Resilient biological hexavalent chromium removal with a two‐stage, fixed‐bed biotreatment system

In: AWWA water science, Volume 1, Issue 4

Abstract

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.