Characterization of effluent water qualities from satellite membrane bioreactor facilities

w a t e r r e s e a r c h 4 7 ( 2 0 1 3 ) 5 0 6 5 e5 0 7 5

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Characterization of effluent water qualities from satellite membrane bioreactor facilities Zakir M. Hirani a,*, Zia Bukhari b, Joan Oppenheimer a, Patrick Jjemba b, Mark W. LeChevallier b, Joseph G. Jacangelo a,c a

MWH, 618 Michillinda Avenue, Suite 200, Arcadia, CA 91007, USA American Water, 1025 Laurel Oak Road, P.O. Box 1770, Voorhees, NJ 08043, USA c The Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21204, USA b

article info

abstract

Article history:

Membrane bioreactors (MBRs) are often a preferred treatment technology for satellite

Received 14 January 2013

water recycling facilities since they produce consistent effluent water quality with a small

Received in revised form

footprint and require little or no supervision. While the water quality produced from

27 April 2013

centralized MBRs has been widely reported, there is no study in the literature addressing

Accepted 25 May 2013

the effluent quality from a broad range of satellite facilities. Thus, a study was conducted to

Available online 11 June 2013

characterize effluent water qualities produced by satellite MBRs with respect to organic, inorganic, physical and microbial parameters. Results from sampling 38 satellite MBR fa-

Keywords:

cilities across the U.S. demonstrated that 90% of these facilities produced nitrified (NH4-N

Membrane bioreactor (MBR)

<0.4 mg/L-N) effluents that have low organic carbon (TOC <8.1 mg/L), turbidities of

Disinfection

<0.7 NTU, total coliform bacterial concentrations <100 CFU/100 mL and indigenous MS-2

Water reuse

bacteriophage concentrations <21 PFU/100 mL. Multiple sampling events from selected

Chlorine

satellite facilities demonstrated process capability to consistently produce effluent with

Bacteria

low concentrations of ammonia, TOC and turbidity. UV-254 transmittance values varied

Virus

substantially during multiple sampling events indicating a need for attention in designing downstream UV disinfection systems. Although enteroviruses, rotaviruses and hepatitis A viruses (HAV) were absent in all samples, adenoviruses were detected in effluents of all nine MBR facilities sampled. The presence of Giardia cysts in filtrate samples of two of nine MBR facilities sampled demonstrated the need for an appropriate disinfection process at these facilities. ª 2013 Elsevier Ltd. All rights reserved.

1.

Introduction

Use of recycled water for non-potable applications has increased dramatically in the United States; recycled water is now used in many applications that include landscape irrigation, fire protection, toilet and urinal flushing, agricultural irrigation, cooling and air conditioning. Most of these applications require a small flow of water and since the points of

application are usually disperse, it becomes cost prohibitive to install conveyance pipelines to transfer recycled water from a centralized water reclamation facility to these points of application. Satellite or decentralized treatment facilities allow treatment of wastewater for local reuse applications and minimize the cost of conveyance infrastructure (Metcalf and Eddy, 2007). Installation of satellite and decentralized facilities, as a viable water recycling solution, has been

* Corresponding author. Tel.: þ1 626 568 6003; fax: þ1 626 568 6015. E-mail addresses: [email protected], [email protected] (Z.M. Hirani). 0043-1354/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2013.05.048

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increasing because of their demonstrated reliability, minimal footprint, elimination of new recycled water distribution pipelines, and potential to postpone central treatment capital improvement projects (Davis, 2009). Water recycling applications with unrestricted access require disinfected tertiary effluent since the effluent is oftentimes utilized for irrigation of green space with unrestricted public access. For many satellite applications, this treatment needs to occur in a small footprint due to site constraints; therefore, footprint minimization and higher effluent quality are usually key drivers for satellite facilities. In addition, most satellite facilities are not staffed for 24 h a day, so a high level of automation is usually desired (Crites and Tchobanoglous, 1998; Davis, 2009). Since MBRs can achieve higher effluent water quality in a much smaller footprint compared to conventional treatment processes and require little or no supervision, it is the most widely used process for satellite facilities. Compared to centralized facilities, decentralized/satellite facilities are typically designed for small service areas such as golf courses, shopping centers, hotels and schools and may not be designed with equalization basins due to footprint constraints. Such conditions often result in a high variation in flow-rates and organic loading that can potentially impact effluent water quality. Further, as noted above, satellite facilities are staffed intermittently, and in some cases, operator supervision is not provided for several days. Therefore, issues with the treatment process can be potentially overlooked at these facilities. Although several studies have reported effluent water quality for pilot and centralized full-scale MBR facilities (van der Roest et al., 2002; Innocenti et al., 2002; Adham and DeCarolis, 2004; Qin et al., 2006; Hirani et al., 2010; Simmons and Xagoraraki, 2011; Hirani et al., 2012), such data have not been reported previously in the literature for satellite facilities. Further, enumerating the presence of traditional or emerging pathogens in effluents of satellite facilities is warranted; organisms of concern include poliovirus, coxsackievirus, echovirus, hepatitis A virus (HAV), rotavirus, norovirus, adenovirus, Cryptosporidium and Giardia (Gerba and Smith, 2005). Therefore, the objective of this study was to characterize effluent water quality produced from numerous satellite MBR facilities. The data provided are particularly important since most existing water reuse guidelines were established before development and implementation of MBRs at satellite installations.

