The hydrolysis and reduction of mixing primary sludge and secondary sludge with thermophilic bacteria pretreatment

Hydrolysis is widely used in sludge treatment as it enables to improve the biodegradability of sludge. However, there was little information about the hydrolysis efficiency with the mixture of primary and secondary sludge. In this study, the hydrolysis and reduction of mixed sludge after thermophilic bacteria (TB) pretreatment was investigated. Volume ratio of 1:3 (primary sludge: secondary sludge) had best release rate of organics, and the soluble chemical oxygen demand (SCOD), carbohydrate and protein in extracellular polymeric substances (EPS) decreased by 7.9, 4.1, 7.2 times, respectively. Meanwhile, the accumulation of SCOD, carbohydrate and protein in dissolved organic matter (DOM) was enhanced with mixed sludge. Excitation-emission matrix (EEM) spectroscopy proved that mixture of sludge was beneficial for the releasing of biodegradable substances. The sludge reduction of mixed sludge was higher than that of single sludge, and mixed sludge (1:3) had the best suspended solid (SS) and volatile suspended solids (VSS) reduction rate of 27.2% and 34.3%.