Design and evaluation of a pilot-scale electro-biochemical reactor

The removal of nitrate, arsenic, and selenium from mining influenced waters (MIW) to ultra-low levels remains difficult. The results achieved from the design and evaluation of a novel Electro-Biochemical Reactor represent a breakthrough in the removal of metals and inorganics, including nitrate, arsenic, and selenium, from mine water.;The Electro-Biochemical Reactor (EBR) can be employed in multiple configurations; its simplest form is a single pass, fixed-bed, up-flow bioreactor for the removal of metals, metalloids, and inorganics from water. The Electro-Biochemical Reactor relies on direct provision of electrons into the bioreactor to develop electron donor/acceptor environments for the transformation of contaminants. The application of an applied voltage (1-3 VDC) potential provides readily available electrons for enhancement of microbial donor/acceptor metabolic reactions and helps control the oxidation/reduction potential of the bioreactor environment.;Several configurations of the Electro-Biochemical Reactor (EBR) were tested at bench-scale (1 Liter/day) and pilot-scale (1-4 Liters/minute) using mine effluent waters from two different mine sites to remove nitrate, arsenic, and/or selenium to effluent target levels.;Results indicate selection and screening of different microbes and microbial support material (MSM) for site-specific waters affected contaminant removal performance; selection of the proper microbes and MSM resulted in significantly improved contaminant transformation kinetics. Side by side bench-scale tests of an EBR vs. CBR (conventional bioreactor) on mine water containing nitrate and arsenic were conducted. In these tests, EBR performance was 13% better than the conventional bioreactor, the CBR, removing arsenic from 350 ppb to a final concentration of 12 ppb versus a final concentration of 50 ppb for the CBR. Pilot-scale tests of the EBR system were conducted at a closed heap-leach Gold mine for nitrate and arsenic removal and at a Base Metal mine for selenium removal from site waters. Pilot-scale results from the gold mine waters indicate the EBR system was able to remove arsenic from 800 ppb to an average of 50 ppb and 20 ppm of nitrate to nondetectable levels in less than 10 hours. Further EBR pilot-scale tests were conducted at a Base Metal mine for selenium removal. The EBR system successfully removed selenium from an average of 2.73 ppm to less than 0.002 ppm in approximately 8 hours.;Additionally, the EBR system's ability to remove other metals and inorganics is shown in Table 22.