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5
Ensuring Water Quality in Water Reclamation
A consistent reclaimed water quality can be
achieved through appropriate treatment strategies
Retention
Retention
(e.g., high-level disinfection, process redundancy), Prevention
Prior to
• Source control
technical controls (e.g., alarm shutdowns, frequent treatment
• Distribution system
• Surface • w/ river water
maintenance
inspection procedures), online monitoring devices storage reservoir
Treatment • w/ stormwater
• Aquifer
After treatment
• Conventional wastewater
(e.g., effluent turbidity, residual chlorine concentra- • River
treatment • In clear well
• Pipe/conduit
tion), and/or operational controls to react to upsets and • Advanced Wastewater • In distribution
treatment system
variability. Similar to drinking water practices, quality • Engineered natural
system (environmental
control in potable reuse projects is provided by moni- buffer)
Blending
Blending
Attenuation
Attenuation
toring and operational response plans, whereas quality (Multiple Barriers)
(Multiple Barriers)
assurance embeds the principle of establishing multiple Monitoring
barriers and an assessment and provision of treatment
reliability. This chapter discusses the state of the sci- FIGURE 5-1 Four elements often used in the design of non-
potable and potable reuse schemes: monitoring, attenuation,
ence of water reuse design and operational principles to
retention, and blending.
ensure water quality. Additionally, the chapter includes
discussion of the role of an environmental buffer within
the multiple-barrier concept. The committee then nant attenuation, retention, and blending required for
summarizes these considerations by presenting 10 steps a particular water reuse application (e.g., industrial,
that can be taken to ensure water quality in potable and agricultural, potable) will depend on project-specific
nonpotable water reuse projects. water quality objectives and the potential impacts from
system failure. The following discussions focus primar-
ily on potable reuse applications, for which rigorous
DESIGN PRINCIPLES TO ENSURE
quality assurance is essential, although the design con-
QUALITY AND RELIABILITY
cepts can be adapted to nonpotable applications as well.
The primary goal of any reuse project is that public
health is protected continually and the finished water Water Quality Monitoring
quality is acceptable to consumers. Four elements—
monitoring, attenuation, retention, and blending—are As with conventional drinking water supplies,
typically embedded into the design of both nonpotable water quality monitoring for potable water reuse is
and potable reuse schemes to ensure a reclaimed water composed of a combination of online monitoring
quality that is suitable for the desired use at all times devices (e.g., filter effluent turbidity, chlorine residual,
(see Figure 5-1). The extent of monitoring, contami- pH) and discrete measurements using grab or compos-
87
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88 WATER REUSE
ite samples (e.g., ammonia, nitrate, dissolved organic production operation is not new. The food and drinking
carbon [DOC], Eschericia coli) to ensure the quality water industries have faced it for some time, particularly
of the finished product water. These practices usually where pathogens are concerned. Where drinking water
follow standards and protocols similar to those applied is concerned, this need has been addressed by a three-
in drinking water treatment. Although these monitor- part strategy: (1) characterizing critical elements that
ing controls can fail, the acknowledged imperfection control the performance of unit processes in removing
of the monitoring technology is comparable to that specific contaminants, (2) identifying parameters that
of drinking water treatment facilities. In some states can be reliably monitored and used to confirm that
potable reuse systems are required to include water these elements are in place and that the processes are
retention after discharge from the treatment plant (e.g., performing as expected, and (3) routine analysis of
in surface or subsurface storage of the product water). certain constituents in samples taken from the finished
In theory, this retention allows time for additional con- water to confirm that the previous measures are reliable.
taminant attenuation and for water to be diverted from Recently, a monitoring approach with similar com-
the distribution system if water quality problems are ponents has been proposed for management of trace
detected. However, significant water retention is often organic chemicals in potable reuse schemes (Drewes et
not cost-effective for potable reuse projects. Addition- al., 2008). This approach combines the monitoring of
ally, past experience with water reuse has demonstrated bulk parameters (i.e., surrogates) and a select number
that unanticipated contaminants can be detected in of indicator chemicals to ensure proper performance of
final product water, even when state-of-the-art treat- unit processes. In this work, performance indicators and
ment and monitoring programs are employed (e.g., see surrogate parameters are defined as follows:
Box 3-2 on NDMA).
