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3
Water Quality
The wastes discharged into municipal wastewater nants pose different hazards in one context than they
collection systems include a wide range of biological, do in another and their associated risks depend on the
inorganic, and organic constituents. Some of these dose and paths of exposure (see Chapter 6). Although
constituents can be harmful to persons and/or eco- the committee provides examples below for a diversity
systems depending on concentration and duration of of potential pathogens and chemical contaminants in
exposure (see also Chapter 6 for a discussion of risk in reclaimed water, it is important to keep in mind that
the context of hazards and exposure types). Some are there are often other sources of exposure (e.g., food,
essential nutrients at low concentrations (e.g., certain distribution system failures, household products) that
trace elements), but may become hazardous at higher are not discussed here.
concentrations. In this chapter the committee briefly
describes the key water quality constituents of concern PATHOGENS
when municipal wastewater is reused or when treated
municipal wastewater is discharged to a watercourse Wastewater contains many microorganisms but
that is later used as a source of municipal water supply. only a subportion of the organisms are potential human
Because water reuse involves multiple potential ap- health hazards, notably enteric pathogens. Classes of
plications (see Chapter 2, Table 2-2), the constituents microbes that can cause infection in humans include
of concern depend upon the final use of the water. For helminths (wormlike parasites), parasitic protozoa,
instance, some constituents in drinking water that may bacteria, and viruses. Some microorganisms are obligate
affect human health may not be of concern in certain pathogens (i.e., they must cause disease to be trans-
landscape irrigation or industrial applications where ferred from host to host), whereas others are opportu-
risk to human health from incidental consumption is nistic pathogens, which may or may not cause disease.
negligible. Other constituents may have an adverse im- In the United States, the enteric protozoa Cryptospo-
pact on aquatic species but no adverse impact on human ridium and Giardia, the enteric bacteria Salmonella, Shi-
health at the same concentration. It is also important gella, and toxigenic Escherichia coli O157:H7, and the
to remember that the occurrence and concentration of enteric viruses enteroviruses and norovirus are the most
these chemicals and microorganisms are likely to vary frequently documented waterborne enteric pathogens
from one location to another, with the treatment meth- (Craun et al., 2006). They cause acute gastrointestinal
ods applied, and according to post-reclamation storage illness and have the potential to create large-scale epi-
and conveyance practice. Depending on the reuse ap- demics. Table 3-1 lists the microbial agents that have
plication, these constituents may need to be addressed been associated with waterborne disease outbreaks and
to differing degrees in water reuse system designs (see also includes some agents in wastewater thought to
Chapters 4 and 5), considering that individual contami- pose significant risk.
55
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56 WATER REUSE
TABLE 3-1 Microbial Agents of Known Hazard Via bacteria, viruses, and protozoa that can cause acute
Water Exposures diseases with even a single exposure, additional physio-
chemical treatment processes (discussed in Chapter 4)
Agent Associated Illnesses
may be required to achieve acceptable levels of removal
Viruses
or inactivation, depending on the beneficial use.
• Noroviruses Gastroenteritis
• Adenoviruses Conjunctivitis, gastroenteritis, respiratory
disease, pharyngoconjunctival fever
• Coxsackieviruses Meningitis, pharyngitis, conjunctivitis, Helminths
encephalitis
• Echoviruses Gastroenteritis, encephalitis, meningitis
Often known as parasitic worms, helminths pose
• Hepatitis A virus Hepatitis
significant health problems in developing countries
• Astroviruses Gastroenteritis
Bacteria
where wastewater reuse is practiced in agriculture
• E. coli O157 Hemorrhagic diarrhea
using raw sewage or primary effluents (Shuval et al.,
• Campylobacter jejuni Campylobacteriosis
• Salmonella Salmonellosis 1986). The World Health Organization (WHO) has
• Shigella Shigellosis
pointed to the need to study the transmission of in-
• Vibrio Gastroenteritis, wound infection
testinal parasites, particularly nematodes, in children
• Legionella Legionellosis
Protozoa
living in areas where untreated wastewater is used for
• Cryptosporidium Cryptosporidiosis
vegetable irrigation (WHO, 1989). Human exposures
• Giardia Giardiasis
• Microsporidia Microsporidiosis to helminths are mainly through ingestion of helminth
eggs in food or water contaminated with untreated
NOTE: These agents are known to be present in treated wastewaters or
surface water and therefore are considered to be potentially present in waters
wastewater or sewage-derived sludge, and these expo-
used for the production of reclaimed water.
sures can cause acute gastrointestinal illness. There are
SOURCE : Asano et al. (2007).
over 100 different types of helminths that can be pres-
ent in sewage, although the number of helminth eggs
The occurrence and concentrations of microbial in untreated wastewater is typically much higher in
pathogens in reclaimed water depend on the health of developing countries than in developed countries. The
concentration of helminth eggs can range from <1 to
the tributary population and the applied wastewater
>1,000 per 0.3 gallon (1.0 L) of sewage, depending on
treatment processes (see Table 3-2). Primary and sec-
ondary treatment (see Chapter 4) attenuate microbial the source of sewage ( Jiménez, 2007; Ben Ayed et al.,
pathogens but do not eliminate them. For pathogenic 2009). Helminth eggs can be largely removed through
TABLE 3-2 Reported Ranges of Reclaimed Water Quality for Key Water Quality Parameters After Different Degrees of
Treatment
Range of Effluent Quality After Indicated Treatment
CAS with
Conventional Biological CAS with Membrane
Untreated Activated CAS with Nutrient BNR and Bioreactor
Constituent Units Wastewater Sludge (CAS) Filtration Removal (BNR) Filtration (MBR)
<2
Total suspended solids (TSS) mg/L 120-400 5-25 2-8 5-20 1-4
Total organic carbon (TOC) mg-C/L 80-260 10-40 8-30 8-20 1-5 0.5-5
<10a
Total nitrogen mg-N/L 20-70 15-35 15-35 3-8 2-5
≤2 <0.3b-5
Total phosphorus mg-P/L 4-12 4-10 4-8 1-2
≤1
Turbidity NTU — 2-15 0.5-4 2-8 0.3-2
400
Volatile organic compounds (VOCs) µg/L 10-40 10-40 10-20 10-20 10-20
Trace constituents µg/L 10-50 4-40 5-30 5-30 5-30 0.5-20
<100
106-109 104-105 103-105 104-105 104-105
Total coliforms No./100 mL
10-104 10-102
Protozoan cysts and oocysts No./100 mL 0-10 0-10 0-1 0-1
10-104 10-103 10-103 101-103 10-103 1-103
Viruses PFU/100 mL
NOTE: None of the treatments in the table include disinfection.
aWith anoxic zone.
bWith coagulant.
