Dishwashing water recycling system and related water quality standards for military use

Science of the Total Environment 529 (2015) 275–284

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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Dishwashing water recycling system and related water quality standards for military use Jared Church a, Matthew E. Verbyla b, Woo Hyoung Lee a,⁎, Andrew A. Randall a, Ted J. Amundsen c, Dustin J. Zastrow c a b c

Department of Civil, Environmental, and Construction Engineering, University of Central Florida, Orlando, FL, USA Department of Civil and Environmental Engineering, University of South Florida, Tampa, FL, USA Mainstream Engineering Corporation, Rockledge, FL, USA

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• A compact ultrafiltration system was developed for field dishwashing water reuse. • A review was conducted to recommend standards for dishwashing water reuse. • A specific dishwashing water reuse standard was developed for military use. • The water standard was cross-evaluated by monitoring reclaimed dishwashing water.

a r t i c l e

i n f o

Article history: Received 6 March 2015 Received in revised form 29 April 2015 Accepted 3 May 2015 Available online xxxx Editor: D. Barcelo Keywords: Dishwashing water Greywater Military use QMRA Recycling Water quality standard

a b s t r a c t As the demand for reliable and safe water supplies increases, both water quality and available quantity are being challenged by population growth and climate change. Greywater reuse is becoming a common practice worldwide; however, in remote locations of limited water supply, such as those encountered in military installations, it is desirable to expand its classification to include dishwashing water to maximize the conservation of fresh water. Given that no standards for dishwashing greywater reuse by the military are currently available, the current study determined a specific set of water quality standards for dishwater recycling systems for U.S. military field operations. A tentative water reuse standard for dishwashing water was developed based on federal and state regulations and guidelines for non-potable water, and the developed standard was cross-evaluated by monitoring water quality data from a full-scale dishwashing water recycling system using an innovative electrocoagulation and ultrafiltration process. Quantitative microbial risk assessment (QMRA) was also performed based on exposure scenarios derived from literature data. As a result, a specific set of dishwashing water reuse standards for field analysis (simple, but accurate) was finalized as follows: turbidity (b1 NTU), Escherichia coli (b50 cfu mL−1), and pH (6–9). UV254 was recommended as a surrogate for organic contaminants (e.g., BOD5), but requires further calibration steps for validation. The developed specific water standard is the first for dishwashing water reuse and will be expected to ensure that water quality is safe for field operations, but not so stringent that design complexity, cost, and operational and maintenance requirements will not be feasible for field use. In addition the parameters

⁎ Corresponding author at: University of Central Florida, 4000 Central Florida Blvd., P.O. Box 162450, Orlando, FL 32816-2450, USA. E-mail address: [email protected] (W.H. Lee).

http://dx.doi.org/10.1016/j.scitotenv.2015.05.007 0048-9697/© 2015 Elsevier B.V. All rights reserved.

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can be monitored using simple equipment in a field setting with only modest training requirements and real-time or rapid sample turn-around. This standard may prove useful in future development of civilian guidelines. © 2015 Elsevier B.V. All rights reserved.

1. Introduction The demand for reliable and safe water supplies for municipal, agricultural, industrial, and military use has been continuously growing over the last few decades with population growth, economic development, climate change, and depletion of traditional freshwater supplies (USEPA, 2012). Greywater is used water from bathroom and kitchen sinks, showers/bathtubs, and laundry facilities (Scholze and Page, 2011) and is typically reused as irrigation and toilet flushing in urban settings. Greywater reuse has attracted a great amount of attention as a water conservation strategy and many greywater reuse systems have been developed and implemented in commercial and residential facilities to achieve significant water savings indoors and outdoors (Yu et al., 2013). However, in remote locations of limited water supply, like those encountered in military installations, greywater applications are expanded to showering and firefighting. For these remote places, it is desirable to expand potential uses to include the recycle of dishwashing water to maximize the conservation of fresh water. This study seeks to develop a specific water reuse standard for a dishwashing water recycling system for military field operations in fresh waterlimited locations and to validate the developed water standard by cross-evaluating the water quality data from a greywater recycling system. For the current scope of work, this study will focus on water reuse within the United States (U.S.) Military, however the results of this study may be applicable for a number of other settings involving traveling individuals in remote and water-scarce locations, such as Peace Corps volunteers. For the reuse of greywater in the U.S., many regulations and standards have been developed based on the U.S. Environmental Protection Agency (USEPA) Secondary Treatment Standard. Water quality standards for greywater reuse should satisfy the following four criteria: hygienic safety, esthetics, environmental tolerance, and economic feasibility (Nolde, 2000). Typical greywater standards are regulated at the state level and exclude greywater generated from dishwashing because of the relatively large concentration of pollutants (USEPA, 2012; Friedler, 2004; Li et al., 2009). However, these standards vary from state to state and there are currently no guidelines or regulations regarding dishwashing water recycling at either the federal/state level or in the U.S. Army Public Health Command (USAPHC) guidelines (USAPHC, 2011). Guidelines for water reuse in military field operations set by U.S. Army Technical Bulletin TB MED 577: “Sanitary Control and Surveillance of Field Water Supplies” differ from state-regulated standards and include standards for shower and laundry water recycling (US Army, Navy, and Air Force, 2010); but there were no standards for dishwater recycling. The gap between state greywater regulations and military guidelines, along with the lack of guidelines for dishwater reuse standards make the deployment of a dishwater recycling system difficult (Lazarova et al., 2003). Given the need to further develop military guidelines for dishwater recycling, the objective of this paper is to recommend standards for the use of reclaimed dishwashing water, based on federal, state, and USAPHC regulations and guidelines for non-potable water use. Water quality data (e.g., BOD5, COD, TOC, pH, Turbidity, TSS, TDS, TP, UV254, and SUVA) from a full-scale dishwashing water recycling system using electrocoagulation (EC) and ultrafiltration (UF) were evaluated, and the chlorine demand and disinfection by-product formation potential (DBPFP) of chlorinated treated dishwashing water were assessed. A quantitative microbial risk assessment (QMRA) model was used to develop recommendations for the maximum tolerable concentrations of