2.

Materials and methods

2.1.

MBR facilities participating in the study

The MBR facilities sampled during the study utilized different process configurations (submerged and external), membrane geometries (hollow-fiber, flat-sheet and tubular), fouling control strategies (relaxation and backwash) and membranes of varying ages (1e10 years). More than 80% of the facilities sampled utilized submerged MBR configuration. Hollow-fiber ultrafiltration membranes were the most commonly utilized membrane systems among the facilities sampled (70% of total), followed by tubular membranes (microfiltration and

ultrafiltration) and flat-sheet microfiltration membranes. Less than 20% of the facilities sampled utilized external MBR configuration with tubular microfiltration or ultrafiltration membranes. Polyvinylidene Fluoride (PVDF) was the most commonly utilized membrane material followed by chlorinated Polyethylene (PE). Majority (83%) of the facilities sampled utilized backwashing as a fouling control strategy whereas the remaining utilized relaxation. The MBR facilities sampled were spread across six different states in the U.S. and three different United States Environmental Protection Agency (USEPA) regions; flow-rates at these facilities ranged from 0.3 to 284 cubic meter per hour (m3/h). The MBR facilities sampled during the study are listed with their assigned identifiers in Table 1; the first two letters represent the name of the state where the facility was located. MBR facilities sampled employed fine screening before wastewater was fed to the biological reactors. The membrane system suppliers require screening the raw wastewater with 1e3 mm fine screens in order to comply with the membrane performance warranty.

2.2.

Initial screening of 38 satellite MBR facilities

An initial screening of satellite MBR facilities was conducted to characterize effluent water quality. A grab sample of MBR effluent was collected from a wide range of satellite facilities (38 MBR facilities across several states in the US) and analyzed for a range of inorganic, organic, physical and microbial parameters. Table 2 presents the water quality parameters targeted during the study, the analytical methods employed, and the associated detection limits. The effluent water quality data obtained from the initial screening of the 38 satellite facilities was utilized to segregate these facilities into one of three different bins. The

Table 1 e eMBR facilities participating in the study. Plant identifier

Design capacity (m3/h)

Plant identifier

Design capacity (m3/h)

13.2 2.5 1.7 3.2 39.4 2.8 1.9 13.4 3.5 2.5 11.0 1.1 4.6 2.8 2.8 0.3 0.3 38.5 2.1

NJ-12 NJ-13 NJ-14 NJ-15 NJ-16 NJ-17 NJ-18 NJ-19 NJ-20 NJ-21 NJ-22 NJ-23 NJ-24 CA-01 NY-01 NY-02 NY-03 NY-04 NY-05

7.9 22.1 51.1 NA NA 0.5 0.5 0.3 0.2 0.5 0.3 0.3 0.3 283.9 NA 4.6 0.6 2.2 3.9

MA-01 MA-02 MA-03 CT-01 MA-04 CT-02 CT-03 RI-01 NJ-01 NJ-02 NJ-03 NJ-04 NJ-05 NJ-06 NJ-07 NJ-08 NJ-09 NJ-10 NJ-11 NA ¼ Not Available.

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Table 2 e Analytical methods/instruments utilized for measurement of water quality parameters. Water quality parameter Ammonia-N TOC UV-254 Turbidity Particle counts Total coliform bacteria Male specific bacteriophage Viruses (rotavirus, hepatitis A virus, adenovirus, enterovirus) Cryptosporidium/Giardia

Analytical method/instrument Method 380 & method 8155 Standard method 5310B Hach DR 5000 UVeVis spectrophotometer Hach 2100N turbidimeter Met one particle counter Standard method 9222B USEPA method 1602 PCR and RT-PCR

0.02 mg/L-N 0.001 mg/L 0.001 cm1

USEPA method 1623

1 per 10 L

purpose of the binning process was to facilitate selection of nine satellite facilities for additional detailed water quality evaluations. Performance levels were assigned to each satellite facility for each water quality parameter evaluated. Facilities were assigned a specific level (1, 2 or 3) if the effluent concentration for that parameter was 50th, >50th to 90th, or >90th percentile, respectively, among the facilities sampled. Once the performance levels were assigned to individual water quality parameters, the facilities were binned based on average performance levels observed for the six parameters: TOC, ammonia, turbidity, total coliform bacteria, UV-254, and total particle counts. The facilities were segregated into Bins A, B or C if the average of performance levels was 33rd, >33rd and up to 66th or >66th percentile value, respectively. Results obtained from the binning process allowed segregation of satellite facilities based on different levels of water quality performance. Since the satellite MBR facilities employed different process configurations and membrane systems, it was also critical to ensure that those selected for detailed water quality evaluations also represented different process configurations and membrane systems in addition to different water quality performance levels. Three satellite facilities were selected from each performance bin to represent facilities that employed different process configurations (submerged or external), membrane geometries (hollow-fiber, flat-sheet or tubular), and fouling control strategies (relaxation or backwash). In addition, the selected facilities were located in different geographies and had a wide range of design flow rates and membranes ages.

