48 APRIL 2016 | JOURNAL AWWA • 108 :4 | STANFORD ET AL.

As continued population growth, increasing urban density, and varying climate place heavy burdens on our nation’s water sup­plies, water agencies and policymakers are exploring innovative ways of ensuring an adequate water supply portfolio. As such, many water agencies in the United States and internationally

have been implementing planned potable reuse of municipal wastewater, either through indirect potable reuse (IPR) or direct potable reuse (DPR). DPR dif­fers from more established indirect approaches to potable water recycling because of the absence of an environmental buffer. Several potential benefits of DPR, relative to IPR, have been identified, including reduced energy requirements, reduced construction costs, reduced operational costs, and the ability to better control and maintain water quality within engineered buffer systems (Walker et al. forthcoming; Trussell et al. 2013, 2012; Schroeder et al. 2012). DPR can also provide a safe, reliable opportunity for potable reuse in situations in which a suitable environmental buffer is not available for IPR. However, the impacts of blending a new water supply must be carefully con­sidered and addressed in a manner analogous to any new water supply evaluation. This article provides an overview of some blending impacts that should be evaluated when considering DPR.

DIRECT POTABLE REUSE

(DPR) INCREASES WATER

SUPPLIES, BUT POSSIBLE

DPR-BLENDING SCENARIOS

AND WATER QUALITY

MUST BE EVALUATED AT

BLENDING LOCATIONS.

BENJAMIN D. STANFORD, WILLIAM C. BECKER, JEAN F. DEBROUX,

STEPHANIE K.L. ISHI I, STUART J. KHAN, AND WENDELL O. KHUNJAR

Planning for Direct Potable Reuse: Operational Aspects of an Integrated Drinking Water System

water quality

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STANFORD ET AL. | 108 :4 • JOURNAL AWWA | APRIL 2016 49

DPR product water can conceiv­ably be blended into the water sup­ply at three locations in a drinking water treatment/distribution sys­tem (Figure 1), including at the head of the water treatment plant, within the water treatment plant, or in the distribution system—any­where from the disinfection system clearwell to the far reaches of the distribution system. However, in accordance with the logic embed­ded in the US Environmental Pro­tection Agency’s Filter Backwash Recycling Rule, water should be blended only at the head of the water treatment plant (before or at the rapid mix stage) in order to minimize adverse effects on the treatment process and to achieve further benefit from the water treatment process. Therefore, because they are most likely to be used by water utilities, the only two options considered in this article are at the head of the water treat­ment plant (Figure 1, pathway 1) and in the distribution system (Figure 1, pathways 3A and 3B).

PREVIOUS RESEARCH AND GUIDANCE ON SOURCE WATER BLENDING

From a practical perspective, incorporating potable reuse into a water supply portfolio presents many of the same challenges as with selecting and blending any other new water source—such as ground­water, desalinated water, or a differ­ent surface water—into an existing system. Blending implications require a high level of operational surety, appropriately sized storage and mixing zones, and a firm under­standing of the potential impacts on process performance and distribu­tion system stability/quality. These factors help ensure compliance with all regulatory requirements, sustain public confidence in the system, and provide adequate time to respond to any upstream process upsets. Fortu­nately, water quality and the im ­pacts of source water blending on distribution systems have been

studied extensively, in previous Water Research Foundation (WRF) projects and elsewhere (Duranceau et al. 2011; Taylor et al. 2009, 2005;

Peet et al. 2001) and have resulted in multiple tools and recommenda­tions for managing blended water quality. Several of those are listed here for reference:

• In 1997, WRF commissioned a team to study the effects of blending multiple source waters (groundwater, rivers, and reservoirs) on aesthetics, health, and infrastructure (Peet et al. 2001). This project resulted in a spreadsheet­based calculator that could be used to calculate blended water quality, but not impacts per se. Bench­top testing was used to develop and confirm algorithms for cal­culating blended water quality.

• In 2000, WRF and Tampa Bay Water, with the University of Central Florida, Orlando,

embarked on a multi­year, two phase, $4.6 million study to model the impact of blend­ing desalinated water with

groundwater and surface water in a massive pilot­scale treatment plant and distribu­tion system. The project developed predictive models and recommendations for alkalinity control, pH control, and phosphate inhibitor used to manage iron, lead, and copper release in the distribu­tion system (Taylor et al. 2009, 2005).