Escherichia coli, Salmonella, and human norovirus in reclaimed dishwashing water. 2. Materials and methods 2.1. Evaluation of dishwater treatment device 2.1.1. Ultrafiltration dishwashing water recycling system A full-scale prototype of the dishwashing recycling system was constructed and operated by Mainstream Engineering Corporation (Rockledge, FL, USA) for a year (Fig. 1) (Amundsen et al., 2013). Water collected from three 76 liter sinks (wash, rinse and sanitize) was first treated by electrocoagulation using zinc electrodes to destabilize emulsions and precipitate suspended particles from the high-pH greywater (due to detergents used in dishwashing). Then the water was further processed by ultrafiltration using a hollow fiber, cross-flow, modified polyethersulfone membrane (WaterSep, Marlborough, MA, USA) with a molecular weight cutoff of 750 kDA (Amundsen et al., 2013). A standard issue powdered detergent (NSN 7930-00-281-4731, NuGentec, Emeryville, California) was supplied as a detergent and a preliminary analysis showed that the detergent's pH was 9.4 and includes sodium phosphate derivative anionic surfactant (Fig. S1). The electrocoagulation system was constructed with PVC with dimensions of 27 cm (H) × 5 cm (L) × 6 cm (W). The electrodes were constructed with zinc measuring 27 cm (H) × 5 cm (L) × 0.3 cm (W) and were separated by 0.6 cm. The seven electrode plates were put in the cell with one electrode as the anode, one electrode as the cathode (the anode and cathode were located at opposite ends of the reactor) and five inner plates operating in a bipolar fashion. The total electrode area was 810 cm2 with an applied potential of 20 V (AC). The current density was 1.85 mA/cm2 and the cell residence time was 7 min. The UF membrane was operated at 25 °C with a transmembrane pressure of 0.10 MPa and a feed flow rate of 400 mL/min. The filter was backflushed for 30 s every 3 min at 0.14 MPa using permeate. The filter was also cleaned, alternating between white vinegar and 1.0 M NaOH, for 10 min for every 4 h of runtime. Samples were collected weekly for testing. A synthetic surrogate dishwashing water used during the system operation as a representative sample of US Army field dishwashing effluent. Concentrated food mixture (3 kg baked beans, 1.28 kg chili con carne and 1.9 L of water) (8.3 mL), vegetable oil (2.5 mL) and NSN 7930-00-281-4731 dishwashing soap (20.0 g) were combined with 3.79 L (1 gal) of fresh tap water to produce the synthetic greywater with a BOD5 of 1000 mg/L and TSS of 850 mg/L (Natick Soldier Center, 2007). 2.1.2. Water quality analysis On-site samples were collected weekly from the dishwater recycle device at 25 °C and analyzed in the UCF laboratories within 3–6 h. Sample collection was performed in accordance with Standard Methods for the Examination of Water and Wastewater (APHA, AWWA, and WEF, 1998). Water quality analyses were performed in accordance with Standard Methods for the Examination of Water and Wastewater (APHA, AWWA, and WEF, 1998). The parameters measured included biological oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), total dissolved solids (TDS), total phosphorus, pH, temperature, total organic carbon (SM 5310), UV254 (EPA 415.3), SUVA (EPA 415.3), trihalomethanes (THMs) (SM 6232 B), and haloacetic acids (HAAs) (EPA 552.2). HAAs were analyzed by a certified

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Fig. 1. Schematic diagram of a greywater recycling process for dishwashing water.

external lab (Advanced Environmental Laboratories, Inc. Altamonte Springs FL, USA).

2.1.3. Potential microbial growth: the effect of surfactant and ultrafiltration treatment of dishwashing water on E. coli The current water recycling system has multiple barriers to remove microbial contaminants: zinc electrocoagulation, ultrafiltration, and chlorination. However, under specific circumstances in field operations (e.g., hot weather condition), it may not be easy to maintain the chlorine residuals required for bacterial control in the chlorinated holding tank. In this case, the presence of surfactants may inhibit bacterial growth, or cause their decay, during the event of the absence of free chlorine.

Therefore, the degree of disinfection due to contact with the surfactant (without chlorination) was evaluated in batch experiments. E. coli was selected for microbiological testing because of its use as an indicator organism in U.S. greywater regulations (USEPA, 2012). E. coli (K-12 strain S 4362, ATCC 29181) was propagated in tryptic soy broth (Difco, Detroit, MI), according to the manufacturer's specifications, and incubated for 48 h at 37 °C. After allowing the E. coli to stabilize (5 days at 37 °C), 0.5 mL of the liquid culture (3.6 × 108 CFU/100 ml) was added to five beakers with 500 mL of sterilized (autoclaved) UF/ EC treated synthetic dishwater and different detergents and surfactants (1) no detergent, 2) powdered detergent (NSN 7930-00-281-4731, NuGentec, Emeryville, California,) 3) anionic surfactant (sodium lauryl sulfate), 4) cationic surfactant (cethyl trimethylammonium chloride

Table 1 QMRA model parameter assumptions. Parameter

Units

Value or distribution

References

Acceptable risk of illness Maximum tolerable cases of illness

Ratio

1 in 50,000 exposures

Two orders of magnitude less than the current estimated disease incidence for military field personnel Riddle et al. (2006)

Exposure to pathogens Volume ingested for direct potable reuse Volume accidentally ingested during reuse for irrigation Volume accidentally ingested during reuse for dishwashing Volume accidentally ingested during reuse for showering

mL/person/day mL/person/day mL/person/day mL/person/day

V = 3000 V=1 V=1 V = 1.9

USEPA (2011) Ottoson and Stenström (2003) Assumed to be the same as irrigation Ahmed et al. (2010)

Hypergeometric model: α = 0.04, β = 0.055, ηNV = 0.00255, rNV = 0.086, a = 0.9997 Approximate beta-Poisson model: α = 0.3126, β = 2884 Approximate beta-Poisson model: α = 0.1705, β = 1.61 × 106

Teunis et al. (2008)

Dose–response models Norovirus (based on best fit parameters for 8fIIa & 8fIIb inocula) Salmonella spp. E. coli O157:H7

