Variation of dissolved organic matter during excess sludge reduction in microbubble ozonation system

Sewage sludge is the major by-product of wastewater treatment plants, and about 30% readily biodegradable organic matters might be reused through the mass reduction process, which could be also reduced the disposal fee. In this study, the microbubble ozonation (MB-O₃) was employed to improve the oxidation efficiency for sludge solubilization. At 160 mgO₃/gSS, the maximum mixed liquor suspended solids (MLSS) reduction ratio was 37.5% and the protein and polysaccharide contents increased to 31.6 and 138.6 mg/L, respectively. It was proposed that aromatic protein and soluble microbial in sludge were oxidized preferentially by MB-O₃, and the dissolved organic matter (DOM) fractions (mainly humic-acid-like substances) exhibited low degradability according to the variations of fluorescence excitation-emission spectrum coupled with fluorescence regional integration. MB-O₃ could enhance the settleability, but deteriorate sludge dewaterability at low dosage (< 160 mgO₃/gSS) due to a reduction in particle size from 61.7 to 47.5 μm. MB-O₃ has a good performance on the mass reduction of sludge through the improvement of the radical generated.