SOURCE: Asano et al. (2007).
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57
WATER QUALITY
secondary treatment supplemented by finishing ponds forms (a classification that includes E. coli) and entero-
or filtration and disinfection (Blumenthal et al., 2000). coccus in the United States and in many nations around
the world (NRC, 2004). It is important to note that
most E. coli and enterococcus are not pathogenic. Rather
Protozoa
they are part of the normal microflora in the human di-
Protozoa are single-celled eukaryotes that are gestive tract and are necessary for proper digestion and
heterotrophic and generally larger in size than bacte- nutrient uptake. E. coli and enterococcus are employed as
ria. Some protozoa are mobile using flagella, cilia, or indicators of the presence of human waste (also called
pseudopods, whereas others are essentially immobile. fecal indicator bacteria) in water quality monitoring
M alaria, probably the best-known disease caused and protection because they are present in high con-
by protozoa, is caused by the genus Plasmodium. In centrations in human feces and sewage and they are
U.S. water systems, Giardia lamblia, Cryptosporidium more persistent than most bacterial pathogens. They
parvum, and C. hominis have been associated with gas- are, therefore, used to indicate inadequate treatment
trointestinal disease outbreaks through contaminated of sewage to remove bacterial pathogens (NRC, 2004).
water. In 1993, an outbreak of cryptosporidiosis caused Fecal indicator bacteria in undisinfected secondary ef-
fluent range from 102 to 105/100 mL depending on the
an estimated 400,000 illnesses and more than 50 deaths
through contaminated drinking water in Milwaukee, quality of the influent water (Bitton, 2005). However,
W isconsin (Mac Kenzie et al., 1994; Hoxie et al., the concentration of fecal indicator bacteria (i.e., total
1997). Part of the protozoan life cycle often involves coliform, fecal coliform, enterococcus, and E. coli) in
spores, cysts, or oocysts, which can be highly resistant filtered, disinfected secondary effluent can be brought
to chlorine. Cryptosporidium oocysts and Giardia cysts below the nominal detection limit of 2.2 organisms/100
of human origin are frequently detected in secondary mL and with advanced treatment, they can be brought
wastewater effluent (Bitton, 2005), and these may still even lower.
persist in disinfected effluent after granular media or
membrane filtration (e.g., Rose et al., 1996). Thus, in Viruses
potable reuse applications, additional treatment pro-
cesses (see Chapter 4) are needed to reduce the risk of Viruses are extremely small infectious agents that
infection from Cryptosporidium and Giardia. require a host cell to replicate. They are of special inter-
est in potable reuse applications because of their small
size, resistance to disinfection, and their low infectious
Bacteria
dose. There are many different viruses, and they in-
Bacteria are single celled prokaryotes and are fect nearly all types of organisms, including animals,
ubiquitous in the environment. However, domestic plants, and, even bacteria. Aquatic viruses can occur at
concentrations of 108 to 109 per 100 mL of water in
wastewaters contain many pathogenic bacteria that are
the ocean (Suttle, 2007) and 109 to 1010 per 100 mL
shed by the human population in the sewershed. Par-
ticularly important are pathogenic bacteria that cause in sewage (Wu and Liu, 2009); however, most of these
gastroenteritis and are transmitted by fecal-oral route are bacteriophages—viruses that infect bacteria. The
(enteric bacterial pathogens). From 1970 to 1990, en- viruses of concern in water reuse or in the discharge of
teric bacteria were estimated to account for 14 percent treated wastewater to drinking water sources are human
of all waterborne disease outbreaks in the United States enteroviruses (e.g., poliovirus, hepatitis A), noroviruses
between 1971 and 1990 (Craun, 1991) and 32 percent (i.e., Norwalk virus), rotaviruses, and adenoviruses.
between 1991 to 2002 (Craun et al., 2006). Based on Human viruses are usually present in undisinfected
hospitalization records, the most severe bacterial infec- secondary effluent and may still persist in effluents
tions result from E. coli (14 percent), Shigella (5.4 per- after some advanced treatment (e.g., Blatchley et al.,
cent), and Salmonella (4.1 percent) (Gerba et al., 1994). 2007; Simmons and Xagoraraki, 2011). Fecal indicator
Because of the public health significance of bacte- bacteria that are currently used for water quality moni-
rial pathogens, monitoring systems and water quality toring are not an adequate indication of the presence or
standards have been established based on fecal coli- absence of viruses because bacteria are more efficiently
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58 WATER REUSE
removed or inactivated by some wastewater treatment stituents in water are total dissolved solids (TDS) and
processes than are enteric viruses (Berg, 1973; Har- conductivity, although both TDS and conductivity
wood et al., 2005). Thus, viruses need to be carefully measurements may include contributions from some
addressed whenever treated municipal wastewater is organic constituents. Because human and industrial
discharged or reused in a context where there may be activities consistently increase the TDS in water, the
human contact, particularly when it makes up all or part reuse of water will increase the TDS in the water supply.
of a drinking water supply.
