Lin S.D. Water and Wastewater Calculations Manual

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Source water protection. Many of the drinking water utilities in the

United States had invested a great deal of time, energy, and capital

into source water protection (SWP). In addition, efforts were made to

develop mechanisms for protection against the impact of sudden

changes in inﬂuent water quality. Some of these mechanisms include

investment in excess capacity and development of emergency

procedures.

Source water protection measures are the important step to prevent

contamination and reduce the need for treatment of drinking water

supplies. SWP includes managing potential contamination sources

and developing contingency plans that identify alternate drinking

water sources. A community may decide to develop an SWP program

based on the results of a source water assessment, which includes

delineation of the area to be protected and an inventory of the poten-

tial contaminants within that area. SWP from quality degradation by

microbial contaminants (i.e. bacteria, protozoa, viruses, helminthes,

and fungi) is any activity undertaken to minimize the frequency, mag-

nitude, and duration of occurrence of pathogens or indicators (e.g.

indicator microorganisms, such as TC, FC, and FS (Lin, 2002); or tur-

bidity) in source waters. SWP may also, by reducing the concentra-

tion of natural organic matter (NOM), a DBP precursor, reduce the

formation of DBP.

SWP strategies comprise the ﬁrst stage in the multiple-barrier

approach to protecting the quality of drinking water. Other major

drinking-water-quality protection barriers include water quality mon-

itoring and selective source withdrawal, water treatment processes for

removal or inactivation of pathogens and control of DBP formation,

water distribution practices for preventing intrusion or regrowth of

pathogens, and point-of-use treatment where required.

SWP strategies are a speciﬁc subset of a large watershed protection

strategy applied when the protected receiving water is used as a water

supply. Conceptually, watershed protection is heavily linked to pollution

prevention, contaminant source identiﬁcation, and risk management.

Although watershed management does not have a universally accepted

deﬁnition and connotes alternate approaches, each interpretation has

an underpinning of holistic approaches to prevent or mitigate threats

to the receiving water over a geographic region deﬁned by a common

hydrology.

Many groundwater supplies have proven to be vulnerable as well, result-

ing in various states implementing wellhead protection programs. The

1986 amendments included provisions for Protection of Ground Water

Sources of Water. Two programs were set up under this requirement: the

“Sole Source Aquifer Demonstration program,” to establish demonstration

programs to protect critical aquifer areas from degradation; and the

Public Water Supply 495

“Wellhead Protection Program,” which required states to develop pro-

grams for protecting areas around public water supply wells to prevent con-

tamination from residential, industrial, and farming-use activities.

In the 1996 amendments to the SDWA, protection of source waters

was given greater emphasis to strengthen protection against microbial

contaminants, particularly Cryptosporidium, while reducing potential

health risks due to DBPs. Two major threats to source water quality with

respect to DBP control and microbial protection are natural organic

matter and microbial pathogens. From a waterborne outbreak and

public health viewpoint, both Giardia and Cryptosporidium are cur-

rently of primary concern.

Managing microbial contaminant risks in watersheds requires iden-

tiﬁcation and quantiﬁcation of organisms. Because of difﬁculties in asso-

ciation with assaying for speciﬁc pathogens, monitoring programs have

been tested for indicator organisms, including total coliform (TC), fecal

coliform (FC), and fecal streptococcus (FS), to identify possible fecal

contamination in water. The analytical methods for indicators are easier,

faster, and more cost effective than methods for speciﬁc pathogenic

organisms. The limitations of relying on indicator organisms for deter-

mining the presence of pathogens include the occurrence of false posi-

tives and the fact that indicators measure bacteria that live not only in

human enteric tracts, but also in the enteric tracts of other animals

(Toranzos and McFeters, 1997; Lin, 2002).

The potential sources of microbial pathogens in source water are many

and varied, including nonpoint runoff, discharges from treated and

untreated wastewaters, storm water runoff, and combined sewer over-

ﬂows. Animal feed lot is the main source of Cryptosporidium. Many fac-

tors affect the types of organisms found and the concentrations at which

they are detected. These include watershed contributions, treatment plant

efﬁciency, and length of antecedent dry weather period. These treatment

technologies can be both sources of contamination as well as protection of

source water quality. In addition to the installation of wastewater treat-

ment and combined overﬂow systems, there are passive pollution pre-

vention and mitigation techniques called BMPs. The BMP techniques can

be found elsewhere (US EPA, 1990, 1992) and vary dramatically in appli-

cation, ranging from social practices to engineering applications.