2.3.

Detection limit

Detailed water quality evaluations

The objective of the detailed water quality evaluations was to assess the filtrate water qualities produced from satellite facilities with respect to a broad range of water quality parameters as well as to assess the variability in water qualities through multiple sampling events. While the initial MBR filtrate screening was conducted using a single grab sampling event for each facility, the detailed water quality evaluation of the nine selected plants consisted of three sampling events over a period of three months. The effluent samples were also analyzed for additional microbial parameters such as Cryptosporidium sp., Giardia sp. and a range of viruses (hepatitis A virus (HAV), adenovirus, rotavirus and enterovirus) to

0.001 NTU >2 mm particles 1 per 100 mL 1 per 100 mL 103 per 25 mL reaction

determine the performance of satellite MBRs in regards to the filtrate microbial quality. Protozoa are amongst the most environmentally stable organisms and can present a public health issue; Cryptosporidium and Giardia are the most salient protozoa in wastewater and therefore, were included in MBR effluent water quality analysis. Viruses were chosen since they pose a significant challenge to membrane filtration systems due to their size and concentrations. Adenovirus is the most challenging virus for UV disinfection. Enterovirus, rotavirus and HAV can present a public health issue if present in recycled water.

2.3.1.

Quantitative analysis of Cryptosporidium and Giardia

To assess the concentration of Cryptosporidium and Giardia, 10 L samples of MBR effluent were collected using Envirochek HV filters (1.0-mm nominal pore size) at flow rates ranging from 2 to 4 L per min. The sampling/elution procedures were followed as specified in Method 1623 (USEPA, 2005). Laureth12 buffer was added to the capsule, shaken to recover entrapped oocysts and cysts in a total elution buffer volume of 250 mL, which was subsequently concentrated to 10 mL and subjected to immunomagnetic separation to specifically recover the target organisms. Cryptosporidium oocysts and Giardia cysts were fixed onto glass slides, stained with fluorescence conjugated monoclonal antibodies, visualized and enumerated by Long Term 2-Enhanced Surface Water Treatment Rule (LT2) certified analysts using an Olympus BH2 fluorescence microscope. The microscope was equipped with a blue filter block (excitation 490 nm; emission 510 nm) for visualization of oocysts/cysts labeled with FITC at 200fold magnification. Confirmation of oocysts/cysts was achieved at 400 magnification by using a UV filter block (excitation 400 nm; emission 420 nm) for visualization of 4-6 diamidio-2-phynyl-indole staining of nuclei. Internal morphology of oocysts/cysts was observed by using Nomarski-DIC microscopy.

2.3.2. Qualitative analysis of enterovirus, HAV, rotavirus and adenovirus For qualitative analysis of viruses, the MBR effluent samples were filtered using Virosorb 1MDS cartridge filters (CUNO Filtration, Carlstadt, NJ) and viruses were eluted from each filter by adding 1 L of a 1.5% beef extract (BBL Microbiology Systems; pH ¼ 9.5) followed by acid flocculation according to the Information Collection Rule procedure (USEPA, 1995). The

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Table 3 e RT-PCR conditions for different viruses. Target virus

Primer quantities

RT-PCR conditions

Reference

Enterovirus

300 nM

Wang et al., 2002

HAV

300 nM

Rotavirus

200 nM

Adenovirus

400 nM

Incubate at 65  C (2 min); 48  C (40 min); 95  C (10 min); [60 cycles of denaturation at 94  C (15 s) and amplification at 58e61  C (1 min)] Incubate at 65  C (2 min); 45  C (40 min); 95  C (5 min); [60 cycles of denaturation at 94  C (15 s) and amplification at 60e62  C (1 min)] Incubate at 65  C (2 min); 45  C (40 min); 95  C (10 min); [40 cycles of denaturation at 94  C (15 s) and amplification at 57e61  C (1 min)] Incubate at 94  C (3 min); [35 cycles of denaturation at 94  C (30 s); 55  C (30 s); 72  C (30 s) and final extension at 72  C (5 min)]