• In 2007, WRF published an overview report, detailing the history of distribution system water quality research and management strategies, along with research needs (Hasit et al. 2007).

• Later, Duranceau et al. (2011) studied the impact of blend­ing desalinated water into

1

2

3A

3B

Water supply Distributionsystem

Water treatmentplant

Water recyclingplant

FIGURE 1 Possible blending locations of DPR product water

DPR—direct potable reuse

Blending locations can be (1) at the head of the water treatment plant, (2) within the water treatment plant, or (3) in the distribution system, including anywhere from the disinfection system clearwell (3A) to the far reaches of the distribution system (3B).

From a practical perspective, incorporating potable

reuse into a water supply portfolio presents many

of the same challenges as with selecting and

blending any other new water source into

an existing system.

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50 APRIL 2016 | JOURNAL AWWA • 108 :4 | STANFORD ET AL.

distribution systems and pro­vided recommendations on blending ratios, stability, dis­infection, and many other parameters. This work re ­sulted in a set of target post­t reatment water qual i ty guidelines that characterize stabilized seawater, or brack­ish water, prior to blending

(Table 1). When using these recommended water quality ranges, it is important to strike a balance between being within the appropriate range for an individual water quality param­eter and being within the appro­priate range for indexes that consider combinations of water quality parameters (e.g., cal­cium carbonate precipitation po tential and Langelier satu­ration index). For example, Table 1 shows two sets of hypo­thetical DPR product water quality that were input into the Rothburg–Tamburini–Windsor (RTW) model (Tetra Tech Inc. 2011). The RTW input for DPR example 1 includes water quality parameter val­ues that are all within the rec­ommended ranges f rom Duranceau et al. (2011), and the resulting output includes favorable precipitation poten­tial and Langelier index val­ues. The RTW input for DPR example 2 also includes water quality parameter values that are within recommended ranges; however, target values for both of the corrosion indexes are not achieved in

the output. These examples highlight the need to consider individual water qual i ty parameters, as well as indexes that consider the synergistic impacts of parameters taken together.

• Finally, AWWA has an updated version of the RTW model, which now incorporates

blending calculations with numerous water quality and stability indexes (Tetra Tech Inc. 2011).

Despite the large amount of infor­mation available, there are several factors that may be unique to DPR or, at a minimum, require special consideration when evaluating the feasibility of blending DPR product water into an existing drinking water distribution system. These considerations are discussed in the following sections and are based on whether DPR blending is being con­sidered at the head of the drinking water treatment plant or in the dis­tribution system, although many of the considerations are significant at both locations.

CONSIDERATIONS FOR DPR: BLENDING AT THE HEAD OF THE PLANT

Rapid changes in water blending ratios and water quality. The high potential for a loss of DPR product water supply is an operational aspect that is not unique to DPR facilities but should be carefully considered. This loss of supply may be a result of economics (i.e., higher­cost DPR water may not be in demand year­round) or part of a risk management

strategy (e.g., partial shutdowns or sudden reductions in flow from unit processes with alerts or alarms). The impact of a sudden shift from blended DPR water to 0% DPR water in a matter of minutes must be evaluated because water treatment facilities will need to be prepared to respond to process upsets or shut­downs of the water recycling facility. Such rapid changes in blending ratios (and thus influent water qual­ity) can have significant implications for the operation of the water treat­ment plant, including coagulant dos­ing, filter performance, granular acti­vated carbon (GAC) performance, residuals handling, corrosion con­trol, and disinfection. In cases where there is minimal opportunity to buf­fer variations in water quality (i.e., storage capacity), there is an increased need for ongoing, finely tuned process control. At a mini­mum, utilities should consider this scenario and have an understanding of the impact such changes might have on their system.

Variable concentrations of ammonia, nitrite, and/or nitrate. Wastewater treatment plants commonly experi­ence frequent variations in effluent ammonia, nitrite, and/or nitrate con­centrations that may be diurnal, daily, or seasonal. Even plants with nitrogen­reduction processes experi­ence variability, as demonstrated in Figure 2, which shows this variabil­ity for two North American waste­water treatment plants (WWTPs)—one of which practices anaerobic/anoxic/oxic treatment with a pre­anoxic zone (WWTP 1) and the other step­feed biological nutrient removal (WWTP 2). Nitrogen con­centrations and variability are even greater in WWTPs that do not have nitrogen­reduction processes, and conversely will be even less in plants with very stringent nitrogen controls.