An idealized monitoring program would measure • Indicator—“An indicator compound is an indi-
critical microbial and chemical contaminants in real vidual chemical occurring at a quantifiable level, that
time in the finished product water before it leaves the represents certain physicochemical and biodegradable
reclamation plant. The availability of instantaneous characteristics of a family of trace organic constituents
monitoring techniques could allow significant reduc- that are relevant to fate and transport during treat-
tion of required reclaimed water retention times. Water ment. It provides a conservative assessment of removal.”
quality goals would need to be well defined, and mea- (Drewes et al., 2008).
suring techniques would need to be selected with sensi- • Surrogate—“A surrogate parameter is a quantifi-
tivity suitable for confirming that water treatment goals able change of a bulk parameter that can measure the
have been achieved. Although several new techniques performance of individual unit processes or operations
to monitor pathogens and a diverse set of chemicals in in removing trace organic compounds” (Drewes et al.,
real time have recently been proposed (Panguluri et al., 2008). Surrogates can often be used in real time.
2009; Cahill et al., 2010; Puglisi et al., 2010), significant
additional research is required to develop reliable and As an analogy, the measurement of indicators plays a
appropriate approaches to real-time monitoring that similar role to the measurement of E. coli in drinking
are suitable for water reclamation settings. Also, to water, and the monitoring of surrogates plays a role
be truly protective of public health, such monitoring similar to the monitoring of chlorine residual and con-
programs would need to be comprehensive enough to tact time. This analogy makes it clear that the indica-
include all potential contaminants that pose significant tors and surrogates concept can be extended to address
risks in the anticipated reuse applications. Real-time virtually any constituent targeted by a treatment train.
monitoring techniques that are both sufficiently com- In 2010, an independent scientific advisory panel
prehensive and sensitive are unlikely to be available in appointed by the California State Water Resources
the next decade. Thus, in the meantime, alternative Control Board endorsed this concept to ensure proper
approaches to quality assurance are needed to address performance of water reclamation processes that re-
shortcomings in real-time monitoring of contaminants. move trace organic chemicals. The panel suggested a
The problem of ensuring the quality of an ongoing combination of appropriate surrogate parameters and
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89
ENSURING WATER QUALITY IN WATER RECLAMATION
performance-based and health-based indicator chemi- ensuring that performance goals are met. Multiple
cals for monitoring reclaimed water quality of surface barriers accomplish this objective in two ways: (1) by
spreading operations (i.e., soil aquifer treatment) and expanding the variety of contaminants the process
direct injection projects in California (Anderson et al., train can effectively address (i.e., robustness) and (2)
2010). Indicator chemicals were selected with a range by improving the degree to which the process can be
of properties in an attempt to account for unknown relied upon to remove any one of them (i.e., reliability,
chemicals and newly developed compounds that may or the extent of consistent performance of a unit process
be released to the environment in the future, provided to attenuate a contaminant). These principles are illus-
they fall within the range of chemical properties cov- trated in Figure 5-2. Multiple barriers can also provide
ered. This committee encourages further development redundancy (defined as a series of unit processes that is
of this concept. capable of attenuating the same type of contaminant) so
Monitoring requirements usually become more that if one process fails another is still in the line (Haas
stringent (e.g., more frequent sampling and more and Trussell, 1998; NRC, 1998). Additionally, even
constituents to be monitored) as the potential for hu- when true redundancy is not provided, multiple barriers
man contact with the reclaimed water increases. Mu- can reduce the consequences of a failure when it does
nicipal wastewater can contain thousands of chemicals occur (Olivieri et al., 1999; Crittenden et al., 2005).
originating from consumer products (e.g., household Given the nature of the associated risk, the per-
chemicals, personal care products, pharmaceutical resi- formance criteria of multiple barriers are generally
dues), human waste (e.g., natural hormones), industrial different for pathogens, which can cause acute (sudden
and commercial discharges (e.g., solvents, metals), or and severe) health effects, as compared with organic
chemicals that are generated during water treatment chemicals, which can cause chronic health effects after
(e.g., transformation products; see also Chapter 3). prolonged or repeated exposures in drinking water
Thus, it is appropriate for monitoring programs for scenarios (see also Chapter 6). Acute health effects
reclaimed water used for potable applications to be from exposure to organic chemicals in drinking water
more comprehensive than programs commonly used
for monitoring water quality for conventional drinking
Contaminant Contaminant
water supplies. Contaminant
A B C
Attenuation
Attenuation of microbial and chemical contami-
nants of concern can be achieved by establishing
multiple barriers. A reuse scheme usually is composed
of a combination of treatment barriers that are suitable
to reduce the concentrations of compounds of concern
and preventive measures that control exposure to certain
contaminants, although the actual number of barriers
Barrier 2 Barrier 2
differs among different reuse projects (Drewes and
Khan, 2010). Tailored source control programs that
limit the discharge from industrial activities to a mu-
nicipal sewer system or the maintenance of a reclaimed
water distribution system are examples of preventive
a) Robustness b) Reliability
barriers. Attenuation of water quality constituents of
FIGURE 5-2 Multiple barriers function in two ways: (a) robust-
concern can occur through conventional wastewater
ness—increasing the variety of contaminants addressed and
treatment, advanced water treatment, or engineered
(b) reliability—decreasing the likelihood that any one contami-
natural systems. nant will fail to be removed, in this example by incorporating
Multiple barriers are an important concept in redundancy.
