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

•Simultaneous biological nitrate and sulfide removal at 25-10 °C was documented.•Sulfide removal was from 98 (25 °C) to 89.2% (10 °C) with complete nitrate removal.•Elemental sulfur yield ranged from 83.7% at 25 °C to 67% at 10 °C.•Accumulation of elemental sulfur decreased with temperature.•Metabolic shift at lower temperature was indicated by increased sulfate production.

The simultaneous removal of NO3− and HS− at temperature stress (25-10 °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 S0 production) under constant sulfur loading rate of 0.4 kg S/m3 d. The simultaneous removal of NO3− and HS−, was achieved at applied conditions. Average HS−-S removal varied from 98 (25 °C) to 89.2% at 10 °C, with almost complete NO3− removal. Average S0 yield ranged from 83.7 at 25 °C to 67% at 10 °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.

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