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Big Bear–area regional wastewater brine management pilot testing and endocrine disrupter water-quality analysis
By Robyn Dack
The Big Bear Area Regional Water Agency (BBARWA) project provided a pilot test of an innovative brine management technology at a municipal facility, as well as comprehensive pilot testing of emerging contaminants of concern in recycled water. Potable water in Big Bear Valley is provided by local groundwater, but during periods of drought, demand can exceed supply. The use of recycled water, treated to a high quality and artificially recharged, was identified as the best means of supplementing the native groundwater supply. An advanced water treatment facility, consisting of microfiltration or ultrafiltration (MF or UF), reverse osmosis (RO), and UV with advanced oxidation, was identified.
CH2M Hill, a key player in the development of the world’s first major advanced wastewater treatment plant, undertook a brine management study to identify potential treatment technologies to reduce and/or dispose of the reject stream from an advanced-treatment water-recycling project. As part of this effort, Vibratory Shear Enhancing Process (VSEP), a patented technology of New Logic Research, was pilot tested. VSEP can reduce RO concentrate volumes with lower operation and maintenance costs and a smaller footprint. Prior to this study, the relatively new technology had never been applied to municipal wastewater. As part of a concentrate management study, VSEP was tested at the BBARWA to determine the feasibility of this technology in reducing RO concentrate volumes.
The VSEP unit was operated at a recovery range of between 75% and 92%. Flow, pressure, temperature, and pH were continuously monitored. Samples were collected from feed (ATF Pilot RO Concentrate), permeate, and concentrate streams. The VSEP pilot test results showed that both RO and nanofiltration (NF) membranes can reduce the conventional RO system concentrate volume by up to 85%, if a two-stage VSEP unit is implemented. VSEP recoveries exceeding 85% resulted in less than optimal operation of the unit (for example, decreased flux and high feed pressure) with increased life cycle costs. Acid and caustic cleanings of the membrane module, which are required to maintain flux, were performed using NLR 404 and NLR 5005, respectively. Cleaning frequency is estimated to be twice per week, a high frequency relative to conventional RO. The RO membrane exhibited better performance than the NF membrane at similar flux range; permeate quality for the RO membrane was excellent. The photo below compares VSEP feed (left), permeate (middle), and reject (right) streams at 85% water recovery.
Another component of this study was to investigate emerging contaminants of concern, or micro-pollutants, in the BBARWA’s recycled water. In this project, a pilot-scale MF (providing pretreatment for RO) and a two-stage RO process receiving secondary treated wastewater effluent from the BBARWA wastewater treatment plant were tested to determine the rejection capabilities of the RO membranes for California Department of Health Services’ specified notification level chemicals and endocrine disrupter chemicals (EDCs). Compounds evaluated during testing included acetaminophen, bisphenol A, caffeine, 17b-estradiol, EDTA, fluoxetine, gemfibrozil, ibuprofen, iopromide, 4-methyl phenol, polybrominated diphenyl ethers, progesterone, testosterone, triclosan, and sulfamethoxazole. This work was undertaken to determine the water quality of the recycled water and to assist with mitigating public concerns regarding the recharge of recycled water.
The BBARWA pilot advanced wastewater facility (AWF) consists of a US Filter/Memcor 3M10C Microfiltration with a nominal filtrate flow of 10 gallons to 12 gallons per minute (gpm) and a two-stage RO unit with a nominal permeate flow range of 3.8 gpm to 4.0 gpm. The pilot system included provisions for continuous feed of aqueous ammonia and sodium hypochlorite upstream of the MF to form chloramines at a target dose of 1.0 milligrams per liter (mg/L) to 2.0 mg/L. This was done to minimize biological fouling of both the MF and RO membranes. An oxidation-reduction potential meter was installed downstream of the dosing points, and a set point value of +450 millivolts (mV) was used to pace the hypochlorite feed rate to ensure that free chlorine was not present in the feed water.
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Microfiltration Unit
The 3M10C consists of three M10C submodules made from hollow-fiber polypropylene membranes that allow continuous filtration of liquid to 0.2 micron. The pilot unit was equipped with a programmable logic controller (PLC), differential pressure transmitters, a flowmeter on the filtrate side, a temperature sensor, and other required instrumentation. The MF system was operated using a manually adjusted filtrate flow valve and automated backwash procedures controlled by the system’s PLC. Readings of system flow, temperature, pressure, and other operational data were manually logged once a day. The membranes were cleaned prior to the start of this study using manufacturer standard procedures. Chloraminated secondary effluent was available to the MF system via a standpipe with an overflow, allowing the chloramination process to function continuously, independent of the MF system operation. An automated valve on the MF skid opened to draw chloraminated secondary effluent into the feed tank, as needed. Characteristics of the 3M10C membrane are presented in Table 1.
