Metabolic divergence in simultaneous biological removal of nitrate and sulfide for elemental sulfur production under temperature stress

The simultaneous removal of NO3 and HS at temperature stress (25-10 degrees C) is evaluated here. An expanded granular sludge bed (EGSB) reactor was run over 120 days at N/S molar ratio of 0.35 (for S-0 production) under constant sulfur loading rate of 0.4 kg S/m(3) d. The simultaneous removal of NO3 and HS , was achieved at applied conditions. Average HS -S removal varied from 98 (25 degrees C) to 89.2% at 10 degrees C, with almost complete NO3 removal. Average S-0 yield ranged from 83.7 at 25 degrees C to 67% at 10 degrees C. The temperature drop caused a decrease in granular sludge accumulated S0 fraction by nearly 2.5 times. Decreased temperature caused metabolic pathway change observed as higher SO42 production, apparently allowing the biomass to obtain more energy per HS consumed. It is hypothesized that the metabolic shift is a natural response to compensate for temperature-induced changes in energy requirements. (C) 2017 Elsevier Ltd. All rights reserved.