Effect of Arsenic (III) on the Denitrification Process
A sequencing batch reactor (SBR) was operated to develop denitrifying bacteria that had a mean specific denitrification rate of 0.11 g NO₃⁻-N/gVSS/day. Another system (an anaerobic digester) was operated to generate volatile fatty acids (VFAs) with the effluent concentration being measured to be 5655 ± 876 mg/L as acetic acid. Using the denitrifying biomass developed in the SBR and VFAs generated in the digester as an external carbon source, a series of denitrification batch tests were conducted. The denitrification batch reactors were spiked with NO₃⁻- N (to get a C:N ratio of 3.0) and different arsenite concentrations to quantify the effect of arsenite on the denitrification rate. A steady deterioration in the ability of the biomass to denitrify under increasing arsenite concentrations was observed, with the mean specific denitrification rate dropping from 0.183 g NO₃⁻-N/gVSS/day at an arsenite concentration of 5 mg/L, to 0.047 g NO₃⁻-N/gVSS/day at a concentration of 25 mg/L.