Treatment of chromate-polluted groundwater in a 200 dm3 pilot bioreactor fed with hydrogen
Abstract
Chromate is a highly soluble, toxic and carcinogenic oxyanion commonly found in groundwaters and soils. A 200 dm3 pilot bioreactor was designed to treat typical Cr(VI)-polluted groundwater. A fixed bed column was filled with pozzolana, inoculated with a bacterial population containing the sulfate-reducing organism Desulfomicrobium norvegicum and fed with an H2 + CO2 gas mixture. The pilot was operated under continuous feed conditions for 3 months, first with a synthetic solution and then with real polluted groundwater containing 15 mg dm−3 Cr(VI). The residence time was decreased to 7 h, while the Cr(VI) concentration in the outflow remained lower than 0.2 mg dm−3. The bacterial population did not need any organic carbon supply thanks to acetogenesis. The highest Cr(VI) reduction rate was 2.2 mg dm−3 h−1. The CO2 flow rate was regulated in order to maintain the pH in the interval 7.5–8.5. The CO2 consumption rate increased with feed flow rate and sulfate reduction activity. The process worked satisfactorily between 10 and 35 °C