floc containing the virus particles was centrifuged at 3100 rpm for 15 min and the supernatant was discarded. The pellet was suspended in a 4 mL sterile solution of sodium hydrogen phosphate (0.15 M; pH 9.5 Na2HPO4) and centrifuged at 4500 rpm for 15 min. The supernatant was adjusted to pH 7.2 and the final volume was recorded. Sample concentrates were stored at 80  C until DNA/RNA extraction was performed. A Qiagen QIAamp UltraSens virus kit was used to extract viral RNA or DNA. The reagents for Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) were purchased from Promega (Madison, WI), and the Access RT-PCR system was used as recommended by the manufacturer with the use of 25-mL reaction volumes for individual detection of enterovirus, hepatitis A virus, and rotavirus. To detect the amplification signal, the primers listed in Table 3 were complemented with probes labeled with the fluorescent dyes 5-carboxyfluoroscein (FAM) on the 50 end and N,N,N0 ,N0 -tetramethyl-6-carboxyrhodamine (TAMRA) on the 30 end. When the two dyes are near each other, as is the case with an intact oligonucleotide probe, TAMRA acts as a quencher for FAM by absorbing at the FAM emission spectra (Desjardin et al., 1998). As the PCR progresses, the 50 exonuclease activity of Taq polymerase degrades the probe, enabling the fluorescence signal to be detected. The primers and probes were synthesized by Operon Biotechnologies (Huntsville, AL). On the other hand, adenovirus, a DNA virus, was detected using a PCR protocol modified from Allard et al., 2001. PCR reactions were carried out in 20-mL reaction mixtures containing 1 U of Perfecta SYBR Green FastMix kit (Quanta Biosciences). Thermal reactions to synthesize the first strand copy DNA from RNA (for enterovirus, hepatitis A virus, and rotavirus) or from DNA (for adenovirus) are summarized in Table 3, by using the Roche LightCycler 480 system II RT-PCR device (Roche Diagnostics, Indianapolis, IN). The RT-PCR product curves were examined, and their threshold cycle (the number of cycles at which the fluorescence generated within a reaction crosses the threshold, referred to as the crossing point [Cp] value) was evaluated. The PCR products were electrophoresed in 1.6% agarose for 1 h using 100 V and visualized by staining with 0.25 mg of ethidium bromide per mL and observed under UV light. PCR products were purified using ExoSAP-IT (USB Products, Affymetrix, Cleveland, OH) and sequenced at Genewiz Inc.

Modified from Costa-Mattioli et al., 2002 Pang et al., 2004

Modified from Allard et al., 2001

(South Plainfield, NJ) using an ABI 3730xl DNA analyzer with appropriate internal primers. Sequences were aligned and analyzed with published reference sequences using Clustal W (Thompson et al., 1994).

3.

Results and discussion

3.1. Effluent water qualities produced from screening of 38 MBR facilities 3.1.1.

Inorganic parameters

Filtrate samples collected from 38 MBR facilities demonstrated the process’ capability to achieve a high level of nitrification; ninety percent of the facilities sampled produced effluents with ammonia concentrations below 0.44 mg/L-N while the median concentration was at the method detection limit (MDL) of 0.02 mg/L-N (Fig. 1A). The effluent ammonia concentration varied from the MDL to 3.4 mg/L-N. Typically, MBR systems are designed to operate at a high MLSS concentration to take advantage of a smaller footprint (Judd, 2011); this is usually achieved by designing the systems at high SRTs (typically higher than 12 days). Operation at a high SRT typically results in substantial nitrification and subsequently very low effluent ammonia concentrations, as observed for most of these facilities. Effluent ammonia concentrations of <0.5 mg/ L-N and greater than 97% removal of ammonia have been reported in many pilot and large-scale MBR studies (Adham and DeCarolis, 2004; Hirani et al., 2007; Innocenti et al., 2002; Lesjean et al., 2002; Qin et al., 2006; Wintgens et al., 2002). The results presented here and those noted in the literature are particularly important because the presence of ammonia will convert free chlorine to chloramine, which is poor disinfectant compared to free chlorine and reduces chlorine’s ability to inactivate pathogens by approximately two orders of magnitude (Metcalf and Eddy, 2007). Online ammonia analyzers can measure and monitor ammonia concentrations semi-continuously at user defined intervals; such tools may be helpful at facilities employing chlorine disinfection to ensure sufficient free chlorine is available to achieve desired level of disinfection. It should also be noted that many of the MBR facilities sampled in this study did not have discharge limits for ammonia nitrogen and hence were not designed and/or

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D

TOC Concentration (mg/L)

B

10.00

10.00

Filtrate Ammonia Turbidity (NTU)

Filtrate Turbidity

1.00

0.10

.1

1

0.10

50 45 40 35 30 25 20 15 10 5 0 1

5 10 20 30 50 70 80 90 95

10

7

10

6

10

5

10

4

Filtrate Total Particle Counts

10

3

.01 .1

99 99.9 99.99

1

300

Filtrate UV-254 Total Coliform Bacterial Concentration (CFU/100 mL)

UV-254 Absorbance (cm-1)