Ammonia is partially removed by reverse osmosis membranes, but residual concentration or residual chloramine concentration can pres­ent an operational challenge for a drinking water treatment plant.

While ammonia may be a common problem

for utilities in certain geographies, it can be

a completely new challenge for utilities

not accustomed to disinfecting water

with ammonia present.

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STANFORD ET AL. | 108 :4 • JOURNAL AWWA | APRIL 2016 51

These challenges include impacts on the speciation of disinfectants present, impacts on the breakpoint chlorination process (by requiring a higher chlorine dose to reach breakpoint), and importantly,

ammonia can cause disinfection contact time (CT) compliance issues if not properly monitored and managed. In addition, areas of the distribution system could expe­rience low or no chlorine residual.

While ammonia may be a common problem for utilities in certain geographies, it can be a completely new challenge for utilities not accustomed to disinfecting water with ammonia present.

FIGURE 2 Concentrations of (A) NH3 and (B) NOx in secondary wastewater ef�uent over the course of one year

Source: Adapted from Khunjar et al. 2015

NH3—ammonia, NOx—combined nitrite and nitrate, WWTP—wastewater treatment plant

The brown series pertains to WWTP 1 (anaerobic/anoxic/oxic, or A2O, with pre-anoxic zone), and the gray series pertains to WWTP 2 (step-feed biological nutrient removal).

0

2

4

6

8

10

12

14

16

Sec

on

dar

y E

fflu

ent

NH

3—m

g/L

Sec

on

dar

y E

fflu

ent

NO

x—m

g/L

0

5

10

15

20

May 20

11

July

2011

Sept.

2011

DateNov.

2011

Jan. 2

012

Mar. 2

012

May 20

12

May 20

11

July

2011

Sept.

2011

DateNov.

2011

Jan. 2

012

Mar. 2

012

May 20

12

A B

TABLE 1 Water quality recommendations for stabilized seawater and brackish watera and two example RTW simulations using water quality parameters within the recommended rangesb

Water Quality Parameter

Recommendations From Duranceau et al. (2011)

RTW Inputs and Outputs for Example DPR Product Water Quality

Seawater Brackish water DPR example 1 DPR example 2

pH 6.5–9.5 7.5–8.4 7.7 7.7

Alkalinity—mg/L as CaCO3 50–125 75–150 125 80

Hardness—mg/L as CaCO3 50–85 75–110 — —

Calcium—mg/L 50–75 60–100 72 60

Calcium—mg/L as CaCO3 123–184 147–245 180 150

TDS—mg/L 100–500 85–350 210 210

Sulfate—mg/L — — 10 10

Chloride—mg/L — — 10 10

Sulfate-to-chloride ratio 1–1.3 0.5–1 1 1

Turbidity—ntu 0.6–3 0.2–2 — —

Boron—mg/L 0.5–1 — — —

Precipitation potential—mg/L (target: 4–10 mg/L) — — 5.6 (✓) –0.73 (✗)

Langelier saturation index (target: > 0) — — 0.22 (✓) –0.05 (✗)

CaCO3—calcium carbonate, DPR—direct potable reuse, RTW—Rothberg–Tamburini–Windsor model, TDS—total dissolved solids

aTable values from Duranceau et al. (2011) represent appropriate ranges for various water quality parameters, and in practice, all water quality parameters must be considered together to achieve appropriate bulk water quality.bThe two example RTW simulations include input values that fall within all of the recommended ranges from Duranceau et al. (2011) and represent bulk water qualities that result in favorable (DPR example 1) and unfavorable (DPR example 2) precipitation potential and Langelier saturation index values. Dashes indicate “no data,” checkmarks indicate “stable water quality condition,” and ✗’s represent “unstable water quality condition.”

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52 APRIL 2016 | JOURNAL AWWA • 108 :4 | STANFORD ET AL.

