&EPA
United Slates
Environmental Protection
Agency
Office of Water (4601M)
Office of Ground Water and Drinking Water
Total Coliform Rule Issue Paper
Effect of Treatment on Nutrient Availability
January 2007

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PREPARED FOR:
U.S. Environmental Protection Agency
Office of Ground Water and Drinking Water
Standards and Risk Management Division
1200 Pennsylvania Ave., NW
Washington DC 20004
PREPARED BY:
HDR/EES, Inc.
Background and Disclaimer
The USEPA is revising the Total Coliform Rule (TCR) and is considering new possible
distribution system requirements as part of these revisions. As part of this process, the
USEPA is publishing a series of issue papers to present available information on topics
relevant to possible TCR revisions. This paper was developed as part of that effort.
The objectives of the issue papers are to review the available data, information and
research regarding the potential public health risks associated with the distribution
system issues, and where relevant identify areas in which additional research may be
warranted. The issue papers will serve as background material for EPA, expert and
stakeholder discussions. The papers only present available information and do not
represent Agency policy. Some of the papers were prepared by parties outside of EPA;
EPA does not endorse those papers, but is providing them for information and review.
Additional Information
The paper is available at the TCR web site at:
http://www.epa.gov/safewater/disinfection/tcr/requlation revisions.html
Questions or comments regarding this paper may be directed to TCR@epa.gov.
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Table of Contents
1	Introduction	1
2	Nutrients of Concern	3
2.1	Organic Carbon Compounds	4
2.1.1	Forms of Organic Carbon in Drinking Water	4
2.1.2	Typical Source Water Levels	5
2.1.3	AOC, BDOC, and Bacterial Growth	6
2.1.4	Additional Impacts	8
2.2	Nitrogen	9
2.3	Phosphorus	9
2.4	Metals and Other Substances	10
3	Applicable Drinking Water Regulations	10
4	Treatment Impacts on Nutrients of Concern	13
4.1	Coagulation, Flocculation, and Sedimentation	13
4.2	Powdered Activated Carbon	15
4.3	Filtration	16
4.3.1	Biological Filtration	16
4.3.1.1 Additional Biological Filtration Issues	19
4.3.2	Membrane Filtration	19
4.4	Oxidation and Disinfection	22
4.4.1	Chlorination	23
4.4.2	Chloramination	23
4.4.3	Ozonation	24
4.4.4	UV	25
4.4.5	Dechlorination	25
4.5	Corrosion Control	26
4.6	Distribution System	26
4.6.1	Booster Chlorination	26
4.6.2	Distribution System Operations and Maintenance	26
5	National-Level Assessment of Control of Nutrients of Concern	28
6	Further Research	29
7	Summary	30
References	32
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List of Tables
Table 1 BDOC and AOC Levels Enhancing or Controlling Bacterial Growth	6
Table 2 Federal Drinking Water Regulations Affecting Nutrient Levels and
Microbial Growth in the Distribution System	11
Table 3 Coagulation and Drinking Water Nutrients	14
Table 4 Summary of Filtration and Nutrient Impacts	21
Table 5 Intrusion Volume Comparison of Chemical Tracer and
Volumetric Methods	28
Table 6 National Distribution of Treatment Processes	29
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Effect of Treatment on Nutrient Availability
1. Introduction
As discussed in the paper "Total Coliform Rule and Distribution System Issue Papers
Overview," EPA plans to assess the effectiveness of the current Total Coliform Rule (TCR) and
determine what alternative and/or additional monitoring strategies are available, and to consider
revisions to the TCR with potential new requirements for ensuring the integrity of the
distribution system. Part of this assessment is to examine how various treatment processes
contribute to nutrient availability in the distribution system and the resultant implications for
influencing microbial growth in the distribution system, which is the purpose of this paper. As
part of this same effort, the USEPA has issued a white paper detailing the public health concerns
associated with distribution system bacteria growth entitled Health Risks from Microbial Growth
andBiofilms in the Water Distribution Systems (2002a).
One of the primary drinking water quality concerns in the distribution system is the presence of
microorganisms. The public health impacts of bacteria growth in the distribution system have
been explored and well-documented. Distribution system conditions conducive to bacterial
growth can result in a loss of disinfectant residual, violation of drinking water regulations
focusing on microbial water quality in the distribution system (Total Coliform Rule), and growth
of opportunistic pathogens. Opportunistic pathogens are a serious concern because they can
cause disease in people with compromised immune systems, such as people with AIDS or
cancer, or very young or old people.
The USEPA is concerned with relatively high nutrient levels in drinking water because nutrients
may lead to the following drinking water problems:
•	Increased levels of microbes, including opportunistic pathogens, in the bulk water, as well as
in the pipe biofilm and sediments.
•	Loss of disinfectant residual through reactions between disinfectant and nutrients.
•	Production of toxic and/or carcinogenic disinfection by-products through reactions between
disinfectant and nutrients.
•	Unreliability of total coliform sampling due to increased growth of heterotrophic bacteria,
resulting in false-positives or false-negative coliform tests. Coliform sampling may also
become unreliable due to stimulated growth on pipe biofilms and sediments. These increased
numbers may not be represented in coliform samples of bulk drinking water.
•	Development of aesthetic problems.
Several studies have investigated the link between microbial growth and nutrient levels. Van der
Kooij and Hijnen (1982) and Servais et al. (1995) found that the main factor governing bacterial
growth was the presence of bacterial nutrients. In some cases, however, nutrient availability is
not the only controlling factor. For example, LeChevallier et al. (1996) studied the relationship
between disinfectant residual and assimilable organic carbon finding that systems with high
assimilable organic carbon needed to have high disinfectant residuals throughout their systems to
control coliforms.
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Typically, drinking water utilities control the presence of microorganisms in the distribution
system through:
•	Treatment to remove microorganisms present in the source water supply;
•	Disinfection of drinking water to inactivate microorganisms;
•	Maintaining a residual disinfectant throughout the distribution system; and
•	Conducting distribution system activities in a manner to prevent contamination.
Utilities normally select treatment for the capability to remove pathogens and other
contaminants. Treatment processes are not usually evaluated for their potential to produce a
drinking water with low levels of nutrients. It is possible that selected treatments, while meeting
criteria for pathogen removal, may produce water with a nutrient supply that can stimulate
bacterial growth.
Microorganisms can not be prevented from being present at the drinking water customer's tap
through treatment alone. Even if the drinking water at the distribution system entry point were
completely sterile, most distribution system piping surfaces have an attached biofilm
(LeChevallier et al., 1990), which is where the mass of microorganisms in the distribution
system are found. It is also possible for microorganisms to enter the distribution system through
events such as cross-connections, main breaks, construction activities, and intrusions. In
addition to the presence of a disinfectant residual, controlling nutrients and "starving" the
microorganisms present can minimize bacterial growth. Likewise, nutrients do not enter the
distribution system through treatment alone, but can enter the distribution system through the
pathways mentioned above. Storage tanks are another potential source for nutrients to enter the
distribution system.
From the perspective of improving control of pathogens within the distribution system, utilities
should consider the implications that their treatment and disinfection practices can have on
limiting the nutrient levels of their drinking water. This paper provides a literature review
examining the degree that various water treatment processes influence nutrient levels that can
promote microbial growth and describes the effects with respect to drinking water quality. The
following sections will examine the nutrients of concern, applicable drinking water regulations,
and treatment impacts on these nutrients. This paper also discusses these nutrients and treatment
impacts on a national level and needs for future research.
2. Nutrients of Concern
Microorganisms in the distribution system can thrive if provided with organic and inorganic
nutrients that promote growth (USEPA, to be published). These nutrients are:
•	Organic carbon,
•	Nitrogen,
•	Phosphorus, and
•	Metals and other substances.
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The critical nutrients for the growth of heterotrophic microorganisms in the distribution system,
carbon, nitrogen, and phosphorus, are needed in relative proportions of 100 to 10 to 1,
respectively (Geldreich, 1996; van der Kooij and Hijnen 1982, LeChevallier et al., 1996a;
Camper, 1996). Control of heterotrophic microorganisms is important because all of the primary
pathogens found in drinking water, and most of the opportunistic pathogens in humans, are
heterotrophic microbes. Coliforms are heterotrophic, but their growth on standard heterotrophic
plate counts can be limited by the presence of other organisms that suppress the growth of
coliforms (LeChevallier et al., 1980). Coliform bacteria generally need more nutrients than the
bacteria that are enumerated using the heterotrophic plate count method (LeChevallier and
McFeters, 1985).
Carbon is typically the growth-limiting nutrient in North American drinking water systems
(Camper et al., 2000). Much of the research presented in this paper focuses on the levels of
biodegradable organic carbon present in drinking water. This reflects the significance of carbon
as limiting nutrient in distribution systems. However, not all bacteria growth is limited by the
presence of organic carbon. As described later, the presence or absence of nitrogen, phosphorus,
and metals can enhance or limit growth in drinking water distribution systems. For example, a
few studies have determined that phosphorus levels could limit microbial growth in the
distribution system. Investigators (Sang et al., 2003; Miettinen et al., 1997a) indicate that in
some regions, such as Finland, China, Norway, or Japan, phosphorus can be a limiting nutrient in
drinking water supply sources. Carbon becomes the limiting nutrient, however, when nitrogen is
added. Additionally, some microbes, including opportunistic pathogens, such as Pseudomonas
aeruginosa, can degrade a range of complex nutrients present in water. Others are more
fastidious in their nutritional needs and may be starved by eliminating one important nutrient.
2.1 Organic Carbon Compounds
As discussed above, organic carbon is needed by heterotrophic microorganisms for growth in
much larger quantities than other nutrients, and as such, is often the limiting nutrient. Therefore,
much of the research on biological stability of treated drinking water focuses on organic carbon
(Servais et al., 1993; LeChevallier et al., 1991; van der Kooij, 1992; LeChevallier et al., 1994,
LeChevallier et al., 1996a; Camper et al., 2000; van der Kooij, 1997).
2.1.1 Forms of Organic Carbon in Drinking Water
Organic carbon in drinking water, measured as total organic carbon, may be comprised of
compounds such as amino, humic and fulvic acids, polymeric carbohydrates, proteins, and
carboxylic acids. These organic compounds can be separated into two categories: biodegradable
dissolved organic carbons (BDOC) that can be used by heterotrophs as a nutrient; and refractory,
or non-biodegradable, dissolved organic carbons (RDOC) which can not be consumed by
heterotrophs. AOC is a sub-category of BDOC, the most readily available fraction of the BDOC.
Volk and LeChevallier (1999) point out that while amino acids are generally a small proportion
of organic carbon in drinking water, these compounds can support a high biomass production per
unit substrate, in comparison with other biodegradable organic carbon compound.
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For the purpose of assessing carbon compounds that can impact bacterial growth in the
distribution system, AOC and BDOC are currently the appropriate parameters to measure
(Camper et al., 2000; Hambsch and Warner, 1996; Najm et al., 2000). AOC is an indirect
measurement that involves the inoculation of a sterile water sample by two specific bacteria
(usually Pseudomonas fluorescens strain P-17 and Spirillum strain NOX) and monitoring for
growth by plate count. This procedure assumes that nitrogen and phosphorus are not limiting,
and some variations of the method call for the addition of inorganic salts to assure that carbon is
the limiting nutrient. (The AOC method probably underestimates the total amount of easily
