Effect of different concentrations of sodium selenite on anaerobic digestion of waste sewage sludge

Abstract

The effect of sodium selenite on anaerobic digestion of waste sewage sludge (WSS) was studied. Interestingly, methane production was enhanced at 2 mg/L and inhibited at 100 mg/L of sodium selenite during the anaerobic digestion of WSS. Hydrolytic activity increased in correlation with increased concentrations of sodium selenite (0 to 100 mg/L). At the acidogenesis stage, acetic acid accumulated at the concentrations more than 25 mg/L of sodium selenite whereas it was consumed for 10 days at the concentration of 2 mg/L of sodium selenite. Also, the concentration of propionic acid decreased and that of butyric acid increased at 100 mg/L of sodium selenite. Although methanogenic activities were totally inhibited at 100 mg/L of sodium selenite, a high hydrogenotrophic methanogenic activity was observed at 2 mg/L of sodium selenite. The abundance of hydrogenotrophic methanogens (Methanospirillum and Methanocorpusculum) increased in the WSS at 2 mg/L of sodium selenite. Moreover, the results of pure-culture experiments using Methanosarcina acetivorans C2A show that the growth promotion or inhibition was observed at 2 mg/L or at 100 mg/L of sodium selenite. In conclusion, sodium selenite has the double-sided effect during the anaerobic digestion of WSS as shown by the results that methane production was promoted at a low concentration and inhibited at a high concentration.