Probability of infection resulting in illness Illness: Infection (I)

probability; proportion

NoV: pilljinf ¼ 1− 1 þ ηNV cNV V Salmonella: 0.2 E. coli: 0.28


−rNV

Soller et al. (2010) Soller et al. (2010)

Soller et al. (2010), Teunis et al. (2008)

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Table 2 A selection of greywater reuse standards, guidelines, and regulations. Parameter

pH

Turbiditya (NTU)

TSS (mg/L)

CBOD5a (mg/L)

BOD5a (mg/L)

Free chlorine (mg Cl2/L)

Fecal coliformb (FC/100 ml)

U.S. Secondary Treated Wastewater British Standard BS 8525-1:2010

6.0–9.0 5.0–9.5

b30 –

b25 –

b30 –

– 6.5–8.5 –

– b30 b5–b30

– b25 b8–b30

– b25 b5–b30

TB MED 577 (U.S. Army)

5.0-9.0

b10d

–

–

–

– b2.0 (b0.5 for garden watering) – 0.5–2.5 N.R.c -5 1.0 (after 30 min)

b16 Variesf

International Plumbing Code US EPA and NSF Guidelines U.S. State Regulations

b5 b10 (n/a for garden watering) b2 b5 b2–b5

b2.2g b14 b14 N.D.e

a

30 day avg. 7 day avg. N.R: not regulated. d b1 NTU if filtered. e N.D.: non detectable. f For spray applications and washing machine use, guideline is for E. coli (not detected in 100 mL), intestinal Enterococci (not detected in 100 mL), Legionella pneumophila (spray applications only, b10/100 mL), and total coliforms (b10/100 mL); for non-spray applications (toilet flushing and garden watering), guideline is for E. coli (b250/100 mL), Enterococci (100/100 mL), and total coliforms (b1000/100 mL). g Total coliforms per 100 mL (7-day median). b c

(CTAC)), and 5) nonionic surfactant (Triton X-100)). The UF/EC synthetic dishwater was produced by treating synthetic dishwashing water (recipe described in Section 2.1.1) with the developed UF/EC treatment system (i.e., one-cycle system operation) without detergent. Surfactant was then added to produce a 0.05 N solution which is typical of U.S. dishwashing water (Lai, 2012). The manufacturer recommended amount of powdered detergent (5.3 g/L) was used which contains an unknown amount of surfactant. Treated greywater without surfactant or detergent was used as a control. The dishwater environments were maintained at 37 °C ± 1 °C and continuously stirred using a hot plate and magnetic stirrer. Triplicate samples were aseptically withdrawn from each environment at 5, 60, 120 and 240 min for quantification of E. coli. E. coli concentrations were determined using spread plate technique with dilutions on Nutrient Agar (Difco, Detroit, MI). Colony forming units (cfu) were counted after a 48-hour incubation period and E. coli was verified through inspection of colony morphology (Johansson et al., 2004).

bacterial growth if the desired chlorine residuals are not maintained. However, chlorine can also react with natural organic matter (NOM) to form a broad range of disinfection by-products (DBPs) which are harmful to human health (Jumpatong and Buddhasukh, 2003). Not only are DBPs harmful if ingested, they are also volatile and can be inhaled or adsorbed dermally (Hagen, 1998). Although the dishwater will not be ingested, chlorine demands for the treated water were investigated and disinfection by-product formation potential (DBPFP) was also investigated due to relatively high organic levels. DBP vaporization potential was also evaluated. The treated dishwashing water (pH 9.6 ± 0.1) was dosed with chlorine and incubated at 32 °C for different times (2, 4, 6, 24, and 48 h). 32 °C was used to simulate hot water usage. A preliminary test with a single dose of 50 mg Cl2/L showed chlorine depletion within 24 h due to high DOC (data not shown). In this study, chlorine doses were also increased to 60, 70, and 75 mg Cl2/L and chlorine residuals were measured with time during 48 h. 2.2. Quantitative microbial risk assessment (QMRA)

2.1.4. Chlorine demands and disinfection by-products formation potential (DBPFP) of treated dishwashing water Most regulations, including the U.S. EPA Guidelines for Water Reuse, NSF/ANSI 350-1 and many state regulations, require a hydraulic retention time (HRT) of less than 24 h for a water storage tank. Therefore it is recommended to set a HRT of 24 h for the chlorinated holding tank of the dishwater recycling system. This will help ensure water quality by limiting the time for residual depletion and bacterial growth. A HRT of 48 h or more is also sometimes recommended in some state regulations and local plumbing codes. Therefore, the batch tests for chlorine demand were conducted for HRT periods of 24 and 48 h. The treated greywater chlorinated holding tank could be a potential source of

In order to evaluate the reuse potential of greywater from this system for dishwashing, and to compare it with other greywater reuse activities,

Table 4 THM and HAA formation.

THM (μg/L)

Chlorine dose (mg Cl2/L)

Time CHCl3 (h)

CHCl2Br CHClBr2 CHBr3 Totala

60 70

24 24 48 24 48

124.69 125.12 106.33 106.08 135.20

75 Table 3 The developed dishwashing water recycling system effluent characteristics. Parameter

Influent

Effluent from the developed system

Typical greywater reuse standardsa

BOD5 (mg/L) COD (mg/L) TOC (mg/L) pH Turbidity (NTU) TSS (mg/L) TDS (mg/L) Total Phosphorus (mg P/L) UV 254 (cm−1) SUVA (L mg−1 m−1) Total Coliform (MPN/100 ml)

1000 2000 – – 450 850 – – – 1.07 –

65 708 92.5 ± 5.2 9.5 ± 0.1 0.325 ± 0.014 16 2650 88 0.68 ± 0.02 0.71 ± 0.1 Not detectable

30 100 No standard 6.0–9.0 5 30 450 5 0.03–0.07 No standard Not detectable

a

USEPA (2012), Salgot et al. (2006)

Time Chlorine (hr) dose (mg Cl2/L) HAA 70 (μg/L)

