Selection of sulfur oxidizing bacterium for sulfide removal in sulfate rich wastewater to enhance biogas production
Sulfur oxidizing bacteria (SOB) were isolated and tested in order to remove sulfide from high sulfate wastewater to reduce the amount of hydrogen sulfide (H2S) in the produced biogas. A promising SOB isolate, designated as isolate T307, was selected due to its best sulfide removal (86.7%) in the effluent of a sulfate reduction reactor (SRR) over a 24 hrs incubation. The bacterium was able to grow better as a mixotroph (yeast extract as a carbon source) than as a chemolithoautotroph. In addition, as a heterotroph, the bacterium grew well with yeast extract and peptone. Based on partial 16S rRNA gene sequence, the isolated T307 was an Alcaligenes sp. and was able to convert most of sulfide species (total sulfide: TS; dissolved sulfide: DS and H2S) into elemental sulfur or sulfate over a 20 hrs period of cultivation by controlling the speed of shaking. In a biogas reactor set, after pre-treating a sulfide medium with Alcaligenes sp. T307 there was a much higher specific yield of CH4 (238 ml CH4 g-1COD removed) and more biogas (154 ml L-1 d-1) was produced with the biogas containing more methane (48.1% CH4, 51.5% CO2 and 0.41% H2S) in comparison to a control with a specific yield of CH4, (72 ml CH4 g-1COD removed) 86 ml L-1 d-1 biogas produced with a composition of 35.5% CH4, 63.7% CO2 and 0.86% H2S.