Simultaneous bioreduction of nitrate and chromate using sulfur-based mixotrophic denitrification process

Abstract

This study aims at evaluating simultaneous chromate and nitrate reduction using sulfur-based mixotrophic denitrification process in a column reactor packed with elemental sulfur and activated carbon. The reactor was supplemented with methanol at C/N ratio of 1.33 or 2. Almost complete denitrification was achieved at influent NO3−–N and Cr(VI) concentrations of 75mg/L and 10mg/L, respectively, and 3.7h HRT. Maximum denitrification rate was 0.5g NO3−–N/(L.d) when the bioreactor was fed with 75mg/L NO3−–N, 150mg/L methanol and 10mg/L Cr(VI). The share of autotrophic denitrification was between 12% and 50% depending on HRT, C/N ratio and Cr(VI) concentration. Effluent total chromium was below 50μg/L provided that influent Cr(VI) concentration was equal or below 5mg/L. DGGE results showed stable microbial community throughout the operation and the presence of sulfur oxidizing denitrifying bacteria (Thiobacillus denitrificans) and Cr(VI) reducing bacteria (Exiguobacterium spp.) in the column bed.