Effect of ozone pretreatment on characteristics of dissolved organic matter formed in aerobic and anaerobic digestion of waste-activated sludge

The characteristics of dissolved organic matter (DOM) formed in aerobic and anaerobic digestion of waste-activated sludge (WAS) after ozone pretreatment were investigated with three ozone dosages (4.72, 10.96, and 13.8 mg O3/min) and four ozonation times (0, 10, 20, and 30 min) using six aerobic and six anaerobic digestion reactors. High decreasing rate of volatile suspended solid/total suspended solid indicated enhanced destruction of volatile solids and efficient sludge reduction. The results of TOC and UV absorbance indicated that increasing ozone dosage and time significantly enhanced hydrolysis and degradation of DOM. Data analysis with a first-order sequential reaction model revealed that, for aerobic digestion, kh increased in the range of 0.00049–0.00154 day−1; and for anaerobic digestion of WAS, kh increased in the range of 0.00302–0.00796 day−1 and kd increased in the range of 0.24910–0.54548 day−1. Detailed analysis of the composition of DOM showed that ozone pretreatment increased irreversible membrane resistance (IMR) and enhanced the breakdown of large DOM molecules, the formation of aromatic proteins, and tryptophan- and tyrosine-aromatic amino acids, as well as the accumulation of humic acid– and fulvic acid–like substances.