degradable organic carbon because, among other reasons, the two organisms may not be able to
easily degrade certain types of organic carbon that other organisms in the distribution system can
easily degrade.) This method is not considered applicable for routine use at utilities due to its
complexity. In contrast, biodegradable dissolved organic carbon (BDOC) can be measured by
inoculating a sterile water sample with autochthonous bacteria (e.g., a small volume of a
nonsterile water sample), and measuring the decrease in DOC concentration due to the carbon
oxidization by bacteria. In comparison with AOC, the non-AOC portion of BDOC is likely to be
made up of compounds which are more complex and have higher molecular weights (Najm et
al., 2000; Camper et al., 2000). Hambsch and Werner (1996) point out that AOC provides a
snapshot of the easily available carbon nutrients, while BDOC provides a more complete picture
of the nutrient pool available to microorganisms. In addition, since the BDOC method measures
the change in DOC directly, the results can be directly compared with TOC, chlorine demand,
DBP formation potential and other direct measures. It is important to note that there are a variety
of methods available for the measurement of AOC and BDOC, as well as a number of studies
that compare the individual methods.
From the standpoint of measuring nutrients that can stimulate bacterial growth in the distribution
system, total organic carbon is not as applicable as AOC and/or BDOC. LeChevallier et al.
(1991) determined that while TOC appeared to be related to coliform growth in the distribution
system, the levels did not decrease as water moved through the distribution system. These
results indicate that TOC may not be a good predictor of growth episodes and may not act as a
bacterial nutrient, or that most of the total organic material is not readily digestible by
microorganisms.
BDOC and AOC do not often closely correlate. This may be due to the significant differences in
measurement methodology or the substances comprising these parameters. Camper et al. (2000)
surveyed untreated and treated drinking water quality at 64 utilities and found a "weak but
significant" relationship between the two parameters. This relationship captures the variation of
the compounds measured by these parameters. However, because both types of compounds can
eventually be consumed, Camper et al. (2000) recommend that utilities evaluating their drinking
water nutrients monitor both AOC and BDOC.
2.1.2 Typical Source Water Levels
Most organic carbon enters water from natural sources, usually dying or decaying vegetation.
Thus, the type of source water used as source of supply can influence AOC in the distribution
system. Camper et al. (2000) surveyed 64 surface water treatment plants throughout the US and
measured a range of AOC of 3 - 806 |ig C/L in the source water. AOC was typically 10% of
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total organic carbon, on the higher side of the range of 0.1 to 9% cited as typical by LeChevallier
et al. (1991). However, the AOC bioassay is not a direct measure of nutrient concentrations, so
comparing the AOC number to actual TOC values are typically not appropriate. River supplies
were associated with the highest AOC levels, on average 123 |ig C/L, and the lowest levels were
associated with utilities relying on infiltration galleries or blending surface and groundwaters
(average of 41 |ig C/L) (Camper et al., 2000). Unless contaminated, groundwater is not
associated with a significant presence of organic compounds. In good quality, untreated
groundwater, AOC levels are typically very low. Haddix and LeChevallier (2003) indicate that
lower levels of AOC may be present in groundwater because microbial activity uses up the
BDOC as water moves through the soil.
Organic carbon can reach surface waters through wastewater and industrial effluent, surface
water run-off from agricultural areas, and natural organic matter (NOM). Vegetation contributes
humic matter through decay, especially in summer months, as does the growth of algae.
Nutrients can vary significantly across surface waters and seasonally. Another factor that
affected the level of AOC was watershed protection. Sources with full watershed protection had
significantly lower AOC levels.
2.1.3 AOC, BDOC, and Bacterial Growth
Studies have shown that AOC and BDOC levels correlate to controlling or enhancing bacterial
growth. Table 1 summarizes the levels of AOC and BDOC that have been associated with
increased or controlled bacterial growth. As shown, in most of the studies, higher AOC levels
are associated with promoting coliform and HPC growth. This potential relationship is
dependant upon site specific conditions such as residence time, temperature, pipe material, and
disinfectant residual concentrations.
Table 1
BDOC and AOC Levels Enhancing or Controlling Bacterial Growth During Treatment
Citation
Disinfection
Finding
BDOC
Servais et al., 1993
5 chlorinated and 2 ozonated (not
followed by chlorination) systems
Water can be considered
biologically stable when BDOC is
less than 0.16 mg C/L.
Levi aand Joret, 1990 WQTC
procddings
Unchlorinated
Water is biologically stable when
BDOC is <0.2 to 0.3 mg/L
AOC
LeChevallier et al., 1991
Chlorinated
Coliform bacteria growth was
limited by AOC of 50 |ig C/L.
vanderKooij, 1992,
vanderKooij 1997
vanderKooij andHijnen, 1982
Unchlorinated
Heterotrophic bacteria levels do not
increase when AOC is less than 10
HgC/L.
LeChevallier et al., 1994
Chlorinated
AOC levels greater than 118 ng C/L
have 57% more positive coliform
samples and 16 times higher
bacterial levels (on average) than
systems with AOC below 82 |ig
C/L.
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LeChevallier et al., 1996b and
Camper et al., 2000
Chlorinated
A trend of increasing coliform
presence was associated with AOC
levels greater than 100 ng C/L.
LeChevallier et al., 1996b
Chloraminated systems
Coliforms were not more likely to
occur in systems with AOC greater
than 100 |ig C/L compared to
systems with less than 100 |ig C/L.
However, a direct link between levels of BDOC and/or AOC in drinking water and distribution
system biological stability is not always apparent. Volk and LeChevallier (1999) concluded that
conditions causing distribution system bacterial growth are "complex and site-specific." For
example, in one study performed by LeChevallier et al. (1991), a correlation was found between
coliform bacteria and AOC in that elevated AOC levels corresponded to elevated coliform levels
seven days later. However, in the same study, Lechevallier et al. (1991) found that nutrient
levels were not predictive of HPC levels, suggesting that these organisms are not nutrient
limited. LeChevallier et al. (1991) found that HPC levels were mainly influenced by temperature
and chlorine residual levels.
Distribution system physical and chemical conditions can enhance or diminish the impact AOC
has on growth. Research has shown that in addition to AOC (or another indicator of nutrient
availability), these factors play a significant role in heterotrophic growth conditions
(LeChevallier, 2003):
•	Removal of particulate matter by filtration,
•	Disinfectant type and level,
•	Temperature,
•	Corrosion, and
•	Pipe materials.
In addition, in a 12-month study of 64 surface water utilities, Camper et al. (2000) found that
positive coliform samples were related to these factors:
•	Nutrient availability - AOC greater than 100 |ig C/L;
•	Temperature - Temperatures greater than 59 °F (15 °C); and
•	Disinfectant residuals - free chlorine residual of less than 0.5 mg/L or less than 1.0 mg/L in
chloraminated systems.
Camper et al. (2000) determined that the interaction of these factors can result in bacterial
growth problems. Utilities experiencing none of these conditions are not likely to have problems
(a probability of less than 2% of a positive coliform occurrence). In the study, 70% of the
positive coliform samples occurred when two or more of the above conditions were in place. A
utility with all three factors in place is eight times more likely to have a positive coliform sample
than utilities without any of the factors in place.
Camper et al. (2000) indicated that this difficulty in establishing a direct link between organic
nutrient levels and bacteria growth in the distribution system may also be due to following:
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•	Significant influence exerted by other factors present;
•	Difficulty in performing laboratory tests;
•	Inadequate number of samples; and/or
•	Presence of materials that may enhance the environment for growth.
2.1.4 A dditional Impacts
Organic compounds in drinking water can cause both public health and aesthetic water quality
problems. Certain species of disinfection by-products, which may be carcinogenic, are formed
by reactions between the disinfectant and organic materials in drinking water. Some organic
compounds form DBPs and exert a chlorine demand, lowering residual concentrations as DBPs
are formed. This can result in growth occurrence or the need to use higher quantities of
disinfectant. Growth occurrence can cause a regulatory violation and increased potential for
pathogen presence. Higher disinfectant levels can cause higher levels of disinfection by-
products. Organic compounds are also associated with causing unpleasant tastes and odors in
drinking water.
Little research has been done linking the presence of biodegradable carbon to the presence of
waterborne pathogens. Researchers have investigated the correlation between organic nutrient
levels and Mycobacterium avium growth in the distribution system (Falkinham et al., 2001 and
Norton et al., 2004). Falkinham et al. 2001 found a correlation between increasing AOC and
BDOC levels in the distribution system and increasing levels of Mycobacterium avium in the
distribution system. Norton et al. (2004) also found that Mycobacterium avium was able to grow
in waters with relatively low AOC and BDOC levels, >53 |ig C/L and > 0.17 mg C/L,
respectively. The impact of biodegradable carbon on the potential for regrowth of other
opportunistic and frank pathogens has not been fully quantified (Prevost et al., 2005).
2.2 Nitrogen
Nitrogen occurs naturally in source water as organic nitrogen, ammonia, nitrate, and nitrite.
Ammonia reaches surface waters through surface water run-off from fertilized fields and
agricultural feedlots, and wastewater effluent. Nitrate may be naturally present in groundwater
or reach aquifers through percolation of agricultural fertilizers, livestock manure, and surface
water run-off Geldreich (1996) indicated that in groundwater, nitrate concentrations can range
from 1.0 to 400 mg/L. Camper (1996) indicates that it is generally assumed that nitrogen is not a
growth-limiting factor due to the low concentrations needed for growth and maintenance and
high turnover of existing cellular nitrogen. Thus enough nitrogen is usually present for bacteria
to meet their nitrogen requirements for growth. Donlan and Pipes (1988) found no correlation
between organic nitrogen, ammonia, nitrate, or nitrate, and microbial population density of
biofilms in the distribution system. LeChevallier et al. (1991) studied possible microbial
nutrients in the distribution system, finding that nitrogen levels did not decrease as water traveled
in the distribution system, indicating that it was not consumed by the microorganisms to support
growth.
Skadsen (1993) determined that nitrification usually occurs when an excess of ammonia is
present in drinking water. This nutrient promotes the growth of nitrifying bacteria which convert
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ammonia to nitrites and nitrates. Nitrification causes increased nitrite and nitrate levels and can
interfere with corrosion control by reducing alkalinity, pH, and dissolved oxygen. Nitrification
consumes alkalinity at the rate of 8.64 mg/L HCO3 (Gujer and Jenkins 1974) for each mg/L of
ammonia oxidized. For waters with low buffering capacity, this can reduce pH. Additionally,
nitrification produces increased nitrite levels which can interfere with disinfectant residual,
presenting a public health concern due to the potential for unchecked bacterial growth. Cowman
and Singer (1994) demonstrated that 1.0 mg/L of nitrite exerts a free chlorine demand of
5.0 mg/L. Watson et al. (1989) determined that nitrifying bacteria secrete organic compounds
which may stimulate growth of heterotrophic bacteria. Kirmeyer et al. (to be published) points
out that nitrifying bacteria even accelerate corrosion by secreting nitric acid. The impacts of
nitrification on distribution system water quality are further detailed in the USEPA white paper
(undated) entitled Nitrification.
Nitrate and nitrite have the potential to pose threats to public health. The USEPA has set
Maximum Contaminant Levels (MCLs) for nitrate and nitrite at 10 mg/L and 1 mg/L (as
nitrogen), respectively. Nitrate can interfere with the oxygen-carrying capacity of blood in
infants, resulting in serious illness, shortness of breath and blue skin. Chronic exposure to nitrite
or nitrate can affect the spleen and there is question of whether these compounds are associated
with cancer.
2.3 Phosphorus
As discussed above, a few studies have demonstrated that phosphorus can be the limiting