In summary, long-term and effective management for pathogens and

DBP is source water protection to control NOM, the DBP precursor.

SWP includes effective watershed protection and water resources man-

agement strategies. It involves controlling algal growth and the pro-

duction of organic carbon precursors in our raw water sources (lakes and

rivers) by limiting nutrient discharges into these bodies of water.

Once NOM is controlled, there would be beneﬁts to the water treatment

system, such as less pretreatment and easier down-stream treatment,

496 Chapter 5

more effective unit process, and cheaper water treatment costs. Coagulant

dosage requirements will be reduced and then less sludge will be produced

if there is less dissolved organic carbon (DOC) in the raw water, because,

for most waters, the concentration of DOC controls coagulant dosage

requirements. Chlorine dioxide doses will be lowered if there is less DOC

in the raw water to consume chlorine dioxide and generate chlorite.

Powdered and/or granular activated carbon dosage rates for the control

of taste- and odor-causing organic compounds will be reduced if there is

less DOC in the raw water to compete with these target tracing organic

pollutants for adsorption sites on the activated carbon. Membrane foul-

ing will be lowered and ultraviolet irradiation for microbial inactivation

will be more effective if there are less DOC and ultraviolet-adsorbing

organics in the raw water. Less chlorine will be required for disinfection,

and lower concentrations of all halogenated organic by-products—not

just the THMs and HAAs—will be formed (Singer, 2006).

Use of alternative disinfectants. As discussed previously, chlorination of

drinking water results in the formation of numerous DBPs, several of

which are regulated. Water systems seeking to meet MCLs for regulated

DBPs might consider various approaches to limiting DBPs such as

removing precursor compounds before the disinfectant is applied, using

less chlorine, using alternative disinfectants to chlorine, or removing

DBPs after their formation. Combinations of these approaches might

also be considered. As mentioned previously, removing DBPs after their

formation is a method that is generally not considered, but no matter

which approach is selected, the effectiveness of the disinfection process

must not be jeopardized.

Studies have been conducted by or funded by the US EPA’s Ofﬁce of

Research and Development in Cincinnati to examine the use of three

alternative oxidants: chloramines, chlorine dioxide (ClO

), and ozone.

Chloramines. Based on the researches cited (Steven et al., 1989;

Miltner, 1990), the formation of halogen-containing DBPs by chlo-

ramines is signiﬁcantly lower than by free chlorine. An exception is the

formation of cyanogens chloride with chloramination. Formation of non-

halogenated DBPs such as aldehydes and assimilable organic carbon

(AOC) is found to be minimal with chloramination.

Chloramines are the second most commonly used ﬁnal disinfectant in

drinking water treatment after free chlorine. Although generally not as

effective a disinfectant as free chlorine, an advantage of chloramination

is minimization of the formation of DBPs.

Chlorine dioxide. Chlorine dioxide is another widely used disinfec-

tant in drinking water treatment. It has long been used for taste and

odor control and for iron and manganese control, and has gained in

acceptance as an effective disinfectant.

Public Water Supply 497

An advantage of ClO

treatment is minimization of the formation of

DBPs; it does this by oxidation of DBP precursors and by relatively

minimal formation of DBPs themselves. The formation of DBPs by ClO

is also signiﬁcantly lower than with free chlorine and with chloramines

(Stevens et al., 1989). ClO

oxidizes DBP precursors in the treated water

to the extent that lower concentrations of DBPs are formed with sub-

sequent chlorination. Using ClO

results in the formation of nonhalo-

genated DBPs such as aldehydes, ketones, and AOC.

The use of ClO

can result in the formation of chlorite and chlorate.

Chlorite can be controlled by GAC and through the use of reducing

agents. Sulﬁte and metabisulﬁte can reduce chlorite, but may form chlo-

rate. Thiosulfate can reduce chlorite without forming chlorate. Ferrous

ion can reduce chlorate, but pH adjustment is required to minimize

chlorate formation. The use of a reducing agent like thiosulfate or fer-

rous ion can complicate the application of postdisinfectants.

