The sensitivity of fixed-bed biological perchlorate removal to changes in operating conditions and water quality characteristics

Flow rate, electron donor addition, and biomass control were evaluated in order to optimize perchlorate (ClO4-) removal from drinking water using biologically active carbon (BAC) filtration. Influent dissolved oxygen (DO) was lowered from ambient conditions to approximately 2.5 mg/L for all experiments using a nitrogen sparge. When influent nitrate concentration was 0–2.0 mg/L, 1.6–2.8 mg/L as carbon of acetate or ethanol was required to achieve and sustain the complete removal of 50 (mu)g/L was observed and, once electron donor was reapplied, 9 days were required to reestablish complete perchlorate removal. During a 24-h electron donor feed failure simulation, the maximum effluent perchlorate concentration detected was 6.7 (mu)g/L perchlorate to below detection. Although biomass growth diminished the filterʹs ability to consistently remove perchlorate, a cleaning procedure immediately restored stable, complete perchlorate removal. This cleaning procedure was required approximately every 50 days (4800 bed volumes) when influent DO concentration was 2.5 mg/L. Empty-bed contact time (EBCT) experiments showed that 80% perchlorate removal was achieved using a 5-min EBCT, and complete perchlorate removal was observed for an EBCT of 9 min. It was also demonstrated that BAC filtration consistently removed perchlorate to below detection for influent perchlorate concentrations ranging from 10 to 300 (mu)g/L, influent sulfate concentrations between 0 and 220 mg/L, influent pH values of 6.5–9.0, and operating temperatures of 5–22°C.