75

a b

2.25 4.00 6.00 24.00 48.25 2.00 4.00 5.75 24.00 48.00

1562.45 1660.90 2025.23 1577.37 2078.13

6.25 2.77 b1 1.07 b1

2.24 b1 b1 b1 b1

1695.64 1788.79 2131.56 1684.51 2213.33

MCAA MBAA DCAA

TCAA

DBAA Total

25.70 29.45 34.15 53.40 70.20 22.25 31.15 36.30 62.40 57.20

122.80 149.10 164.85 284.50 349.40 106.15 199.05 210.70 317.30 281.50

4.60 4.95 5.30 6.50 ND 2.80 5.00 4.75 ND ND

4.45 4.35 4.65 NDb ND 4.65 5.35 5.20 ND ND

Total does not include values below 1 ppb. ND: not detected

285.55 321.00 361.35 621.30 644.10 223.10 334.50 364.90 647.10 632.70

443.10 508.85 570.30 965.70 1063.70 358.95 575.05 621.85 1026.80 971.40

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such as irrigation, showering, or even direct potable reuse, a QMRA model (Haas et al., 2014) was used. The assumptions for model parameters are summarized in Table 1. This model was designed to estimate the maximum tolerable concentrations of three reference pathogens (human norovirus, Salmonella spp. (non-typhi), and E. coli O157:H7). Norovirus is a highly-infectious, non-enveloped virus (Le Pendu et al., 2006) known to cause water- and food-related outbreaks (Goodgame, 2007) and Salmonella spp. and Shiga toxin-producing E. coli strain O157:H7 are bacteria that have also been widely associated with foodborne outbreaks (USEPA, 2010; FSIS, 2001). As such, these pathogens may be present in food preparation materials and utensils and can potentially contaminate the dishwashing water. For this QMRA, it was assumed that all individuals may be susceptible to infections by any of the reference pathogens, despite the fact that up to 20% of the population may have genetic resistance to norovirus (Soller et al., 2010). Greywater from dishwashing could become contaminated by food preparation materials, and contaminated water in dishwashers can cross-contaminate dishware (Ståhl Wernersson et al., 2004). The use of electrocoagulation, ultrafiltration and chlorination should have high efficiency for pathogen removal from greywater, however there may be some exceptions. For example, Westrell et al. (2003) reported that virus removal in single-membrane ultrafiltration systems can be as low as one log10 unit, due to micro-defects in filter construction, partiallydamaged membranes, and leaky seals (Westrell et al., 2003). Bacteria can also form biofilms on the product side of membranes (Jacangelo et al., 1989). Also, many non-enveloped viruses (e.g. echovirus and coxsackievirus) are highly resistant to chlorination (Black et al., 2009). Previously-published dose–response models for the three pathogen groups (Teunis et al., 2008; Fiona Barker et al., 2013; Mok et al., 2014; Soller et al., 2010; Teunis and Havelaar, 2000) were used to estimate the probability of infection (pinf) for a given dose (see Supplementary information), and the probability of illness (pill) was modeled as

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3. Results and discussion 3.1. Review of global greywater reuse criteria Water quality requirements for water reuse vary greatly between applications and governing agencies throughout the world, which can make deployment of a new water reuse system disconcerting. Greywater reuse is growing rapidly worldwide, especially in areas of high water stress (Oron et al., 2014), however regulations vary greatly from country to country. In some jurisdictions, greywater reuse is allowed with restrictions, while in others it is prohibited in all circumstances (Allen et al., 2010). Most greywater reuse standards are also limited to reuse for irrigation or toilet flushing; reuse standards for dishwashing are generally nonexistent (USEPA, 2012; NSF, 2010; WHO, 2006).

ð2Þ

3.1.1. Regulations, standards, and guidelines from different countries Greywater reuse standards from around the world generally exclude kitchen greywater, only governing water from bathtubs, showers, handwashing basins, and washing machines. In some Australian states, untreated greywater can be used for toilet flushing, subsurface irrigation, or both; in others, greywater must be treated (Allen et al., 2010; Radcliffe, 2010). In Oman, greywater must be treated to potable water standards in order to be reused (Allen et al., 2010). In Israel, Spain, Japan and Germany, greywater cannot be reused for cleaning dishes (Allen et al., 2010; Gross et al., 2015), and plumbing codes in Canada prohibit the distribution of reclaimed greywater through faucets (Allen et al., 2010). In Great Britain, Standard BS 8525-1:2010 specifies water quality guidelines reclaimed greywater used for doing laundry, washing cars, power-washing outdoor areas, flushing toilets, and watering gardens (Table 2); it does not allow this water to be used for drinking, food preparation, cooking, dishwashing or personal hygiene (British Standards Institutions, 2010). In the United States, greywater standards are enforced at the state level and regulated by the Clean Water Act (USEPA, 2012), which requires treated wastewater to meet the following criteria (which also serve as minimum criteria for treated greywater): BOD b 30 mg/L, TSS b 30 mg/L, pH 6–9, and Turbidity b 5 NTU (Table 2). Enforceable water reuse standards in the U.S. differ from state to state (Li et al., 2009) (Fig. 2), and are governed by state regulatory agencies (e.g. Departments of Environmental Protection, Plumbing Codes, Department of Health) (Yu et al., 2013). The U.S. EPA recognizes 30 states that allow for greywater reuse; the other states either do not regulate or do not allow greywater reuse. Yu et al. (2013) examined state regulations and found that of 29 states that promote greywater reuse, 22 had internal inconsistencies in regulation. Discrepancies in greywater reuse stems from the adoption of plumbing codes like the UPC (8 states) or the IPC (10 states), which often differ from regulations found within environmental, health, or sewage disposal codes. Precedence is typically given to the stricter regulation (Glenn, 2012). The U.S. EPA's Guidelines for Water Reuse are used by state regulators in the U.S. to develop water reuse standards, however dishwater recycling is not addressed in this document. The water quality guidelines set by the U.S. EPA generally vary depending on the reuse application (see example in Table S1), with human exposure being the most important factor. Plumbing codes used in the U.S. often have greywater reuse guidelines and regulations built into them. There are several states in the U.S. that do not have their own water reuse standards, and leave regulation to the plumbing codes (e.g., Uniform Plumbing Code and International Plumbing Code). Plumbing codes do not normally contain quantitative water quality parameters, but regulate by installing certain treatment requirements (e.g., disinfection and filtering).

where V is volume of water ingested per person per day for each of the reuse scenarios (showering, irrigation, dishwashing, direct potable reuse). It was assumed that exposure would occur daily.