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90 WATER REUSE
or reclaimed water are highly unlikely absent cross con- of reclaimed water in engineered processes or after
nections or backflows. From a public health standpoint, treatment prior to a distribution system. For advanced
disinfection, which addresses acute risks, is the process treatment processes that demineralize reclaimed water
element that requires the highest degree of reliability and remove trace chemicals, it may be necessary to bal-
for applications involving significant human contact. ance the water chemistry by blending after treatment
In the case of pathogens in potable reuse projects, for public health concerns (e.g., absence of magnesium
the performance expectation is that the overall objec- and calcium), to enhance taste, to prevent downstream
tive for pathogen reduction needs to be met even if a corrosion (e.g., calcium saturation index), and to mini-
single treatment barrier fails (NRC, 1998). The level of mize damage to soils (e.g., sodium adsorption ratio)
redundancy applied to address microbial constituents and crops (e.g., magnesium deficiency) (Tchobano-
is typically not applied in the same way to multiple glous et al., 2011). Blending with traditional sources
barriers for chemicals, because of the long-term ex- can also ensure some degree of contaminant dilution
posure associated with significant elevated risks for if a treatment system failure occurs. It is noteworthy
most chemical constituents. Instead, multiple barriers that in many cases the blending water might actually
for organic contaminants are designed to encompass represent a lower quality source. Therefore, a careful
a sequence of different processes capable of targeting evaluation of the water quality prior to and after blend-
c lasses of chemicals with different physicochemical ing is warranted to avoid any degradation of the final
properties, given the wide range of different chemicals product water.
present in reclaimed water (Drewes and Khan, 2010).
For example, multiple barriers for chemical contami- Balancing Monitoring, Attenuation, Retention,
nants might consist of an advanced oxidation process and Blending
followed by granular activated carbon, where GAC
is attenuating chemicals that are not amendable to The need for using retention and/or blending to
oxidation. ensure water quality is dependent on the reliability and
robustness of the measures taken for attenuation and
monitoring. Early projects using limited technologies
Retention
for attenuation and monitoring depended heavily on
Within a water reuse context, retention time may retention and blending. In the future, as more advanced
serve two purposes: (1) to allow additional opportuni- technologies are used for attenuation that address a
ties for attenuation of contaminants and (2) to provide broader variety of contaminants with greater reliability
time to respond to system failures or upsets. Retention and as these technologies are supported by improved
time can be provided by storing reclaimed water in a techniques for monitoring and control, retention and
surface storage reservoir, storing it in an engineered blending will have less significance. However, an over-
storage tank, recharging it to an unconfined or confined arching comprehensive monitoring program tailored
aquifer, releasing it into a segment of a river, or convey- to the specific barriers and local conditions of a reuse
ing it through a pipeline system. Proper documentation scheme is necessary in all water reuse systems to ensure
should be provided of how the water provider would proper performance of each barrier.
be able to respond to specific types of upsets, includ-
ing strategies for diverting compromised product water Role of the Environmental Buffer in the Multiple-
to avoid contaminated water reaching consumers and Barrier Concept
to ensure that the desired retention time is actually
provided. Up to the present time, the environmental buffer
has often been a core element of the multiple-barrier
concept in potable reuse projects. As discussed in
Blending
Chapter 2, an environmental buffer is a water body or
Blending of reclaimed water with a water source aquifer that is perceived by the public as natural and
other than wastewater (e.g., surface water, stormwater, serves to eliminate the connection between the water
native groundwater) may occur prior to treatment and its past history. It also may provide some or all of
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91
ENSURING WATER QUALITY IN WATER RECLAMATION
the following design elements discussed in the previous to respond to potential problems should they arise
section: (1) attenuation of contaminants of concern, (Ruetten et al., 2004). NRC (1998) described a “loss
(2) provision of retention time, and (3) blending (or of identity” that occurs in an environmental buffer, al-
dilution). The performance of various environmental though the committee noted that “loss of identity is an
buffers is discussed in Chapter 4. issue that seems more relevant to public relations than
Attenuation of contaminants can occur in certain public health protection” (NRC, 1998).