Metals and Metalloids
Prions
Metals and metalloids, such as lead, mercury,
A prion is an infectious agent that is primarily chromium, arsenic, and boron, can result in adverse
a protein. The prion causes a morphological change effects to human health when consumed in excessive
to native proteins, which can, in turn, lead to disease amounts. However, regulatory statutes and industrial
symptoms. The best-known example of prion-based pretreatment regulations promulgated through the
disease is bovine spongiform encephalopathy (“mad Clean Water Act specifically target toxic metals and,
cow disease”). In animals, prions can cause a variety of as a result, most municipal effluents have concentra-
diseases including scrapie and chronic wasting disease tions of toxic metals below public health guidelines
(CWD); however, the spectrum of cross transmission and standards. Therefore, toxic metals in contemporary
of different prion agents is not clear. It has been dem- treated domestic wastewaters in the United States do
onstrated that CWD can be transmitted to animals by not generally exceed human health exposure.
direct oral ingestion of prion-containing animal tissue Boron (a metalloid) occurs in domestic wastewater,
(Mathiason et al., 2009). It has not been demonstrated most likely resulting from its use in household products
that prions can be transmitted by the ingestion of such as detergents (WHO, 2009). However, boron
drinking water, and their occurrence in water is poorly typically is not an issue for water reuse systems because
understood. concentrations are generally less than 0.5 mg/L (Asano
Currently, sparse data exist on the occurrence of et al., 2007), although in certain unique geologies or
prions outside of animal flesh or on the fate of prions coastal communities boron can be elevated. Boron is
in water or wastewater treatment. Prions are thought of particular interest because no removal occurs during
to substantially partition into the sludge during bio- conventional biological treatment, and even advanced
logical wastewater treatment, although according to water treatment processes (i.e., reverse osmosis) are
a pilot study reported by Hinckley et al. (2008), some not highly effective at ambient pH. Although boron is
remain in effluent. Nichols et al. (2009) developed an not regulated in drinking water in the United States,
analytical technique for measuring prions in water and the U.S. Environmental Protection Agency (EPA)
environmental samples. Using this assay they reported published a health advisory level of 7 mg/L for adults
detection of prions in one of two surface water samples and a level of 3 mg/L for 10-kg children (EPA, 2009b).
in an area known to be endemic for CWD. They also Similarly, WHO has established a human health guide-
reported detection of prions from water drawn from line for boron of 2.4 mg/L (WHO, 2009). Thus, typical
the flocculation stage of a water treatment plant using boron levels in domestic wastewaters are well below
this source, but none in the water in subsequent stages drinking water guidelines.
of treatment. There are many ornamental plants, however, that
are more sensitive to boron (Tanji et al., 2008). Al-
though boron is essential for plant growth and develop-
INORGANIC CHEMICALS
ment, it can be toxic to plants at concentrations above
Wastewater contains a variety of inorganic con- 0.5 to 1 mg/L (Brown et al., 2002). In some settings,
stituents including metals, oxyhalides, nutrients, and boron may place limits on the types of plants that can
salts. Generally, aggregate measures of inorganic con- be successfully irrigated with reclaimed water.
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59
WATER QUALITY
Salts ment options are limited and costly and because sig-
nificant residuals are produced. Virtually all processes
The reuse of water generally increases the con- employed for salinity reduction result in a concentrated
centration of dissolved salts because of significant liquid waste (brine), which must subsequently be dis-
contributions of various salts through municipal and posed (see also Chapter 4).
industrial water uses. In general, the levels of salts as
measured as TDS do not exceed thresholds of concern
Oxyhalides
to human health; however, excess salt concentrations
can result in aesthetic concerns (i.e., unpalatable water) Oxyhalides are anionic salts consisting of a halo-
as well as agricultural and infrastructure damage. Cer- gen covalently bonded to one or more oxygen atoms.
tain salts in elevated concentrations can lead to scaling In water reuse, the primary oxyhalides of concern are
and corrosion issues. Calcium and magnesium con- bromate, chlorite, chlorate, and perchlorate. Bromate
centrations are primarily responsible for hardness, and is of primary concern when water containing bromide
excess levels can cause damage to household appliances is ozonated, because its maximum contaminant level
and industrial equipment (Hudson and Gilcreas, 1976). (MCL) is 10 µg/L and EPA has been made it clear it
In service areas with elevated hardness, households will seek even lower levels when feasible (EPA, 2006b).
commonly employ ion exchange–based water soften- S odium hypochlorite, commonly known as bleach,
ers as a local remedy for “hard water,” but these units can contain elevated levels of bromate, chlorate, and
significantly increase the total salinity of the wastewa- perchlorate, depending upon the manufacturing and
ter, particularly chloride. High levels of chloride are of storage conditions (Asami et al., 2009).
concern because these ions exacerbate the corrosion Neither chlorate nor perchlorate is currently regu-
of metals and reinforced concrete (Crittenden et al., lated under EPA’s primary drinking water standards,
2005; Basista and Weglewski, 2009). The U.S. Bureau although both are included on EPA’s Contaminant
of Reclamation estimated in 2004 that excess salinity in Candidate List 3. Additionally, the state of California
the Colorado River caused more than $300 million per has established a notification level of 800 µg/L for chlo-
year in economic damages in the United States (U.S. rate and an enforceable MCL of 6 µg/L for perchlorate.
Bureau of Reclamation, 2005). Excess exposure to chlorate and perchlorate can result
Excess salinity can also be detrimental to plant in inhibition of iodide uptake, resulting in decreased
growth (Tanji et al., 2008; Goodman et al., 2010). High production of thyroid hormones (Snyder et al., 2006b).
sodium and chloride concentrations in reclaimed water Chlorate is generally associated with the decomposition
used for irrigation can cause leaf burn, and high sodium of bleach, where bleach age and handling procedures
concentrations can also reduce the permeability of greatly influence the degree of chlorate formation
clay-bearing soils and adversely affect the soil structure. (Gordon et al., 1997).