In scenarios in which alternatives to reverse osmosis and nanofiltra­tion are used at the water recycling plant (e.g., flocculation/sedimenta­tion/filtration­ozone­biofiltration­GAC­ultraviolet light­chlorine),

nitrate concentrations need to be managed from an acute­risk stand­point because of the 10­mg/L max­imum contaminant level that pro­tects bottle­fed infants. As such, fluctuations in nitrate and the amount of acceptable blending must be planned for and managed on a continual basis to keep nitrate (and nitrite) below the maximum contaminant level.

As next­generation nitrogen removal technologies employing shortcut nitrogen removal become more widespread, the presence of nitrite in biological process effluent must be addressed. Similar to nitrate, nitrite concentrations must be managed to avoid acute health risk in infants. Operationally, nitrite can affect chlorine­dosing require­ments, thus also affecting chlorine CT compliance.

Disinfection by-product formation. The formation and speciation of regulated disinfection by­products (DBPs) may be influenced by the higher temperatures associated with DPR product water (relative to ambient surface or groundwater temperature), as well as the poten­tial presence of bromide. However, counteracting this temperature effect is the typically low­dissolved organic carbon concentration in DPR product water (e.g., reverse osmosis permeate, GAC effluent) and the dilution effect it offers. Thus, loss of DPR product water could potentially result in increased

DBPs as a result of the loss of the low­dissolved organic carbon con­centration in DPR product water compared with other conventional source waters. Alternatively, DBPs could increase with a rise in DPR

product water if the DPR product water is relatively warm and con­tains high levels of bromide. While not a fatal flaw and not entirely dif­ferent from standard blending of multiple source waters, DBP forma­tion potential should be considered in DPR blending scenarios.

Stabilization of DPR product water. While in most cases stabilization of DPR product water is expected to be similar to stabilization of desalinated water, it is important to consider because of similar water quality impacts. Changes in alkalinity, total organic carbon content, pH, calcium content, and potentially even the chloride­to­sulfate mass ratio (Edwards & Triantafyllidou 2007) will all have implications for the drinking water treatment processes at the plant, as well as the distribution system. Additionally, operations and management teams may have strong opinions on the method of stabilizing DPR water; therefore, selecting the appropriate method should be a com­ponent of planning for DPR. For example, if pH adjustment is required, utility perspectives on lime contactors and other potentially required equip­ment should be identified.

Taste and odor. Taste and odor con­cerns are typically associated with surface waters; however, taste and odor issues that occur in a blended system of surface water and DPR product water may be incorrectly attributed to the DPR aspect of the system, and negatively affect public

perceptions of DPR product water. The ability to evaluate the flavor profile of the various source waters being used, as well as a plan to address taste and odor complaints, is expected to be critical for sustained public acceptance of DPR. Accord­ingly, managing taste and odor from reservoir operations and treatment­process perspectives is an important aspect of DPR planning. Likewise, preparing a solid communications plan to respond to such events will assist in providing timely responses to customer concerns.

CONSIDERATIONS FOR DPR: BLENDING IN THE DISTRIBUTION SYSTEM

Maintenance of distribution system flow/pressure. Similar to high­quality groundwater wells, DPR product water could be introduced in the far reaches of a distribution system instead of at the water treatment plant. Thus, there may be important issues regarding changes in pressure gradients and direction of water flow in the distribution system, especially when shutdowns or decreases in pro­duction occur. These issues must be addressed from a qualitative level at a minimum, and should be a part of any evaluation for DPR facilities.

Rapid changes in water blending ratios and water quality. Similar to the issues mentioned in the previous sec­tion, changes in blending ratios, and thus water quality, have the potential to affect lead, copper, and iron release; disrupt biofilms; and alter taste and odor profiles. In addition to the use of corrosion inhibitors (e.g., zinc orthophosphate), a com­prehensive water quality manage­ment and flushing plan needs to be in place to handle such events.

Variable concentrations of ammonia, nitrite, and/or nitrate. As mentioned previously, variable concentrations of ammonia would need to be addressed in order to maintain a consistent chlorine residual, and variable nitrite and nitrate levels must be addressed to meet all rele­vant maximum contaminant levels.

While not a fatal flaw and not entirely different

from standard blending of multiple source

waters, DBP formation potential should be

considered in DPR blending scenarios.