3.1.2. International guidelines Volume IV of the World Health Origination (WHO) Guidelines for the safe use of wastewater, excreta and greywater addresses the reuse of all

pill ¼ pinf  pillj inf

ð1Þ

where pill|inf is the conditional probability of illness (given a positive infection). Since this study focuses on the application of this system in a military field setting, a maximum tolerable daily probability of illness of 2 × 10−5 was used to establish acceptable concentrations of the reference pathogen groups. This limit is two orders of magnitude lower than the current incidence of food- and water-related illness in military field settings, meaning that the reuse of greywater would contribute less than 1% of the existing health burden. This approach has been taken previously to establish guidelines (see Supplementary information). Eq. (S1) through (S3) were used to estimate the maximum tolerable dose of Salmonella spp., E. coli O157:H7, and human norovirus, given the maximum daily tolerable probability of illness of 2 × 10−5 per person. For Salmonella spp. and E. coli O157:H7, the maximum tolerable dose was solved analytically, and an iterative approach was used to solve for the maximum tolerable dose for norovirus, given the convoluted nature of the dose–response equation (which uses the hypergeometric function). Calculations were done in ‘R’ Version 3.1.0 (The R-Project for Statistical Computing, Vienna, Austria), using the ‘hypergeo’ package (Hankin and Lee, 2006). Given the maximum tolerable dose (λ) for each of the three reference pathogens, the maximum acceptable concentrations (c) in the recycled dishwater were plotted against the volume of water ingested per day of exposure, using the equation λ¼cV

280

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Fig. 2. Guidelines and regulations for greywater reuse applications in the United States.

types of greywater (including kitchen greywater); however, it does not specifically address greywater reuse for dishwashing, focusing instead on reuse in agriculture (WHO, 2006). The WHO guidelines are based on a microbial risk assessment approach, recommending a maximum health burden that does not exceed 10− 4 to 10− 6 DALYs per person per year. NSF International (NSF) and the American National Standards Institute (ANSI) recently published international guidelines for water reuse. The NSF/ANSI Standard 350: On-site Residential and Commercial Water Reuse Treatment Systems and the NSF/ANSI Standard 350-1: On-site Residential and Commercial Greywater Treatment Systems for Subsurface Discharge provide guidance on water quality standards (Table 2), methods of evaluation, product specifications, and product literature for greywater treatment systems. In addition to producing these guidelines, NSF and ANSI also certify treatment systems. While NSF/ANSI certification does not necessarily satisfy regulations in all countries or states, it does provide a consistent standard that is recognized internationally. 3.1.3. Military guidelines The U.S. Army is guided by state, federal, or international regulations, when not in deployment or in the presence of any host nation requirements (US Army, Navy, and Air Force, 2010). However, in areas of active U.S. military operations, greywater reuse is guided by the guidelines of TB MED 577 “Sanitary Control and Surveillance of Field Water Supplies” (US Army, Navy, and Air Force, 2010), which are less stringent than regulations in the U.S. (Table 2) and include water standards for applications that are not typically regulated in other standards, such as showering, laundering, and firefighting. Water quality standards for the use of water for showering (Table S2) are as follows (Engelbrecht, 1986): pH 6.5–7.5, turbidity b5 NTU, free chlorine residual 5 mg/L and hardness b500 mg/L. These standards were selected as the best framework for developing dishwater recycling standards in the current study, especially since human contact with water and the use of detergent would be similar for showering and dishwashing. 3.1.4. Initial water standards for dishwater recycling Currently available literature on the development of greywater reuse regulation was extensively reviewed to obtain an overall understanding of existing water quality parameters and standards. The driving force behind the standards is human health. One parameter directly dealing with human health is the removal of microbial pathogens, requiring disinfection which is typically accomplished with chlorine.

Shower reuse standards for military use most closely address dishwater recycling; however, has limited water quality parameters. This is probably due to typical field situations where access to lab facilities is limited and the assumption that the high chlorine residual required will disinfect the water and suppress growth. Initial water standards for dishwashing water recycling for field operations were developed to include not only the parameters in TB MED 577, but also water quality standards based on other water reuse standards in the literature: Lab test: General water quality requirement in applications where lab facilities are available ○ pH 6–9 ○ Turbidity b 5 NTU ○ Free chlorine (in the storage tank): 1–5 mg Cl2/L ○ UV254 (as surrogate for organics): the correlation with TOC or BOD5 should be evaluated in the laboratory and calibration curves should be created to use UV254 in each specific field application. Field application: Minimum water quality requirement ○ pH 6–9 ○ Turbidity b 5 NTU ○ Free chlorine (in the storage tank) : 1–5 mg Cl2/L ○ UV254 once a water/site specific correlation with organic parameter such as TOC is established (Fig. S2) ○ BOD5 b 30 mg/L ○ TSS b 30 mg/L. The use of chlorine for residual disinfection in the dishwashing water storage tank may help prevent bacterial growth, but this is not necessarily recommended as a requirement for the reuse of dishwashing water (especially if pathogen removal is achieved to suitable levels by other means, such as ultrafiltration). 3.2. Evaluation of dishwater treatment device 3.2.1. Effluent water characteristics Table 3 shows the effluent characteristics of the dishwashing water recycling system. BOD5, and COD were significantly reduced after ultrafiltration with average concentrations of 65 (93.5% removal) and 708 (64.6% removal), respectively. The system also produced water with TSS, TDS and Turbidity of 16 mg/L (98.1% removal), 2650 mg/L, and

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0.3 NTU (99.6% removal), respectively, with a pH of 9.5. Based on the UF pore sizes ranging from 0.01 and 0.1 μm (Amundsen et al., 2013), TSS removal of 98.1% seems to be resulted from dissolved organic carbon (DOC) removal. UV 254 was found to have an absorbance of 0.68 cm−1 resulting in a SUVA254 (= UV254/DOC) of 0.71. The value of the SUVA was relatively low indicating that the large aromatic molecules are being adsorbed and filtered out by coagulation and ultrafiltration (De la Rubia et al., 2008). The values of effluent water quality still exceeded typical greywater reuse standards (Table 3), but fresh potable water at an elevated temperature will be used for the sanitization step, resulting in the dilution of any treated water droplets which are carried over when dishes are transferred from the rinse stage to the sanitation (final) stage of the dishwashing process.

