. These alkalinity species associated with calcium and

magnesium, respectively, have a low solubility at the elevated pH allowing them to come

out of solution (precipitate). Under these conditions the remaining alkalinity is barely

soluble and is just at equilibrium. This remaining alkalinity is considered unstable

because even slight changes in either temperature or pressure will cause it to plate out on

the inside of pipes and plumbing fixtures slowly plugging them.

More importantly, if this unstable water is applied to the filters, which immediately

follow recarbonation, this alkalinity will plate out on the filter sand increasing the

effective size of the sand grains. This increase in grain size will reduce the ability of the

filters to remove small particles.

Recarbonation is the process used to alter the alkalinity species and adjusted them to a

more soluble form. The process is the addition of carbon dioxide gas directly to the water.

Upon contact with the water, the carbon dioxide gas reacts with the water to form the

weak acid, carbonic acid, and dissolves. The carbonic acid first reacts with the hydroxide

anions to form carbonate and water. Once all of the hydroxide anions have been

converted, the remaining carbonic acid reacts with the carbonates to produce bicarbonate

anions, which are slightly acidic. (Edwards, M., Scardina, P. (2006))

A proper balance of the carbonate to bicarbonate alkalinity will produce finished water

that will neither corrode metal components nor deposit on the interior surfaces of pipes

and fixtures. At this point the water is considered chemically stable.

Here the operators performed laboratory analyses to monitor the process. These analyses

are:


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Alkalinity

pH

The alkalinity test indicates the species and concentrations of the alkalinity present. Since

at this point the pH is a function of the balance of the alkalinity species, (OTCO, 2007,

Precipitative Softening) it serves as an indicator of the correctness of the alkalinity tests.

d) Water Quality after Filtration

Following recarbonation, the treated water is applied to three high rate (rapid) sand

filters. Filtration is normally looked upon as a polishing process. However, the filtration

process, when operated correctly provides a highly efficient barrier against

microorganisms and the cysts of several pathogens.

Because of this process importance to the health of the systems users, the performance

of the filtration process is the most tightly regulated of all of the treatment processes.

There are three analyses performed of the filtered water. These are:

Turbidity

Alkalinity

pH

The overall performance of the filter and the preceding processes are evaluated by the

turbidity of the filtered water. By federal law, the filtered water turbidity must be less

than 0.3 Nephelometric Turbidity Units (NTU) in 95 percent of the samples taken every15 minutes and the turbidity may not exceed 0.5 NTU at any time.

The reason for this is that it has been found that microorganisms can live on and within

the small particles passing through the filter and possibly avoid deactivation by the

disinfection process in this way.


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Therefore, when the filter operation records were examined, great attention was given to

any exceedances and the quality of the water being applied to the filters.

There are several other operating parameters that can be extracted from the basic filter

operating data pertaining to the economic efficiency of the filters. These parameters will

be elaborated on in Section II, 2, Evaluation of Individual Unit Processes.

The alkalinity of the filtered water is monitored closely. This parameter directly indicatesif carbonate deposits are being formed on the sand grains. If there is a decrease in the

alkalinity of the filtered water it would indicate that the water had not been fully

stabilized by the recarbonation process.

If deposition is determined to be occurring, the amount that is being deposited can be

estimated by converting the difference in alkalinity between the filtered and unfiltered

water to pounds per day. Deposition on the sand grains will increase the effective size of

the sand grains and reduce the filters effectiveness at removing smaller particles.

Again here pH is looked at to verify the accuracy of the alkalinity test.

e) Water Quality at the Plant Tap

The finished water at the plant tap is subjected to a battery of tests that are mandated by

the Ohio and US Environmental Protection Agencies (inclusive, EPA). A list of these tests

is shown in Table 1 and the two year average of these tests is shown in the Finished Water

column.

The parameters most frequently tested for are:


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Turbidity

Alkalinity pH

Hardness

Chlorine residual

Here again the turbidity of the finished water is the primary indicator of the success of the

preceding processes. Here also the same limits for turbidity are enforced that apply to the

filter effluent and for the same reasons.

The alkalinity, pH and hardness are used to determine the stability of the water. These

parameters combined with the water temperature, allow stability indexes to be calculated.

On Table 1 these indexes are the Langelier Index (LI) and the Calcium Carbonate

Precipitation Potential (CCPP). The Langelier Index is a non-dimensional number. Values

greater than zero (0) indicate a tendency for carbonates to precipitate and values less than

zero (0) indicate corrosive water.

The CCPP calculation is much more complex than the Langelier Index, and will give a

result that indicates in milligrams per liter how much alkalinity may be lost from the

water (precipitated) or gained by it (corrosion) to reach stability.

The chlorine residual present in the finished water is a measure of the chlorine left

following disinfection with chlorine gas or sodium hypochlorite. This parameter is also

regulated by the EPA (Formation of Chlorinated Organics in Drinking Water (2005)).

To remain in compliance with the regulations the amount of free chlorine (hypochlorite

ion) remaining in the water must be >0.2 mg/L at any point in the distribution system but


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One parameter closely studied in an optimization study is the chlorine demand. This is

the difference between the chlorine residual present in the finished water and the amount

of chlorine gas or hypochlorite ion applied to the water.

Since the primary focus of this optimization study is to reduce disinfection by product

and since the level of disinfection by product produced can be closely correlated to the

chlorine demand of the water; this parameter is of great interest and value.

