The Effect of Pretreatment of Residual Sludge with Thermal-Alkaline Combined with Hydrolysis Process

Thermal-alkaline combined with hydrolysis process (TAHP) pretreating residual sludge can rapidly achieve sludge disintegration, release organic matter from residual sludge, promote the conversion of substances in the hydrolysis process, and facilitate the recovery of carbon source from residual sludge. In this study, temperature, pH and reaction time, as the influence factors in sludge disintegration, were investigated to determine the appropriate thermal-alkaline pretreatment conditions. The concentrations of SCOD, volatile fatty acids (VFAs), nitrogen and phosphorus, protein and carbohydrates during TAHP under different hydraulic retention time (HRT=0~120h) were compared, and the conversion of substances in the hydrolysis process was analyzed. The experimental results showed that the higher pH (pH11), higher temperature and longer reaction time were beneficial to increasing the effect of sludge disruption. The appropriate conditions of thermal-alkaline pretreatment were as follows: temperature of sludge disintegration was 70C, initial pH was 11, and reaction time was 1 h respectively. Under this condition, the concentration of SCOD could exceed 11500 mg/L and the sludge lysis ratio was 44%. When HRT was 24 h in hydrolysis process, the concentration of VFAs and SCOD could exceed 2400 mg/L and 5800 mg/L respectively. TAHP reached equilibrium at about 120 h, protein and carbohydrates were stable at 130 mg/L and 190 mg/L respectively. And nitrogen and phosphorus were mainly present in the form of ammonia nitrogen and PO43-, with the corresponding proportions being 89% and 94% respectively. TAHP could accelerate the hydrolysis of sludge by accelerating the sludge disintegration and releasing intracellular organics, which will provide technical support and theoretical basis for the application of TAHP.