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harmful health effects. Extensive research on the health effects of THMs have been published due to the volatile nature of this class of DBPs including adverse respiratory and allergy related effects (Kabsch-Korbutowicz, 2005) and increased risk of liver and bladder cancer (Hagen, 1998). Given that chloroform production reached 1661 μg/L after 24 h of the exposure to chlorine, a dynamic model software (STELLA, isee systems, Lebanon, NH, USA) was used to predict potential accumulation of chloroform in the air within military field tents. The model was developed based on rate constants derived from experimental data (Table 4) under worst case scenarios (i.e., high temperature water [55°], minimal ventilation [0.2 air exchanges per hour] and high doses of chlorine [70 mg Cl2/L every 24 h]). Additional details on DBP vaporization are provided in the Supplementary data. If volatilized, chloroform concentrations spiked at 1.16 ppm shortly after dosing the holding tank with chlorine and fell to 0.47 ppm over the remainder of the day. The U.S. Occupational Safety & Health Administration (OSHA) requires chloroform concentrations to be below 50 ppm, but recommend that the permissible exposure limit be reduced to 2 ppm within an hour. Although the model predicts chloroform concentrations will not exceed the OSHA standards, proper ventilation (especially after adding chlorine) will ensure the safety of the dishwashing personnel.

3.2.3. Microbial disinfection from surfactant effects The effect of surfactants on E. coli disinfection is presented in Fig. 4. The data shown represents the mean values of triplicate samples. Among the surfactants tested, the presence of cationic surfactant (0.05 N CTAC) resulted in more than 7-log10 reduction within 5 min (data not shown); however, cationic surfactants are generally not used in dishwashing detergents. The control test (treated water without detergent or surfactant) showed that the microbial growth was inhibited probably due to the surfactant residuals in the ultrafiltration membrane. The greywater with the current detergent (powdered detergent soap (NSN 7930-00-281-4731, NuGentec, Emeryville, California) effectively reduced the E. coli concentration in the synthetic dishwater along with the anionic and nonionic surfactants. The presence of surfactants showed 97.8–99.8% reduction of E. Coli within 1 h and the rate of microbial decay was 2.5 times faster compared to the water without any detergent or surfactant. With the exception of the cationic surfactant, the effect of surfactant type on the survival of E. coli was insignificant in this batch test. All surfactants at a concentration of 0.05 N significantly reduced E. coli concentrations within the 4 h experiment (the HRT of the storage tank is approximately 1 day), indicating that the detergent used can provide an additional barrier against microbial growth. The pHs for surfactant tests were in the range of 6.8–8.6, which meet the typical greywater reuse standard. 8 7

60 mg/L 70 mg/L

60

75 mg/L

40 20

Log10 (E.coli CFU/100ml)

Chorline Residual (mg Cl2/L)

3.2.2. Chlorine demands and the formation of disinfection by-products Chlorine is typically used as a secondary disinfectant because chlorine residues in the system permit the continued inactivation of microbes (Salgot et al., 2006). To investigate chlorine demands required for maintaining chlorine residuals in the holding tank, the treated greywater was chlorinated and the chlorine consumption and the associated DBPs formation were investigated for 24 and 48 h. As shown in Fig. 3, the chlorine demand of the treated dishwater was relatively high due to high TOC. For the treated water, a chlorine dose of 60 mg Cl2/L resulted in a residual of 2.8 mg Cl2/L at 24 h but was unable to maintain a concentration above 1 mg Cl2/L after 48 h. However, dosages of 70 and 75 mg Cl2/L both maintained a concentration above 1 mg/L after 48 h (1.1 and 4.7 mg Cl2/L of chlorine residual, respectively). As a result, 60 mg/L was sufficient for maintaining the recommended chlorine residual in a holding tank with a 24 h HRT, but a dosage of 70 or 75 mg/L would be required at a 48 h HRT depending on what factor of safety was decided upon. However, the high chlorine dosages used resulted in significant DBP formation because of relatively high organic compounds even in the UF permeate/effluent. It is well known that chlorine reacts with natural organic matter (NOM) to form a broad range of DBPs (Jumpatong and Buddhasukh, 2003). Table 4 shows the DBPs formation after chlorination of the effluents. Given that U.S. drinking water standard for DBPs are 80 ppb for total THMs and 60 ppb for total HAAs (40 CFR Parts 9, 141, and 142), the DBP formation potential was relatively high. Table 4 shows after 24 h total THMs of 1789 and 1685 ppb were generated with chlorine doses of 70 and 75 mg Cl2/L respectively. The THMs formed were mostly chloroform (CHCl3). Total HAAs were 966 and 1027 ppb after 24 h with chlorine doses of 70 and 75 mg Cl2/L respectively. DBP levels were similar between the different chlorine doses, inferring that organic concentration and reaction time were major factors in the formation of DBPs. Even though the water from the system was not designed for ingestion, exposure to these concentrations of DBPs via accidental ingestion, dermal adsorption, or inhalation of vaporized DBPs could lead to

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y = -0.0078x + 7.236 R² = 0.9158

6 5

y = -0.0174x + 6.5942 R² = 0.8746

4 3

y = -0.0224x + 6.6668 R² = 0.9318

2

y = -0.0187x + 6.587 R² = 0.9276

1

0

0

20 Time (hrs)

40

Fig. 3. Chlorine demands for treated dishwashing water (pH 9.5) at 32 °C with chlorine doses of 60, 70, and 75 mg Cl2/L.

0 0

50

100 150 Time (Minutes)

Fig. 4. Effect of surfactants on E. coli decay.