2) Evaluation of Individual Unit Processes

During this phase each of the individual unit processes are evaluated from three

perspectives. These are:

1) Their average performance over the preceding two years

2) Physical characteristics in relationship to accepted minimum industry standards

3) Their present mode of operation.

a) Existing Pretreatment Capabilities

Pretreatment is generally used as a conditioning process. The most common chemicals

used for pretreatment are chemical oxidizers and adsorbents. The purpose of these

chemicals is to oxidize both organic and inorganic contaminants and to adsorb

contaminants and some of the contaminants conditioned by oxidation prior to them

entering the following treatment processes.

Currently there were no facilities dedicated to providing pretreatment.

There are two chemicals available for pretreatment. These are potassium permanganate

and powdered activated carbon (PAC) (Gaulinger, Siegfried. (2007)).


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b) Raw Water Supply and Low Service Pumping

The Blanchard River serves as the raw water source. An above ground reservoir,

constructed in 1971 is used to store raw water for the treatment plant. A river pumping

station is located adjacent to the Blanchard River. The pumping station contains screening

equipment and three pumps. Pump capacities are shown in Table 4.

The reservoir is a 28-acre impoundment basin that has a storage volume of 121 million

gallons at an average depth of 21 feet. The usable volume based on ODNR water

overflow restrictions is approximately 106 million gallons. The reservoir does not

provide sufficient storage volume based on current guidelines. According to current

guidelines, the Ohio EPA recommends that total raw water storage should provide a

minimum of 270 days based on the average plant production rate. The current average

plant production rate is approximately 1.6 MGD. Based on this the reservoir currently

only provides 66 days of storage. At the current plant design flow, the reservoir will

provide only approximately 35 days of storage. Additional raw water reservoir storage

should be considered. Any additional reservoir capacity needs to be evaluated based on

existing river flow data and Ohio EPA recommendations.

The elevation of the water in the reservoir is normally maintained at a height sufficient to

supply the head (pressure) necessary to move the water through the initial treatment

processes at a rate of 2,400 gpm. When the water elevation in the reservoir is below this

minimum, two raw water pumps provide the necessary head. Normally these pumps are

not used.

Each of these pumps has a capacity of 2,100 gpm at a head of 25 feet. Each is driven by a

20 horsepower motor. Firm raw water pumping capacity (capacity with one pump out of


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service) is 3.0 MGD. Any future plant expansion plans should address additional raw

water pumping capacity.

c) Rapid Mixing

One in-line mixer is located in the raw water inlet pipe, although it is currently not used.

The mixer is driven by a one horsepower motor. The estimated detention time in this

mixer is less than one second. The estimated velocity gradient (G value) for the mixer,

when used, is between 2,270 sec

-1

and 3,320 sec

-1

. High G values are necessary for in-linemixers particularly when charge neutralization coagulation is employed (Zeta-Meter Inc.

Fourth Edition).

Here however, sweep coagulation treatment is used rather than charge neutralization for

both turbidity removal and organics control. Mixing energies of this magnitude have been

found to be detrimental to sweep coagulation where the intent is to develop a large fragile

floc particle.

When the mixer is operating, the G value produced is greater than that required for sweep

coagulation and the detention time provided is too short. For these reasons, it appears that

the in-line mixer serves little purpose in the existing treatment process and should be

removed.

There are two rapid mix basins complete with mechanical mixers. The basins can be

configured for either series or parallel flow depending on treatment needs. One basin is

dedicated to each clarifier. The primary (west) rapid mixer currently was operated at

approximately 30 percent of its maximum speed. The east rapid mixer is currently not

used. Each rapid mix basin has a volume of approximately 1,500 gallons. This provides a

detention time of 43 seconds at the design flow rate under series operations. The


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detention time in each basin under parallel operations is 87 seconds. The current

recommended standard for rapid mixing establish a detention time of not more than 30

seconds (Recommended Standards for Water Works, (2003)). The existing rapid mixers

are five horsepower units that can produce an estimated velocity gradient (G value)

between 505 sec-1 and 740 sec-1 depending upon the raw water temperature. The primary

(west) rapid mixer currently is operated at a speed that produces a G value between 290

sec-1 and 424 sec-1 depending on the water temperature. The current recommended

standard is a minimum G value for rapid mixers of 900 sec-1 (Recommended Standards

for Water Works, (2003))

The existing rapid mix basins and mixers do not meet current recommended standards.

The excessively long detention time is most likely interfering with the coagulation

process because the newly formed floc particles are not taken away from the vicinity of

the mixer quickly enough and are being sheared prior to leaving the basin. Additionally,

the large cross sectional area of the basin in relationship to the diameter of the mixer

impeller is likely allowing substantial amounts of water to bypass the mixing process.

The existing basin flow configurations exhibit desirable rapid mix design characteristics.

Water flow enters the top of each rapid mix basin and is directed downward toward the

clarifier influent piping. Properly sized, each basin would be very beneficial to the

optimization efforts for coagulation treatment. Optimum rapid mixing conditions employ

the proper G value for mixing, pinpoint application of the coagulant chemical, and the

use of counter current mixing.