F

0.4

0.3

0.2

0.1

0 .01

5 10 20 30 50 70 80 90 95 99 99.9 99.99

Percent Less Than

Percent Less Than

C

5 10 20 30 50 70 80 90 95 99 99.9 99.99

Percent Less Than

Filtrate TOC

.1

1

E

60 55

.01 .1

99 99.9 99.99

5 10 20 30 50 70 80 90 95

Percent Less Than

.01

1.00

0.01

0.01 .01

Total Particle Concentrations for 2-15 um Particles (Count/100 mL)

Ammonia Concentration (mg/L-N)

A

.1

1

5 10 20 30 50 70 80 90 95

99 99.9 99.99

Filtrate Total Coliform Bacteria 250 200 150 100 50 0 .01 .1

1

Percent Less Than

Indigenous MS-2 Bacteriophage Concentration (PFU/100 mL)

G

5 10 20 30 50 70 80 90 95 99 99.9 99.99 Percent Less Than

1000

Filtrate Indigenous MS-2 Bacteriophage 800 600 400 200 0 .01 .1

1

5 10 20 30 50 70 80 90 9 5 99 99.9 99.99

Percent Less Than

Fig. 1 e Cumulative probability distributions for water quality parameters measured in effluents of MBR facilities participating in screening study. (A) ammonia (B) TOC (C) UV-254 (D) turbidity (E) total particle concentrations for 2e15 mm particles (F) total coliform bacteria (G) indigenous MS-2 bacteriophage.

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operated to achieve complete nitrification. Although the majority of the facilities produced fully nitrified effluents, as noted above, some MBR facilities reported effluent ammonia concentrations as high as 3.4 mg/L-N. These facilities utilized UV for disinfection, so the presence of ammonia did not impact the downstream disinfection process.

3.1.2.

Organic parameters

The effluent TOC concentrations for the MBR facilities varied from 1.7 to 26.7 mg/L. Ninety percent of the MBR facilities sampled produced effluents with TOC concentrations below 8.1 mg/L; the median concentration was 4.0 mg/L (Fig. 1B). Typically, TOC concentrations in the effluent of MBR systems treating municipal wastewater are less than 7 mg/L (Qin et al., 2006; Ottoson et al., 2006; Kang et al., 2007), which was observed for most of these facilities. MBRs are typically operated at low food to microorganism ratio (F/M), which results in complete (biologically mediated) oxidation of organic carbon in the influent wastewater and low effluent TOC concentrations. However, one of the facilities sampled had an effluent TOC concentration of 26.7 mg/L, indicating a possibility of upset in the bioreactor basins for that facility. The UV-254 absorbance for effluents ranged from 0.06 to 0.35 cm1 with corresponding transmittance values (UVT) ranging from 88% to 45%. As shown in Fig. 1C, 90% of the satellite facilities sampled produced effluents with UV-254 absorbance below 0.22 cm1 (UVT above 60%). Additionally, one-fourth of the facilities sampled produced effluents with UVT of less than 65% indicating that investigation of operation and maintenance of these facilities is warranted. The National Water Research Institute (NWRI) guidelines for UV disinfection of drinking water and water reuse recommend filtrate UV transmittance values of 65 percent or greater at 254 nm for low pressure membrane (MF and UF) filtered effluent (NWRI/ AWWARF, 2012). Lower transmittance reduces the efficacy of UV disinfection and NWRI’s recommended UV dose for membrane filtered effluent (80 mJ/cm2) may not suffice for MBR facilities producing effluents with UV transmittance values below 65 percent. When online monitoring of UV absorbance is employed, it allows the UV disinfection control system to respond with higher UV intensity when lower UVT values are detected. However, the lower incoming UVT, the more the UV system is limited in its flow capacity to produce a specific applied UV dose.

3.1.3.

Physical parameters

The median effluent turbidity for the MBR facilities was 0.2 NTU but 10% of the facilities sampled produced effluents with turbidity above 0.7 NTU (Fig. 1D), indicating that some of these facilities may be operating with breached membranes or may have biological regrowth occurring in the filtrate line. Since MBR systems utilize microfiltration or ultrafiltration membranes for solids separation, they can achieve high removal of particles and are expected to produce effluents with turbidity typically below 0.2 NTU (Hirani et al., 2007). The filtrate turbidity for some of MBR facilities were measured at exceptionally high levels (1.1e8.6 NTU) but many of these facilities were not required to meet any filtrate turbidity limits. It should be noted that unlike California, many states in the U.S. require neither continuous monitoring of filtrate turbidity nor

mandatory shutdown of MBR facilities if the filtrate turbidity exceeds 0.5 NTU (CDPH, 2012). Therefore, many of the MBR facilities residing in other states do not measure or record filtrate turbidity continuously. California’s Title 22 regulations require that membrane filtrate turbidity of MBR systems should stay below 0.2 NTU for 95% of the time and never exceed 0.5 NTU during a 24-h period (CDPH, 2012). Based on the results, only half of the facilities sampled met Title 22 water quality requirements for membrane filtration systems including MBRs. The total particle count (>2 mm) for the MBR facilities ranged from 2600 to over 2,000,000 per 100 mL and 90% of these facilities produced effluents with total particle counts of less than 146,000 per 100 mL (Fig. 1E). The median concentration was 26,700 particles per 100 mL. The presence of particles affects the disinfection efficacy since particles shield pathogens from inactivation; disinfection efficacy has been shown to decrease with increasing particle size (Winward et al., 2008). Therefore, it is critical to utilize online turbidity analyzers to continuously monitor turbidity to ensure that the filtration process is working adequately to prepare effluent for disinfection. Results also showed that the total particle counts did not always correlate with turbidity (data not shown).