nutrient in some systems. Sang et al. (2003) investigated the influence of P043"-P on bacterial
growth in effluent from pilot-scale drinking water treatment. The results demonstrated that
phosphorus became the limiting nutrient when AOC was 200 |Lxg C/L and phosphorus was below
4 |Lxg C/L. Increasing phosphorus above this level resulted in corresponding increases in bacterial
growth. Sang et al. (2003) point out that little research exists on controlling distribution bacterial
growth through controlling phosphorus presence in drinking water. As described above,
Jegatheesan et al.'s (2004) bacterial growth model demonstrated that when nutrients were at low
levels or when only carbon and phosphorus were present in significant quantities, phosphorus
appears to control the estimated amount of bacterial growth. Miettinen et al. (1997a) conducted
a laboratory study of microbial growth in a Finnish drinking water by observing growth
occurring after addition of phosphorus. Even a very small amount of phosphorus (1 |ig/L of
PO4-P) resulted in increased bacteria growth in drinking waters from groundwater and surface
source waters.
In general, phosphorus naturally occurs in groundwater or may be added as part of corrosion
control treatment. The range of naturally occurring phosphorus can vary widely. Phosphorus
has been found to be present at levels as high as 300 |ig/L or as low as 0.1 |ig/L (Geldreich,
1996). Miettinen et al. (1997a) indicates that most total phosphorus in drinking water sources is
associated with particles. In general, the dissolved total phosphorus portion, which is
biodegradable, is present in very small amounts (Miettinen et al., 1997a). Phosphate-based
corrosion inhibitors are widely used to control corrosion in drinking water distribution systems.
Several studies have shown that orthophosphates and possibly polyphates are bacterial nutrients.
Thus, typical concentrations of phosphate-based corrosion inhibitors added (1 to 5 mg P/L) may
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stimulate growth if phosphorus is the limiting nutrient as such levels greatly exceed the
nutritional requirement of bacteria (Laurent et al., 2005).
High phosphorus levels are not directly associated with adverse public health effects. However,
the discharge of phosphates and other phosphorus compounds into inland lakes is of concern
because the phosphorus is often the limiting nutrient in surface waters. Introduction of
phosphorus often increases the oxygen demand and biomass present in lakes.
2.4 Metals and Other Substances
In addition to carbon, nitrogen, and phosphorus, microorganisms also need trace amounts of iron,
sulfur, potassium, magnesium, manganese, and other substances for growth. Metals and other
elements can serve as nutrients for distribution system bacteria. Iron and sulfur reducing bacteria
are two common types of bacteria found in the distribution system. Iron bacteria are a varied
group of microorganisms that can precipitate iron (AWW A, 2004). These bacteria convert Fe2+
(soluble iron) to Fe3+ (iron precipitate). Gallionella ferruginea is one of the most important of
several types of iron bacteria which can foul water supplies. Sulfur bacteria reduce sulfur,
sulfates, and other forms of sulfur, to hydrogen sulfide gas (AWW A, 2004). In general, both
types of bacteria are considered nuisances and are not considered to directly threaten public
health. Both iron and sulfur bacteria have been proven to cause odor, taste, and color in
distribution water. Slime of iron bacteria will impart a reddish tinge and an unpleasant odor to
water (AWWA et al., 1989). These bacteria can cause flow reductions in distribution systems
(due to accumulations of ferric hydroxide) and bad tastes and odors (Christian, 1976).
Many researchers have hypothesized that water quality problems typically attributed solely to
iron bacteria fouling of wells and distribution systems may be due to the presence of a more
diverse microbial community. Iron and sulfur bacteria are not the only producers of slime; they
may be associated with slimes of other bacteria (AWWA et al., 1989).
3. Applicable Drinking Water Regulations
Table 2 presents a summary of regulations that are pertinent to the presence of nutrients and
bacteria in the distribution system. In general, regulatory limits for nutrients such as nitrate or
iron are not set to prevent bacterial growth from occurring in the distribution system. Rather,
they represent levels at which the nutrient becomes a direct public health hazard, causes aesthetic
problems, or results in other water quality problems.
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Table 2
Federal Drinking Water Regulations Pertinent to the Presence of Nutrients
and Microbes in the Distribution System
Regulation
Pertinence to nutrients or
microbes
Summary of Key Elements
Inorganic contaminant MCLs
Controls levels of nitrate and nitrite.
¦	Sets maximum contaminant
level (MCLs) for nitrate and
nitrite at the plant effluent.
¦	Sets secondary maximum
contaminant level (SMCLs) for
iron and manganese.
Surface Water Treatment Rule
(SWTR) and Interim Enhanced
Surface Water Treatment Rule
(IESWTR) and Long Term 1
Enhanced Surface Water Treatment
Rule (LT IESWTR)
Establishes controls for viruses
(4-log reduction), Giardia lamblia
(3_log reduction), and
Cryptosporidium (2-log reduction).
Systems use a combination of
filtration and disinfection to
accomplish these levels of reduction.
¦	For unfiltered systems: source
water turbidity and microbial
requirements, watershed
protection, disinfection before
entry point to the distribution
system to meet treatment
requirements.
¦	For filtered systems: sets
filtration performance (effluent
turbidity) and CT inactivation
to meet treatment
requirements.
¦	Utilities must maintain
disinfectant residual through
distribution system or meet
requirement for heterotrophic
bacteria.
¦	Sets limit for turbidity.
¦	Requires pathogen removal.
¦	Specifies treatment technique
or watershed control for
Crypto spori dium.
Total Coliform Rule
Indicates vulnerability of system to
fecal contamination and efficacy of
treatment.
¦	Sets requirements for
distribution system coliform
sampling.
¦	Sets acute MCL for fecal
coliform and E. coli.
Stage 1 Disinfectant/Disinfection
Byproduct Rule
Reduces DBP precursors (TOC)
entering the distribution system for
some systems; controls
trihalomethanes and haloacetic
acids.
¦	Remove total organic carbon
through enhanced coagulation.
¦	Controls disinfection
byproducts in the distribution
system.
¦	Sets maximum residual
disinfectant levels in the
distribution system.
Lead and Copper Rule
Sets P04"3 addition as one of the
optimal corrosion control strategies
¦	Controls corrosion of lead and
copper
¦	Requires implementation of
corrosion control strategies.
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The treatments used to comply with the following rules may have an impact on the nutrient
levels in the distribution system:
•	Chemical standards - The USEPA has set enforceable standards (National Primary Drinking
Water Regulations, 40 CFR 141.62) for nitrate-N (1 mg/L), and total nitrate-N and nitrite-N
(10 mg/L). The USEPA has also set non-enforceable standards (National Secondary
Drinking Water Regulations, 40 CFR 143.3) for iron (0.3 mg/L), manganese (0.05 mg/L),
sulfate (250 mg/L), and total dissolved solids (500 mg/L). These non-enforceable standards
were set to address issues not associated with public health, such as taste, odor, and color.
•	Surface Water Treatment Rules - The Surface Water Treatment Rule (SWTR), Interim
Enhanced SWTR, and the Proposed Long-Term 2 Enhanced SWTR require all systems using
surface water to disinfect and most systems to filter. Nutrients may be removed by filtration
and by the pre-treatment processes of coagulation, flocculation, and sedimentation. As
discussed later in this paper, disinfectants can oxidize some organic compounds, and
sometimes increase the amount of available biodegradable organics.
•	Total Coliform Rule (TCR) - The TCR requires all systems to monitor for total coliforms at a
frequency that depends upon the number of people served. The TCR does not directly affect
the nutrient levels or microbial growth on the pipes and sediment. However, if a high
nutrient level creates a significant pipe biofilm, coliforms are likely to be part of that biofilm.
When coliforms are sloughed off the biofilm into the water, they may be detected by TCR
compliance monitoring. The detection of such coliforms may interfere with the TCR by
undercutting the utility of total coliforms for detecting problems with treatment or with cross-
connections. In contrast, the detection of total coliforms may also prompt identification and
control of the problem.
•	Disinfectant and Disinfection By-Product (DBP) Rules - The Stage 1 DBP and the Proposed
Stage 2 DBP Rules set limits on the concentration of potentially toxic/carcinogenic DBPs in
the distribution system. The Stage 1 Rule achieves this purpose by requiring removal of
TOC through enhanced coagulation before filtration. This process also should remove a
significant portion of the carbon and other nutrients that microbes in the distribution system
need to proliferate.
While these regulations can impact the presence of nutrients reaching the distribution system,
none of them directly regulate drinking water nutrients. As indicated earlier, drinking water
suppliers do not typically evaluate a potential change in treatment with respect to its impact on
drinking water nutrients. In response to some regulations, utilities may actually increase nutrient
levels while implementing a treatment that meets regulations for a different parameter. For
example, the majority of disinfecting utilities use free chlorine to control bacterial growth in the
distribution system and to meet treatment requirements, per the Total Coliform Rule and Surface
Water Treatment Rule. However, chlorine has been shown to increase the levels of BDOC, as
discussed in Section 4.4.1. Additionally, as a result of the DBP rule, some utilities are
considering changing disinfectant. As described below, some disinfectants can directly affect
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nutrient levels. For instance, chloramination can result in nitrifying conditions in the distribution
system.
4. Treatment Impacts on Nutrients of Concern
Some water treatment processes influence the levels of bacterial nutrients entering the
distribution system. Additionally, the sequence of these processes can be critical to controlling
biodegradable organic carbon. Many of the aspects affecting the efficacy of these processes in
producing a biologically stable drinking water have been studied by drinking water researchers.
This section describes the impact that various treatments can have on drinking water nutrient
levels. Throughout this discussion, the impacts to BDOC and AOC are emphasized due to the
significant amount of research existing on these nutrients and because in typical conditions,
carbon is the limiting nutrient.
This section describes research that has been performed evaluating the influence of treatment
processes on nutrients resulting in decreased bacterial growth in the distribution system. These
technologies are discussed:
•	Coagulation, flocculation, and sedimentation,
•	Powdered activated carbon,
•	Filtration - biological and membranes,
•	Disinfectants and/or oxidants,
•	Corrosion control, and
•	Distribution system treatment and operations.
4.1 Coagulation, Flocculation, and Sedimentation
Coagulation is a step associated with pre-treating water prior to conventional and direct filtration.
The purpose of coagulation is to form large aggregate particles from smaller particles naturally
present in source water. This is accomplished through the addition of chemicals (coagulant,
typically alum or other chemicals) that destabilize negatively-charged particles, preventing them
from repelling each other and allowing them to form larger particles. Flocculation and
sedimentation are the subsequent steps of this process. After coagulation, the water is stirred to
facilitate the formation of larger particles, known as floe. The floe are removed from the water
through settling during the sedimentation step using conventional filtration or during filtration
for direct filtration facilities. In this discussion of coagulation and how it influences nutrient
levels in drinking water, it is assumed that "coagulation" includes the formation and removal of
large particles. In general, available research does not appear to separate out these steps and
nutrient levels are reported after these steps have been completed.
Coagulation is primarily associated with removing the hydrophobic, high molecular weight
fraction of organic compounds present in the water typically associated with humics (Owen et al.
1993). Under the Stage 1 DBP Rule, certain surface water systems (and systems under the direct
influence of surface water) must enhance their water coagulation or softening process to achieve
a specified TOC removal level because coagulation removes natural organic matter.
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Table 3 summarizes findings regarding the manner in which coagulation affects nutrients in
drinking water.
Table 3
Coagulation and Drinking Water Nutrients
Nutrient and/or
Parameter
Findings
Reference
BDOC
Coagulation removes BDOC.