Coagulant dispersion is best accomplished when the coagulant is applied near the eye of

the mixer impeller. To take advantage of counter current mixing technology, the rapid

mixer is configured to push water against the flow through the basin. This is


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accomplished by setting the mixer drive unit for the correct rotation based on the impeller

design and water flow characteristics.

d) Clarifiers (Coagulation, Flocculation, Sedimentation)

i) Coagulation

At this time coagulation is provided by adding ferric chloride to the raw water through a

connection to the in-line mixer, even though the mixer is not operated. Coagulation isused to foster the gathering of suspended particles and colloids into a settleable floc

material. Coagulation also can be used to remove dissolved and suspended organics from

the water (Enhanced Coagulation for Surface Water (2006)).

The average dosage of ferric chloride presently applied for treatment (32 mg/L) indicates

that sweep coagulation is the mechanism of coagulation. Sweep coagulation is a term

used to indicate how particles and solids are removed from the water. In sweep

coagulation the coagulant reacts with the alkalinity in the water to form sticky hydroxide

floc particles. These hydroxide floc particles act like a net to sweep other particles and

solids from the water. Particles and solids absorbed into the floc particles materials are

later removed during sedimentation.

However, the G value produced in the rapid mixing appears to be insufficient for sweep

coagulation. As previously mentioned, new rapid mix units should be installed to match

the proposed basin modifications.

Enhanced coagulation, either by pH adjustment or by increased coagulant dosage, is most

likely needed to effectively reduce DBP precursor concentrations prior to chlorination of

the water (Enhanced Coagulation for Surface Water (2006)). DBP precursors are organic


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contaminants that create disinfection byproducts (DBPs) following chlorination of the

water. The DBPR established requirements for enhanced coagulation, TOC removal, and

maximum contaminant levels for DBPs. Bench-scale evaluations will be performed to

predict the needs for coagulation and to identify the needs for effective DBP precursor

and TOC removal (Garca, Indiana (2005)).

Currently, lime and soda ash are added to the raw water flume upstream of the primary

(west) rapid mix basin for softening. The lime may be acting as a coagulant aid for

improved turbidity removal. The current application of lime and soda ash at this locationare most likely interfering with coagulation treatment.

These two chemicals quickly increase the water pH well above the optimum pH for

coagulation. Since sweep coagulation is employed in treatment, lime and soda ash should

be applied at least 10 seconds downstream of the coagulant feed point.

ii) Flocculation

The flocculation zone of each clarifier was designed to aid in the development of floc

material from the chemically treated water to increase the removal of certain

contaminants. The existing flocculation mixing equipment has been out of service since

1973. It appears that lime scale accumulations on the mixers rendered them inoperative.

No mechanical mixing of the chemically treated water occurs at this time. For effective

flocculation, it is recommended that the mixing intensity (G value) be maintained

between 20 sec-1 and 70 sec-1. Adjustment of the flocculation mixer speeds is crucial to

the optimization of flocculation treatment. Mixer speeds must be adjusted based on floc

density, floc settling characteristics, and water temperature.


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The original flocculation mixers had variable speed capabilities. New mixing equipment

is needed for flocculation and should have variable speed capabilities.

Floc settling rates and filterability index tests were performed as part of the evaluation of

existing treatment. The floc settling rate test helps determine the ability of floc material to

settle and allows the estimation of the clarifier up-flow rate necessary to allow effective

settling of the floc. The test results showed that the floc size (0.5 mm diameter) is

sufficient, but the floc density is too low for effective sedimentation.

Floc density is a function of coagulant dosage, mixing intensity, and detention time.

Variable speed mixingequipment is needed to enhance flocculation and to increase floc

density. The maximum clarifier up-flow rate determine from the test procedure was

estimated to be 0.63 gpm/ft2. On the day of the test, the actual up-flow rate was calculated

to be 0.66 gpm/ft2. More agitation (higher G value) is needed to increase the density of

floc material produced during the flocculation process.

Filterability index is a rough measure of the efficiency of particle removal from

treatment. Index values typically range between 1.05 and 1.3 in well optimized treatment

processes. A filterability index of 1.6 was determined for the settled water produced by

the primary (west) clarifier. A filterability index of 1.5 was determined for the settled

water produced by the secondary (east) clarifier. Index values greater than 1.3 indicate a

need to improve treatment.

Necessary improvements may include proper dosage control, changes in rapid mix and

flocculation mixing intensity, and the use of a polymer as a coagulant aid. Deficiencies in

rapid mixing and flocculation mixing were previously discussed. Polymer addition and

other coagulants will be evaluated to determine if they could improve floc density and

settling capabilities.


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Recommended Standards establishes a detention time for flocculation at no less than 30

minutes at the design flow rate. The current rated design detention time for flocculation is

approximately 45 minutes using both clarifiers in parallel operation. At the normal

treatment flow rate (approx. 2.25 MGD), each clarifier provides a flocculation detention

time of approximately 30 minutes. Actual flocculation detention time is approximately 30

minutes since only the primary (west) clarifier is presently used for flocculation treatment

at 2.25 MGD. The secondary (east) clarifier is presently only used for additional settling.

Although the clarifiers appear to meet the detention time requirements for flocculation,

the mixers are inoperative. Flocculation, therefore, fails to create the proper floc density

for effective particle removal. New mixers are necessary to optimize flocculation and to

improve floc density.

An estimate of the solids concentration in the reaction (mixing) zone of the primary

(west) clarifier was determined to be 19 percent by volume. An estimate of the solids

concentration in the reaction zone of the secondary (east) clarifier was not determined

since its present function is only as a secondary sedimentation basin. Optimal

flocculation treatment occurs when the reaction zone solids concentration is between 5

percent and 25 percent by volume. It appears that an optimal solids concentration is

maintained in this clarifier for treatment.