3.1.4.

Microbial parameters

The total coliform bacterial concentrations in the effluents of MBR facilities (prior to disinfection) ranged from <1 to 293 CFU/100 mL; the median concentration was 1 CFU/100 mL. Ninety percent of the facilities sampled produced effluents with total coliform bacterial concentrations below 100 CFU/ 100 mL (Fig. 1F). Since the effluent total coliform bacterial concentration is usually monitored after the disinfection process for meeting regulatory requirements, it is typically not monitored for MBR effluents. The presence of coliform bacteria at a high concentration in an MBR effluent may be an indication of a membrane breach or post-membrane biological regrowth. The total coliform bacterial concentrations in the influent ranged from 1.0  103 to 1.6  108 CFU/100 mL while the log removal values (LRVs) ranged from 2.8 to 7.4 logs with a median LRV of 5.7 logs. Since MBRs utilize membranes for solids separation, total coliform bacteria are expected to be removed to a high extent due to, at least in part, size exclusion. Several studies have shown greater than 5-log removal of total coliform bacteria by MBRs (Ueda and Horan, 2000; Adham and DeCarolis, 2004; Ottoson et al., 2006; Zhang and Farahbakhsh, 2007; Hirani et al., 2010). Several studies have reported very high removals of indigenous male specific bacteriophage from wastewater by MBR systems (Adham and DeCarolis, 2004; Zhang and Farahbakhsh, 2007; Hirani et al., 2010). Since viruses are primarily particle-associated in wastewater effluents (Wong et al., 2009) and the membranes retain much of the particulate matter in the reactor, many but certainly not all, of these organisms are expected to be removed to a high extent by the satellite MBRs. Among the 38 facilities sampled in this study, ninety percent of the facilities had filtrate male specific bacteriophage concentrations below 21 PFU/100 mL (Fig. 1G). The median concentration was below the detection limit (1 PFU/100 mL); however, samples collected from two MBR

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facilities had bacteriophage concentrations of 110 and 848 PFU/100 mL.

3.2. Detailed water quality evaluations of selected satellite MBR facilities Based on the results from the initial screening of the satellite facilities, nine facilities were selected for detailed water quality evaluations (Table 4). The selected facilities utilized different process configurations, membrane geometries and fouling control strategies; membrane ages varied from 1 to 6 years. The average flow rates at these facilities varied from 2000 to 1,800,000 gpd. Table 5 summarizes the results obtained for the inorganic, organic and physical parameters from these evaluations. All nine satellite facilities demonstrated high nitrification efficacy during the repeat sampling events with filtrate ammonia concentrations below 0.1 mg/L-N for most facilities and below 1 mg/L-N for all facilities. Ammonia concentrations were consistently lower for all three samples collected from these facilities, which indicates that when properly designed and operated, satellite MBR facilities can consistently achieve a high level of nitrification. Satellite facilities produced filtrate TOC concentrations mostly below 6 mg/L (ranged from 3.3 to 10.5 mg/L) and values were consistent during the three sampling events for each facility. The CT-03 facility had a relatively higher effluent TOC concentration (10.5 mg/L) during the first sampling event, which may have been due to a temporary upset in the bioreactor basin. Transmittance values (based on UV-254 absorbance) in the filtrate samples ranged from 48 to 79% and were found to vary substantially amongst different sampling events from the same facility, indicating the variation in character of organics in the filtrate samples. Since these satellite facilities treat wastewater from shopping malls, hotels, schools, golf clubs, and other small complexes, they are more likely to experience variation in wastewater quality depending on the time of day when the samples were collected. It should also be noted that the effluent TOC concentrations did not correlate with UV-254 absorbance values indicating that the character of the organics may be different for different MBR facilities (data not shown). Filtrate turbidities were below 0.2 NTU for the majority of satellite facilities sampled and were consistent during the

