Perchlorate is a widespread groundwater contaminant in California, and conventional treatment options that produce high-strength brines are becoming exceedingly expensive, especially in inland areas with limited options for disposal. The objective of this project was to evaluate the efficacy of a two-stage fixed-bed biological treatment (FXB) system to treat perchlorate-impacted groundwater in Rialto, California and produce water that meets all drinking water standards.
The FXB system process is a cost-effective and sustainable alternative for removing perchlorate from groundwater as it does not produce a concentrated waste stream and, therefore, waste disposal costs tend to be lower than other treatment options. Backed by almost 20 years of bench- and pilot-scale experience, a full-scale FXB biological treatment facility was designed, constructed, and tested to address systemic perchlorate contamination of groundwater utilized by the West Valley Water District. Specific objectives were to demonstrate the system’s treatment efficiency, ease of operation, and suitability for use by the West Valley Water District and other communities that rely on perchlorate-impacted groundwater.
After design and construction, the FXB system was started up in November 2017. Rapid perchlorate and nitrate removal were observed within four weeks of operation during biological acclimation. During a ten week period from February to April, perchlorate in the biofilter effluent was 1.4 ± 3.2 μg/L. Turbidity in the biofilter effluent remained at 0.07 ± 0.1 Nephelometric Turbidity Units (NTU) with 96.8 percent of samples below the 0.3 NTU threshold. Furthermore, complete and consistent removal of 1.85 μg/L trichloroethene (TCE) was observed. Treatment performance and rapid recovery after shutdowns or challenge events confirmed the flexibility and robustness of the system.
Challenge testing confirmed the system resiliency to short- and long-term system shutdowns, chlorinated backwash, and a phosphoric acid feed failure. As expected, an acetic acid feed failure resulted in contaminant breakthrough; however, a rapid recovery was observed illustrating the robustness of the system. Most importantly, there was a significant lag phase between contaminant breakthrough from the bioreactor and the biofilter, allowing for preventative measures to be taken in case of an emergency. Finally, the biofilter provided a buffering capacity that dampened the magnitude of contaminant breakthrough.
The full-scale FXB system successfully removed perchlorate and produced water that met all performance goals and water quality objectives. Several key findings and lessons were learned from this project, including the optimal chemical dose, backwash frequency, and plant hydraulics to be incorporated in future designs and operations.