Discrimination of chemical and biological sulfide oxidation in a hybrid two-phase process

Hydrogen sulfide having the detrimental effect on humans and ecosystems can be metabolized by sulfur-oxidizing bacteria (SOB) as an energy source, however, SOB cannot tolerate high sulfide levels. A hybrid two-phase process was therefore proposed in this work to enhance the high-level sulfide oxidation based on discrimination of abiotic versus biotic oxidation. Separate experiments were performed to investigate the chemical and biological oxidations of sulfide at 500-2000 mg l(-1). Products distribution showed that thiosulfate and intermediate products were the major products (more than 88%) of chemical oxidation, while sulfate was the predominant product in the biological oxidation. Nonetheless, sulfate formation declined from 90.5 to 35.5% with increasing sulfide level due to sulfide toxicity. To enhance oxidation, the effect of pH and adaptation methods were investigated, where insignificant changes were observed. The hybrid process resulted in complete sulfide transformation in the abiotic phase into less toxic products, which were further oxidized in biotic phase. This enhanced sulfate formation by 41% (55) at 1000 mg l(-1) (2000) sulfide compared to the conventional biological case. The superiority of this hybrid two-phase process especially at higher sulfide levels was shown to be mainly due to complete sulfide detoxification.