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Reverse Osmosis Unit
The RO unit consists of 2.5-inch-diameter by 40-inch-long membrane elements that were arranged in a 2:1 configuration to accommodate 18 TFC-HR membrane elements (12 in the first stage and six in the second stage). Stage 1 consists of four pressure vessels where the flow is fed to pressure vessels 1 and 3. Concentrate flow from these pressure vessels serves as feed to pressure vessels 2 and 4, respectively. Stage 2 has two pressure vessels that are connected in series (5 and 6) with vessel 5 receiving the combined concentrate from vessels 2 and 4 as feed. Each vessel houses three membrane elements.
The RO system used in this study was configured with a data acquisition system that recorded flow, temperature, and pressure data. The data acquisition system also maintained permeate flow and product water recovery automatically based on operator-selected set points. A log sheet was provided as a backup to the data acquisition system. Y2K brand anti-scalant was continuously dosed into the RO feedwater at a 4-milligrams-per-liter dose to minimize inorganic scaling. No acid was fed to RO feed water based on Koch Membrane Systems projections. Table 2 summarizes the characteristics of the RO membrane and operating parameters selected for this study.
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During pilot testing, MF removed particulate material and provided acceptable treatment for the RO unit with average turbidity and SDI values of less than 0.2 NTU and 2.3, respectively. RO performance was very robust as reflected in fairly constant differential pressure, recover, normalized permeate and salt rejections, and permeate water quality. Salt rejection was between 99.1% and 99.5% while limiting salt passage no higher than 0.9% during testing. Table 3 is a summary of operating conditions during pilot testing.
Two sets of sampling were performed at BBARWA pilot AWF to identify concentrations of selected endocrine disrupting chemicals in RO feed and permeate streams. The samples were also collected to analyze these selected EDCs in RO reject (concentrate). High chloride concentration (greater than 50 milligrams per liter) interfered with the analytical results. The RO concentrate EDC results were not included in this text.
The current testing methods are very limited so that identification and quantification of entire EDCs specified by DHS are not possible. For example, amoxicillin, atorvastatin calcium, and ibuprofen were not quantified with the current testing methods. Table 4 summarizes EDC test results for the identified compounds. All analytical testing was performed at Montgomery Watson and Harza (MWH) Laboratories located in Monrovia, CA.
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Photo: CH2M Hill |
| Feed, permeate, and concentrate samples |
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Photo: CH2M Hill |
| Two-stage VSEP units can reduce RO system concentrate volume by 85%. |
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Photo: CH2M Hill |
| The BBARWA groundwater recycle program had no major technical flaws. |
With respect to water reuse, the greatest concerns associated with EDCs are related to a series of field and laboratory studies demonstrating that chemicals in wastewater effluent caused male fish to exhibit female characteristics, commonly referred to as feminization. The hormones involved in fish feminization include 17b-estradiol, estradiol, and nonyphenol and alkylphenol polyethoxylates (EPA 2004). The major source of estradiol is birth control pills, whereas 17b-estradiol and estrone are naturally produced by animals. All tested and identified hormones including estradiol, progesterone, and testosterone were found not detectable in RO feed and permeate streams from the BBARWA pilot testing facility.
RO exhibited very good rejection capability (greater than 91%) to acetaminophen and caffeine, which are all below their detection limits in RO permeate. RO revealed more than 99% rejection to sulfamethoxazole and trimethoprim. However, a low concentration of sulfamethoxazole (2.4 nanograms per liter) was detected in RO permeate. EDTA was slightly higher than its threshold concentration value in RO feed. However, no EDTA was detected in RO permeate. Polybrominated diphenyl ethers are classified as industrial EDCs. Landfill runoff is the major source of these compounds. All tested and identified brominated diphenyl ethers are non-detectable in both RO feed and reject streams from the BBARWA pilot testing facility.
There is an ongoing effort to develop and further improve analytical methods for the identification of EDCs. Current methods are expensive, lengthy, and sometimes unsuccessful in identifying the target EDCs. It is clear that more research is required to improve the analytical methods as well as to understand the impact of EDCs on human and aquatic life. The potential of reclaimed water to cause endocrine disruption in humans is unclear.
The brine management study, VSEP, and constituent pilot testing benefited the BBARWA in the following ways:
- Provided information regarding how concentrate waste could be managed
- Provided exposure and training opportunities for BBARWA operations staff to work with new technologies
- Provided the BBARWA Board with a better understanding of the recycled water quality to assist with public perception concerns
- Gave the BBARWA exposure as a leader in testing innovative technologies
- Gave the BBARWA Board the necessary information to show that the groundwater recharge recycled water project was feasible and no major technical flaws existed in implementing the project
Robyn Dack is a Forester Communications staff writer.
OW - May/June 2007 |