environmental buffers (e.g., wetlands, soil aquifer During the past decade, extensive research on
treatment, riverbank filtration). In this function, an the performance of reuse operations using modern
engineered natural treatment system can be used before engineered systems (Ternes et al., 2003; Drewes et
or after an aboveground water reclamation plant. How- al., 2003b; Snyder et al., 2006c; Bellona et al., 2008)
ever, the role of environmental buffers in attenuation of as well as those using environmental buffers (Fox et
contaminants is not well documented. As detailed in al., 2001; Laws et al., 2011; Maeng et al., 2011) has
Chapter 4, contaminant attenuation has been reported demonstrated some engineered systems can perform
for some environmental buffers. However, consider- equally well as some existing environmental buffers in
ing site-specific differences, environmental buffers are diluting and attenuating contaminants, and the proper
likely to exhibit some variability in performance with use of indicators and surrogates in the design of reuse
respect to contaminant attenuation. systems offers the potential to address many concerns
There is no widely accepted standard for reten- regarding quality assurance (Drewes et al., 2008). This
tion time in environmental barriers for potable reuse committee concludes that the practice of classifying po-
systems. The retention provided by various examples table reuse projects as indirect and direct based on the
discussed in this report varies from days to more than presence or absence of an environmental buffer is not
6 months. Retention is particularly uneven where de meaningful to an assessment of the final product water
facto reuse is concerned. Additionally, relying on en- quality because it cannot be demonstrated that such
vironmental buffers as the only means of lengthening “natural” barriers provide any public health protection
response times is questionable, especially in systems that is not also available by other means. Moreover, the
with short hydraulic residence times. science required to design for uniform protection from
For potable reuse projects implemented through one environmental buffer to the next is not available.
groundwater recharge, blending or dilution of re - Accordingly, although the committee does view
claimed water with water deemed not to be of waste- environmental buffers as useful elements of design that
water origin can occur before application or in aquifers. should be considered along with other processes and
For surface water augmentation, blending typically management actions in formulating potable water reuse
occurs in a raw drinking water reservoir. The extent projects, the committee does not consider environmen-
of dilution varies with the different natural systems, tal buffers to be an essential element of potable reuse
and can range from substantial dilution (<1 percent projects. Rather than relying on environmental buffers
reclaimed water) to minimal dilution (>50 percent to provide public health protection that is poorly de-
reclaimed water). As mentioned before, the need for fined, the level of quality assurance required for public
blending depends heavily on the nature of the process health protection needs to be better defined so that po-
train employed for attenuation. table reuse systems can be designed to provide it, with
Currently, the use and application of an environ- or without environmental buffers. A more quantitative
mental buffer for potable reuse is based on regulatory understanding of the protections provided by different
guidance and current practice rather than specific sci- environmental buffers will allow engineered natural
entific evidence. Sufficient science does not currently systems to be more effectively designed and operated.
exist to determine if current guidance is, in fact, appro-
priately protective, overprotective, or underprotective Case Studies for System Design
of public health. From a public outreach perspective,
environmental buffers have often been perceived as The role of the design elements mentioned earlier
important for gaining public acceptance as they create (monitoring, attenuation, retention, blending) can be
the perception of a “natural” system and provide time illustrated using three case studies that practice drink-
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92 WATER REUSE
ing water augmentation. The three case studies employ case of a water reclamation plant, reliability might be
different treatment processes including engineered defined as the likelihood of the plant achieving an efflu-
unit processes as well as engineered natural treatment ent that matches or is superior to predetermined water
systems providing attenuation of contaminants, and reuse quality objectives. Traditional drinking water
provide a final quality of drinking water that is consid- treatment plants consider reliability in their operations,
ered safe by public health agencies and accepted by the but even greater attention to reliability is necessary in
public. It is noteworthy that the sequence and location water reclamation facilities that supply water for po-
of the individual treatment barriers within the potable table reuse or other applications with significant human
reuse scheme also differs. exposures. Failure of wastewater reclamation treatment
processes could result in exposure of the population
• Case Study 1 describes a groundwater recharge served by nonpotable or potable reuse applications to
project favoring direct injection of reclaimed water into considerable health risk, particularly from acute ill-
a potable aquifer after advanced treatment (Figure 5-3). nesses caused by microbial pathogens (see Chapters
This case study is similar to the practice of groundwa- 3 and 6). It is therefore important to minimize the
ter recharge established by the Orange County Water probability of failure, or, in other words, to increase
District (see also Box 2-11) or West Basin Municipal reliability. Although appropriate design is necessary to
Water District in California. ensure reliable delivery of a product such as reclaimed
• Case Study 2 (Figure 5-4) illustrates a ground- water (as discussed in the previous section), it is also
water recharge project employing surface spreading necessary to maintain an operational protocol to cope
followed by soil aquifer treatment. The case study is with intrinsic variability and react to process and con-
similar to the groundwater recharge operation in the veyance upsets.