Based on the evaluation of flocculation treatment in the existing clarifiers, improvements

are needed to optimize flocculation.

iii) Sedimentation


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The outer portion of the two up-flow clarifiers provides sedimentation for the treated

water. The clarifier design characteristics are shown in Table 5.

The existing clarifier design characteristics appear to meet current recommended

standards. Clarification and sedimentation detention time must be at least four hours

based on current recommended standards. The combined detention time for

sedimentation also exceeds the detention time recommended under current recommended

standards (Recommended Standards for Water Works, (2003)).

Each clarifier has an up-flow rate lower than current recommended standards. The

maximum up-flow rate for clarifiers using softening treatment is 1.75 gpm/ft2based on

recommended standards. Up-flow rates for clarifiers using coagulation treatment only is

1.0 gpm/ft2based on recommended standards using the present calculated up-flow rate of

0.66 gpm/ft2. The existing clarifiers currently meet the standards for coagulation

treatment established in the recommended standards (Recommended Standards for Water

Works, (2003)).

The weir overflow rate (WOR) for clarifiers is established in Recommended Standards at

not more than 20 gpm per linear foot of weir. Both the design and operational WOR are

less than the recommended standards. The WOR for each clarifier was calculated to be

1.8 gpm/ft and 3.6 gpm/ft at design flow for parallel and series operations, respectively.

These low flow velocities reduce the tendency for solids billowing and vortexing leading

to excessive solids carryover from the basins.

The settled solids concentration in the sludge withdrawal pipe from the primary (west)

clarifier was found to be 100percent by volume. Optimal treatment has been found to

occur when this solids concentration is maintained between 70 percent and 95 percent by

volume. It appears that settled solids are not removed from the clarifiers at an adequate


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rate. Improvements to the solids management practices and adjustment of the solids

removal schedule are needed for this clarifier. Adjustments to the solids removal schedule

for the secondary (east) clarifier were also found to be needed. The solids removal rate

must be adjusted to match the solids production rate during treatment. Estimating the

solids production rate could be added to the routine process control schedule. Results of

the calculations can be used to establish solids removal rates for each clarifier.

The sludge collector operating speed was measured as part of the evaluation. Based on

measurements, the tip speed of the sludge collector was determined to be 2.8 feet/minute.Recommended Standards establish the operating speed of sludge collector mechanisms at

no more than 10 feet/minute. The collector mechanism is operating at a speed

significantly lower than permitted by current recommended standards. This desirable

operating condition helps prevent solids billowing within the clarifiers.

The existing clarifiers can be operated either in a parallel or series flow mode. Ohio EPA

requires that both parallel and series operating conditions be available for solids contact

clarifiers. Currently, the clarifiers are operated in series flow with treatment only being

provided in the primary (west) clarifier. The secondary (east) clarifier is used only for

secondary sedimentation. The water quality produced by this operation meets current

drinking water standards. Compliance with anticipated drinking water standards should

be achieved utilizing some improvements or modifications. Proposed clarifier

improvements are discussed later.

Settled water turbidity averages 1.0 NTU with maximum turbidity levels at

approximately 2.3 NTU. Sedimentation should produce water having a turbidity level

less than 5 NTU and preferably less than 3 NTU, placing the present resulting turbidity

within acceptable parameters.


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Lime is applied to the water for softening. The average alkalinity concentrations typically

produced in the treated water produces a total alkalinity and hydroxide alkalinity

concentration of 53 mg/L and 20 mg/L, respectively. An optimum total alkalinity

concentration for effective corrosion control is typically between 60 mg/L and 80 mg/L.

The hydroxide alkalinity concentration necessary for optimum softening treatment is a

function of the raw water magnesium concentration which determines the lime dosage

necessary for magnesium precipitation. Further discussion on optimum hydroxide

concentrations is provided under softening treatment.

Enhanced coagulation requirements under the DBPR were previously described. Current

TOC removal was determined to be approximately 37 percent. Although the minimum

TOC removal requirements appear to be met using the current treatment, additional TOC

removal is needed to achieve compliance with future THM requirements. However,

compliance with enhanced coagulation and TOC removal requirements does not assure

compliance with the maximum disinfection byproducts limits.

e) Recarbonation Basins

A recarbonation basin and carbon dioxide generating equipment were constructed as part

of original plant. In 1993, the carbon dioxide generating system was replaced with a

liquid carbon dioxide storage tank and a diffuser system.

The existing basin configuration has a mixing zone and a stabilization zone. The mixing

zone provides a detention time of three minutes, while the stabilization zone provides a

detention time of 31 minutes. Recommended Standards establishes a total recarbonation


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detention time of 20 minutes including a mixing detention time of at least three minutes

at design flow. The existing recarbonation basin provides a detention time that exceeds

current recommended standards.

The recarbonated water typically has average carbonate alkalinity and bicarbonate

alkalinity concentrations of 24 mg/L and 25 mg/L, respectively. Optimal recarbonation

for stability control should produce a water quality that is nearly equal in bicarbonate

alkalinity and carbonate alkalinity concentrations. Based on this guidance, it appears that

recarbonation of the settled water will produce adequate stability control. Water having

carbonate alkalinity concentrations greater than approximately 35mg/L will tend to plate

out on surfaces including the filter sand grains causing growth of the grains. Filter sand

growth can increase turbidity levels by allowing the smaller particles to pass through the

filter.