200

250

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3.3. Quantitative microbial risk assessment The results of the QMRA are displayed in Fig. 5. If the reclaimed dishwashing water is to be used again for dishwashing (assuming ingestion of 1 mL of water per day), the concentrations of norovirus, Salmonella spp., and E. coli O157:H7 in the holding tank should not exceed 8.7, 0.92, and 8.2 × 10−3 per mL, respectively. If the water is reused for showering (assuming ingestion of 1.9 mL of water per day), the concentrations of norovirus, Salmonella spp., and E. coli O157:H7 should be no greater than 4.6, 0.5, and 4.3 × 10-3 per mL, respectively. To reuse the water for direct potable use (assuming ingestion of 3 L of water per day), concentrations should be less than 2.9 × 10− 3 noroviruses per mL, 3.1 × 10− 4 Salmonella per mL, and 2.7 × 10− 6 E. coli O157:H7 per mL. Routine monitoring for E. coli O157:H7, Salmonella, and human norovirus in water samples may not be practical in military field settings. However, culture-based methods for monitoring E. coli in greywater are simple and cost-effective. Coliform bacteria may not always be the most adequate indicator of foodborne pathogens in treated dishwashing water (Sheikh, 2010), and more research is needed to determine typical concentrations of foodborne pathogens in dishwashing greywater, as well as their fate and transport in treatment systems. However, the results of this QMRA indicate that the maximum tolerable concentrations for E. coli O157:H7 are lower than they are for Salmonella spp. and norovirus. Also, enterotoxigenic strains of E. coli and E. coli strains producing Shiga-like toxins (e.g. O157:H7) are the most commonly-implicated disease agents in foodborne outbreaks and among traveling military populations (FSIS, 2001; Riddle et al., 2006). Therefore, culturable E. coli may be one possible indicator that can be used to monitor the microbial risk of reusing dishwashing greywater in this setting. The concentration of E. coli O157:H7 in dishwater may only be a fraction of the concentration of total culturable E. coli, however no information was found in the literature about the ratio of E. coli O157:H7 to culturable E. coli in dishwashing greywater. In ground beef, this ratio can be estimated to be as high as 1.7 × 10−5 (see Supplementary information), and since ground beef has been implicated in the majority of food-related E. coli outbreaks (FSIS, 2001), it was assumed that this ratio also may apply to E. coli concentrations in dishwashing greywater. Thus, after applying a factor of safety of one order of magnitude to account for uncertainty, this ratio was used to recommend maximum concentrations of culturable E. coli for different reuse activities, given the results of the QMRA for E. coli O157:H7. The recommended

concentrations of E. coli in reclaimed dishwashing greywater are as follows: 50 cfu mL− 1 for reuse in dishwashing or irrigation; 3.0 × 104 cfu mL−1 for reuse in showers; and 1.6 × 10−2 cfu mL−1 for direct potable reuse. Even without chlorination, a concentration of 50 cfu mL−1 should be easily achieved with the treatment system described in this paper, especially given the decay of E. coli in the presence of dishwashing surfactants in the holding tank (Fig. 4). Direct potable reuse may require additional treatment to remove surfactants and other dissolved contaminants. 3.4. Development of standards There are many physical, chemical and biological water quality parameters for evaluating water after greywater treatment (Mollah et al., 2004). While some water parameters (e.g., pH and turbidity) can easily be monitored using simple techniques (e.g., potable pH meter and turbidity meter), others like BOD, COD, and TOC are timeconsuming, complicated and not applicable for field use. For the scope of the project, the water parameters which can be easily measured and evaluated for field use were the parameters of interest to be evaluated. Turbidity, pH, and UV254 were selected as surrogate parameters for field use of dishwasher recycle based on parameters used in TB MED 577 and due to the effectiveness of UV254 as a surrogate for organic monitoring (Potter and Wimsatt, 2012; Reckhow et al., 1990). In addition, a chlorine residual was also considered to achieve pathogen inactivation and prevent the regrowth of bacteria in the system. If the treated dishwashing water is used for dishwashing, using a factor of safety of approximately one log10 unit, it is recommended that maximum E. coli concentrations should not exceed 50 cfu per mL. Maximum norovirus concentrations should also not exceed ~1 per mL, and maximum Salmonella concentrations should not exceed ~ 0.1 per mL as demonstrated by the QMRA (Fig. 5). Reducing the concentration of these pathogens beyond these recommended levels would require additional expenses, and may not be necessary to ensure a level of health protection that is suitable for individuals in this setting. Concentrations of water- and food-borne pathogens, including bacteria, protozoa and viruses, should be sufficiently removed by ultrafiltration (Blyth et al., 2007). While a chlorine residual of at least 1.0 mg Cl2/L is often recommended in water reuse guidelines to provide additional microbial inactivation and to prevent bacterial growth in reclaimed water holding tanks, the use of chlorine in this context may not be necessary, and may even cause unintended health risks (due to the formation of

Fig. 5. Maximum tolerable concentration of reference pathogens vs. volume of recycled dishwater ingested (accidentally or intentionally) per person per day, based on a limit of one illness per 50,000 exposures, assuming that exposure occurs daily.

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DBPs). It is recommended that BOD5 be monitored and maintained at values of below 30 mg/L for water reuse, which is the same limit set by the U.S. EPA Secondary Treatment standard as well as other U.S. state regulations for greywater reuse. The chlorination of water with high BOD5 concentrations is expected to result in the production of DBPs and to promote bacterial growth and the associated biological contamination. Currently, TB MED 577 sets guidelines for water quality during field operation but lacks regulation of organic contaminates (US Army, Navy, and Air Force, 2010). On the other hand, U.S. state and federal agencies carefully monitor and regulate organic pollutants in drinking and wastewater treatment because of the contribution of organic compounds to microbial growth, oxygen consumption, and chlorine residual depletion (USEPA, 2012). The gap between water quality standards from state regulations and TB MED 577 is likely due to the difficulty in monitoring organic contaminates in field operation. While typical methods are unsuitable for field operation, several optical techniques have been developed for quick and simple monitoring of organic contaminates (e.g., UV280, UV254, color436 and color400) (Uyguner-Demirel and Bekbolet, 2011). Since BOD5 and other organic parameters (e.g., TOC and COD) are not easy to measure in field environments, UV254 will be a good candidate for ensuring proper levels of organics. UV254 has gained significant attention because of its strong correlation with DBP formation potential (Becker and Wattier, 1985; Pifer and Fairey, 2014), thus enabling its' use for chlorinated water systems. It is expected that the parameter can also be useful for monitoring organics in military operations with the aid of commercially available spectroscopy devices. TB MED 577 has no regulation on the DBP formation from chlorine disinfection; but, it is recommended to monitor the organic contaminants for public safety. Measurement of UV254 can be a useful tool for providing a simple monitoring parameter for water quality of treated dishwater during field operation. Dishwater quality varies from meal to meal, which could pose a problem for using UV254 for organic regulation. To employ UV254 as a parameter of organic contaminants, the relationship between UV254 and other organic parameters needs to be further investigated. Turbidity and pH are easily measured parameters that can also provide information on the effectiveness of the treatment. Based on the results and discussion above, a final set of dishwashing water reuse standards for field analysis was proposed as follows (Table 5): pH (6–9), turbidity (b 1 NTU), and E. coli (b 50 cfu mL− 1). UV254 was also recommended as a surrogate for organic contaminants of the water to be recycled; but calibration steps for its correlation with BOD or TOC would be required. 3.5. Environmental discharge considerations For environmental discharge in the U.S., the dishwater recycling system requires a BOD5 less than 30 mg/L and pH needs to be adjusted between 6 and 9, which meet U.S. EPA greywater reuse guideline as well as many state regulations (Table 2). These standards could also be adopted for military applications. This practice will also be beneficial for DBPs reduction.