Montebello Forebay operated by the County Sanita- Some definitions of reliability only encompass the
tion Districts of Los Angeles County and the Water variability associated with treatment processes and as-
Replenishment District of Southern California (see sume that the plant is properly designed, operated, and
also Box 4-2). maintained. Expansion of the definition of reliability to
• Case Study 3 (Figure 5-5) represents a ground- include the probability that the plant will be nonfunc-
water recharge scenario using a combination of engi- tional at any given time requires an evaluation of plant
neered natural treatment systems with advanced engi- operational reliability, separate from reclaimed water
neered unit processes for drinking water augmentation, quality variability. Operational reliability is affected
similar to that established by the Prairie Waters Project by mechanical, design, process, or operational failures,
of the City of Aurora, Colorado (see also Box 4-1). which may be triggered by a wide range of causes,
including human error or severe weather events. Previ-
For each case study, the key processes that provide ous sections of this chapter discuss ways to incorporate
attenuation of contaminants are highlighted, the reten- reliability into project design.
tion process is identified, and the role of blending in Reliability analysis can also be used to reveal
these projects is characterized. These examples reveal weak points in the process so that corrections and/or
that multiple combinations and sequences of treatment modifications can be made. Even a well-maintained,
processes can be selected for a potable reuse scheme well-operated plant is not perfectly reliable, and some
resulting in comparable qualities of finished drinking variation will necessarily be inherent in any system (e.g.,
water. variations in influent flow and quality can lead to varia-
tion in effluent characteristics). Other factors, includ-
ing power outages, equipment failure, and operational
OPERATIONAL PRINCIPLES TO ASSURE
(human) error also affect plant reliability and need to
QUALITY AND RELIABILITY
be incorporated into the reliability analysis (Olivieri et
Treatment plant reliability is defined as the prob- al., 1987). There are a number of formal techniques for
ability that a system can operate consistently over assessing reliability by looking at historical performance
extended periods of time (Olivieri et al., 1987). In the of individual components (e.g., pumps, valves, electric
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ENSURING WATER QUALITY IN WATER RECLAMATION
Urban water use
Conventional water Source control
treatment
• Industrial/residential
• Disinfection at well head
source control
after groundwater
abstraction
Retention/Blending Conventional wastewater
treatment
• Direct injection into deep
• Primary and secondary treatment
aquifer
• Disinfection
Advanced wastewater treatment
• MF/RO
• UV/AOP
Retention
Retention Alternatives
Prevention
• Prior to
• Source control
injection
Treatment • >6 months in
• Blending with
deep aquifer
• Secondary treatment native
• Microfiltration groundwater in
aquifer
• Reverse osmosis
• After
• Advanced oxidation
groundwater
(UV/H2O2)
abstraction in
• Disinfection
distribution
• Disinfection after
system
groundwater abstraction
Attenuation
Attenuation Blending
Blending
(Multiple Barriers)
)
Monitoring
FIGURE 5-3 Case Study 1: Potable reuse design elements (including attenuation, retention, and
blending) used for groundwater recharge of reclaimed water.
NOTE: Residential source control could include voluntary programs to reduce the discharge of poten-
tially problematic chemicals.
supply) and the potential for various hazards (e.g., or event trees can be constructed (Rasmussen, 1981;
storms, wind, earthquakes) to occur. By using histori- Kumamoto and Henley, 1996), and the probability dis-
cal data of these individual events (including data from tribution of consequences of different levels of severity
individual components in other applications), failure can be illustrated.
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94 WATER REUSE
Urban water use
Source control
Conven onal water
treatment
• Industrial/residen al
• Disinfec on at well head source control
a er groundwater
abstrac on
Reten on/Blending Conven onal wastewater
treatment
• Recharge to aquifer
• Primary and secondary treatment
• Blending in distribu on
• Disinfec on
system
Engineered natural treatment
• Soil-aquifer treatment (SAT)
Retention
Retention
Prevention Alternatives
• Source control • Blending with
native
Treatment • >6 months groundwater in
• Primary and secondary in shallow aquifer
treatment aquifer
• Blending with
• Tertiary filtration and conventional
disinfection supply in
• Soil-aquifer treatment distribution
• Disinfection at well head system
Attenuation
Attenuation Blending
Blending
(Multiple Barriers)
(Multiple Barriers)
Monitoring
FIGURE 5-4 Case Study 2: Potable reuse design elements (including attenuation, retention, and blending) used for surface spreading
of reclaimed water followed by soil aquifer treatment.
