This study investigated the effects of residual H2O2 on hydrolysis-acidification and methanogenesis stages of anaerobic digestion after microwave-H2O2 (MW-H2O2) pretreatment of waste activated sludge (WAS). Results showed that high sludge solubilization at 35-45 % was achieved after pretreatment, while large amounts of residual H2O2 remained and refractory compounds were thus generated with high dosage of H2O2 (0.6 g H2O2/g total solids (TS), 1.0 g H2O2/g TS) pretreatment. The residual H2O2 not only inhibited hydrolysis-acidification stage mildly, such as hydrolase activity, but also had acute toxic effect on methanogens, resulting in long lag phase, low methane yield rate, and no increase of cumulative methane production during the 30-day BMP tests. When the low dosage of H2O2 at 0.2 g H2O2/g TS was used in MW-H2O2 pretreatment, sludge anaerobic digestion was significantly enhanced. The cumulative methane production increased by 29.02 %, but still with a lag phase of 1.0 day. With removing the residual H2O2 by catalase, the initial lag phase of hydrolysis-acidification stage decreased from 1.0 to 0.5 day.
Keywords: Anaerobic digestion; Enzyme activity; Hydrogen peroxide; Inhibition; Microwave; Sludge.