¦ Coagulation removed almost 30% of BDOC
Camper et al., 2000, and
LeChevallier et al., 1996b
¦ Enhanced coagulation removed an additional 20% of
BDOC compared to baseline coagulation.
Camper et al., 2000,
LeChevallier et al., 1996b
¦ Enhanced coagulation removed an average of 38% of
BDOC in ten different source waters.
Volk et al., 2000
AOC
Studies have presented mixed findings.

¦ Neither baseline or enhanced coagulation changed
AOC levels in seven of ten sources.
Volk et al., 2000
¦ Plants using iron-based coagulant had lower AOC
levels in treatment plant effluent in comparison to
alum or polymer coagulants.
Volk and LeChevallier, 2002
¦ Coagulation removed 56% of AOC.
Easton and Jago, 1993
¦ Coagulation removed up to 85% of AOC
Hucketal., 1991
Phosphorus
¦ Coagulation removes significant portions of
phosphorus.

¦ Combined with filtration, 80% of phosphorus was
removed.
Sang et al., 2003
Nitrogen
Coagulation removes significant amounts of nitrogen.

¦ Alum coagulation at treatment plants, with doses of 5
- 10 ppm, removed 25 to 37% of dissolved organic
nitrogen.
Esparza-soto et al., 2003
Research findings shown in Table 3 indicate that coagulation is able to remove biodegradable
organic carbons (BDOC). This removal may be increased by optimizing coagulation practices or
selecting a different coagulant. Camper et al. (2000) reported that, overall, studies have shown
that coagulation can be expected to provide partial removal of aldehydes, oxacids, carbolic acids,
and amino acids. Higher molecular weight humic substances are readily removed by
coagulation, while smaller sugars and carbohydrates are not removed. Camper et al., (2000)
indicate that the BDOC portion removed in coagulation could contain large molecules, humic
substances, and/or biodegradable compounds bound to the humic substances removed by
coagulation. However, the researchers noted that in the majority of samples, the proportion of
BDOC removed with respect to DOC decreased when using enhanced coagulation in comparison
to using conventional coagulation. In general, the investigators point out that enhanced
coagulation appears to remove the nonbiodegradable DOC in preference over the BDOC fraction
of DOC. Removal of BDOC may depend on the relative fractions of BDOC and non-
biodegradable dissolved organic carbon as well as size of BDOC molecules and what percentage
are bound to humic substances.
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Investigations into the removal of AOC through coagulation have provided mixed results. AOC
removal rates are questionable when aluminum-based coagulants are used because of
interference in the AOC P17 test, which may account in part for the variable findings. Camper et
al. (2000) found that AOC, composed of small, non-humic molecules, was not changed by
coagulation in the majority of water samples. Volk et al. (2000) indicated it was difficult to
remove AOC through coagulation. Easton and Jago (1993) found substantial removal of AOC,
shown in Table 3, resulted when using coagulation with a long residence time for sedimentation,
allowing for biological reactions to take place. LeChevallier et al. (1996) also point to biological
reactions as being the reason for Huck et al.'s (1991) findings that up to 85% of AOC could be
removed during coagulation. Easton and Jago (1993) found that AOC removal through
coagulation was significantly affected if a disinfectant was added prior to coagulation. In their
study, coagulation without pre-chlorination resulted in 56% reduction of AOC, on average.
However, with pre-chlorination, an average of 11% of AOC was removed. Volk et al. (2000)
explain the inability to remove AOC through coagulation as being due to characteristics of
organics composing AOC. It appeared that much of the DOC removal in their study was related
to large molecular weight, humic molecules. Coffey et al. (1995)'s findings support the idea that
biological processes may account for removal of AOC during
coagulation/flocculation/sedimentation. After implementing ozonation, 20-48%) of AOC was
removed by coagulation. However, when chlorination was used for pre-disinfection, no AOC
removal occurred. A disinfectant residual may have prevented bacterial consumption of AOC.
Phosphorus is much more easily removed through conventional treatment (coagulation,
flocculation, sedimentation, sand filtration) than organic compounds (Sang et al., 2003 and
Miettinen et al., 1997a).
Enhanced coagulation has been shown to affect nitrification (Harrington et al. 2002). Enhanced
coagulation in comparison with conventional coagulation of the same source water resulted in
delaying the on-set of nitrification at a four-day residence time. This was attributed to the
removal of natural organic matter, which causes chloramine residual instability.
4.2 Powdered Activated Carbon
Utilities may apply powdered activated carbon (PAC) to treatment processes to address taste and
odor concerns as well as remove synthetic organic chemicals (Volk and LeChevallier, 2002).
Addition of PAC to the clarification process can enhance nutrient removal (Volk and
LeChevallier, 2002). LeChevallier et al. (1990) determined that the use of PAC reduces AOC
levels. This AOC reduction, along with the reduction in TOC, may contribute to the subsequent
chlorine demand reduction that was observed in the distribution system. Camper et al. (2000)
found that PAC added in a solids contact clarifier removed 50%> more AOC from the same
source water comparable to a treatment train using conventional settling basins. Volk and
LeChevallier (2002) indicate that the advantage of PAC addition in a solids contact clarifier
maximizes the residence time for the PAC, providing a matrix for biological growth. Baudin et
al. (1999) and Camper et al. (2000) demonstrate that the application of PAC prior to UF, in a
CRISTAL treatment train, can result in significant reductions in nutrients. This is discussed
further in the membrane filtration section.
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At one utility Najm et al. (2000) studied, the system added CRISTAL (powdered activated
carbon used in conjunction with ultra filtration) to the treatment process after ozonation. This
significantly affected BDOC, reducing levels from 0.8 mg C/L to less than 0.2 mg C/L (below
detection of the TOC analyzer used in this evaluation). Nonetheless, heterotrophic bacteria
counts remained essentially the same, still relatively high (up to 1400 CFU/mL for heterotrophic
plate counts). The investigators found that although the reduction in organic carbon resulted in
the ability to maintain higher chlorine residuals in the distribution system, samples containing
low chlorine residuals were likely to have high bacterial counts, indicating that disinfectant
residual had a more significant impact on heterotrophic bacteria than did organic carbon levels.
4.3 Filtration
Filtration of source water or of pre-treated water can remove AOC through two mechanisms:
biological consumption of nutrients as water passes through the filter and separation of nutrients
from treated water through use of a membrane. Research has been conducted to identify how the
type of filtration process, media type, and addition of an oxidant can impact nutrient removal. It
is important to note that the removal of nutrients by filtration may be counteracted by the
subsequent addition of chlorine as a residual disinfectant, which can increase levels of AOC and
BDOC as discussed in Section 4.4.2.
Unless biological filtration is being conducted, conventional filtration with media such as sand
and anthracite appears to decrease the level of bound nutrients, but not dissolved nutrients.
Camper et al. (2000) point out that there has been little research to date on how conventional
filtration affects biostability. Research performed by Camper et al. (1996) and Camper et al.,
(2000) demonstrated that the use of pre-chlorination prior to filtration with sand/anthracite filters
resulted in increased AOC levels. BDOC removal through these filters was mixed (Camper et
al., 1996; Camper et al., 2000). Volk and LeChevallier (2002) report that as part of their
research on 64 utilities, conventional treatment (including pre-chlorination, coagulation,
flocculation, sedimentation, and filtration) reduced levels of dissolved organic carbon and
increased AOC, especially at sites using sand/anthracite filters. Additionally, some treatment
processes removed AOC, BDOC, and DOC. However, this is attributed to biological activity
taking place in single-stage GAC/sand filters (Volk and LeChevallier, 2002).
4.3.1 Biological Filtration
In biological filtration, the treatment process includes conditions that will enhance microbial
growth. Biological filtration removes nutrients by providing conditions in which
microorganisms consume organic carbon prior to entering the distribution system. Biologically
active filters are any filter media that allow microorganisms to become attached, usually forming
a biofilm coating on or between the media grains. Slow sand (SSF), riverbank filtration (RBF),
rapid gravity filtration (RGF), and granular activated carbon (GAC) have been used successfully
(USEPA, 2003). These filter media provide physical, chemical, and biological processes that
clean the water. Organic removal during filtration can be site-specific because it can be
influenced by organic matter quality and quantity and will vary by temperature, season, media
type, contact time, and back-washing strategy (Camper et al., 2000).
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Researchers have investigated the nutrient removal realized by SSF, RBF, RGF, and GAC
(Kuehn and Mueller, 2000; Hambsch and Werner, 1996; Langlais et al., 1991; Volk and
LeChevallier, 2002; Coffey et al., 1995). Biological treatment has been shown to remove
aldehydes, oxoacids, carboxylic acids, and AOCs (Camper et al., 2000). A summary for each
filtration mechanism follows.
•	Slow Sand Filtration (SSF) - Slow sand filtration consists of passing water through a bed of
media (usually sand) at rates of 0.016 to 0.16 gpm/ft2. These filters can be composed of
sand, of mixed media, such as sand and anthracite, or include three different media. The
filter bed has a uniform sand mixture of small grain sizes that is able to trap particulates and
provides a large amount of surface area for biological growth. Rachwal et al. (1996) point
out that slow sand has a specific surface area about 2.5 times larger than that of typical RGF
and GAC. Much of the biological treatment occurs in the "schmutzdecke," a layer
containing debris, inorganics, and microbial growth, which forms at the top of the filter bed.
Removal of NOM in slow sand filters results from a combination of adsorption and
biodegradation processes in both the schmutzdecke and deeper in the sand bed (Huisman and
Wood, 1974; Collins etal., 1992).
•	Riverbank Filtration (RBF) - In RBF, water moves from the source, a river, through
riverbanks to an aquifer. This slow movement through riverbank and aquifer media filters
the water and provides an opportunity for microorganisms to consume nutrients. RBF can be
used to remove particles, bacteria, viruses, parasites, pollutants, organic compounds, and
inorganic compounds (Kuehn and Mueller, 2000). Depending on the quality of the source
water, it may be necessary to follow RBF with further treatment. For instance, GAC would
be necessary to treat water after RBF for adsorption of pollutants. In addition to removing
organic nutrients, RBF provides conditions for biological nitrification, removing ammonia
from source water very efficiently. Kuehn and Mueller (2000) indicate that it is reasonable
to expect that with aerobic conditions, RBF can result in a nearly complete removal of
ammonia.
•	Rapid Gravity Filtration ( RGF) - RGF passes water through a granular bed at rates of
2-10 gpm/ft2. These filters can be composed of sand, composed of mixed media, such as
sand and anthracite, or include three different media. The USEPA (1999a) points out that
while studies of rapid gravity filtration after ozonation have demonstrated AOC removal,
most of these studies have measured AOC only and may not provide a complete picture of
the biological stability of finished water. As described previously, measuring AOC only
would not present a complete picture of the biodegradable organic compounds
microorganisms could use for growth and energy.
•	Granular Activated Carbon (GAC) - Granular activated carbon can remove substances from
drinking water through two mechanisms: adsorption or biological treatment. Biological
treatment is the more effective manner for removal of nutrients using GAC. Rachwal et al.
(1996) note that GAC has a significantly larger molecular internal pore surface than other
types of filter media, but these spaces are not large enough to promote biofilm growth. GAC,
however, may provide a better surface for biofilm growth than slow sand or RGF because of
surface roughness (Rachwal et al., 1996).
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Lambert and Graham (1995) reviewed the impacts of SSF on nutrient levels and determined that
between 5 and 40% (mean=16%) removal of DOC from raw waters was achieved, with variable
results due to differences in plant configurations, season, and source water. SSF also removes
between 14 and 40% of AOC (mean=26%), again depending on the plant configuration and
season. BDOC removal by SSF was found to be higher, ranging from 40 to 75% (mean=60%).
Nutrient removal rates for RBF vary based on the organic loading of the rivers. AOC removal
from Rhine River waters was approximately 80 to 90%, but this may be the result of both
biodegradation and dilution with groundwater (van der Kooij et al., 1987). However, AOC
removal from the Elbe River, which has a higher organic loading than the Rhine, was 63% by
RBF (Kuehn and Mueller). In another humic-rich later, average AOC removal by bank filtration
was 69% (Miettinen et al., 1997b). One study looked into nutrient removal rates by RBF in three
U.S. utilities and determined that AOC and BDOC were reduced by 50 to 90% (Weiss et al.,
2003, 2004).
Research presents varying results on whether GAC-sand filtration removes more AOC than
sand-anthracite filters. LeChevallier et al. (1992) investigated the use of biologically active
filters in a pilot plant, comparing AOC removal using mixed media (sand-anthracite) and GAC-
sand filters. The mixed-media reduced AOC levels by 75% of levels seen after ozonation, and
the GAC-sand filters reduced AOC by 86% of levels present after ozonation. Camper et al.