Strategies for Incorporating Reliability into System water need to incorporate deliberate strategies to ensure
Operation reliable operation. The centrality of the operational
plan in ensuring water quality has been emphasized by
No matter how well designed a treatment system the World Health Organization (WHO, 2005) in its
is, there will be inevitable fluctuations in performance concept of water safety plans.
due to intrinsic variability of processes, variability in One formal approach for ensuring operational
the influent stream, equipment failures, and human reliability is the hazard analysis and critical control
error. Therefore, systems delivering potable reclaimed points (HACCP) framework. HACCP was developed
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ENSURING WATER QUALITY IN WATER RECLAMATION
Urban water use
Source control
Conven onal water
treatment
• River water monitoring
• Disinfec on in clearwell program
• Early warning system for spills
Reten on/Blending Conven onal wastewater treatment
• Blending w/ river water • Secondary treatment
• Recharge into shallow • Disinfec on
aquifer (RBF/ARR) • Discharge to river
• 36 mile pipeline to • Riverbank filtra on (RBF)
advanced treatment • Ar ficial recharge and recovery
facility (ARR)
• Blending in clearwell
Advanced wastewater treatment
• So ening
• UV/AOP
• Biological ac vated carbon filtra on
• Granular ac vated carbon filtra on
• Disinfec on
Reten on
Reten on
• Blending
Prevention
with na ve
• Source control • >15 days in groundwater
Treatment RBF in aquifer
• So ening • >15 days in • Blending
ARR
• Advanced oxida on with
• 35 mile
(UV/H2O2) conven onal
pipeline supply prior to
• Biological ac vated
between ARR clearwell
carbon filtra on
and advanced disinfec on
• Granular ac vated carbon
treatment
• Disinfec on
B le ndi ng
Blending
A enua on
enua on
(Mul ple Barriers)
(Mul ple Barriers)
Monitoring
FIGURE 5-5 Case Study 3: Potable reuse design elements (including attenuation, retention, and blending) used for riverbank filtra-
tion of reclaimed water followed by softening, advanced oxidation, and carbon adsorption.
in the late 1950s to ensure adequate food quality for the international food safety protection system. The
the nascent National Aeronautics and Space Admin- development of HACCP broke reliance on the use
istration program. HACCP was further developed by of testing of the final product as the key determinant
the Pillsbury Corporation and ultimately codified by of quality, but rather emphasized the importance of
the National Advisory Committee on Microbiologi- understanding and control of each step in a processing
cal Criteria for Foods (NACMC, 1997). The ultimate system (Sperber and Stier, 2009).
framework consists of a seven step sequence outlined Havelaar (1994) was one of the first to note that
in Box 5-1. These principles are important parts of the drinking water supply, treatment, and distribution
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96 WATER REUSE
BOX 5-1
Steps of the HACCP Framework and Application to Potable Reuse
The following seven steps represent the key components of the HACCP framework (adapted from NACMC, 1997), which was originally developed
for food safety but has been applied to other areas, including drinking water quality.
1. Conduct a hazard analysis. Under HACCP, hazards are chemical or microbial constituents likely to cause illness if not controlled.
2. Determine the critical control points (CCPs). Defined originally for the food sector, a critical control point is “any point in the chain of food
production from raw materials to finished product where the loss of control could result in unacceptable food safety risk” (Unnevehr and Jensen,
1996).
3. Establish critical limit(s). Critical limits are performance criteria—specific maximum or minimum values of biological, chemical, or physi-
cal parameters that are readily measurable—that must be attained in each process (at the CCPs) to prevent occurrence of a hazard or reduce it to
an acceptable level. These parameters will be process-specific and determined through experimentation, computational models, quantitative risk
analysis, or a combination of such methods (Havelaar, 1994; Notermans et al., 1994).
4. Establish a system for monitoring the CCPs.
5. Establish the corrective action(s) that will be taken when monitoring signals that a CCP is not under control.
6. Establish verification procedures to confirm that the HACCP system is working effectively.
7. Document all procedures and records relevant to these HAACP principles and their application.
Application to Potable Reuse
As an illustration of the use of HACCP, the committee developed the following set of steps that might be followed to implement this framework
in the potable reuse context using an example of managing risks from pathogenic organisms:
1. Identify the critical organisms of interest, considering the type of source water used, that are likely to cause illness if not controlled. De-
termine the overall log reductions needed after treatment, given the nature of an incoming water to achieve the targeted final acceptable risk level
and allocate these reductions among individual treatment processes.
2. Enumerate CCPs for water reclamation, considering each particular treatment process in the treatment train as well as the overall treatment
method.
3. Given criteria in the finished reclaimed water, determine the minimum performance criteria for each treatment process. Note that these
performance criteria should be based on easily measurable parameters (e.g., surrogates, residual chlorine) that can be used for operational control.
4. Establish a monitoring system to track the identified performance criteria at the critical control points. The finished product of a reclamation
system is only acceptable for utilization when the performance criteria are all within the acceptable bounds.