The suitability of a water source for irrigation can be Perchlorate as a water contaminant is generally
assessed by the electrical conductivity and the sodium associated with anthropogenic activities, including
adsorption ratio (SAR), a calculated ratio of sodium to solid propellants for missiles and spacecraft, flares,
calcium and magnesium ions;1 the higher the electrical and fireworks (Urbansky, 2000). More recent data
conductivity and the SAR, the less suitable the water is have demonstrated that perchlorate also is found in
for use in irrigation. Therefore, careful control of salts bleach, with the concentration dependent primarily
and salt compositions is critical to water reuse, with upon bleach storage conditions and age (Snyder et
specific limits dictated by end-use applications (i.e., al., 2009). Although, there is no federal regulation for
irrigation vs. potable). perchlorate in drinking water, several states have pro-
Salinity control is quite challenging because treat- mulgated enforceable regulations, with Massachusetts
having the most stringent standard at 2 µg/L (Pisa-
renko et al., 2010). Perchlorate has been demonstrated
1 SAR = [Na+]/{([Ca2+] + [Mg2+])/2}1/2, where the concentrations
to accumulate in certain plants (Sanchez et al., 2005);
are provided in milliequivalents per liter.
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60 WATER REUSE
therefore, irrigation of food crops with reclaimed water largely on the intended use of the produced water. In
containing elevated levels of perchlorate could result in water reuse for irrigation, the presence of nitrogen
elevated levels of perchlorate in certain food products. and phosphorus are generally beneficial and promote
However, perchlorate also is naturally occurring as the growth of plants or crops. However, ammonia, par-
result of formation in the atmosphere and subsequent ticularly in its un-ionized form (i.e., as NH3), is highly
deposition with rainfall (Dasgupta et al., 2005), thus toxic to fish; therefore, wastewater discharges to surface
complicating investigations of perchlorate bioaccumu- waters generally are regulated to prevent excess am-
lation from natural versus artificial irrigation. Water monia release. Ammonia can reach levels of 30 mg/L
reuse practitioners employing ozonation should be in secondary treated effluents; however, ammonia can
aware of the potential for bromate formation, and those be oxidized to nitrite and further to nitrate by aerobic
using bleach should be cautious purchasing and storing autotrophic bacteria during wastewater treatment.
bleach, to avoid excess chlorate and perchlorate forma- Although the nitrification process leads primarily to
tion. As in drinking water treatment, with the exception nitrate, water reuse facilities often also denitrify to
of perchlorate, the oxyhalide problem is not so much a reduce nitrate levels, converting nitrate to nitrite and
problem of source water quality but one that requires ultimately to nitrogen gas. When nitrogen is not re-
proper design and operation of treatment facilities to moved, it is usually present at levels that are above the
minimize their formation during treatment. Among EPA MCL for nitrate (as N). This can be a concern
the processes that are employed in conventional drink- because in the natural environment, all forms of ni-
ing water treatment and in advanced wastewater treat- trogen in effluent are generally transformed to nitrate.
ment, oxidation and disinfection processes are those Although reclaimed water is frequently desirable
that have the greatest potential for creating oxyhalides. for irrigation, excess irrigation can lead to nutrient con-
Disinfection is especially important in potable reuse tamination of underlying aquifers and of surface waters
projects; therefore, the formation of oxyhalides will be a through runoff. An additional concern for nutrients
key consideration in process train selection and design. in reclaimed water stored or reused in ponds, lakes,
or streams arises from eutrophication wherein excess
nitrogen and phosphorus stimulate the rapid growth
Nutrients
of algae, which can cause problems including a deple-
Human waste products are rich in nitrogen and tion of oxygen concentrations in water, alteration of the
phosphorus, and the human body metabolizes and ex- trophic state of the system, impairment of the operation
cretes both phosphorus and nitrogen in various forms. of drinking water treatment plants, and production of
The primary forms of nitrogen in wastewater effluent compounds that affect taste and cause odors in drinking
are ammonia, nitrate, nitrite, and organic nitrogen. water. The processes for management of nitrogen in
Phosphorus also occurs in wastewater mainly in inor- wastewater treatment are now well-understood (Tcho-
ganic forms. These nutrients can pose environmental banoglous, 2003). As a consequence the challenge is
concerns but also carry potential benefits to nonpo- matching the appropriate treatment with the intended
table water reuse applications that involve irrigation. use and assessing the affordability of the project.
Elevated nitrate in drinking water can also present
public health issues, especially in infants. To protect Engineered Nanomaterials
human health, EPA established an MCL in drinking
water of 10 mg (as N)/L for nitrate and 1 mg (as N)/L Nanomaterials are generally considered to be
for nitrite.2 materials with at least one dimension from 1 to 100
Therefore, the need for removal of nutrients during nm ( Jiménez et al., 2011). Nanomaterials exhibit this
treatment of wastewater for subsequent reuse depends geometry in one dimension (i.e., nanofilms), two di-
mensions (i.e., nanotubes, nanowires), or three dimen-
sions (i.e., nanoparticles). Nanoscale particles are not
2 S ee http://water.epa.gov/drink/contaminants/index.cfm. Ad -
new to the water and wastewater field. Many natural
ditionally, WHO (2011) set a guideline value of 11 mg/L nitrate
as N (or 50 mg/L as nitrate) and 1 mg/L nitrate as N (or 3 mg/L subcolloidal particles in this range, including viruses
as nitrite).
