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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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93 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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95 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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97 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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99 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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