Ozone. Ozone is a less commonly used disinfectant in drinking water

treatment in the United States. Among the many beneﬁts of ozonation

of drinking water are effective inactivation of microbes, taste and odor

control, iron and manganese control, oxidation of DBP precursors, and

the enhancement of biological oxidation in filters. However, ozone

results in the formation of bromate and of biodegradable organic matter

(BOM). Bromate is regulated under the D/DBP Rule. BOM includes

ozonation by-products (OBPs) like aldehydes, keto acids, carboxylic

acids, AOC, and biodegradable dissolved organic carbon (BDOC). These

OBPs may be responsible for regrowth of bacteria in distribution sys-

tems and can be controlled in-plant if biological oxidation is allowed to

occur in downstream ﬁlters. (Refer to the section of DBP control through

biological ﬁltration.)

The formation of halogen-containing DBPs by ozone is signiﬁcantly

lower than that by free chlorine. Ozone can form bromo-DBPs like bro-

moform (CHBr

), bromoacetic acid, and dibromoacetic acid, but at rel-

atively low concentrations. Ozone oxidizes DBP precursors such that

lower concentrations of TTHM, HAA6, HAN4 (haloacetonitrile 4), and

TOX (total organic halide) are formed with subsequent chlorination.

However, preozonation alters the nature of the precursors to the extent

that higher concentrations of chloral hydrate, chloropicrin, and 1,1,1-TCP

are formed with subsequent chlorination (Miltner, 1990).

Ozone converts portions of the humic fraction to nonhumic com-

pounds and converts portions of the higher-molecular-weight fraction

to lower-molecular-weight compounds. Examples of lower-molecular-

weight materials formed by ozone are aldehydes, keto acids, AOC, and

BDOC. Concentrations of these may be appreciable and necessitate

control to ensure distribution system biostability. Generally, much of

498 Chapter 5

the formation of these OBPs occurs at lower ozone doses. Ozone stag-

ing (when it is applied in the treatment plant) can inﬂuence OBP for-

mation. Ozonation of raw water results in higher OBP formation than

ozonation of downstream waters in which some ozone demand has been

removed (Miltner, 1993).

NOM and bromide are the two principal precursors of DBPs in raw

water supplies. Bromate can result from the use of ozone. Bromate con-

centration increases with increasing dissolved ozone residual and with

increasing bromide. Bromide control strategies may involve more energy-

intensive membrane processes, such as RO. Singer (2006) pointed out

that source water protection involves creative solutions to minimizing

saltwater intrusion into our raw (surface and ground) water supplies

because such saltwater intrusion is the primary source of bromide.

Ultraviolet (UV) irradiation. Carlson et al. (1985) reported that cysts

of Giardia muris were signiﬁcantly more resistant to UV treatment

than E. coli or Yersinia spp. Results suggested that hydraulic short cir-

cuiting and entrapped air in UV reactors may decrease the efﬁciency of

inactivation. G. lamblia cysts were found to be resistant to high doses

of germicidal UV irradiation (Rice and Hoff, 1981). There has been

renewed interest in the use of UV light for inactivating waterborne pro-

tozoan parasites. A study suggested that UV irradiation is an effective

treatment option for inactivating oocysts of Crytosporidium (Clancy et al.,

1998). UV irradiation was not considered for controlling DBP. Currently,

due to the improvement of technology, UV has been commercially avail-

able to be used to control DBP.

Enhanced coagulation. Coagulation has historically been used for the

control of particulates in drinking water, while simultaneously con-

trolling organic carbon. With the D/DBP Rule, many water systems

will move from conventional to enhanced coagulation and expand their

coagulation objectives from removing turbidity to removing total

organic carbon (TOC) as well. It is anticipated that many systems will

be able to meet the requirements of enhanced coagulation for TOC

removal with only moderate changes in conventional coagulation.

Making the change from conventional to TOC-optimized coagulation

generally results in improved removal of heterotrophic plate count

(HPC) bacteria, TC, FC, FS, viruses, Cryptosporidium parvum oocysts

(3.1 to 7.0 µm), Cryptosporidium oocyst-sized particles, Giardia cyst-

sized particles (8.2 to 13.2 µm), total plate count (TPC) organisms, and

bacterial endospores.