three sampling events. Filtrate turbidities for NJ-08 and NJ-14 facilities were significantly higher (2.0e14.6 NTU), raising possibilities of either a membrane breach or post-membrane biological regrowth at these facilities. The particle counts in the filtrate samples ranged from 2900 to 1,481,000 per 100 mL of sample and were found to be consistently high in the samples collected from the CT-03 and NJ-14 facilities during all three sampling events. About 40% of the total particle counts (for >2 mm particles) were in the size range of 3e7 mm for most of these facilities, while the 7e15 mm size range was found to contribute the least to the total particle count concentration (data not shown). The exceptions were the CT-03 and NJ-14 facilities, which had much higher percentages of large particles contributing toward their higher overall particle counts. It should be noted that the NJ-14 facility had high filtrate turbidity whereas the CT-03 facility did not, suggesting that particle counts do not always relate directly to turbidity in MBR effluents. The satellite MBR facilities demonstrated 2.0e7.5 log removal for total coliform bacteria (median 5.3 logs) while the filtrate concentrations varied from less than 1 to 90,000 CFU/ 100 mL. It should be noted that the filtrate samples from the NJ-14 facility were collected from the clearwell (filtrate reservoir) due to absence of a sampling port on the filtrate line, so coliform re-growth in the reservoir probably contributed to these high counts. Similarly, high counts in the filtrate samples from the CT-03 facility were probably due to coliform regrowth at the sampling port. The LRVs for indigenous male specific bacteriophage varied from 2.3 to 5.8 logs (median 3.2 logs) while the filtrate concentrations varied from less than 1 to 24 PFU/100 mL. It should also be noted that these viruses were measured at the detection limit (1 PFU/100 mL) in the filtrate samples collected from the NJ-14 facility although high concentrations of coliform bacteria were found in these samples, again indicating the possibility of re-growth of bacteria in the clearwell at this facility. Enterovirus, rotavirus and hepatitis A virus were not detected in any of the filtrate samples (Table 6). However, adenoviruses were found in filtrate samples from all nine facilities (Table 6). Kuo et al., 2010 investigated removal of adenovirus in a full-scale MBR facility and found 103 viral particles/L in the MBR effluent. There are several possible explanations for these observations that still need to be substantiated. Since adenoviruses are present in

Table 4 e MBR facilities selected for detailed water quality evaluations.

Bin A

Bin B

Bin C

Plant identifier

Average/maximum flow (gpd)

Process configuration

Membrane geometry

Fouling control strategy

Membrane age (years)

NJ-05 NJ-04 NJ-23 CA-01 CT-03 NJ-08 NJ-07 NJ-06 NJ-14

2600/8400 4500/18,500 200/2000 1,100,000/1,800,000 3900/16,500 2400/2400 8000/18,400 3600/12,500 220,000/324,000

Submerged Submerged External Submerged Submerged External Submerged Submerged Submerged

Hollow-fiber Hollow-fiber Tubular Hollow-fiber Flat-sheet Tubular Hollow-fiber Flat-sheet Hollow-fiber

Backwash Backwash Backwash Relaxation Relaxation Backwash Backwash Relaxation Backwash

5 5þ 6 1 6 5 1 5.5 1.5e6

5072

w a t e r r e s e a r c h 4 7 ( 2 0 1 3 ) 5 0 6 5 e5 0 7 5

Table 5 e Measured levels of inorganic, organic and physical parameters in samples collected from MBR effluents during detailed water quality evaluations. Bin

A

Plant identifier

Sampling event

TOC (mg/L)

Ammonia (mg/L-N)

Turbidity (NTU)

UV-254 (cm1)

NJ-05

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

4.2 6.0 3.8 4.6 6.5 6.0 5.6 7.5 8.1 4.9 4.9 5.3 10.5 4.6 4.8 5.3 5.3 5.3 5.8 5.8 6.9 4.1 3.8 4.4 3.3 4.1 4.0

0.02 0.02 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.50 0.02 0.02 0.50 0.45 0.61 0.04 0.02 0.02 0.02 0.02 0.05 0.09 0.12 0.27 0.02 0.02 0.02

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.2 0.1 0.1 0.2 0.2 14.6 2.7 4.0 0.2 0.2 0.2 0.4 0.3 0.3 3.8 2.9 2.0

0.10 0.11 0.22 0.11 0.16 0.20 0.12 0.17 0.29 0.12 0.12 0.12 0.13 0.13 0.21 0.32 0.19 0.14 0.17 0.15 0.28 0.11 0.16 0.19 0.19 0.20 0.16

NJ-04

NJ-23

B

CA-01

CT-03

NJ-08

C

NJ-07

NJ-06

NJ-14

wastewater at high concentrations (Bofill-Mas et al., 2006; Kuo et al., 2010), they are more likely to be present in the MBR filtrate. Further, adenoviruses were also found to be among the most thermally resistant viruses (Gerba et al., 2002) and survive longer in water than enterovirus and HAV (Enriquez et al., 1995). The detection of these organisms by qPCR does not determine infectivity. Although low free chlorine CT values (<10 mg-min/L) would be sufficient to achieve 2-log inactivation of adenovirus (USEPA, 1989), passage of adenovirus in MBR effluents, if infectious, can pose a challenge for the downstream UV process due to their resistance to low pressure UV. According to the USEPA guidance manual on UV disinfection, a UV dose of 100 mJ/cm2 would be required to achieve 2-log inactivation of adenovirus (USEPA, 1996), indicating that current dose of 80 mJ/cm2 proposed under NWRI guidelines may not suffice. Based on the observations from this study, additional research and risk assessment on presence of adenovirus in MBR effluents is warranted. In the meantime, disinfection systems should be carefully designed and operated to nullify the effect of adenoviruses. Giardia cysts were detected in filtrate samples from two satellite facilities (CT-03 and NJ-14) whereas Cryptosporidium oocysts were not detected in any filtrate samples (Table 6). It should be noted that samples from both CT-03 and NJ-14 facilities also had much higher particle and bacterial counts than the other satellite plants. The percent contribution of 7e15 mm particles to the total particle count was almost double for these facilities compared to the other facilities, indicating a possibility that these facilities may