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STANFORD ET AL. | 108 :4 • JOURNAL AWWA | APRIL 2016 53

Stabilization of DPR product water. Similar to the issues described in the section on water treatment plant blending, DPR product water quality must be matched as closely

as possible within the distribution system to avoid corrosion (espe­cially stripping of iron oxide/hydroxide tubercles in unlined cast­iron pipe), scale formation,

dissolution of lead, and/or loss of disinfectant residual.

Nitrosamine formation. Nitrosa­mines, including N­nitrosodimethyl­amine (NDMA), are not currently

TABLE 2 Summary of DPR considerations for blending at the head of the plant or in the distribution system, and associated pilot testing/planning evaluations and water quality monitoring for pre- and post-implementation of DPR blending, respectively

DPR Considerations Pilot Testing/Planning EvaluationsPriority Water Quality Parameters

for Ongoing Monitoring

Rapid changes in blending ratio

• Drinking water demand projections, accounting for economically and seasonally driven variability in DPR product water demand

• Identification of acceptable DPR/conventional source water blending ratio

• If blending in the distribution system: Development of a distribution system flushing program that includes actions to be taken in the case of a DPR product water shutdown; evaluation of scenarios that would result in flow reversal and pressure issues

• DPR product water flow to the blending point• Conventional source water flow to the blending

point• Electrical conductivity or online TOC

monitoring at the head of the plant as a surrogate measure of the blending ratio and indicator of downstream treatability

• Critical control points at the water reclamation facility to anticipate any necessary shutdowns

Distribution system flow/pressure

• If blending in the distribution system: Distribution system modeling, including temporally variable demand for DPR product water production (if any) and the possibility of DPR system shutdowns

• DPR product water flow to the distribution system blending point

• Conventional source water flow to the distribution system blending point

• If blending in the distribution system: Pressure sensor in the distribution system, downstream of the DPR blending point

NH3 impacts on disinfection compliance

• Evaluation of diurnal, daily, and seasonal NH3 variation in source water and DPR product water

• Conduct chlorine dosing tests over a range of DPR product water blending ratios using DPR product waters and conventional source waters of appropriate quality and temperature

• Incorporation of NH3 removal prior to disinfection or adaptation of disinfection processes to the identified NH3 range

• Chlorine dose• Free chlorine residual in the clearwell and

distribution system• Online ammonia monitoring of DPR product

water

Variable NO2– and/or

NO3– concentrations

• Evaluation of diurnal, daily, and seasonal NO2– and NO3

– variation in DPR product water

• Identification of acceptable DPR/conventional source water blending ratios based on expected NO3

– and NO2–

concentrations in DPR product water and removal at the WTP

• If blending at the head of the plant: NO2– and

NO3– concentrations in finished drinking water

• If blending in the distribution system: NO2– and

NO3– concentrations in DPR product water and

drinking water from conventional source water

Disinfection by-product formation

• Disinfection by-product formation potential tests over a range of DPR product water blending ratios, using DPR product waters and conventional source waters of appropriate quality and temperature

• THM and HAA concentrations/formation in the distribution system

NDMA formation • NDMA formation potential tests, assuming different blending/disinfection scenarios (e.g., blending at the head of the plant with subsequent disinfection of combined water versus blending in the distribution system with residual disinfection of DPR product water)

• Chlorine and/or chloramine dose• Free chlorine residual in the clearwell and

distribution system• If UV/AOP used for NDMA destruction: UV

present power ratio, chemical oxidant dose, UV transmittance of feed water

Corrosion control and stabilization of DPR product water

• Identification of acceptable DPR/conventional source water blending ratios based on expected corrosion potential indexes

• Coupon corrosion tests• Stabilization is expected to be less of an issue if DPR

product water is effectively blended at the head of the plant instead of in the distribution system

• pH, corrosion inhibitor dose, total dissolved solids, alkalinity of blended water or blended water

• Calculated corrosion potential indexes: calcium carbonate precipitation potential, Langelier saturation index, chloride-to-sulfate mass ratio

Taste and odor • Flavor profile analysis of the individual finished waters to be blended (e.g., DPR product water and treated conventional source water)

• If DPR product water is to be blended with a surface water, a taste and odor event management plan is needed

• Threshold odor number of finished blended water

• Chlorophyll a, TOC, UV254, algae counts/speciation, and geosmin/2-methylisoborneol in raw conventional (surface water) source water for anticipation of taste and odor events