(2000) also saw more removal with GAC than sand-anthracite. Krasner et al. (1993) showed that
GAC-sand and mixed media achieved comparable AOC removal rates. Pre-disinfection using
chlorine reduces the efficiency of GAC filters in removing nutrients because it disrupts the
biological processes occurring within the filter (Camper et al., 2000 and Miltner et al., 1992), and
the chlorine reacts with the TOC to form AOC and BDOC. Coffey et al. (1995) indicated that
RGF, and GAC-biologically active filters appear to exhibit similar biological performance with
respect to AOC and BDOC removal. In Volk and LeChevallier's (2002) survey of conventional
water treatment plants, treatment plants that use GAC filters generally had lower plant effluent
AOC levels (mean of 83 |ig C/L) than systems that used sand or anthracite filter media (mean of
110 - 113 |ig C/L). However, Volk and LeChevallier (2002) did not compare AOC removal
provided by the GAC and anthracite filters only.
Biological filtration is often paired with the application of a pre-oxidant, such as ozone, and the
absence of a disinfectant residual. The pre-oxidant is applied for the purposes of disinfecting
pathogens, oxidation of iron and manganese, controlling taste and odor, and oxidation of
inorganic and organic compounds (LeChevallier et al., 1992). Oxidation of organic compounds
in the source water may increase the easily biodegradable nutrient level in the water. Ozonation
(but not chlorination) before the biological filtration step will increase the biological activity in
the filter, and this increases the efficacy of biological filtration in reducing the easily
biodegradable nutrient level. LeChevallier et al. (1992) compared AOC removal in GAC-sand
filters between pre-ozonated water and water that had not been pre-ozonated. In this case
ozonated AOC was only slightly higher on average than the non-ozonated water (100 |ig C/L vs.
92 |ig C/L, respectively). Price (1994) found that combining ozonation with biological filtration
did increase the biodegradability of organic matter, but also appeared to prevent bacterial growth
in the distribution system. Langlais et al. (1991) found that the biodegradation occurring in the
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GAC filter was such that BDOC levels of treated water were lower than water prior to ozonation.
Coffey et al. (1995) compared the use of GAC/sand after ozonation to using anthracite/sand
RGF. In general, both filters removed similar amounts of AOC. However, during short-term
chlorination events, the GAC/sand treatment efficacy was not affected, likely due to adsorption
of the disinfectant residual, while the sand-anthracite filter's removal efficiency was reduced.
GAC filters in combination with granular media (such as sand) for removal of particles have
been shown to produce a biologically stable drinking water (Coffey et al., 1995). GAC is made
biologically active by the absence of a residual disinfectant in the filter. Like the other biological
filtration applications, GAC may be used with or without pre-ozonation. Biological consumption
of nutrients will still occur. However, because ozone degrades recalcitrant organic substances,
pre-ozonation increases microbial activity in the GAC and other biological filters.
Oxidant selection may affect nutrient removal. Typically, a key requirement in selection of the
pre-oxidant is ensuring that no residual is present when the water reaches the filtration media to
allow accumulation of biomass on the media, which is one reason ozone is often used. Wang et
al. (1995) compared biomass accumulation on anthracite-sand filters with and without
chlorination as a prior treatment step. At the end of 3 months the level of biomass detected on
the pre-chlorinated filter was about the same as clean anthracite. The unchlorinated filter had an
order of magnitude more biomass. The unchlorinated filter was significantly effective at
removing BDOC and AOC. Both AOC and BDOC were higher in the effluent of the chlorinated
filter than in the source water. This is the result of both the absence of biological activity in the
media and the chlorine reacting with the TOC to form AOC and BDOC
Some research has demonstrated significant nutrient removal for pre-chlorinated GAC filters
(LeChevallier et al., 1992). For example, in a comparison of nutrient removal on GAC-sand
filters preceded by pre-ozonation or pre-chlorination, both processes resulted in significant
nutrient removals. However, pre-chlorination is not a desirable option for GAC biological
filtration. Pre-chlorination paired with GAC does not result in less effective biological filtration
because the chlorine is quickly decomposed by the GAC through a redox reaction (Urfer et al.,
1997). This rapid quenching of chlorine allows biomass to accumulate and, therefore, does not
interfere with biological processes.
4.3.1.1 Additional Biological Filtration Issues
To maintain filtration efficacy, biological filters (except SSF) must be backwashed.
Backwashing of biological filters can adversely affect biological filtration because it disrupts the
biofilm growth in filtering media (Volk and LeChevallier, 2002) through scour or introduction of
a disinfectant. As part of backwashing practices, it is important to understand and control how
backwashing with chlorinated water impacts the microorganisms present on the biological filter
(Huck et al., 2000). Miltner et al. (1995) compared using chlorinated and unchlorinated water to
backwash anthracite-sand filters, finding that backwashing with unchlorinated water did not
affect biological filtration. However, chlorinated backwash removed biomass at the top of the
filter by about 22 percent. This also coincided with an inability to control disinfection by-
products and nutrient levels for a period of 12 hours after backwashing. Miltner et al. (1995)
determined that because the filter ripening time was relatively short, and filters are usually
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backwashed at different times, providing an opportunity to blend water from different filters,
these effects are not significant. However, the authors recommended using unchlorinated
backwash water (Miltner et al., 1995).
Several design parameters are critical in controlling the performance of biological filters and the
nutrient removal raters, including the empty bed contact time (EBCT), the hydraulic loading rate
(HLR), media depth, water temperature, the concentration and composition of BOM in the filter
influent, support media and operational practices such as backwashing and the use of oxidants in
the feed or backwash water (Servais et al., 1991, 1992; Langlais et al., 1991; Miltner and
Summers, 1992; Miltner et al., 1992; Prevost et al., 1992; Wang et al., 1995; Coffey et al., 1995;
Urfer et al., 1997; Niquette et al., 1998). For example, Prevost et al. (1990) report that 62% -
90% of AOC was removed with a two-minute EBCT. However, twenty minutes were needed to
remove more than 90% of the BDOC.
4.3.2 Membrane Filtration
Membrane filtration essentially consists of a thin layer of material which separates water as a
function of chemical and physical characteristics when a driving force, such as pressure is
applied across the membrane. Microfiltration (MF), ultra filtration (UF), nanofiltration (NF),
and reverse osmosis (RO) are membrane processes that rely on pressure as the driving force. MF
and UF primarily remove particles from the source water. For instance, MF and UF can be used
to replace the conventional coagulation and filtration processes. Membrane removal of
substances depends on the molecular size (MF and UF) or molecular weight (NF and RO) cut-off
of the given membrane. The molecular weight cut-off is an approximation of the molecular size
of a substance that will not be able to pass through the membrane. Some types of membranes are
associated with removal of nutrients from drinking water. Both MF and UF are not associated
with removal of BDOC from source water, except when a pre-treatment, such as ozone, is
applied (Camper et al., 2000).
RO and NF remove biodegradable organic compounds from drinking water (Kartinen and
Martin, 2001; Liu et al., 2003; Laurent et al., 1999, Randall and Escobar, 2000). Both RO and
NF use semi-permeable membranes that do not have definable pores. Operating pressures for
both types of membranes can depend on the dissolved solids in the source water. For example,
to use RO to desalt seawater, pressure may need to be as high as 1,000 psi. The typical
molecular weight cut-off for an RO membrane is less than 100 daltons. NF uses a flat sheet
membrane configured in spiral-wound modules. This process typically operates at 60 - 150 psi.
NF molecular weight cut-off limits can range from 200 - 1000 daltons. This type of filtration is
associated with removing THM precursors, micro pollutants, humic and fulvic acids, and
softening water by removing 80 - 90% of calcium and magnesium ions present. Kruithof (2001)
indicates that UF in conjunction with RO can produce a biologically stable drinking water.
Reverse osmosis can remove organics and also remove phosphate and nitrate in source water.
Kartinen and Martin (2001) evaluated the use of RO for the purpose of nitrate removal and
determined that nearly all of the source water nitrate concentrations could be removed. Liu et al.
(2003) compared the nutrient levels of pilot distribution system water that was treated by RO,
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NF, conventional treatment with ozonation, and aeration in a pilot-scale distribution system,
finding that RO effluent had the lowest AOC levels.
Laurent et al. (1999) documented the changes in treated and distribution system water quality
after switching from biologically treated water, including conventional treatment, ozonation, and
GAC filtration, to nanofiltration. Effluent water from the NF plant had BDOC levels at or below
the detection limit of 0.1 mg C/L for their analyzers. Effluent water BDOC levels prior to
implementation of NF were near 1 mg C/L. Laurent et al. (1999) indicated that because of the
more biologically stable water, chlorine residuals could be reduced significantly without any
increase in biological activity. Randall and Escobar (2000) indicate that BDOC is removed by
NF due to molecular size. Treated BDOC levels in water entering the distribution system, which
included a portion that did not go through the NF plant, were reduced by 73%-93% after
implementation of NF. Distribution system sampling indicated that BDOC remained constant
throughout the distribution system, instead of decreasing at areas with higher water ages as
before. Researchers pointed out that there was no apparent carbon consumption in the
distribution system that could be attributed to bacterial activity.
Escobar and Randall (1999) found that NF was effective in removing much of the DOC present
in water, except for the AOC fraction. In their study, essentially no AOC removal was seen
using NF. Further research (Randall and Escobar, 2000) indicated that AOC removal by NF is
affected by total dissolved solids and pH because AOC removal by NF relies on charge
repulsion. Otherwise, AOC molecules are small enough to pass through NF. In both cases, the
researchers (Escobar and Randall, 1999; Randall and Escobar 2000) indicated that significant
amounts of AOC were passing through. However, the overall pool of carbon had effectively
been reduced by NF, reducing the amount of BDOC that could be converted to AOC by
microorganisms or reactions with chlorine in the distribution system. Randall and Escobar
(2000) indicated that resulting AOC concentrations of more than 95 |ig C/L reaching the
distribution system did not appear to stimulate growth of the heterotrophic bacteria and coliform
populations. This was attributed to high chloramine residual in the distribution system.
Baudin et al. (1999) discuss a treatment train called CRISTAL, which involves using PAC
followed by UF. They indicate that BDOC was reduced by at least 70%, producing a non-
detectable level of BDOC (less than 0.2 mg C/L). The investigators attribute improved residual
maintenance to the reduction in organic matter accomplished by the PAC and UF combination,
and in turn, a reduction in biofilm throughout the system. Camper et al. (2000) reported that
PAC addition prior to UF, increased removal of DOC by 40% -50%.
Table 4 summarizes the findings on filtration and associated treatments and their influence on
nutrients available in the literature reviewed.
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Table 4
Summary of Filtration and Nutrient Impacts Based on Literature Reviewed
Treatment Used in Study
Findings
Source
Conventional Treatment with pre-chlorination
Overall Findings: More research would be needed to establish nutrient removal trend.
Chlorination, Sand/Anthracite Filters
Increased AOC levels caused by chlorination.
Camper et al.,
2000; Camper et
al., 1996
No AOC removal.
Coffey et al., 1995
Mixed BDOC removal.
Volk and
LeChevallier 2002;
Camper et al. 2000
Biological Treatment
Overall Findings: Biological filtration using SSF, RBF, RGF, and GAC results in removal of nutrients, specifically
AOC.
SSF
Can remove up to 40% AOC.
Huck et al., 1998;
Sontheimer et al.,
1978
Removes between 14 and 40% AOC (mean-26%),
depending on plant configuration and season.
Removes 40 to 75% BDOC (mean-60%)
Lambert and
Graham (1995)
Typically removes less than 50% of untreated
BDOC.
Collins and
Graham, 1994
RBF
Removed 63% of AOC.
Kuehn and
Mueller, 2000
Removed 71% of ammonia.
Kuehn and
Mueller, 2000
Removed of 80 to 90% AOC
Van der Kooij et
al., 1987
Removed of 69% AOC
Miettinen et al.,
1997b
Removed 50 to 90% of AOC and BDOC in three
utilities
Weiss et al., 2003,
2004
RGF
Most studies find that AOC removal occurs.
USEPA, 1999a
GAC/Sand Filters
Removed AOC, BDOC, and DOC.
Volk and
LeChevallier, 2002
GAC
Removed 30% of AOC, less than RBF.
Kuehn and
Mueller, 2000
Ozonation, RGF- Sand/Anthracite
Removed 30-75% of AOC reaching RGF. However,
effluent AOC was still same as source water AOC.
Coffey et al., 1995
Ozonation, Sand/Anthracite
AOC removal of 75% from that of influent to filter.
LeChevallier et al.,
1992
Ozonation, GAC
AOC levels were lower than those in source water.
Langlais et al.,
1991
Removed 30-75% of AOC reaching GAC.
However, effluent AOC was still same as source
water AOC.
Coffey et al., 1995
Ozonation, GAC/Sand
AOC removal of 86% from that of influent to filter.
LeChevallier et al.,
1992
RGF compared with RBF, and GAC.
Studies presented similar nutrient removal for RGF,
RBF, and GAC.
Coffey et al., 1995
21