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61
WATER QUALITY
and natural organic matter (Baalousha and Lead, 2007; Ongoing research is exploring possible health
Song et al., 2010), have been dealt with for decades in effects from engineered nanoparticles (and associate
water and wastewater treatment. More recent examples mechanisms of effect) via various exposure pathways
of natural nanoscale particles include oxidation prod- (NRC, 2009a, 2011b). So far, the trace levels of en-
ucts of manganese, iron, and perhaps lead (Lytle and gineered nanoparticles in wastewater have not been
Snoeyink, 2004; Lytle and Schock, 2005). However, linked to adverse human health impacts (O’Brien
the purposeful manufacturing of nanoscale materials and Cummins, 2010). At present, most engineered
(called engineered nanomaterials) for consumer prod- nanoparticles in municipal wastewater originate from
ucts is rapidly increasing.3 Because nanoscale particles household and personal care products, and for these, di-
have an extraordinary surface-to-volume ratio, they are rect exposure in the household itself is likely far greater
of interest in many applications where surface chem- than from potential ingestion of wastewater-influenced
istry or catalysis is important (Weisner and Bottero, drinking water. Because the use of engineered nanopar-
2007). Potential applications of nanotechnology in the ticles in consumer products is expected to continue to
environmental industry itself are also evolving (Savage rise, continued exposure and risk assessments will be
and Diallo, 2005; Chong et al., 2010; Pendergast and important for assessing impacts on the environment
Hoek, 2011). As a result, many new questions have and public health.
emerged about the fate of engineered nanomaterials
when released to the environment. ORGANIC CHEMICALS
Engineered nanomaterials can be organic, in-
organic, or a combination of organic and inorganic Wastewater is generally rich in organic matter,
components. Because of the complexity and diversity which is measured as TOC, dissolved organic carbon
of engineered nanomaterial structure and composition, (DOC; that portion of the TOC that passes a 0.45-mm
the behavior and toxicity of particles released to the pore-size filter), and particulate organic carbon (POC;
environment will vary greatly. A recent review discusses that portion of the TOC that is retained on the filter).
the potential implications of engineered nanomateri- Of the DOC present in highly treated reclaimed water,
als in the environment (Scown et al., 2010). However, the vast majority is generally natural organic matter and
specific information is limited regarding the occurrence soluble microbial products, with small concentrations
and fate of engineered nanomaterials in municipal of a variety of individual organic chemicals (Table 3-3;
wastewater, their response to treatment, and their pub- Namkung and Rittman, 1986; Shon et al., 2006).
lic health and environmental significance. Trace organic chemicals originate from industrial
Some research has been conducted on the fate and domestic products and activities (e.g., pesticides,
of engineered nanoparticles in wastewater treatment. personal care products, preservatives, surfactants, flame
Kaegi et al. (2011) studied the fate of silver nanopar- retardants, perfluorochemicals), are excreted by humans
ticles added to the inflow of a pilot-scale conventional (e.g., pharmaceutical residues, steroidal hormones), or
wastewater treatment plant. Most of the silver nanopar- are chemicals formed during wastewater and drinking
ticles became associated with sludge and biosolids and water treatment processes. The vast majority of these
were not detected in the pilot plant effluent. Another trace organic chemicals occur at microgram per liter
study investigated the removal of titanium nanopar- and lower levels. This complex mixture of low con-
ticles at wastewater treatment plants. Kiser et al. (2009) centrations of contaminants has long been recognized;
found that the majority of titanium in raw sewage was Ram (1986) reported that 2,221 organic chemicals had
associated with particles >0.7 µm, which were gener- been identified in nanogram per liter to microgram per
ally well removed through a conventional process train. liter concentrations in water around the world, includ-
However, titanium associated with particles <0.7 µm ing 765 in finished drinking water. Modern analyti-
(near the nanoscale) were found in the treated waste- cal tools are extremely sensitive and often capable of
water effluents. detecting nanogram per liter or lower concentrations
of organic contaminants in water. In this report, these
3 http://www.nanotechproject.org/inventories/consumer/analy-
compounds are termed trace organic contaminants,
sis_draft.
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62 WATER REUSE
TABLE 3-3 Categories of Trace Organic Contaminants considered when that wastewater becomes part of a do-
(Natural and Synthetic) Potentially Detectable in mestic water supply. These include solvents, detergents,
Reclaimed Waters petroleum mixtures, plasticizers, flame retardants, and a
host of other products or product ingredients. A few of
Category Examples
these chemicals are not completely removed by conven-
Industrial 1,4-Dioxane, perflurooctanoic acid, methyl tertiary
Chemicals butyl ether, tetrachloroethane tional water and wastewater treatment processes. For
example, an industrial chemical that has caused concern
Pesticides Atrazine, lindane, diuron, fipronil
in water reuse programs in California is 1,4-dioxane,
Hormones (17β-estradiol), phytoestrogens, geosmin,
Natural
chemicals 2-methylisoborneol
a common industrial solvent considered a probable
Pharmaceuticals Antibacterials (sulfamethoxazole), analgesics
carcinogen, which has been shown to break through
and metabolites (acetominophen, ibuprofen), beta-blockers (atenolol),
reverse osmosis membranes.
antiepileptics (phenytoin, carbamazepine), antibiotics
In 1986, EPA estimated that as much as one-third
(azithromycin), oral contraceptives (ethinyl estradiol)
of all priority pollutants entering U.S. waters from
Personal care Triclosan, sunscreen ingredients, fragrances, pigments
products
wastewater discharges were the result of industrial dis-
Household Sucralose, bisphenol A (BPA), dibutyl phthalate,
charges into public sewers (EPA, 1986). Additionally,
chemicals and alkylphenol polyethoxylates, flame retardants
pulsed releases from certain industries have been known
food additives (perfluorooctanoic acid, perfluorooctane sulfonate)
to disrupt the biological processes at wastewater treat-
Transformation N-Nitrosodimethylamine (NDMA), bromoform,
ment plants, resulting in reduced treatment efficiency
products chloroform, trihalomethanes
(Kelly et al., 2004; Kim et al., 2009; You et al., 2009).