Recarbonation treatment is discussed further under chemical feed applications in this

section.

The existing recarbonation basin has no roof. Consequently, sunlight and warm water

conditions foster the growth of algae in the basin. Algae growth creates a distinct green

coloration in the treated water and may be producing additional organic contaminant

concentrations in the water applied to the filters. These organics, if left untreated before

chlorination, could contribute significantly to the disinfection byproduct (THM andHAA5) concentrations created by disinfection.

A roof should be constructed over the recarbonation basin to reduce algae growth during

warm weather months. This roof would provide additional protection against birds and


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other small animals that could enter the basin and cause bacterial contamination of the

treated water.

f) Filtration

There are three rapid sand dual media filters to remove fine particles for final polishing

treatment of the water. Each filter is provided with backwash and surface wash

capabilities.

Currently no equipment or piping is supplied for filter-to-waste operations.

Filtration typically is the last barrier to remove contaminants that may be present in the

treated water. Treatment ahead of the filters should remove a significant portion of the

contaminants so that the filters can be operated effectively for particulate and microbial

removal.

Each of the filters has a surface area of 351.5 ft2, providing an approved treatment

capacity of 1.0 MGD each at the current approved filtration rate of 2 gpm/ft 2. Each filter

bed consists of approximately 12-inches of gravel, 15-inches of sand, and 7.5-inches of

anthracite. The existing filter media and gravel was installed in 1989.

The filter bed was examined by probing and excavation to determine the media depth.

This examination indicated that approximately 4.5-inches of anthracite had been lost

since the media was installed.

The approved filtration rate of the filters is 2 gpm/ft2. This is in accordance with current

recommended standards. Current operating practices produce an average rate of

approximately 1.5 gpm/ft2.


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Average filter run times are 86 hours, although the established maximum filter run time is

100 hours. Filter runs longer than 72 hours are desirable and usually indicate effective

filtration. Excessively long filter runs (greater than 150 hours) can deposit too many

solids deep into the media making it difficult to clean the filter media during backwash

cycles. It may be possible to increase filter run times without adversely affecting filtered

water quality. Any efforts to increase filter run times should be accompanied by careful

monitoring of the primary filtered water quality parameters.

Gross water production (GWP) is commonly used to help determine filtration efficiency

and filterability of the treated water. GWP of approximately 10,000 gal/ft2 per filter run is

accepted as indicating good filterability of the treated water. A typical GWP was

determined to be approximately 7,840 gal/ft2 per run. Based on the GWP determined, the

treated water appears to be filterable and the filters appear to be operating properly.

Increasing the filter run times would increase the GWP.

Filter performance can also be evaluated using filter efficiency calculations. These

calculations determine the percentage of water filtered versus wash water used to clean

the media. Filter efficiencies greater than 95 percent are accepted as indicating effective

treatment. Using this method, the filtration efficiency was determined to be 98 percent.

One backwash pump is used to supply wash water to the filters for cleaning. The

backwash pump has a capacity of 5,200 gpm. The typical wash water usage is

approximately 867,000 gallons per month or 1.8 percent of the monthly raw water

treated. Normal wash water usage should average approximately two percent to four

percent of the monthly raw water pumpage.


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The filters are currently backwashed at a rate of approximately 12.0 gpm/ft2. This rate is

lower than the existing design backwash rate and current recommended standards for

backwash. Records indicate that plant personnel do not change the backwash rate based

on water temperatures. Some media loss has been noted based on data from the original

filter media records. The cause of this media loss may be due to excessively high

backwash rates during the winter months when the water is colder and therefore denser.

As a general guideline, for each 1oC change in water temperature, the wash water rate

should be adjusted by two percent. This would provide a higher flow as the water warms

and lower flow as the water cools. Adjustment to the backwash rate should improvebackwash efficiency.

The backwash pump is capable of providing a maximum rate of 5,200 gpm which is

approximately 15 gpm/ft2.

The actual filter media expansion was measured using a bed expansion device during a

typical backwash cycle. Results of the bed expansion test are given later in this section.

The backwash rate should be established by direct measurement of the bed expansion at

different water temperatures. The expansion of a filter bed should be at least 30 percent.

The average backwash cycle uses approximately 54,400 gallons of water. As a guideline,

a typical backwash cycle would range between 100 gallons and 150 gallons per square

foot of filter area. Using this guideline, each filter backwash should use between 35,200

gallons and 52,700 gallons of wash water. Based on this, it appears that the filters are

backwashed too long during a normal wash cycle. This excessive backwash duration may

in part be caused by the backwash rate being too low (12.0 gpm/ft2 vs. 15.0 gpm/ft2) for

proper cleaning of the media at certain water temperatures.


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The condition of the existing filter beds, current filter operation, and current backwash

procedures were reviewed. The bed of Filter 2 was assumed to be representative of all of

the filters. It was probed to identify the position of the existing gravel layers. Probing

revealed that the gravel layers were intact with no significant mounding of the gravel.

Some areas of the filter bed, however, did show some disruption of the gravel.

Measurements of the gravel profile analysis revealed some areas of the filter bed had in

excess of 2-inches difference in media depth. A difference in media depth of more than

one-inch indicates potential problems with the gravel layer.

Filter 2 was cored using a coring tube to examine the media for particle retention and

backwash efficiency. Acid solubility testing and sieve analyses were performed to

evaluate the filter media to determine if the media is suitable for continued use or will

require replacement.