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Ozonation compared Chlorine, paired
with RGF
Ozonation creates significantly higher AOC levels
than chlorination (2.3 vs 1.75).
LeChevallier et al.,
1992
Chlorination in addition to biological filtration
results in lower AOC levels than ozonation in
combination with biological filtration.
LeChevallier et al.,
1992
Membrane Filtration
Overall Findings: NF, RO, and UF with PAC can remove organic carbon nutrients. AOC is not removed by NF.
NF
Resulting BDOC levels were below the detection
limit.
Laurent et al., 1999
Removed 73% - 93% of BDOC present in source
water.
Randall and
Escobar, 2000
May allow AOC to pass through.
Escobar and
Randall ;1999;
Randall and
Escobar, 2000
UF, RO
Can produce a biologically stable drinking water
under certain conditions.
Kruithof, 2001
PAC, UF
This treatment process removed at least 70% of
source water BDOC.
Baudinetal., 1999
4.4 Oxidation and Disinfection
Typically, disinfectants may be applied during the treatment processes for three main purposes:
oxidation; to inactivate pathogens during treatment processes; and to provide a disinfectant
residual through the distribution system. As discussed previously, oxidants can also provide
benefits such as reducing taste and odor-causing compounds. Regardless of the intended
application, most disinfectants are oxidants and as such, react with organic and inorganic
compounds present in the water.
Oxidants are added to source waters as the first step in treatment for the purposes of controlling
nuisance species, such as iron bacteria; oxidizing iron and manganese; removing tastes and
odors; improving coagulation and filtration efficiency; and preventing algal growth in treatment
plants (USEPA 1999b). In this manner, oxidation can reduce nutrients available for iron bacteria
and manganese-oxidizing bacteria before water reaches the distribution system as well as provide
more aesthetically pleasing water to customers. Chlorine or chloramines are applied to all
surface water systems, all groundwater systems under the direct influence of surface water, and
many groundwater systems to ensure that a disinfectant residual of 0.2 mg/L is present at the
entry-point of the distribution system and that a detectable disinfectant residual exists within the
distribution system. Chlorine, monochloramine, and chlorine dioxide can provide a disinfectant
residual in the distribution system. However, chlorine dioxide is used by few systems (see
section 2.3 of U.S. EPA paper Effectiveness of Disinfectant Residuals in the Distribution System
for estimates of the number of systems that use chlorine dioxide). Ozonation and UV application
do not result in a disinfectant residual and, therefore, must be paired with a second disinfectant to
ensure a residual in the distribution system.
Depending on source water TOC and the conditions of oxidation, oxidation can have a
significant effect on the levels of BDOC and AOC present in the water. Oxidants break down
non-biodegradable organic compounds with large molecular weights into smaller compounds
that can be hydrolyzed by microorganisms (Geldreich et al., 1996). This can result in increased
22

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AOC and BDOC. As discussed below, ozone can have a significant impact on AOC levels if not
followed by biological filtration.
4.4.1 Chlorination
Application of free chlorine as an oxidant and to provide a disinfectant residual can increase the
concentration of AOC, (Camper, 1996; LeChevallier et al., 1994; Camper et al., 2000) promoting
bacterial growth. Easton and Jago (1993) reported that pre-chlorination dose providing a
1 to 1.5 mg/L free chlorine residual resulted in AOC levels 83% higher than those in the source
water (156 |ig C/L on average in untreated water). LeChevallier et al. (1992) found that both
chlorination before and after treatment increased AOC levels. Post-disinfection increased AOC
levels by 20%. In comparison with using ozone as a pre-disinfectant and following with
chlorination, LeChevallier et al. (1992) determined that using chlorine for pre-and post-
disinfection resulted in lower treated AOC levels, about two-thirds the levels resulting from pre-
ozonation and post-chlorination. In addition to increased AOC levels, chlorination forms
haloacetic acids, which can be consumed by microorganisms, although these acids do not likely
contribute to bacterial growth as levels are regulated.
Other studies have investigated the impact of chlorine on BDOC. While post-chlorination alone
has not been found to significantly increase BDOC (Joret et al., 1988; Wang et al., 1995),
chlorination of ozonated water increased BDOC levels by 11 percent (Wang et al., 1995). In
another study, BDOC did not increase significantly compared to what was present in the raw
water, but large increases with residence time in the distribution system, which the authors
attributed to partial DOC or pipe material oxidation by available free chlorine (Escobar and
Randall, 2001).
While chlorine can increase AOC and BDOC, it can also effectively control microbial growth in
the drinking water supply. Gagnon et al. (1998) investigated the effects that biodegradable
organic matter and chlorine residual have on bacteria growth in the distribution system. As part
of this study a critical amount of chlorine residual, Ccrit, was defined. If free chlorine residuals
are below the Ccrit for the individual distribution system, then levels of biodegradable organic
matter significantly affect distribution system microbial growth. At residual levels greater than
CCTit, biodegradable organic matter did not promote bacterial growth. As Gagnon et al. (1998)
indicate, the Ccrit can be system-specific, depending on other factors which may promote
bacterial growth, such as water age or pipe materials. In a survey of 64 drinking water utilities,
Camper et al., (2000) found that chlorine residual at dead-end mains greater than 0.5 mg/L could
control coliform growth. However, for some utilities, a much lower Ccrit is appropriate. After
switching to ozone as an oxidant (not followed by filtration), Greater Vancouver Regional
District (Ferguson et al., 2001) determined that chlorine residual of 0.1 mg/L throughout the
system could control distribution system bacterial growth.
Studies of haloacetic acids, disinfection by-products formed by chlorination and chloramination,
have found that these compounds are degraded by heterotrophic bacteria in the distribution
system (Williams et al., 1994, 1995). Further information on the effects of treatment on
disinfection by-products, including haloacetic acids, can be found in the 2001 USEPA document
Controlling Disinfection By-Products and Microbial Contaminants in Drinking Water.
23