Total particle concentration (count/100 mL) 40,542 71,344 29,692 13,677 154,435 36,126 41,051 31,157 15,730 25,130 2884 35,283 1,227,325 1,480,723 831,558 23,542 17,135 9013 135,526 36,481 15,174 65,117 24,181 44,668 1,208,739 1,348,011 741,504

have had breached membranes. Presence of Giardia cysts in MBR effluents has been reported in another study (Bukhari et al., 2012). Such results demonstrate a need for continuous membrane integrity monitoring for MBR facilities since these organisms are not expected to pass through intact microfiltration or ultrafiltration membranes (Jacangelo et al., 1995).

4.

Summary and conclusions

A comprehensive assessment was conducted to evaluate the overall water quality produced from 38 satellite MBR facilities located in various parts of the United States. The study showed that if designed and operated correctly, satellite MBRs have the capability to produce nitrified effluents that have low levels of organic carbon, and indicator organisms. Although effluent turbidity values for 90% of these facilities were below 0.7 NTU, half of the facilities sampled did not meet the turbidity requirements stated in the Title 22 regulations of California. Results from the detailed water quality evaluation demonstrated the consistency in the effluent water quality with respect to low concentrations of ammonia, TOC and turbidity. The data suggest these effluents would be effectively disinfected by free chlorine. The UV-254 absorbance varied substantially during the three sampling events, indicating that the UV disinfection process, if applied to these effluents, should be designed carefully to account for changes in the characteristics of residual organics present in these effluents. The presence of adenovirus

Table 6 e Detection and levels of selected microorganisms in samples collected from MBR effluents during detailed water quality evaluations. Bin

A

Sampling event

NJ-05

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

NJ-04

NJ-23

B

CA-01

CT-03

NJ-08

C

NJ-07

NJ-06

NJ-14

Viruses

Bacteria

Protozoa

Male specific bacteriophage (PFU/100 mL)

Enterovirus

Rotavirus

Hepatitis A virus

Adenovirus

Total coliform bacteria (CFU/ 100 mL)

Giardia cysts (cysts/10 L)

Cryptosporidium oocysts (oocysts/10 L)

1 10 1 1 2 1 1 1 4 1 24 4 24 6 2 1 8 1 1 1 1 1 22 1 1 1 1

Negative Negative Negative Negative Negative NA Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative

Negative Negative Negative Negative Negative NA Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative

Negative Negative Negative Negative Negative NA Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative Negative

Negative Positive Positive Positive Positive NA Negative Positive Positive Positive Positive Positive Positive Positive Negative Positive Positive Positive Negative Negative Positive Positive Positive Positive Positive Positive Positive

4 1 151 68 2500 3100 1 1 1 17 10 47 50,000 90,000 35,000 1 1 1 160 79 29 4 5 41 9300 34,000 1200

0 0 0 0 0 0 0 0 0 0 0 0 3 3 3 0 0 0 0 0 0 0 0 0 18 3 17

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

w a t e r r e s e a r c h 4 7 ( 2 0 1 3 ) 5 0 6 5 e5 0 7 5

Plant identifier

5073

5074

w a t e r r e s e a r c h 4 7 ( 2 0 1 3 ) 5 0 6 5 e5 0 7 5

in MBR filtrate samples, as observed during this study, may pose a challenge for UV disinfection and raises a need for more detailed research and risk assessment. Finally, frequent assessment of membrane integrity is crucial to ensure complete removal of Cryptosporidium oocysts and Giardia cysts. While these organisms are not expected to pass through intact MBRs, they were still observed in effluents of two of the nine MBR facilities sampled.

Acknowledgments The authors would like to express their gratitude to the following individuals and organizations for their contributions to the successful completion of the project.  WateReuse Foundation for providing the funding for this study under project funding agreement WRF-08-07,  James Stahl (MWH), Roger Stephenson (MWH), Michael Selna (independent consultant), Simon Judd (Cranfield University) and Charles Haas (Drexel University) for their insightful comments.  Jeff Noelte of the Inland Empire Utilities Agency for providing the technical support for the pilot studies,  Hitachi Plant Technologies and Meurer Research Inc. (MRI) for providing the MBR pilot systems and for providing technical support,  William Johnson, Patrick Jjemba and Matthew Lutz of American Water for conducting some of the water quality analyses.

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