Core samples revealed that particle retention was close to normal. Identical quantities of

these core samples were washed with identical quantities of water. The turbidity of this

water was measured to give an indication of the quantity of particles being retained in the

media samples. Based on these turbidity measurements, particle retention was found to be

greater in the first 2-inches of the media than would be expected.

Particle retention turbidity measurements from below the top 15-inches of media should

be less than 150 NTU/100 grams. The existing filters showed a particle retention

measurement of less than this limit. A graph of the particle retention profile is shown in

Figure 1.

Core samples taken after backwash confirmed that the backwash efficiency was less than

required. Turbidity measurements taken from the media following a typical backwash

cycle show that the filter media retained a significant amount of particles in the top


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portion of the filter following the backwash cycle. As noted previously, the bottom media

layers were found to retain few particles. The top layers of the media had turbidity

measurements greater than the recommended 30 NTU/100 grams to 60 NTU/100 grams.

Turbidity measurements in this range indicate the filter media to be sufficiently clean.

Based on the turbidity profiles found, the filter examined is considered to be dirty at the

top and too clean at the bottom. This indicates improvements are needed in backwash

practices. Typical backwash profile criteria are shown in Table 5. Figure 2 is a graph of

the backwash profile found.

Current operating practice is to start the surface wash operation and then begin the

backwash flow at 3,200 gpm. Each filter is washed for approximately two minutes at

3,200 gpm along with the surface wash. The backwash flow is then increased to

approximately 4,200 gpm and continues for eight minutes. The surface wash is allowed to

operate approximately 1.5 minutes into the high rate wash period and is stopped. After

the eight-minute high rate wash, the backwash rate is reduced over three minutes from

4,200 gpm to zero gpm. Analysis of the wash water during a typical backwash period

revealed that the backwash appears to be too long and is at a rate too low for proper

cleaning of the media. It appears from the data that a shortened backwash cycle at a

higher rate is needed to improve filter media cleaning. Turbidity analyses obtained during

a typical backwash cycle are shown in Table 6.

Established operating criteria indicate that a backwash cycle is complete when the wash

water turbidity falls below 10 NTU. It is generally accepted that once the wash water

turbidity falls to 10 NTU, the backwash cycle should be terminated. Removing too many

solids from the filter media increases the filter ripening period and the initial filtered

water turbidity. The current backwash turbidities are reduced well below 10 NTU after a

typical backwash period. Based on the backwash turbidities collected, it appears that the


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filter media is clean after approximately 4.5 minutes. Periodic evaluations can easily be

made to adjust the backwash length as needed based on actual operating conditions.

A bed expansion test was performed during the filter inspection. During the test, the bed

expansion was measured to be 20.8 percent. Based on this low bed expansion, a higher

backwash rate is needed. A second test was performed at the maximum backwash rate

(5,277 gpm or 15 gpm/ft2). Bed expansion measured at the higher flow rate was found to

be 29 percent. The second test confirms that proper bed expansion can be achieved.

An acid solubility test was performed on the filter media to identify the calcium

carbonate deposition rate on the media. Calcium carbonate deposition increases the

diameter of the media grains and can increase filter effluent turbidities and particle

counts. Typical acid solubility should be no more than 2 percent per year. The acid

solubility for the anthracite and sand media were found to be 0.8 percent and 0.3 percent,

respectively. These values equate to 0.08 percent per year for the anthracite and 0.03

percent per year for the filter sand. Based on this analysis, it is apparent that

recarbonation is being used properly and is providing stable water to the filters

preventing excessive calcium carbonate deposition.

Representative samples of the filter media were analyzed using sieve analysis to identify

the current effective size (ES) and uniformity coefficient (UC) of the filter media. Sieve

analysis results showed the anthracite media has an ES of 0.39 mm and a UC of 3.85. The

1989 specifications for the anthracite during media replacement indicated an ES of 0.93

and a UC of 1.60. The anthracite media no longer meets its original specifications.

Sieve analysis results for the sand showed its ES to be 0.42 mm and its UC to be 2.06.

The 1989 specifications for filter sand were an ES of 0.492 and a UC of 1.44. The sand

media, like the anthracite, no longer meets its original specifications.


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Current Recommended Standards for filter media establish an ES for anthracite at 0.8

mm to 1.2 mm and a UC less than 1.65. Recommended Standards establishes an ES for

filter sand at 0.45 mm to 0.55 mm and the UC to be less than 1.65. The existing filter

media does not meet the recommended design criteria.

The high uniformity coefficient indicates that a higher backwash rate is necessary to

properly clean the media. Based on computer modeling, the sand and anthracite exhibit

dissimilar backwash needs for proper bed expansion. The calculated backwash rateneeded for existing anthracite is 45 gpm/ft2. The calculated backwash rate needed for the

existing sand is 31 gpm/ft2. These backwash rates cannot be achieved using the backwash

equipment and piping available.

Replacement of the filter media is considered necessary at this time to meet turbidity

regulations. Sieve analysis and acid solubility analysis should be preformed at least every

two years to determine the condition of the filter media. If the ES of the sand changes

more than 10 percent from design specifications, the media should be replaced.

Media having a low uniformity coefficient should be considered for the next filter media

replacement to reduce the backwash rate needed. This would more closely match the

filter backwash requirements to the capabilities of the backwash pump.

