Live Steam-Pretreatment and Anaerobic Digestion of Waste Activated Sludge

Abstract

Steam pretreatments mixing waste activated sludge (WAS) with live steam were applied to decompose WAS, and to enhance its anaerobic digestion performance. Results showed that the optimum pretreatment condition was 120°C for 10 min. Chemical oxygen demand (COD) of the pretreated group was improved to 14,000 mg/L, 18 times higher compared with the control group. The concentration of extracellular polymeric substances and soluble protein increased to 1866 mg/L and 1495 mg/L, respectively. Soluble COD increased exponentially with increasing specific energy; only a specific energy input of 271 kJ/kgTS was required. Analysis indicated that the particle size of sludge was reduced and the distribution was more uniform after the pretreatment. Results from the subsequent batch anaerobic digestion indicated that higher stability of the system and biogas production were obtained in the pretreated group. Compared with raw sludge, biogas production of pretreated sludge was improved by 122%, corresponding to 600 mL/g of volatile solids. The present study mostly assesses the live steam pretreatment of WAS and compares obtained results with previously examined thermal, chemical, or ultrasound pretreatments. Results demonstrate that live steam pretreatment significantly enhances the biogas production while requiring limited energy input only.