Effects of N/S molar ratio on product formation in psychrophilic autotrophic biological removal of sulfide

Abstract

The excessive H2S presence in water and wastewater can lead to corrosion, toxicity, and biological processes inhibition-i.e., anaerobic digestion. Production of H2S can occur in psychrophilic conditions. Biological removal of HS- by addition of NO3- as an electron acceptor under psychrophilic (10 °C) conditions in a continuous flow experiment is evaluated here. Four different N/S molar ratios-0.35, 0.40, 0.60, and 1.30-were tested in an expanded granular sludge bed (EGSB) reactor. Samples were analyzed daily by ion chromatography. Efficient psychrophilic HS- removal with sulfur products oxidation control by NO3- supply is documented. The highest HS- removal was obtained at N/S = 0.35 and 1.30 (89.1 ± 2.2 and 89.6 ± 2.9%). Removal of HS- was less at mid-N/S with the lowest value (76.9 ± 2.6%) at N/S = 0.60. NO3- removal remained high for all N/S ratios. N/S molar ratio influenced the sulfur products distribution with less S0 and increase in SO42- effluent concentration with increasing N/S ratio. Oxidation of HS- and accumulated S0 occurred simultaneously at N/S ratios > 0.35. The observations are explained by culture flexibility in utilizing available resources for energy gain.