The removal of H2S from process air by diffusion into activated sludge

Emissions of H2S from publicly owned treatment works is a serious problem, therefore collection and treatment of these emissions is essential. In this work, the performance of a bench scale activated sludge system used for the removal of H2S from foul air was investigated, and the effects of H2S concentration (5 to 50 ppm,) on COD reduction and biomass settleability were studied. After biomass acclimation, the reactor was operated in a continuous mode at a hydraulic retention time of 5 h and a mean cell residence time of 6 days. Results showed that COD and H2S removal were 93.5 and 94.5%, respectively. Furthermore, H2S concentration up to 50 ppm, did not significantly affect the COD reduction. H2S loading rates of up to 7.5 mg(H2S) g(-1)MLSS, d(-1) were treated with greater than 94% efficiency. The only adverse effect of H2S that was observed was an increase in the sludge volume index at loading rates over 4.5 mg(H2S) g(-1)MLSS d(-1), at which bulking of the sludge occurred. Overall, the results indicate that H2S at concentrations usually emitted from wastewater treatment processes (lower than 50 ppm(v)), can be efficiently treated by diffusion into activated sludge without compromising the performance of the activated sludge process.