Suchergebnisse

AbstractHexavalent chromium (Cr(VI)) can be biologically reduced to nontoxic and easily separable trivalent chromium (Cr(III)) without generating concentrated wastes. Using a 6–25 gpm pilot‐scale two‐stage, fixed‐bed (FXB), biologically active carbon (BAC) treatment system, approximately 75 μg/L Cr(VI) was consistently removed to less than 7 μg/L with a 10‐min empty‐bed contact time. Potential Cr(VI)‐reducing bacteria, including members from the Dechloromonas and Acinetobacter genera, were present in the system. The system was resilient, and 91% Cr removal was observed when the system was challenged with a 24‐h phosphoric acid feed shutdown, a 3‐day system shutdown, spiking Cr(VI) to 100 μg/L, or operating intermittently with regular shutdown periods of hours to days. The system recovered within 6 h after a 26‐h acetic acid feed shutdown. Readily settling backwash wastewater was generated with characteristics similar to municipal wastewater. Overall, the results indicated that a two‐stage, FXB BAC system can provide an effective and robust option for Cr(VI) removal.

AbstractNitrate and arsenic often co‐exist in groundwater sources. Reverse osmosis, electrodialysis, and ion exchange are the commonly implemented technologies for nitrate removal. Compared to these technologies that generate high‐strength waste streams, biological treatment converts nitrate to innocuous nitrogen gas without producing a concentrated waste. When nitrate and arsenic co‐exist in a water source, combining a biotic process for nitrate removal with an abiotic process (i.e., chemical–physical process such as coagulation/flocculation) for arsenic removal may provide an effective approach for simultaneous removal of these contaminants. A 12‐month pilot study was conducted with a two‐stage, fixed‐bed biotreatment system, originally developed for nitrate removal, for simultaneous removal of nitrate and arsenic. With an empty bed contact time as low as 10 min in the bioreactor, nitrate was consistently lowered from ~35 mg/L N to <0.1 mg/L N (treatment target was <1 mg/L N), whereas arsenic was effectively lowered from ~14 μg/L to <5 μg/L. Overall, the results demonstrated efficient and resilient simultaneous removal of nitrate and arsenic using a two‐stage biotic‐abiotic treatment system.