The removal of TOC results in improved removal of precursors for

TTHM, HAA6, CH, HAN4, CP, the surrogate TOX, and chlorine demand

(Miltner, 1994; Dryfuse et al., 1995). When coagulated, raw waters

Public Water Supply 499

higher in TOC and in speciﬁc ultraviolet absorbance tend to have higher

percent removals of DBP precursors. As a treatment technique,

enhanced coagulation to remove TOC can result in the removal of pre-

cursors for these DBPs. As a BAT, enhanced coagulation can result in

the control of TTHM and HAA5. Many systems should be able to meet

the requirements of enhanced coagulation for TOC removal with mod-

erate changes to conventional coagulation.

Most DOC and DBP precursors are in the larger-molecular-size range

and are in the humic fraction. Conventional coagulation removes a

greater percentage of the >3K MS (molecular size) fraction than the

smaller-sized fractions. Enhancing coagulation brings about small

improvements in the >3K MS range and the <0.5K MS range; the great-

est improvement with enhanced coagulation is in the 0.5K to 3K MS

range (Dryfuse et al., 1995). Conventional coagulation removes a greater

percentage of the humic fraction than the nonhumic fraction. Enhancing

coagulation brings about similar improvement in the removal of both

fractions.

A general concern associated with coagulation is that, although it

lowers the concentrations of DBP precursor, it shifts the distribution of

the DBPs formed by chlorination toward the more brominated species.

This shift becomes even greater when enhanced or optimized coagula-

tions practiced.

Water systems switching from conventional to enhanced coagulation

may achieve longer ﬁlter run times (FRTs), but the trade-off will be

greater amounts of sludge production. Systems practicing enhanced

coagulation should also consider pH adjustment ahead of the ﬁlter to

achieve longer FRTs. The disadvantage with enhanced coagulation is

that when alum is the coagulant, higher levels of dissolved aluminum

will enter the distribution system.

Filtration. The US EPA researches have been conducted with the use

of bench-, pilot-, and ﬁeld-scale studies to investigate various aspects of

surface water ﬁltration for microbiological removal with various gran-

ular media. Studies found that two of these technologies, slow sand ﬁl-

tration (SSF) and diatomaceous earth (DE) ﬁltration, are especially

applicable to small systems. In addition, the application of granular ﬁl-

tration, which is utilized by medium to large systems, has been inves-

tigated for removal of Giardia and Cryptosporidium. These studies have

considered the various operational conditions that enhance removal

efﬁciency as well as the conditions under which removal efﬁciency

deteriorates.

In the period between 1980 and 1990, Giardia cysts and

Cryptosporidium oocysts were the primary organisms being considered.

The effect of various water quality conditions and particle and pathogen

500 Chapter 5

loadings were evaluated. It was shown that, in combination with effec-

tive chemical addition and coagulation, these processes are capable of

efﬁciently removing efﬁciency in SSF and conventional ﬁltration, but had

little effect n DE performance. Filtration processes are capable of remov-

ing high levels of those organisms, but that removal is dependent on the

operation of those processes. Poor chemical addition and coagulation

reduced the treatment efﬁciency for removing microorganism and other

particles. Temperature was another factor that affected removal. The ﬁl-

tration studies conducted by US EPA concluded that good turbidity

reduction and good particle removal paralleled good microorganism

removal.

One measure of ﬁltration efﬁciency developed by Water Supply and

Water Resources Division (WSWRD), and now widely used, was that of

measuring aerobic endospore removal in a water treatment process.

Although not a surrogate for removal of a speciﬁc organism, endospore

removal was seen as a measure of the overall ﬁltration performance.

Studies conducted by the WSWRD showed that endospore removal

tracked particle removal, turbidity reduction, and pathogen removal. In

studies, if good removal of endospores was achieved, good removal of par-

ticle and pathogens was observed. In some cases, good removal of

pathogens occurred when poor removal of endospores was demonstrated,

but no studies showed poor removal of pathogens when good removal

of spores was achieved. Thus, removal of spores may be considered a con-

servative measure of particle and pathogen removal.