5. Establish an operational procedure for implementing appropriate corrective actions at a particular installed process should a performance
criterion be outside acceptable limits. These actions might include additional holding time, recirculating the water to allow for additional treatment,
or some other measure. These procedures would also include actions to protect public health in the case of systemwide failure (e.g., natural disaster
leading to extended power failure).
6. Establish a quality assurance process for periodic validation and auditing (e.g., by an independent third-party organization) to assess that
the procedures are working effectively.
7. Document all procedures and records.
chain has a formal analogy to the food supply, process- under certain conditions (e.g., filter effluent turbidity
ing, transport, and sale chain and that HACCP could for granular filters) were “credited” with certain removal
be applicable to water treatment. The development of efficiencies, and a sufficient number of removal credits
the U.S. Surface Water Treatment Rule under the Safe needed to be in place depending on an initial program
Drinking Water Act (SDWA; 40 CFR Parts 141-142) of monitoring of the microbial quality of the supply
and subsequent amendments incorporate a HACCP- itself. The use of treatment technique in drinking water
like process. Under this framework, an implicitly ac- regulation is an option when it is not “economically or
ceptable level of viruses and protozoa in treated water technically feasible to set an MCL” (SDWA § 1412(b)
was defined. Based on this, specific processes operated (7)(A)). HAACP has also been used as a framework for
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ENSURING WATER QUALITY IN WATER RECLAMATION
the Australian Drinking Water Guidelines (NHMRC, ensure water quality in potable and nonpotable water
2004), which have been expanded to address potable reuse projects. These steps address potential public
reuse [see Box 5-2; NRMMC/EPHC/NHMRC, health impacts from microbial pathogens and chemical
2008]). Box 5-1 highlights an example of how the contaminants found or likely to be found in reclaimed
HACCP approach might be applied in the context of water and include considerations of reliability and qual-
reclaimed water to ensure operational reliability. ity assurance, and therefore merit careful consideration
from designers and managers of reuse projects. The
extent of each activity will depend on the type of reuse
STEPS TO ENSURE WATER
(nonpotable vs. potable) and degree of exposure:
QUALITY IN WATER REUSE
In the following section, the committee identi- 1. Implement and maintain an effective source
fies reasonable steps that can and should be taken to control program.
2. Utilize the most appropriate technology in
wastewater treatment that is tailored to site-specific
conditions.
3. Utilize multiple, independent barriers, espe-
BOX 5-2
Australian Potable Reuse Guidelines cially for the removal of microbiological and organic
chemical contaminants.
The Australian Guidelines for Water Recycling: Augmenta- 4. Employ quantitative reliability assessments to
tion of Drinking Water Supplies (Phase 2) (NRMMC/EPHC/
monitor and assess performance including major and
NHMRC, 2008), were developed to complement the Australian
minor process failures (i.e., both process control and
Drinking Water Guidelines (NHMRC, 2004).The approach to
final water quality monitoring and assessment as well
risk management for potable reuse is modeled on the approach
as assessment of mechanical reliability).
developed for the Australian Drinking Water Guidelines and
incorporates a generic framework applicable to any system 5. Establish a trace organic chemical monitor-
that is reusing water based on 12 elements focusing on ensur- ing program that goes beyond currently regulated
ing safety and reliability, rather than verification monitoring.
contaminants.
The framework incorporates HACCP principles, based on a
6. Document a strategy to provide retention time
risk management approach designed to assure water qual-
necessary to allow time to respond to system failures or
ity at the point of use. The guidelines also provide detailed
upsets (e.g., this could be based, in part, on turnaround
information on topics such as setting health-based targets for
microorganisms and chemicals, the effectiveness of various time to receive water quality monitoring results).
treatment processes, CCPs, and monitoring. 7. Provide for alternative means for diverting the
In the Australian potable reuse guidelines, approaches for
product water that does not meet required standards.
calculating contaminant guideline values based on toxicologi-
8. Avoid “short-circuiting” in environmental
cal data and specific guideline values for individual contami-
buffers to ensure maintenance of appropriate retention
nants, as outlined in the Australian Drinking Water Guidelines,
times within the buffers (i.e., groundwater, wetlands,
are applied to potable reuse. Microbial risk is evaluated using
disability adjusted life years (DALYs), performance targets, reservoir).
and reference pathogens (based on WHO, 2008; see also 9. Train and certify operators of advanced water
Box 10-4). The tolerable microbial risk adopted in the potable
reclamation facilities regarding the principles of op-
reuse guidelines is 10–6 DALYs per person per year, which is
eration of advanced treatment processes, and educate
roughly equivalent to 1 diarrheal illness per 1,000 people per
them on the pathogenic organisms and chemical con-
year. The approach adopted in these guidelines for chemical
taminants likely to be found in wastewaters and the
parameters is based on approaches and guideline values out-
lined in the Australian Drinking Water Guidelines. The potable relative effectiveness of the various treatment processes
reuse guidelines also describe an approach, using thresholds in reducing microbial and chemical contaminants con-
of toxicological concern, for addressing chemicals without
centrations. This is important because, in general, op-
guideline values or those that lack sufficient toxicological
erators at water reclamation facilities have not received
information for guideline derivation (see also Chapter 6 for
training on the operation of advanced water treatment
further discussion of this and other methods).
