Effect of sodium tungstate on anaerobic digestion of waste sewage sludge: Enhanced methane production via increased acetoclastic methanogens

In this study, the effect of sodium tungstate on anaerobic digestion of waste sewage sludge (WSS) was investigated. Methane production was enhanced by sodium tungstate in a dose-dependent manner. Sodium tungstate did not affect the hydrolysis stage as the same level of protease activity was detected in the WSS sample with or without sodium tungstate. At the acidogenesis stage, the concentration of acetate decreased during the anaerobic digestion of WSS supplemented with sodium tungstate whereas that of isobutyrate increased. The pH of WSS increased in the presence of sodium tungstate, correlating with the result of acetate consumption with time during the anaerobic digestion of WSS. The analyses of methanogenesis via acetoclastic and hydrogenotrophic methanogens indicate that methane production from acetate was high in the WSS with sodium tungstate. In addition, the addition of sodium tungstate to the initial fresh WSS did not enhance methane production from acetate; therefore, sodium tungstate may increase the number of acetoclastic methanogens rather than promote the catalytic reaction related to the methane production. The analyses of archaeal population supported that acetoclastic methanogens (mostly Methanosaeta) increased with time in the WSS with sodium tungstate. In detail, when compared to the control WSS, the percentage of Methanosaeta significantly increased from 3.02% to 31.20% in the presence of sodium tungstate. Furthermore, the addition of sodium tungstate enhanced the growth of Methanosarcina acetivorans C2A. Taken together, sodium tungstate increases methane production via the anaerobic digestion of WSS by increasing the activity of acetoclastic methanogenesis.