Table 5 Developed water quality standard of the dishwashing water recycling system for military use. Parameter

Developed water standard

pH Turbidity UV254 E. coli

6–9 b1 NTU Surrogatea for organics (e.g., BOD5 below 30 mg/L) b50 cfu per mLb

a The correlation with BOD5 for the dishwashing water to be recycled needs to be evaluated in the laboratory and calibration curves (Fig. S2) should be constructed before the use of UV254 in field. b This recommended standard is proposed for reuse of recycled dishwashing water for dishwashing, in military field settings.

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4. Conclusions A tentative water reuse standard for dishwashing water was developed based on federal, state, and military regulations and guidelines for non-potable water and the specific set of dishwashing water reuse standards for field analysis (simple, but accurate) has been finalized as follows: pH (6–9), turbidity (b1 NTU), UV254, and E. coli (b 50 cfu mL−1). The developed specific water standard is the first for dishwashing water reuse and will be expected to ensure that water quality is safe for field operations, but not so stringent as to induce undue design complexity, cost, and operational/maintenance requirements. In addition, the parameters can be monitored using simple equipment in a field setting with only modest training requirements and real-time or rapid sample turn-around. The developed system is expected to provide the military a simple, compact, maintainable, integrated system to reliably process the variable mix of food, oil, and detergents from the dishwashing water for reuse. This study may also prove useful in future development of civilian guidelines. Acknowledgments This project was supported by the U.S. Army Natick Soldier Systems Center under Contract No. W911QY-12-C-0003. This material is also based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. 1144244. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scitotenv.2015.05.007. References Ahmed, W., Vieritz, A., Goonetilleke, A., Gardner, T., 2010. Health risk from the use of roofharvested rainwater in Southeast Queensland, Australia, as potable or nonpotable water, determined using quantitative microbial risk assessment. Appl. Environ. Microbiol. 76 (22), 7382–7391. Allen, L., Christian-Smith, J., Palaniappan, M., 2010. Overview of greywater reuse: the potential of greywater systems to aid sustainable water management. Pacific Institute (November 2010, www.pacinst.org). Amundsen, T.J., Zastrow, D.J., Wagner, A.L., 2013. Coagulation and ultrafiltration of high-alkalinity greywater. AlchE Annual Meeting, San Francisco, CA, USA. APHA, AWWA, WEF, 1998. Standard methods for the examination of water and wastewater. American Public Health Association (APHA), American Water Works Association (AWWA), and Water Environment Federation (WEF). Becker, W.C., Wattier, K., 1985. Surrogate parameters for monitoring organic matter and THM precursors. J. Am. Water Works Assoc. 77, 122–132. Black, S., Thurston, J.A., Gerba, C.P., 2009. Determination of Ct values for chlorine of resistant enteroviruses. J. Environ. Sci. Health A 44, 336–339. Blyth, W., Bradley, R., Bunn, D., Clarke, C., Wilson, T., Yang, M., 2007. Investment risks under uncertain climate change policy. Energy Policy 35, 5766–5773. British Standards Institutions, 2010. Greywater systems — code of practice. Series/doc. No. BS 8525-1:2010. de la Rubia, Á., Rodríguez, M., León, V.M., Prats, D., 2008. Removal of natural organic matter and THM formation potential by ultra- and nanofiltration of surface water. Water Res. 42 (3), 714–722. Engelbrecht, R.S., 1986. A Review of the US Army Construction Engineering Research Laboratory Program for Recycling and Reuse of Laundry and Shower Wastewater. National Academies. Fiona Barker, S., O'Toole, J., Sinclair, M.I., Leder, K., Malawaraarachchi, M., Hamilton, A.J., 2013. A probabilistic model of norovirus disease burden associated with greywater irrigation of home-produced lettuce in Melbourne, Australia. Water Res. 47, 1421–1432. Friedler, E., 2004. Quality of individual domestic greywater streams and its implication for on-site treatment and reuse possibilities. Environ. Technol. 25, 997–1008. FSIS, 2001. Risk Assessment of the Public Health Impact of Escherichia coli O157: H7 in Ground Beef. http://www.fsis.usda.gov/OPPDE/rdad/FRPubs/00-023N/00-023NReport. pdf (Accessed 10/12/14). Glenn, R.T., 2012. Regulatory Issues Associated with Graywater Reuse. Department of Civil and Environmental Engineering. M.S. Colorado State University. Goodgame, R., 2007. Norovirus gastroenteritis. Curr. Infect. Dis. Rep. 9, 102–109. Gross, A., Maimon, A., Alfiya, Y., Friedler, E., 2015. Greywater Reuse. CRC Press. Haas, C.N., Rose, J.B., Gerba, C.P., 2014. Quantitative Microbial Risk Assessment. John Wiley & Sons. Hagen, K., 1998. Removal of particles, bacteria and parasites with ultrafiltration for drinking water treatment. Desalination 119, 85–91.

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