Perchlorate is a highly soluble salt-anion that can negatively affect the ability of the human thyroid to adequately uptake iodine. Since early 1997, with the improvement of analytical techniques, the perchlorate oxyanion has been detected in groundwater in several regions of California. The majority of the perchlorate contamination in groundwater is believed to be attributed to historical disposal practices by the aerospace and ordnance industries, the military, and chemical manufacturers.
The overall objective of this project was to provide an effective and reliable water treatment solution for a perchlorate-laden well in the City of Rialto, CA, allowing the local water authority the ability to utilize a valuable but impaired-quality water source, increasing the water security of the community and reducing its dependence on imported water. In meeting this objective, West Valley Water District (WVWD), located in Rialto, CA, has commissioned the first-of-its-kind full-scale Groundwater Treatment Plant using a fluidized bed reactor (FBR) technology to biologically treat water laden with the oxyanions of perchlorate and nitrate. Highly-contaminated perchlorate-laden water is being treated by the new facility to produce up to 3 million gallons per day (MGD) of quality drinking water for area residents.
The new treatment plant was designed and developed based on a year-long successful pilot demonstration study conducted by Envirogen Technologies, Inc. (Envirogen) and funded through ESTCP. From the pilot study, the FBR was demonstrated to be an effective means to biologically treat perchlorate to a concentration less than the California MCL. Based on the success of the demonstration project, the team headed by Envirogen and WVWD collaborated to design, install, start-up, and operate a full-scale FBR system capable of treating 2,000 gallons per minute (gpm) for the treatment of nitrate- and perchlorate-laden groundwater. Downstream equipment would include dual media filtration, re-aeration, and chlorine disinfection for delivery to the potable supply. The system was built and installed by 2013, and commissioned in 2016, representing the first full-scale permitted drinking water system in the world using this specific FBR technology for these contaminants.
The FBR is a fixed-film reactor in which the biological media, specified granular activated carbon (GAC), is suspended or fluidized within the reactor vessel by the upward flow of water through the system. Because the GAC particles are small and suspended, they present a large surface area for microbial growth and attachment. A precise amount of electron donor was provided to the FBR where, under anoxic conditions, the attached microorganisms performed an oxidation/reduction reaction in consuming all of the dissolved oxygen (DO), nitrate, and perchlorate. The by-products of the process were nitrogen gas, chloride ion, carbon dioxide, heat generation, and additional biomass. This “living” media bed expands and fluidizes further such that longer media bed hydraulic residence times (HRT) can be achieved for effective and complete contaminant removal. The FBR technology completely destroyed the perchlorate, ensuring that it will no longer be an environmental hazard for future generations.
The plant effluent water is required at all times to meet the requirements per California Code Regulations Title 22, Division 4, Chapters 15 and 17 for drinking water, including meeting the current maximum contaminant levels (MCLs) in the state of California of 6.0 micrograms (μg)/liter (L) for perchlorate and 10 milligrams (mg)/L for nitrate-N. These treatment goals applied to all phases of operation after initial start-up and were the completion criteria for the project.
Throughout acclimation and steady-state operations, the full-scale FBRs have proven to be reliable, resilient, and effective in eliminating nitrate and perchlorate from the feed groundwater. The downstream equipment, utilized to remove solids and disinfect the FBR effluent so that it was suitable as potable water, was successful in meeting all drinking water regulatory requirements.
The FBR was naturally inoculated with only the incoming contaminated groundwater. No outside inoculum was provided to the FBR system. Originally, after operating the system in FBR recycle mode and then plant recycle mode, the effluent of the system was discharged through a temporary ion exchange system to a natural basin until the biomass growth occurred and full treatment was demonstrated. Microbial attachment and perchlorate treatment occurred by Day 33, but due to a number of mechanical and process adjustments to both FBRs and downstream equipment, it took until Day 99 for the FBRs to completely acclimate so that discharge could be sent directly to the basin without ion exchange treatment. The FBRs were fully capable of complete elimination of perchlorate from this time forward.
Over the first 250 days of operation, perchlorate and nitrate-nitrogen concentrations ranged from approximately 450 μg/L to 150 μg/L and 5 mg/L to 3.5 mg/L, respectively. Once basin discharge began, there was not a single occurrence of discharge of effluent exceeding any of the California MCLs. The plant was permitted in May 2016, and began full operation providing water to consumers in October 2016.
Both capital and operating data are provided in this report, demonstrating that the FBR technology is predominantly more cost-effective when increasing oxyanion concentrations occur.
A comparison to ion exchange technology is provided, which demonstrates a potential five-year payback is possible as the perchlorate concentrations increase.
Implementation issues of the FBR technology are provided in the Cost & Performance Report, with detailed assessments of numerous lessons learned during the design, fabrication, construction, installation, and operation of the facility. Ultimately, the development of this Groundwater Treatment Plant was a shared responsibility of numerous governmental agencies and private companies, making it possible to treat a significantly impaired resource to produce potable water for the better of the community.