Biological ﬁltration for DBP control. DBP control through biological ﬁltra-

tion or bioﬁltration is deﬁned as the removal of DBP precursor mate-

rial (PM) by bacteria attached to the ﬁlter media. Dissolved organic

matter (DOM), which is a part of the PM, is utilized by the ﬁlter bacte-

ria as a substrate for cell maintenance, growth, and replication. This

effect makes the PM utilized by bacteria unavailable to react with chlo-

rine to form DBPs. The prerequisite for maximizing bacterial substrate

utilization in ﬁlters is the absence of chlorine in the ﬁlter inﬂuent or

backwash water.

Sand, anthracite, or GAC can be colonized by bacteria. Since

anthracite and sand are considered inert because neither interacts

chemically with PM, removal of PM is due solely to biological activity.

GAC will initially remove DOM through adsorption and biological sub-

strate utilization until its adsorptive capacity has been exhausted. After

that point, PM removal is achieved only through substrate utilization,

and the GAC is deﬁned as biological activated carbon (BAC). All drink-

ing water ﬁlters will become biologically active in the absence of applied

disinfectant residuals. The process of biological colonization and sub-

strate utilization is enhanced by ozonating ﬁlter inﬂuent water.

Public Water Supply 501

Data collected, to date, indicate that biologically active ﬁlters remove

signiﬁcant amounts of PM and that preozonated bioﬁlters remove more

PM than do nonozonated ﬁlters. The resulting reductions in tri-

halomethane formation potential (THMFP) and haloacetic acid forma-

tion potential (HAAFP) should help many drinking water utilities meet

the 80 (THM) and 60 (HAA) ␮g/L limits mandated under the Stage II

D/DBP Rule (US EPA, 2001).

Use of GAC. GAC can be used as part of a multimedia ﬁlter to remove

particulates (ﬁlter adsorber) or a postﬁlter to remove speciﬁc contami-

nants (postﬁlter adsorber). When used in a ﬁlter adsorber mode, the ﬁl-

ters are backwashed periodically to alleviate head loss, but the carbon

itself is regenerated infrequently, it at all. When used in a postﬁlter

mode, the carbon bed is rarely backwashed and is regenerated as often

as needed to control the contaminant(s) of interest.

Activated carbon in a ﬁlter adsorber application removes pathogens by

the same mechanisms as any other ﬁlter media. It does not remove par-

ticulates/pathogens to any greater degree than other ﬁlter media types;

so, it is never recommended for particulate/pathogen removal alone.

Activated carbon is an effective process for removing DBP precur-

sors. It is not designed for pathogen removal. The effectiveness for pre-

cursor removal is dependent on a number of design issues such as carbon

type, ﬁlter location, ﬁlter depth, ﬁlter ﬂow rate, and blending choices.

It is also dependent on a number of water quality issues such as initial

precursor concentration, precursor adsorbility, precursor adsorption

kinetics, temperature, dissolved oxygen levels, pH, and bromide con-

centration. Although much progress has been made on the modeling

of GAC system performance, the applicability of this technology to any

drinking water utility will need to be determined by pilot testing

(US EPA, 2001).

Use of membranes. Certain type of membranes can be very effective for

controlling DBPs, while others are speciﬁcally designed to remove par-

ticulates/pathogens. For example, reverse osmosis (RO) membranes are

very tight and are typically used to remove salts from seawater and

brackish waters. Due to their tight membrane structure, they require

high pressures to operate effectively.

Nonoﬁltration (NF) membranes are not as tight as RO membranes,

but have been found to remove a large percentage of DBP precursors.

Because they are not as tight, they can be operated at lower pressures

(typically 5 to 9 bars) than RO membranes while achieving the same,

or greater, ﬂux. Ultraﬁltration (UF) and microﬁltration (MF) mem-

branes are typically used for particulate/pathogen removal only. Details

of MF, UF, NF, and RO are discussed in the membrane ﬁltration section.

502 Chapter 5

Speth (1998) concludes that activated carbon is an effective process

for removing DBP precursors, but is not effective for pathogen removal.

RO and NF are effective processes for removing DBP precursors, and

UF and MF membranes are excellent for removing pathogens and par-

ticulates and, under some conditions, could be considered as a replace-

ment for conventional ﬁltration.

