Effect of temperature phased biological hydrolysis treatment on solubilization of wasted activated sludge

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In this study, batch temperature-phased biological hydrolysis (TPBH) with conditions of biological hydrolysis (BH) at 42 °C for 1.5 days, followed by BH at 55 °C for 4.5 days were conducted to explore the solubilization behavior of wasted activated sludge (WAS) with the actions of endogenous enzymes produced by bacteria affiliated with WAS microbial community. The TPBH treatment resulted in 36.6% reduction in volatile suspended solids (VSS) with 91% of that achieved in the first three days of the treatment. Over the 6 days of TPBH treatment, the soluble chemical oxygen demand (SCOD), volatile fatty acids (VFA), and soluble microbial products (SMP) increased from 60 to 2665.0 mg/L, below 50 to 1309.0 mg/L, and 52.3 to 1042.6 mg/L, respectively, with 77.5% of SCOD, 74.9% of VFA, and 83.3% of SMP produced within 3 days of TPBH treatment. The experimental results and principal component analysis revealed that hydrolysis of extracellular proteins made a major contribution to the SCOD and VFA production. The Illumina sequencing analysis demonstrated that aerobic, facultative, and anaerobic organisms were co-existed in the WAS and BH treatment sludge, indicating that no drastic shift in the dominant bacteria groups occurred over the BH treatment period. Based on the results obtained in this study, we proposed a conceptual model for WAS BH treatment, which emphasizes the BH of WAS is a process to transform WAS biomass from the aerobic sludge microbial community to the anaerobic sludge community under the actions of endogenous enzymes produced by fermenting bacteria.