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4.4.2 Chloramination
Chloramination has the potential to exacerbate nutrient conditions in the distribution system. As
described earlier, the potential for biological nitrification in the distribution system is associated
with the use of chloramines (Skadsen, 1993). White (1992) points out that organic nitrogen and
ammonia nitrogen levels in water as low as 0.3 mg/L can interfere with chloramination.
Monochloramine residuals react with the organic nitrogen, forming non-germicidal
organochloramines. Decomposition of monochloramine increases free ammonia levels which can
be used to provide bacterial nutrients. Woolschlager et al. (2001) modeled disinfection levels in
the distribution system for United Water in New Jersey and found that 60% of the available
nitrate present was produced by the decay of monochloramine.
Controlled nitrification, through the addition of ammonia as part of biological filtration, prior to
entering the distribution system can improve the biological stability of the finished water by
providing an environment for biological consumption of nitrogen (Kirmeyer et al., 1995;
Rittman and Snoeyink, 1984). This consumption results in fewer nutrients available in the
distribution system.
Utilities using free chlorine for the purpose of meeting CT requirements, then adding ammonia
for chloramination, may be increasing the levels of BDOC and AOC present in the finished
water, in the same manner as chlorination alone. However, there is currently very little data on
the levels of AOC and BDOC that form due to chloramination.
The use of chloramines does present several benefits in the distribution system. Levels of total
trihalomethane and haloacetic acids (five) are lower when chloramines are used compared to
when free chlorine is used for residual disinfection. Also, chloramine residual concentrations are
generally more persistent free chlorine residuals, which may help to control biofilm in the
distribution system as well as coliform occurrence (U.S. EPA, 1999b).
4.4.3 Ozonation
Several researchers have determined that ozonation partially oxidizes organic compounds present
in the source water (DeMers and Renner, 1992; Malley et al., 1994; Glaze, 1987, 1989). These
compounds become smaller and more easily biodegradable and result in increased BDOC levels
at typical ozone disinfectant doses (Hambsch and Werner, 1996; Carlson and Amy, 1997, 2001;
van der Kooij et al., 1982, 1989; Bablon et al., 1987; Servais et al., 1987; Hu et al., 1999; Huck
et al., 1991; Bonnet et al., 1992; LeChevallier et al., 1992; Janssens et al., 1984; Gagnon et al.,
1997). When followed by biological filtration, the addition of ozone reduces organic carbon
content overall. Several studies have concluded that biological filtration is necessary if
ozonation is used to avoid regrowth problems in the distribution system (Hu et al., 1999).
Biological filtration is enhanced by pre-ozonation, leading to a more biologically stable finished
water (Gagnon et al., 1998; Hambsch and Werner, 1996). The finished water levels of BDOC in
pre-ozonated and biologically filtered waters are lower than those of the untreated source water
(Hambsch and Werner, 1996; Malley et al., 1994). In some cases, ozonation may improve
24

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nutrient removal when added to a treatment train. Rachwal et al. (1996) compared the removal
of AOC and BDOC by SSF, RBF, and RGF with chemical coagulant addition and pre-ozonation.
They found that RGF following chemical coagulation and ozonation performed better than RGF
without pre-treatment. Langlais et al. (1991) and Miltner et al. (1992) indicate that without
additional ozonation or coagulation, SSF alone can reduce the presence of organic matter in
treated drinking water. However, for SSF, pre-ozonation can be implemented to promote the
biodegradation of BDOC in the biological layer (schmutzedecke) of the filter. Camper et al.,
(2000) demonstrated that adding ozonation as a pretreatment for PAC/UF has been shown to
further increase DOC removals, resulting in up to 99% removal.
However, with no subsequent biological filtration, ozonation may provide nutrients to
microorganisms in the distribution system. It is for this reason that many countries require
biological filtration to be installed if ozonation is used. For instance, in a study conducted by
LeChevallier et al. (1994), systems following ozonation with conventional treatment averaged
AOC levels of 252 |ig C/L, whereas the system using biological filtration after ozonation had an
AOC level of 100 |ig C/L. Malley et al. (1994) found that ozonation increased BDOC by a
factor of two. In some cases, AOC levels in the distribution system have nearly tripled in
comparison to levels prior to ozonation. For example, Greater Vancouver Water District
implemented ozonation for disinfection of the unfiltered Coquitlam surface water supply. After
ozonation, AOC levels increased from 280 |ig acetate-C/L for chlorinated water to 680 |ig C/L
(Ferguson et al., 2001). In another study of ozonation's short-term and long-term impacts, water
quality changes were monitored for the Orlando Utilities Commission, which uses an unfiltered
groundwater (Escobar and Randall, 2001). In the weeks after implementation of ozonation,
distribution system AOC increased to nearly triple pre-ozonation levels. About one year after
ozone implementation, distribution system AOC levels were twice pre-ozonation levels. Wricke
et al. (1996) found that at a proportion of 1 mg/L ozone dose per 1 mg/L DOC dose, 25-30% of
the DOC would be converted to BDOC.
4.4.4 UV
UV is applied to drinking water treatment as a disinfectant during treatment, but can not be used
to provide a disinfectant residual within the distribution system. Research on the effects of UV
on organic nutrients are mixed. Kashinkunti et al. (2002) conducted bench-scale tests
investigating UV impacts on AOC, finding no apparent overall trend. Shaw et al. (2000) found
that UV at lower doses (<130 mWs/cm2) did not significantly increase or decrease AOC or
BDOC in either surface or groundwater levels. Camper et al. (2002) also suggest that at typical
doses, UV is not likely to degrade organic matter. However, higher doses of were shown to
degrade organic matter and enhance bacterial growth (Kulovaara et al., 1996; Corin et al., 1998).
Mofidi et al. (1998) determined that high-intensity pulsed UV increased BDOC levels
significantly, nearly doubling the levels present. A decrease in AOC was also seen in several
waters in one study at both low and high doses, with dose have no impact on the amount of
decrease (Lehtola et al., 2003).
25

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4.4.5 Dechlorination
Some systems using groundwater sources may use a chemical disinfectant to treat the water, but
then remove the disinfectant before it enters the distribution system. The disinfectant is used to
enhance oxidation of hydrogen sulfide, iron, or manganese but is not used to provide disinfectant
residual in the distribution system. Ascorbic acid (C6H806) is a carbohydrate and an established
and recognized dechlorinating agent (Spotts and McClure, 1995). Because this agent is an
organic compound, the most significant concern associated with the use of ascorbic acid is the
potential for enhanced biological growth within the distribution system. Based on stoichiometric
dechlorination requirements, water containing 1 mg/L of chlorine or chloramine will require the
addition of 2.48 mg/L of ascorbic acid. The reaction by-product, dehydroascorbic acid, will be
present at similar levels within the distribution system. Dehydroascorbic acid is also of
nutritional benefit to microorganisms (Mallevialle and Suffet, 1987). There have been no
published growth studies using ascorbic acid as a dechlorinating agent.
Brazos and O'Connor (1987) studied biological growth in water samples dechlorinated with
inorganic sodium thiosulfate (Na2S2C>3) (Brazos and O'Connor, 1987). Water samples were
collected at the filter effluent, clearwell, and at two locations within the distribution system. The
distribution system sample sites correspond to water ages of 36 hours (system maximum) and
18 hours (50% of maximum). Before dechlorination, chloramine concentrations were between
1.2 and 1.6 mg/L as Cb at all locations at the time of sampling. Total and heterotrophic bacteria
were analyzed at 24-hour intervals following dechlorination. Heterotrophic bacteria colony
counts increased by up to 6 orders of magnitude within 3 days. There are two potential causes for
the observed biological proliferation: (1) elimination of the disinfectant residual and/or (2)
addition of sodium thiosulfate to the water.
4.5 Corrosion Control
Orthophosphates and polyphosphates are widely used for corrosion control in distribution
systems. An initial concern associated with the application of phosphorus as part of corrosion
control treatment was that this would be a source of biodegradable nutrients that might stimulate
bacterial growth. AwwaRF (1990) provided an example of the addition of phosphate corrosion
inhibitors to uncovered drinking water reservoirs that resulted in an increased potential for algae
blooms. Several studies have investigated whether these compounds stimulate bacterial growth,
with varied and contradictory conclusions. Many researchers have found that phosphorus-based
corrosion inhibitors have not been associated with increased distribution system bacterial growth
(LeChevallier et al., 1993 and LeChevallier et al., 1994). In fact, these inhibitors have been
associated with fewer positive coliform samples (Abernathy and Camper, 1997; USEPA 1999b)
due to enhanced corrosion control. The South Central Connecticut Regional Water Authority
(USEPA, 1999b) increased their use of zinc metaphosphate from 1 to 2 mg/L. This change in
chemical addition increased the total phosphorus levels in the distribution system from 0.31 to
0.43 mg/L. Over the next two years, positive weekly coliform levels dropped from 12 % to 5%.
Abernathy and Camper (1997) posit the following reasons for improved bacterial conditions
even with an additional bacterial nutrient source:
• The presence of microbial habitat has been decreased by the reduction in mass of corrosion
products on the pipe surface.
26