Membrane technologies are effective processes for removing DBP pre-

cursors. As stated above, MF and UF membranes are excellent for remov-

ing pathogens. NF and RO membranes are excellent for removing DBP

precursors, but are not counted on as a pathogen barrier due to blending

and glue-line-failure issues. These problems have been overcome by new

membrane technologies. Reducing the effect of membrane foulants is a

main consideration in the design of NF and RO plants, especially for plants

treating surface waters. Although much progress has been made on mod-

eling and scaling up small-membrane results, the applicability of this

technology will need to be determined by pilot testing (US EPA, 2001).

For small systems. Small water supply systems have many problems

that make compliance with drinking water standards more difﬁcult

than for medium and large systems. The pilot- and full-scale research

efforts have been made to address some of these needs. Because small

systems often lack of the ﬁnancial, technical, and managerial capabili-

ties of larger systems and are responsible for the majority of the SDWA

violations, they have been targeted in several federal rules and

regulations.

Filtration and disinfection of water supplies are highly effective

public health practices. EPA’s in-house research has focused prima-

rily on ﬁltration and disinfection technologies that are considered to

be viable alternatives to conventional package plants (ﬂocculation,

coagulation, media ﬁltration, postchlorination). Conventional package

plants are site-speciﬁc and require a high level of operator skill to

properly maintain appropriate chemical dosage and ﬂow rates, espe-

cially when used to treat surface water. These difficulties, in con-

junction with the other small system problems, have results. Field

demonstration projects have been used to characterize some of the

problems that can occur for even the best technology when conditions

are not optimal. The remote monitoring and control research efforts

result from the fact that many rural systems are located in topo-

graphically difﬁcult areas or separated by large distances from other

systems, thus precluding any consolidation or regionalization efforts.

The software and sensing systems developed as a product of this

research will allow individual treatment units to be monitored and

operated from a certain location. This approach is called the electric

circuit rider concept. One technique that has promise for improving

Public Water Supply 503

the effectiveness of systems in the ﬁeld is the use of supervisory con-

trol and data acquisition system (US EPA, 2001).

Results from the EPA research indicate that MF, UF, and RO sys-

tems are effective technologies for the removal of pathogens while still

being affordable for small systems. New disinfection technologies

appear to provide improvements over current systems in handling

chemicals and consistency of performance. This is an area undergoing

rapid change. Many organisms are readily removed and inactivated in

the laboratory, but under field conditions, the same effectiveness

cannot be taken for granted.

Control in distribution system. Virtually for any surface contact with the

water in a distribution system, one can ﬁnd bioﬂilms. Bioﬁlms are formed

in distribution system pipelines when microbial cells attach to pipe sur-

face and multiply to form a ﬁlm or slime layer on the pipe. Probably

within seconds of entering the distribution system, large particles, includ-

ing microorganisms, adsorb to the clean pipe surface. Some microor-

ganisms can adhere directly to the pipe surface via appendages that

extend from the cell membrane; other bacteria form a capsular material

of extracellular polysaccharides (EPS), sometimes called a glycocalyx,

that anchors the bacteria to the pipe surface (Geldreich, 1988). The

organisms take advantage of the macromolecules attached to the pipe

surface for protection and nourishment. The water ﬂowing past carries

nutrients (carbon-containing molecules, as well as other elements) that

are essential for the organisms’ survival and growth (US EPA, 1992).

Bioﬁlms are complex and dynamic microenvironments, encompassing

processes such as metabolism, growth, and product formation, and

ﬁnally detachment, erosion, or “soughing” of the bioﬁlm from the sur-

face. The rate of bioﬁlm formation and its release into a distribution

system can be affected by many factors, including surface layers begin

to slough off into the water (Geldreich and Rice, 1987). The pieces of

bioﬁlm released into the water may continue to provide protection for

the organisms until they can colonize a new section of the distribution

system.

The most common organisms found in bioﬁlms are nonpathogenic het-

erotrophic bacteria. Some bacteria that live in bioﬁlms may cause esthetic

problems with water quality, including off-tastes, odors, and colored water

problems. Few organisms living in distribution system bioﬁlms pose a

threat to the average consumer. Bacteria, viruses, fungi, protozoa, and

other invertebrates have been isolated from drinking water bioﬁlms (US

EPA, 1992). The fact that such organisms are present within distribution

system bioﬁlms shows that, although water treatment is intended to

remove all pathogenic bacteria, treatment does not produce a sterile

water. Consequently, if opportunistic pathogens survive in bioﬁlms, they

504 Chapter 5