The Surface Water Treatment Rule (SWTR) establishes criteria for filter ripening to

reduce turbidity and particle count spikes during the initial portion of a filter run. Filter

ripening is a method used to properly condition the media in a freshly washed filter to

achieve the lowest possible turbidity and solids in the water when a filter is initially

placed in service. One of the ripening techniques is the use of filter-to-waste operations.

Filter-to-waste is a procedure of wasting the first portion of water during a filter run until


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the effluent turbidity is within acceptable limits or goals. Current filter-to-waste goals

establish that the turbidity in the filtered (wasted) water should be at or below 0.1 NTU

after a 15-minute filter-to-waste period and should not result in turbidity spikes above 0.3

NTU.

A filter-to-waste simulation was performed by plant personnel following the initiation of

a filter run. An evaluation of this showed that a filter-to-waste period of 15 minutes could

not meet the turbidity goals for filter ripening.

The simulated filter-to-waste period showed that the turbidity did not spike above 0.2

NTU, but approximately 90 minutes was needed to reduce the filtered water turbidity to

0.1 NTU. Turbidity measurements taken during the simulated filter-to-waste period are

shown in Table 7. It is apparent that the solids necessary for proper filter ripening are

being removed during backwash.

Individual filter effluent turbidity meters are needed to optimize filtration. The Long

Term 1 ESWTR requires continuous monitoring of individual filter effluents for turbidity.

Filter wash water currently is drained to a waste wash water wet well below the

recarbonation basin. The wet well was installed as part of the original plant and has a

capacity of approximately 46,000 gallons, which currently is less than one filter wash.

Wash water is pumped back to the raw water reservoir for reuse. It is not recommended to

recycle wash water for reuse unless proper treatment of the wash water is provided. Wash

water typically contains microorganisms, suspended particles, and organic contaminants

that can be 20 times greater than the raw water concentrations. Recycling these


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contaminants can lead to difficulties in treatment especially while trying to meet

disinfection byproduct and enhanced coagulation requirements.

A significant amount of biological activity was observed in the filter media during the

evaluation. It is unknown at this time what effect this biological activity has on filtered

water quality (i.e. organics), however, any such contributions are believed to be

undesirable. Periodic chlorination of the filter influent at a dosage of approximately 0.5

mg/L should control the biological activity and could improve overall filtered water

quality.

g) Transfer Pumping (Intermediate Pumping)

Three transfer pumps currently are used to transfer filtered water from the plant to the

above ground storage tanks (clearwells). Each pump has a capacity of 1,050 gpm at a

head of 42 feet. The firm capacity for transfer pumping is 2,100 gpm (3 MGD, with one

pump out of service.) It appears that the existing transfer pumps are adequate to meet the

current needs of the treatment plant.

h) Clear Well Storage (Finished Water Storage) and Disinfection

Disinfection of the filtered water is accomplished by adding chlorine to the water and

allowing a period of contact for the chlorine to react with the contaminants.

Two above ground clearwells provide finished water storage and provide the necessary

detention time (contact time). One 0.5 million gallon (MG) clearwell and one 1.0 MG

clearwell currently are operated in series following chlorine addition. The clearwells

provide a hydraulic detention time of approximately 12.2 hours at the plant design flow


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rate. The Ohio EPA has assigned an effective volume factor (EVF) of 0.25 to each

clearwell. Typical EVFs in Ohio range from 0.1 to 0.6. The EVF is based on the design

of the clearwell and physical testing by tracer to determine how soon water delivered to

the clearwells appears at the outlet. This factor determines the effective contact time in

each clearwell for CT calculations. At the minimum clearwell operating level and

maximum production rate, the clearwells have an effective detention time of 112 minutes.

Based on plant records of chlorine residuals and calculated CT values, both the minimum

chlorine residuals are maintained and the required CT values are met. Historical data

showed that there were no maximum chlorine residuals above the maximum level of 4

mg/L established in the DBPR.

Future changes in the regulations may increase the required CT values significantly for

inactivation of Cryptosporidium (and/or other microbials). Additional clearwell storage is

not needed at this time to meet CT requirements.

Design standards require that CT values for disinfection be maintained during clearwell

cleaning and maintenance operations. This requirement is met when the clearwell still in

service is operated near its maximum water level.

Baffling within the clearwells would reduce short circuiting to provide a larger EVF and

aid in meeting future CT requirements that are expected to be more stringent. This would

allow the future regulations to be met using the existing clearwells.

Water industry practices are to maintain a free chlorine residual in the finished water of at

least 80 percent of the total chlorine residual. This practice prevents chlorinous tastes and


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odors in the drinking water caused by the partial oxidation of inorganic contaminants.

The ratio of the free to the total chlorine residual in the water produced here currently

averages 86 percent.

The Ohio EPA requires that provisions for chlorination be available for treating the raw

water, settled water, filtered water, and water entering the distribution system. There are

currently chlorination points available for raw water and filtered water. New chlorine

feed points are needed at the high service pump suction header and for the filter influent.

These additional feed points will allow compliance with current recommended standards.

i) High Service Pumping

Currently, there are three high service pumps and an auxiliary connection to provide wash

water from the high service pump header. Existing pump capacities are shown in Table 8.

Based on Recommended Standards, the high service pumping is adequate for the rated

plant capacity. Recommended Standards states that the high service pumps should be

capable of pumping the rated plant capacity with the largest pump out of service. There

also appears to be sufficient variation in pump capacities to allow a variety of pumping

rates. It may be beneficial at some future date to install variable frequency drives to allow

more flexibility in pumping rates. An additional high service pump may be needed to

match pumping capacity to a future plant capacity increase. Space was provided in the

original plant design to install a fourth high service pump.