AOP—advanced oxidation process, DPR—direct potable reuse, HAA—haloacetic acid, NDMA—N-nitrosodimethylamine, NH3—ammonia, NO2–—nitrite,

NO3–—nitrate, THM—trihalomethane, TOC—total organic carbon, UV—ultraviolet, UV254—ultraviolet absorbance at 254 nm, WTP—water treatment plant

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regulated at the federal level in the United States, but they could be regulated in the future and are cur­rently regulated in California at drinking water treatment plants

with a notification level of 10 ng/L. At water recycling facilities, NDMA can be removed by photodegrada­tion during ultraviolet/advanced oxi­dation treatment (if that is included as part of the treatment process). However, precursor material may be present in the DPR product water leaving the water recycling plant, leading to the potential production of NDMA during residual disinfec­tion or blending in the distribution system. Therefore, in light of current and future regulations at state and federal levels (USEPA 2014), NDMA formation should be evaluated as part of a DPR­blending scenario.

CONCLUSIONMany blending considerations

have been extensively studied at various locations over the past decade as part of normal evalua­tions of blending multiple water supplies. Because blending recom­mendations are mostly qualitative in nature, or highly site specific, water treatment managers, consult­ing engineers, and others will need to conduct their own desktop, bench­, and pilot­scale evaluation of DPR­blending implications in a given water treatment system despite the wealth of previous stud­ies. The purpose of the information presented in this article is not to replace these site­specific experi­ments and assessments, but rather to help inform these studies with

regard to the possible DPR­blending scenarios that should be investigated, and the water quality parameters that require monitoring in order to address potential DPR­blending concerns.

Table 2 summarizes the DPR con­siderations presented here, as well as the pilot testing/planning evalu­ations and water quality monitor­ing that should take place pre­ and post­ implementat ion of DPR blending, respectively, in order to address these considerations.

ABOUT THE AUTHORSBenjamin D. Stanford (to whom correspondence may be addressed) is the director of applied research at

Hazen and Sawyer, 4011 Westchase Blvd., Ste. 500, Raleigh, NC 27607 USA; bstanford@hazenandsawyer.com. He manages a portfolio that has spanned more than 50 research grants and also leads the company’s water reuse practice group. Stanford earned his PhD in environmental sciences and engineering from the University of North Carolina at Chapel Hill and has conducted a range of studies across science, engineering, and public health protection for water, water reuse, and wastewater. His current work includes numerous direct and indirect potable water reuse studies and projects. Stanford also serves as an expert advisor to AWWA, the National Science Foundation, municipalities, and several other groups on emerging

contaminants, cyanotoxins, chlorate/perchlorate, disinfection by-products, and control of Legionella in premise plumbing systems. He has authored more than 30 peer-reviewed publications and was awarded the 2012 Publications Award by AWWA. William C. Becker is vice-president at Hazen and Sawyer in New York, N.Y. Jean F. Debroux is chief technology officer at Kennedy/ Jenks Consultants in San Francisco, Calif. Stephanie K.L. Ishii is assistant engineer at Hazen and Sawyer in Fairfax, Va. Stuart J. Khan is associate professor at the University of New South Wales in Sydney, NSW, Australia. Wendell O. Khunjar is an associate at Hazen and Sawyer in Fairfax, Va.

http://dx.doi.org/10.5942/jawwa.2016.108.0061

REFERENCESDuranceau, S.J.; Pfeiffer-Wilder, R.J.;

Douglas, S.A.; Pena-Holt, N.; & Watson, I.C., 2011. Post-Treatment Stabilization of Desalinated Water. Water Research Foundation, Denver.

Edwards, M. & Triantafyllidou, S., 2007. Chloride-to-Sulfate Mass Ratio and Lead Leaching to Water. Journal AWWA, 99:7:96-109.

Hasit, Y.J.; Reiber, S.; & Parolari, A., 2007. Distribution System Water Quality Strategic Initiative: Expert Workshop Report. AWWA Research Foundation (Water Research Foundation) & CH2M Inc., Denver. www.waterrf.org/the-foundation/about/documents/dswqworkshopreport.pdf (accessed Oct. 21, 2015).