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98 WATER REUSE
ing and operational plans to respond to variability,
processes or the public health aspects associated with
e quipment malfunctions, and operator error to
drinking water.
ensure that reclaimed water released meets the ap-
10. Institute formal channels of coordination
propriate quality standards for its use. Redundancy
between water reclamation agencies, regulatory agen-
cies, and agencies responsible for public water systems. and quality reliability assessments, including process
This will, for example, allow for rapid communication control, water quality monitoring, and the capacity
and immediate corrective action(s) to be taken by the to divert water that does not meet predetermined
appropriate agency (or agencies) in the event that the quality targets, are essential components of all reuse
reclaimed water does not meet regulatory requirements. systems. Particularly in potable reuse, systems need to
be designed to be “fail-safe.” The concept of HACCP,
water safety plans, or their equivalent may be used as a
CONCLUSIONS AND RECOMMENDATIONS
guide for such operational plans. A key aspect involves
In both nonpotable and potable reuse schemes, the identification of easily measureable performance
monitoring, contaminant attenuation processes, post- criteria (e.g., surrogates), which are used for operational
treatment retention time, and blending can be effective control and as a trigger for corrective action.
Natural systems are employed in most potable
tools for achieving quality assurance. Today, most reuse
water reuse systems to provide an environmental
projects find it necessary to employ all these elements.
buffer. However, it cannot be demonstrated that such
Attenuation can be achieved through the establish-
“natural” barriers provide public health protection
ment of multiple barriers (consisting of treatment and
that is not also available by other engineered pro-
prevention approaches) to minimize public health risks.
cesses. Environmental buffers in potable reuse projects
O ver the last 15 years, several potable reuse projects
of significant size have been developed in the United may fulfill some or all of three design elements: (1)
States. Although these projects share the design princi- provision of retention time, (2) attenuation of contami-
ple of multiple barriers, the type and sequence of water nants, and (3) blending (or dilution), although the ex-
treatment processes employed in these schemes differ tent of these three factors varies widely across different
significantly. All these schemes have demonstrated that environmental buffers. In some cases engineered natu-
different configurations of unit processes can achieve ral systems, which are generally perceived as beneficial
similar levels of water quality and reliability. In the to public acceptance, can be substituted for engineered
future, as new technologies improve capabilities unit processes. However, the science required to design
for both monitoring and attenuation, it is expected for uniform protection from one environmental buffer
that retention and blending requirements currently to the next is not available.
imposed on many potable reuse projects will become The potable reuse of highly treated reclaimed
less significant in quality assurance. water without an environmental buffer is worthy of
Reuse systems should be designed with treat - consideration, if adequate protection is engineered
ment trains that include reliability and robustness. within the system. Historically, the practice of adding
Redundancy strengthens the reliability of contaminant reclaimed water directly to the water supply without an
removal, particularly important for contaminants with environmental buffer—a practice referred to as direct
acute affects, while robustness employs combinations potable reuse—has been rejected by water utilities, by
of technologies that address a broad variety of con- regulatory agencies in the United States, and by previ-
taminants. Reuse systems designed for applications ous National Research Council committees. However,
with possible human contact should include redundant research during the past decade on the performance of
barriers for pathogens that cause waterborne diseases. several full-scale advanced water treatment operations
Potable reuse systems should employ diverse processes indicates that some engineered systems can perform as
that can function as barriers for many types of chemi- well or better than some existing environmental buffers
cals, considering the wide range of physicochemical in diluting (if necessary) and attenuating contaminants,
properties of chemical contaminants. and the proper use of indicators and surrogates in the
Reclamation facilities should develop monitor- design of reuse systems offers the potential to address
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ENSURING WATER QUALITY IN WATER RECLAMATION
many concerns regarding quality assurance. Environ- assurance in potable reuse projects. Additionally, the
mental buffers can be useful elements of design that classification of potable reuse projects as indirect (i.e.,
should be considered along with other processes and includes an environmental buffer) and direct (i.e., does
management actions in formulating the composition of not include an environmental buffer) is not productive
potable water reuse projects. However, environmental from a technical perspective because the terms are not
buffers are not essential elements to achieve quality linked to product water quality.
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