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The Impact of Temperature on Anaerobic Biological Perchlorate Removal and Aerobic Polishing of the Effluent
Citation:
DUGAN, N., D. WILLIAMS, M. Meyer, R. Schneider, T. F. SPETH, K. KELTY, AND D. Metz. The Impact of Temperature on Anaerobic Biological Perchlorate Removal and Aerobic Polishing of the Effluent. Presented at AWWA Annual Conference and Exposition, Washington, DC, June 12 - 16, 2011.
Impact/Purpose:
To inform the public.
Description:
This abstract describes a pilot-scale evaluation of anaerobic biological perchlorate (C1O4) removal followed by aerobic effluent polishing. The anaerobic biological contactor operated for 3.5 years. During that period, two effluent polishing evaluations, lasting 311 and 340 days, respectively, were conducted. Surface water C1O4 detections in the United States, Japan, and Korea led to the choice of a surface water with widely varying temperatures as the source water for this project. Temperatures over the course of this study ranged from 1.5 to 30 °C (35 to 86 °F). Such temperature variations can affect the efficiency of biological, chemical, and physical treatment processes. The goal of the study was to establish a consistent set of operating conditions and then observe treatment performance as temperatures changed. The anaerobic portion of the pilot-scale treatment system consisted of a fixed-bed, downflow biological contactor filled with anthracite support media. Acetate was used as a carbon source and electron donor. The aerobic portion of the treatment system consisted of hydrogen peroxide (H2O2) addition, aeration, a dual-media (anthracite/sand) biological filter pretreated with 5 mg/L alum, and an ultra-filtration (UF) membrane. In the anaerobic contactor, 10 °C (50 °F) was a critical temperature for biologically mediated processes. At T > 10 °C, average influent concentrations of 52 µg/L C1O4 and 0.80 mg/L nitrate, a competing electron acceptor, were lowered to below method detection limits of 2µg/L and 0.02 mg/L, respectively. At T > 10 °C, effluent dissolved oxygen concentrations were consistently below 0. 1 mg/L; and influent sulfate was reduced to sulfide, generating average effluent sulfide concentrations of 3.3 mg/L. At T ≤ 10 °C, production of sulfide, and removals of C1O4 and nitrate were negligible; and effluent dissolved oxygen concentrations rose to an average of 2.5 mg/L. Effluent acetate concentrations were variable, ranging from below the 1 µg/L detection limit at T ≤ 20 °C (68 °F) to 9.7 mg/L at T ≤ 10 °C. In the aerobic polishing system, at all temperatures, dissolved oxygen concentrations were consistently restored to saturation levels in the aeration tank, sulfide was removed by conversion to sulfate, and acetate was consumed in the biological filter. Particle control in the biological filter, as measured by turbidity, was most effective in warmer weather, with average turbidities consistently below 0.3 NTU at T ≤ 20 °C. UF membrane particle control was not affected by temperature, with effluent turbidities averaging 0.059 NTU. Stopping H2O2 application was associated with rapid rates of head loss development, peaking at 79 cm/hr (31 in/hr), compared to an average of 7.1 cm/hr (2.8 in/hr) when H2O2 was fed . Chlorination of filter and UF membrane influents and effluents yielded TTHM and HAA5 concentrations consistently below the respective Stage 2 D/DBP standards of 80 and 60 µg/L.