but they are also commonly called micropollutants or For these reasons, under the authority of the Clean
contaminants of emerging concern (CECs). EPA has Water Act, EPA established the industrial pretreatment
defined CECs as “pollutants not currently included in program, which requires wastewater treatment plants
processing 5 million gallons per day (19,000 m3/d) or
routine monitoring programs” that “may be candidates
for future regulation depending on their (eco)toxicity, greater to establish pretreatment programs (see also
potential health effects, public perception, and fre- Box 10-1). The pretreatment program also applies
quency of occurrence in environmental media” (EPA, to smaller systems with known industrial input. This
2008a). Trace organic contaminants and CECs are not program was specifically designed to address priority
always newly discovered waterborne contaminants. pollutants, which are defined under the Clean Water
They also include constituents that have been pres- Act in section 307(a). Although the pretreatment pro-
ent in the environment for long periods of time, but gram has been largely successful at reducing the loading
for which analytical or health data have only recently of contaminants into municipal wastewater treatment
become available. plants, a much smaller, but perhaps significant, input
With modern analytical technology, nearly any of these chemicals also enters the sewer system from
chemical will likely be detectable at some concentration household use, leaking sewage conveyance pipes, and
in wastewater, reclaimed water, and drinking water. The illegal connections/dumping (mostly from the former).
challenge is not so much one of detection, but rather
determination of human and environmental health Pesticides
relevance. The following section provides information
on representative classes of trace organic chemicals Despite the fact that pesticides are generally used
present in reclaimed water, although the committee outdoors and would not be expected to be discharged
acknowledges that there may be many other classes and directly to the sewer, some pesticides have been de-
substances present. tected in wastewater effluents. The sources are not
fully characterized, but some loading could be expected
through residues in food products, head lice treatments,
Industrial Chemicals
veterinary/pet care applications, manufacturing or han-
Many chemicals originating from industrial activi- dling facilities, and infiltration of landscape runoff into
ties that have been detected in wastewater need to be sewer conveyance lines. The herbicide atrazine, which
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is used primarily on corn and soybean crops, recently treatment (Heberer, 2002) but also bioaccumulate in
has been shown to be a contaminant in nearly all U.S. fish residing in effluent-dominated streams (Ramirez et
drinking water, appearing in regions far removed from al., 2009). There are many other examples of personal
agricultural activities (Benotti et al., 2009). Subsequent care products, which have been detected in treated
research also has demonstrated that atrazine also oc- wastewater. Many of these key ingredients may also be
curs in most wastewater treatment effluents (Snyder classified as household or industrial chemicals as well.
et al., 2010a), yet the levels detected are generally in
the nanogram-per-liter range, far lower than the EPA Household Chemicals and Food Additives
MCL of 3 µg/L. Considering that wastewater efflu-
ents are generally low in pesticide residues and that Within the typical household, many chemicals are
reclaimed water employed in potable reuse projects is used for cleaning, disinfecting, painting, preparation of
regularly surveyed for all pesticides regulated in drink- meals, and other applications. Many of these chemicals
ing water, it is unlikely that these compounds will pose find their way into the wastewater collection system,
a unique risk to water reuse. and some are detectable in reclaimed water as well. An
interesting illustration is the artificial sweetener sucra-
lose (1,4,6-trichlorogalactosucrose), which is widely
Pharmaceuticals and Personal Care Products
used in the United States. This chlorinated sucrose
Recently, a great deal of attention has been given molecule is predictably difficult to remove through
to the occurrence of pharmaceuticals in wastewater biological treatment and is largely resistant to oxidation
effluents. Although pharmaceuticals were detected during water treatment as well. Therefore, concentra-
in U.S. waters as early as the 1970s (Garrison et al., tions in wastewater are generally in the microgram-per-
1975, Hignite and Azarnoff, 1977), much of the re- liter range, and sucralose has been detected at similar
cent interest was evoked when Kolpin et al. (2002) in concentrations in potable water (Buerge et al., 2009;
a nationwide stream sampling study documented the Mawhinney et al., 2011).
occurrence of 82 trace organic chemicals of wastewa- Of the household chemicals of interest, those
ter origin. Commonly detected chemicals included chemicals with the potential to disrupt the function
triclosan (an antimicrobial compound), 4-nonylphenol of the endogenous endocrine system have been of
(a metabolite of a chemical found in detergents, see particular interest. One particular class of surfactants,
Box 3-1), and synthetic estrogen from birth control, aklylphenol polyethoxylates (APEOs), has become of
which has been implicated as a causative agent in fish concern because of the estrogenic potency of some of
feminization (Purdom et al., 1994). Laboratory studies its degradation products (see Box 3-1). Another com-
have confirmed that ethinyl estradiol (EE2) is capable pound of increasing interest is bisphenol A (BPA),
of affecting fish physiology at subnanogram-per-liter which is used in a variety of consumer products and
concentrations, with a predicted no-effect concentra- has been shown to be estrogenic (Durando et al., 2007).
tion of 0.35 ng/L (Caldwell et al., 2008). It is now quite BPA has been detected in drinking water, but the con-
clear that a wide range of pharmaceuticals can and will centrations are extremely low (Benotti et al., 2009), in
be detected in reclaimed water samples (see Table 3-3 part because of BPA’s rapid oxidation by chlorine and
for examples). ozone disinfectants commonly used in water treatment
Personal care products (e.g., shampoo, lotions, (Lenz et al., 2004). In terms of human exposure, the
perfumes) represent the source of another class of contribution of BPA from drinking water is minute
chemicals that have been widely detected in wastewater compared with exposure from food packaging and
treatment plant effluents. It is logical that a substance storage materials (Stanford et al., 2010). Household
used as an ingredient of a personal care product will products and pharmaceuticals often contain inert sub-
enter the sewer system. For instance, several studies stances at much higher concentrations than the active
have demonstrated that certain synthetic musks used product. In some cases, these inert substances may also
as fragrances in personal care products not only are warrant further investigation as to potential impacts
incompletely removed by conventional wastewater to water treatment systems and environmental health.
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64 WATER REUSE
BOX 3-1
Alkylphenol Polyethoxylates
Alkylphenol polyethoxylates (APEOs) are a family of surfactants that were once widely used in domestic and industrial cleaning products.
This family of relatively benign chemicals serves as an example of how transformation reactions in engineered and natural systems can produce
compounds that pose potential risks to aquatic organisms or human health.