Khunjar, W.O.; Strahota, M.; Pitt, P.; & Gellner, W.J., 2015. Evaluating the Impacts of Cold and Wet Weather Events on Biological Nutrient Removal in Water Resource Recovery Facilities Nutrients. Water Environmental Research Foundation, Alexandra, Va. http://dx.doi.org/10.2166/ 9781780406701.

Peet, J.R.; Kippin, S.J.; Marshall, J.S.; & Marshall, J.M., 2001. Water Quality Impacts From Blending Multiple Water Types. AWWA Research Foundation, Denver.

Schroeder, E.; Tchobanoglous, G.; Leverenz, H.L.; & Asano, T., 2012. Direct Potable Reuse: Benefits for Public Water Supplies, Agriculture, the Environment, and Energy

The ability to evaluate the flavor profile of the

various source waters being used, as well as a

plan to address taste and odor complaints,

is expected to be critical for sustained

public acceptance of DPR.

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STANFORD ET AL. | 108 :4 • JOURNAL AWWA | APRIL 2016 55

Conservation. National Water Research Institute, Fountain Valley, Calif.

Taylor, J.S.; Dietz, J.D.; Randall, A.A.; Hong, S.K.; Norris, C.D.; Mulford, L.A.; Arevalo, J.M. et al., 2005. Effects of Blending on Distribution System Water Quality. AWWA Research Foundation & AWWA, Denver.

Taylor, J.S.; Dietz, J.; Randall, A.; Norris, C.; Alshehri, A.; Arevalo, J.; Guan, X. et al., 2009. Control of Distribution System Water Quality Using Inhibitors. AWWA Research Foundation, Denver.

Tetra Tech Inc. 2011. Tetra Tech (RTW) Water Chemistry, Process, and Corrosion Control Model, Version 2.0. AWWA, Denver.

Trussell, R.R.; Salveson, A.; Snyder, S.; Trussel, R.S.; Gerrity, D.; & Pecson, B.M., 2013. Potable Reuse: State of the Science Report and Equivalency Criteria for Treatment Trains. WateReuse Research Foundation, Alexandria, Va.

Trussell, R.R.; Anderson, H. A.; Archuleta, E. G.; Crook, J.; Drewes, J.E.; Fort, D.D.; Haas, C.N.; Haddad, B.M.; Huggett, D.B.; Jiang, S.; Sedlak, D.L.; Snyder, S.A.; Whittaker, M.H.; & Whittington, D. (2012). Water Reuse: Potential for Expanding the Nation’s Water Supply through Reuse of Municipal

Wastewater. Committee on the Assessment of Water Reuse as an Approach to Meeting Future Water Supply Needs, National Research Council, The National Academies Press, Washington. www.nap.edu/openbook.php?record_id=13303/chapter/1 (accessed Oct. 20, 2015).

USEPA (US Environmental Protection Agency), 2014. Announcement of Preliminary Regulatory Determinations

for Contaminants on the Third Drinking Water Contaminant Candidate List. EPA 79-FR-62715, Washington.

Walker, T.; Stanford, B.D.; Khan, S.; Valerdi, R.; Snyder, S.A.; & Vickers, J., forthcoming. Critical Control Point Assessment to Quantify Robustness and Reliability of Multiple Treatment Barriers of a DPR Scheme. WateReuse Research Foundation, Alexandria, Va.

AWWA RESOURCES• Making Direct Potable Reuse a Reality. Nagal, R., 2015. Journal AWWA,

107:7:76. Product No. JAW_0082136.• New Techniques for Real­Time Monitoring of Membrane Integrity for Virus

Removal: WRF­09­06b. Frenkel, V.S. & Cohen, Y., 2014. Conf. proc. AWWA Water Quality Technology Conference, New Orleans. Catalog No. WQTC_0081678.

• Public Acceptance of Direct Potable Reuse: A Comparison With Current Tap Water Concerns and Perceived Drivers for Implementation. Ishii, S.; Boyer, T.; Cornwell, D.; & Via, S., 2015. Conf. proc. AWWA Annual Conference & Exposition, Anaheim, Calif. Catalog No. ACE_0082555.

These resources have been supplied by Journal AWWA staff. For information on these and other AWWA resources, visit www.awwa.org.

2016 © American Water Works Association