Treatment of a submerged anaerobic membrane bioreactor (SAnMBR) effluent by an activated sludge system: the role of sulphide and thiosulphate in the process.

This work studies the use of a well-known and spread activated sludge system (UCT configuration) to treat the effluent of a submerged anaerobic membrane bioreactor (SAnMBR) treating domestic wastewater. Ammonia, phosphate, dissolved methane and sulphide concentrations in the SAnMBR effluent were around 55 mg NH4-N L(-1), 7 mg PO4-P L(-1), 30 mg non-methane biodegradable COD L(-1), and 105 mg S(2-) L(-1) respectively. The results showed a nitrification inhibition caused by the presence of sulphur compounds at any of the solids retention time (SRT) studied (15, 20 and 25 days). This inhibition could be overcome increasing the hydraulic retention time (HRT) from 13 to 26 h. Among the sulphur compounds, sulphide was identified as the substance which caused the nitrification inhibition. When the nitrification was well established, removal rates of nitrogen and phosphorus of 56% and 45% were reached respectively. The sulphide present in the influent was completely oxidised to sulphate, contributing this oxidation to the denitrification process. Moreover, the presence of methanotrophic bacteria, detected by FISH technique, could also contribute to the denitrification.