The most common members of this family of compounds contain either eight or nine carbon atoms in their alkyl functional group (Montgomery-
Brown et al., 2003; Loyo-Rosales et al., 2009) and are referred to as octylphenol polyethoxylates (OPEO) and nonylphenol polyethoxylates (NPEO),
respectively (see figure below). Most OPEOs and NPEOs in commercial products consist of a mixture of compounds with between 1 and 20 ethox-
ylate groups. The surfactants with more than two carbons in their ethoxylate chain exhibit relatively low toxicity to aquatic organisms in standard
toxicity tests (Staples et al., 2004; Loyo-Rosales et al., 2009). However, the compounds undergo biotransformation in wastewater treatment plants
that employ anaerobic treatment processes (e.g., nitrate removal by denitrification) and in aquifer recharge systems in which anoxic (anaerobic)
conditions occur. Anaerobic biotransformation of OPEO and NPEO occurs through sequential cleavage of the ethoxylate carbons, ultimately leading
to formation of octylphenol or nonylphenol (Ahel et al., 1994a,b). Nonylphenol typically occurs in wastewater effluent at concentrations about 10
times higher than those of octylphenol (Loyo-Rosales et al., 2009). Nonylphenol and the transformation products with only one or two carbons
in the polyethoxylate chain are substantially more toxic to aquatic life than the corresponding OPEO and NPEO surfactants (Staples et al., 2004).
Octylphenol, nonylphenol, and the short polyethoxylate chains have been implicated in the feminization of fish observed in effluent-dominated
streams (Johnson et al., 2005), although steroid hormones (e.g., 17β-estradiol) typically account for about 10 times more estrogenic activity than
octylphenol or nonylphenol.
In recognition of the risks to aquatic life associated with APEOs and their transformation products, their use was restricted in the European Union
in the 1990s. In 2005, EPA set a water quality criterion for freshwater aquatic life of 6.6 μg/L for chronic exposure to nonylphenol (EPA, 2005a)
that is approximately equal to or slightly higher than concentrations typically detected in wastewater effluent in the United States (Montgomery-
Brown et al., 2003; Loyo-Rosales et al., 2009). As a result, many manufacturers have replaced APEOs in consumer products or have reduced their
concentrations. The compounds are still used for certain industrial applications and for specialty cleaning products.
General structure of alkylphenol polyethoxylate surfactants. For the alkyl group, x = 7 for octylphenol and 8 for nonylphenol. For the ethoxylate group, y = 0 to 19.
Naturally Occurring Chemicals and odor represent another important class of natural
chemicals that may pose challenges in water reuse.
Estrogen hormones (e.g., 17β-estradiol) are endog- Of these, the best characterized are geosmin and
R02129
enous4 compounds that are excreted in relatively large 2-methylisoborneol (MIB), which are generally found
Figure 3-1
concentrations by animals. In studies of wastewater in lakes and reservoirs (Medsker et al., 1968, 1969).
bitmapped
effluent, the measured concentrations of endogenous However, geosmin is also naturally occurring in cer-
estrogen hormones in most cases far exceeded those tain vegetables, such as red beets (Lu et al., 2003).
of the synthetic steroid hormones (Snyder et al., 1999; Although geosmin and MIB are not considered toxic
Huang and Sedlak, 2001). Huang and Sedlak (2001) at the concentrations found in water, the olfactory
reported that reverse osmosis treatment (see Chapter 4) displeasure can create great public resistance to water.
removed more than 95 percent of estrogen hormones. Compounds that affect taste and odor can be present
Additionally, free chlorine or ozone disinfection will through naturally occurring compounds or through
effectively attenuate estrogen hormone concentrations anthropogenic substances. However, these two odorif-
in water (Westerhoff et al., 2005). erous compounds that cause great public resistance to
Naturally occurring compounds that affect taste water can and should be considered in reuse planning
for both potable and nonpotable applications in urban
environments (Agus et al., 2011).
4 Synthesized within an organism.
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WATER QUALITY
Transformation Products byproducts of chlorine first identified in the 1970s
are a good example (Trussell and Umphres, 1978).
Wastewater effluents are generally rich in organic N-Nitrosodimethylamine (NDMA; see Box 3-2) is
constituents, and during most wastewater treatment a more contemporary example. NDMA can be an
processes, the majority of organic chemicals are not especially challenging contaminant for water reuse ap-
completely removed or mineralized. Although some plications because chloramination, a common method
treatment processes separate contaminants for subse- of wastewater disinfection, has been linked to NDMA
quent disposal (i.e., sludge, reverse osmosis concentrate, formation and because NDMA is not well rejected by
spent activated carbon), both biological and oxidative reverse osmosis membranes (Mitch et al., 2003) and
processes commonly employed in water and wastewater must be removed by subsequent photolysis. There is
treatment result in the formation of transformation some evidence that polymers used in the management
products. When they result from disinfection processes, of biological wastewater treatment may serve as impor-
these products are generally referred to as disinfection tant NDMA precursors (Kohut and Andrews, 2003;
byproducts; however, some oxidative processes (e.g., Neisess et al., 2003). Continued research examining
o zonation, ultraviolet [UV ] irradiation–advanced how NDMA is formed, how it can be removed, what
oxidation processes [UV-AOP]) are used specifically its precursors are, and how they can be better managed
for contaminant attenuation and not disinfection. in processes upstream of disinfection is needed.