3) Chemical Feed Systems


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The chemical feed systems are at the heart of any conventional water treatment plant.

These systems have to be capable of delivering the chemicals not only in sufficient

quantity but deliver them in very accurate dosages to the right location.

Recommended Standards specifies that at least a 30-day supply of chemicals be available

in storage based on the average plant production rates. An examination of chemical usage

records and the chemical storage facilities show that there is sufficient storage for all

existing chemicals.

Recommended Standards also recommends that redundant or backup feed equipment be

provided for each chemical feed system. Currently, only the lime feed system and

chlorination systems have this redundancy.

A list of the chemical feed equipment, their capacities and application points is given in

Table 9.

a) Potassium Permanganate

At the time of this study no potassium permanganate feed system was installed. It may be

beneficial to install a potassium permanganate feed system. Potassium permanganate is

primarily used as a taste and odor control chemical as well as an oxidizer. Potassium

permanganate is commonly used for the removal of taste and odor compounds that

cannot be adsorbed by activated carbon. Potassium permanganate can also be used to

oxidize various organic compounds and provide an oxygen bond between suspended

particles for improved coagulation treatment.


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Previous to this study, the Village was granted approval by the Ohio EPA to install a

potassium permanganate feed system. The system has not been installed and should be

included in any plant improvements.

Potassium permanganate is usually added ahead of carbon pretreatment and coagulation.

It has been found that even small doses of permanganate can improve overall treatment

and water quality. Jar testing covered in Section III will bear out the viability of

potassium permanganate treatment.

Caution must be exercised when feeding potassium permanganate so that the chemical is

fully reacted prior to the application of activated carbon to avoided interference.

Activated carbon and potassium permanganate feed points must not be close to each

other.

b) Powdered Activated Carbon

Carbon dosages applied to the raw water appear to be in the normal range for a surface

water treatment plant. Carbon is typically applied for taste and odor control. Plant

personnel stated that taste and odor complaints are uncommon indicating that the

chemical dosages may be at the proper concentration for effective treatment of tastes and

odors. Use of a more reactive carbon product (higher iodine number) was recently

implemented for improved removal of taste and odor causing compounds.

It is believed that continuous carbon feed helps to control TOC concentrations which in

turn control the formation of disinfection byproducts after chlorination.


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The current carbon feed point allows for minimal carbon contact time before other

treatment chemicals are added. Shortly after carbon treatment, lime and soda ash are

applied to the water, which quickly increases the pH. Carbon is most effective at lower

water pH values (below pH 8.5).

A pretreatment basin should be considered in the future to provide sufficient carbon

contact time for optimal treatment. Normally, a 15-minute to 30-minute contact time is

recommended for carbon pretreatment.

c) Coagulant Feed System

The current ferric chloride dosage appears to be sufficient for turbidity control based on

the filtered water turbidity levels and filter run hours. The treated water results in a low

turbidity filter effluent averaging about 0.09 NTU.

Jar testing was performed to determine the coagulant type and dosage needed for

optimum organics removal, particularly for DBP precursor control. It is expected that a

much higher coagulant dosage may be needed for organics control to meet future

drinking water standards.

The most effective application point for coagulant chemicals is to the water at or near the

rapid mix impeller. This provides the best dispersion into the water in the shortest amount

of time.

Ferric chloride is currently applied to the raw water at the in-line mixer upstream of the

primary (west) rapid mix basin. The feed point should be relocated to the rapid mix basin

and should discharge immediately above the mixer impeller.


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d) Lime Feed System

Lime is applied to the water for softening. It raises the pH through the addition of

hydroxide anions that convert the more soluble calcium bicarbonate to the less soluble

calcium carbonate form allowing a portion of the calcium to precipitate.

There are two identical lime feeders currently in operation. Both feeders are capable of

supplying substantially more than the required dosage individually. Since the feeders are

supplied by separate silos they are operated in rotation on approximately a 30 day cycle.As one silo goes empty, the other is placed in service until a new load of lime arrives.

Lime is applied to the raw water inlet flume ahead of the primary (west) rapid mix basin

for softening. Typically, lime and coagulant chemical applications should be separated to

allow the coagulation reactions to proceed to completion before the higher pH chemical

is added. The most effective treatment method is to add a coagulant to the water first to

take advantage of the lower raw water pH for more effective treatment. Additionally, lime

treatment can interfere with activated carbon treatment.

The lime feed point should be relocated to the mixing zone of the clarifiers since lime

does not need high intensity mixing for effective treatment like a coagulant. Relocation of

the lime feed point also should improve coagulation by providing a more effective pH for

coagulation reactions in the rapid mix basins. Minor lime feed system modifications and

the construction of an eductor box will allow lime to be fed to the existing clarifiers

where needed.

e) Soda Ash (Sodium Carbonate) Feed System


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Soda ash aids in softening because the sodium has a lower electronegativity than either

calcium or magnesium and will exchange with them on sulfate and chloride anions. This

exchange results in the formation of calcium or magnesium carbonate, depending upon

pH, which will then precipitate.

The soda ash is presently fed at the same point as the lime, and as with the lime, this

point should be relocated to the clarifier mixing zone. As with lime, soda ash does not

need high intensity mixing for effective treatment making the clarifier mixing (reaction)

zone a

Optimization for Disinfection Byproducts_11!15!2008

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