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•	Reduced disinfectant demands of existing corrosion products and increased penetration of
disinfectant to core of corrosion tubercules.
•	Reduction of disinfectant demand of pipe surface and increased presence of disinfectant in
outer-reaches of the distribution system.
However, other studies have shown that the addition of phosphates can promote bacterial growth
in distribution systems where phosphorus is the growth-limiting nutrient (Miettinen et al., 1997b;
Lehtola et al., 2002).
Such variable results are likely due to differences in water quality and nutrient concentrations in
the bulk water. Various analytical methods may also have had an impact on the variable results.
Overall, for systems with significant corrosion, industry experiences show that corrosion control
along with proper residual maintenance may be as important or more important than nutrient
levels in controlling microbial growth.
4.6 Distribution System
4.6.1	Booster Chlorination
In general, booster chlorination is the only treatment drinking water suppliers implement within
the distribution system. Systems use booster chlorination to supplement disinfectant residuals in
problem areas of the distribution system, such as downstream of finished water reservoirs. The
effects of booster chlorination on nutrient levels have not been studied.
Tryby et al. (1999) qualitatively evaluated the use of booster chlorination as a means to reduce
the chlorine dose applied at the drinking water treatment plant. Through a targeted application of
chlorine at problem areas, less chlorine may be needed to maintain a disinfectant residual
throughout the rest of the distribution system. Further research is needed to evaluate the effects
of a lower overall finished water residual and increased disinfectant residual at specific locations
within the distribution system on nutrients.
4.6.2	Distribution System Operations and Maintenance
Distribution system operations, such as reservoir operations and maintenance procedures, can be
used to protect distribution system water quality. Additionally, distribution system operations
such as flushing, can be used to control distribution system bacteria growth resulting from
numerous factors such as treatment breakthrough, production of a biologically unstable drinking
water, or intrusion of contaminants into the distribution system. Findings by Camper et al.
(2000), LeChevallier et al. (1996), and Gagnon et al. (1998) point to the importance of
maintaining a disinfectant residual throughout the distribution system. This may be done in the
distribution system by flushing areas subject to long water ages or "cleaning" the distribution
system periodically by pigging (a pipeline cleaning technique) or implementation of a
comprehensive uni-directional flushing program. Camper et al., (2000) specifically studied the
resultant coliform levels when high AOCs, temperatures, and low disinfectant residual
conditions occurred. Practices such as flushing dead-end mains regularly and operation of
storage tanks and reservoirs such that storage residence times are controlled and mixing is
enhanced, can improve residual concentrations.
27

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Distribution procedures should be in place to prevent the entry of microorganisms or other
contaminants, such as nutrients, that would exert significant disinfectant demands during
activities such as main break repair. The following events can provide an opportunity for entry
of microorganisms and/or nutrients to enter the distribution system:
•	Cross-connection,
•	Intrusion,
•	Main installation,
•	Main repair,
•	Openings in covered reservoirs, and
•	Uncovered reservoirs.
To date, there have been no studies specifically on the entry of nutrients into the distribution
system, describing how frequently this occurs, the levels of nutrients entering, and their impacts
on microorganisms in the distribution system. However, studies have been conducted to
investigate the possibility of pathogens entering the distribution system via contaminated water
that enters the distribution system through the six mechanisms listed above. Friedman et al.
(2004) investigated the volume of water entering the distribution system during low or negative
pressure transients (intrusions). Table 5 presents results from two different approaches for
quantifying the volume of water entering through 1/8-inch and 1/4-inch orifices. The volumetric
method provides the better estimate of how much intruded into the pipe. The tracer method
provides the better estimate of how much stayed in the pipe after the pressure transient occurred.
Table 5
Intrusion Volume Comparison of Chemical Tracer and Volumetric Methods1'2
Trial
No.
Intrusion Volume for
1/8" Orifice (mL)
Intrusion Volume for
%" Orifice (mL)

Chemical Tracer
Method
Volumetric
Method
Chemical Tracer
Method
Volumetric
Method
1
2
3
4
Average
9.9
12.8
11.4+2.1
44.0
46.8
49.5
49.5
47.5+2.6
64.9
52.5
75.4
91.8
71.2+16.7
121.0
99.0
126.6
121.0
116.9+12.2
Friedman et al., 2004.
2Steady state conditions were established at 132 gpm and 30 psi prior to valve closure. The magnitude of the first (and largest)
pressure drop in each trial was about 42 psi resulting in a minimum internal head of approximately -12 psi and remaining negative
for about 1 second.
Further information on distribution system operations that can prevent intrusion of contaminated
water and optimize water quality can be found through the American Water Works Association
and American Water Works Association Research Foundation. In many systems, intrusion may
not represent a significant addition of nutrients when compared with the global flux of nutrient
into the distribution system. However, because the primary concern is preventing the ingress of
dirty water into the drinking water system, similar means would be used to prevent the entry of
28

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nutrients into the distribution system via other pathways. Some examples of control methods are
(Kirmeyer et al., 2001):
•	Application of a risk assessment model to identify, manage, and prevent entry of dirty water;
•	Enforcement of a cross-connection control program;
•	Maintenance of adequate pressure throughout the distribution system;
•	Monitoring water quality and pressure throughout the distribution system;
•	Implementation of standard operating procedures and training for distribution system
personnel; and
•	Regular maintenance and inspections for finished water storage facilities.
5. National-Level Assessment of Control of Nutrients of Concern
Table 6 presents information on the treatment processes discussed in this report and the
prevalence of their use according to the USEPA 2000 Community water system survey (USEPA,
2002b). As new drinking water rules have been promulgated since the survey, the distribution of
treatment processes has been changing. It is difficult to predict the future distribution of
treatment processes and how they may impact nutrient issues on a national basis.
Table 6
National Distribution of Treatment Processes
Treatment Process
Type of Source
Percent of Systems
(all sizes)1 2
Chlorination only
Surface
13
Groundwater
72
Pre-disinfection/Oxidation prior to sedimentation
Chlorine
Surface
36
Groundwater
8
Chloramines, Ozone
Surface and Groundwater
<5
Pre-disinfection/Oxidation prior to filtration
Chlorine
Surface
24
Groundwater
8
Chloramines, Ozone
Surface
<5
Groundwater
0
Coagulation/Floccul
ation
Surface
64
Groundwater
<5
PAC
Surface
8
Groundwater
0
Filtration
Slow sand
Surface and Groundwater
<5
Rapid Gravity
Surface
18
Groundwater
<5
Riverbank filtration
Surface and Groundwater
No information
GAC
Surface
9

Groundwater
<5
Dual/Multi-media
Surface
45
29

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Groundwater
<5
Post-disinfection after filters
Chlorine
Surface
71

Groundwater
14
Chloramines
Surface
8

Groundwater
<5
Ozone, UV
Surface and Groundwater
<5
Membranes
Surface and Groundwater
<5
Corrosion Control
Surface
42

Groundwater
17
Adapted from USEPA, 2002b.
253,4 1 0 community water systems were included in the survey.
6. Further Research
Extensive studies have evaluated the impacts of certain treatment processes on nutrient levels.
Treatment processes meriting future research are:
•	UV,
•	Filtration pre-coats, such as diatomaceous earth,
•	Ozonation both with and without subsequent biological filtration,
•	Chlorine dioxide,
•	Booster chlorination,
•	Desalination/deionization,
•	Softening,
•	Fluoridation, and
•	Corrosion control chemicals in the presence of chlorine and chloramines.
Further research is also needed to better understand the net effect of microbial death and lysis to
the pool of nutrients available for biological consumption. It is important to understand this
contribution with respect to source water nutrient levels and the effects of treatment on nutrient
levels. A better understanding of the impact of nutrient levels on the potential for regrowth of
opportunistic and frank pathogens is also needed. Finally, while studies have demonstrated that
some treatment processes reduce nutrients, it would also be important to determine if other
impacts of the same process outweigh this benefit with respect to preventing microbial growth.
For instance, RO removes significant amounts of AOC levels, but also increases the water's
corrosivity, which can cause biofilm growth.
In some cases, research has been conducted to evaluate the treatment process on natural organic
matter, but further information is necessary to determine if the process causes any changes in the
levels of biodegradable organic matter. For instance, Pommerenk and Schafran (2002) discuss
how pre-fluoridation may severely affect the removal of particles and organic matter when it is
added to water prior to aluminum sulfate. However, this does not provide an indication of how
biological stability may be affected. A more complete understanding of disinfectant
mechanisms on suspended and fixed bacteria, especially on pathogens resulting from intrusion,
must also be answered by applied research.
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As discussed previously, Camper et al. (2000) determined that a correlation exists between
biodegradable organic compounds and source water protection. Further research is necessary to
determine how these two are related and whether utilities may use source water protection to
provide a more biologically stable drinking water. The impact of climate change and intensive
urbanization on nutrient levels should also be examined as part of these efforts because if
nutrient levels in the source water change over time, treatment barriers currently in place may no
longer be adequate to remove sufficient biodegradable organic matter.
Another area for research is how the composition of the biofilms and specifically the growth of
coliforms and pathogens is affected by nutrient level or the make-up of the nutrient pool. Most
of the studies to date look specifically at HPC.
Finally, AOC and BDOC are difficult parameters to measure and do not always directly indicate
biological stability of water. More research is needed to determine a more effective
measurement of a water's biological stability.
7. Summary
This paper provides a review of completed research on the extent that various water treatment
processes affect nutrient levels in the distribution system. Organic carbon, nitrogen, phosphorus,
metals, and other substances can promote microbial growth. Typically, carbon is considered to
be the limiting nutrient in the distribution system. Studies have shown that a direct correlation
can exist between the level of AOC or BDOC and the level of microbial growth in the system.
However, factors such as disinfectant levels and pipe materials have a significant influence, too.
Some treatment processes influence the levels of nutrients entering the distribution system.
Much of the available research focuses on the effects of treatment on AOC and BDOC. In
general, coagulation, sedimentation, and flocculation remove phosphorus and are associated with
significant removal of BDOC but not AOC. Biological and some membrane filtration
applications have been associated with removal of organic nutrients. Disinfectants that are
oxidants, such as ozone or chlorine can increase organic nutrient levels. However, when pre-
oxidation is paired with treatment such as biological filtration, effluent organic nutrient levels
may be lower than source water nutrients. Further research is needed on the impacts of treatment
on nutrients and improved measurement of biological stability.
References
Abernathy, C. G., and A. Camper. 1997. Interactions between pipe materials, disinfectants,
corrosion inhibitors, organics, and distribution biofilms. In Proceedings of the Water Quality
Technology Conference. AWWA: Denver CO.
AWWA (American Water Works Association). 2004. Manual of Water Supply Practices M7:
Problem Organisms in Water: Identification and Treatment. AWWA: Denver CO.
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AWWA, APHA (American Public Health Association), WPCF (Water Pollution Control
Federation). 1989. Standard Methods for the Examination of Water and Wastewater,
Seventeenth Edition: Section 9240 Identification of Iron and Sulfur Bacteria.
AwwaRF (American Water Works Association Research Foundation). 1990. Lead Control
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Bonnet, M. C., B. Welte, and A. Montiel. 1992. Removal of Biodegradable Dissolved Organic
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Brazos, B. and J. O'Connor. 1987. Relative contributions of regrowth and aftergrowth to the
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Camper, A., K. 1996. Factors Limiting Microbial Growth in the Distribution System:
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