Therefore, the term transformation product is more Municipal wastewater is often elevated in nitrogen,
applicable to the range of water reclamation processes. iodine, and bromine constituents as compared with
Through most oxidation processes, the total con- ambient waters (Venkatesan et al., 2011), which may
centration of DOC remains relatively unchanged lead to increased levels of nitrogenous, iodinated, and
( Wert et al., 2007), although the attenuation of many brominated disinfection products, respectively, when
specific trace organic chemicals is observed (Snyder et chlorination is applied ( Joo and Mitch, 2007; Krasner
al., 2006c). This empirical observation dictates that the et al., 2009), but this has not yet been documented.
vast majority of chemicals attenuated during oxidative Iodinated and brominated disinfection products are
processes are not truly removed, but rather transformed among the most genotoxic of those disinfection by-
into oxidation products. Most biological and oxidative products currently identified in water (Plewa et al.,
transformation products have not been characterized. 2004; Richardson et al., 2008). Recently, medium-
For instance, in drinking water it has been estimated pressure UV-AOP has been shown to form genotoxic
that the majority of total organic halides (TOX) formed organic transformation products when applied to wa-
during disinfection with chlorine have not been identi- ters containing nitrate, although subsequent treatment
fied (Krasner et al., 2006; Hua and Reckhow, 2008). with granulated activated carbon was able to remove
One example is triclosan, an antimicrobial com- the formed genotoxic products to levels below detection
pound used frequently in soap and other personal care (Heringa et al., 2011).
products and thus commonly detected in wastewater As water conservation efforts grow in many urban
(Singer et al., 2002). Triclosan is known to react with regions, concentrations of salt and organics will likely
chlorine to form various disinfection byproducts, in- increase in wastewater. Thus, a better understanding
cluding chloroform (Rule et al., 2005; Greyshock and of disinfection byproduct precursors, ways to minimize
V ikesland, 2006). Studies have also demonstrated that the disinfection byproduct formation, and ways to
when triclosan is exposed to UV irradiation, it can remove them is important for enhancing the safety of
form dioxin-like compounds that may be toxicologi- water reuse scenarios, including de facto reuse. Trans-
cally significant (European Commission, 2009) but are formation products in reclaimed water will also be
easily biodegraded. widely variable in concentration and structure because
It is also well known that certain compounds, of the highly complex mixtures and different source wa-
which may be innocuous in their original form, can ter characteristics. Water reuse projects would therefore
t ransform into toxic substances through water or benefit from improved methods for understanding the
w astewater treatment processes. The disinfection toxicity of complex mixtures (see Chapter 11).
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66 WATER REUSE
BOX 3-2
N-Nitrosodimethylamine
N-Nitrosodimethylamine (NDMA) has been considered a carcinogen for some time (Magee et al., 1976), and EPA has calculated the one in one
million cancer risk from drinking water to occur at approximately 0.7 ng/L. Along with other members of the nitrosamine family, NDMA received
attention in the 1970s in connection with processed foods and beverages, but it was not found in drinking water or domestic wastewater until the
turn of the century when analytical methods improved to the point where NDMA could be identified at submicrogram-per-liter levels (Taguchi et
al., 1994). Subsequently, NDMA was found in groundwater downgradient of rocket engine testing facilities, in water leaving ion exchange facilities,
and in wells influenced by reuse projects (Najm and Trussell, 2001). Recently, as part of EPA’s unregulated contaminant monitoring rule (UCMR2),
NDMA was detected in 25 percent of the drinking water distribution systems sampled, at levels between 2 and 600 ng/L. For the most part, these
drinking water systems reported that their source water was influenced by wastewater and used chloramines for disinfection (Blute et al., 2010).
NDMA often appears both in raw and treated wastewaters in the United States and Europe (Mitch et al., 2005, Krauss et al., 2009). A 2005 survey
of 10 wastewater plants found NDMA in the influent up to 140 ng/L; two plants were 20 ng/L or below, but most were between 20 and 70 ng/L.
Effluent samples, however, ranged as high as 960 ng/L (Valentine et al., 2005). Others have reported levels as high as 1,820 ng/L (Gan et al., 2006).
Control of NDMA in treated reclaimed water involves three components: (1) control of the sources of NDMA and its precursors in treatment plant
influents, (2) management of the conventional wastewater treatment process, and (3) application of advanced treatment to remove what remains.
Both Orange County and Los Angeles have had some success in identifying sources of NDMA and its precursors and have improved the quality of
the influent (Valentine et al., 2005). However, it is unclear how much of the NDMA may be the result of domestic sources (e.g., pharmaceuticals,
personal care products) that are more difficult to control (Sedlak et al., 2005; Krauss et al., 2009; Shen and Andrews, 2011). Wastewater disinfec -
tion practice, particularly chloramination (Pehlivanogllu-Mantas et al., 2006) appears to be an important target. Research by wastewater authorities
has demonstrated several factors important to NDMA formation during wastewater chlorination and a number of strategies that may be employed
to reduce it (Neisess et al., 2003; Huitric et al., 2005, 2007; Tang et al., 2006; Farée et al., 2011). Although these strategies show promise, NDMA
remains an issue in wastewaters disinfected with chloramines, where levels above 100 ng/L are common (Najm and Trussell, 2001; Valentine et
al., 2005; Huitric et al., 2007). As a result, facilities designed to produce reclaimed water for direct injection into groundwater include treatment
processes designed to remove it (e.g., UV-AOP).
CONCLUSIONS thresholds. Some constituents, such as microbial patho-
gens and trace organic chemicals, have the potential to
The very nature of wastewater suggests that nearly affect human health, depending on their concentration
any substance used or excreted by humans has the and the routes and duration of exposure (see Chapter
potential to be present at some concentration in the 6). Additionally, not only are the constituents them-
treated product. Modern analytical technology allows selves important to consider but also the substances
detection of chemical and biological contaminants at into which they may transformed during treatment.
levels that may be far below human and environmental Pathogenic microorganisms are a particular focus of
health relevance. Therefore, if wastewater becomes water reuse treatment processes because of their acute
part of a reuse scheme (including de facto reuse), the human health effects, and viruses necessitate special
impacts of wastewater constituents on intended ap- attention based on their low infectious dose, small size,
plications should be considered in the design of the and resistance to disinfection. Chapter 4 discusses the
treatment systems. Some constituents, such as salinity, treatment processes often used to attenuate concen-
sodium, and boron, have the potential to affect agri- trations of chemical and biological contaminants of
cultural and landscape irrigation practices if they are suspected health risk to humans.
present at concentrations or ratios that exceed specific
