Enhancing the decomposition and volatile fatty acids production of excess sludge: Synergistic pretreatment by endogenous lysozyme and rhamnolipid

Abstract

This study investigated a green and efficient pretreatment strategy for enhancing excess sludge (ES) decomposition using combined pretreatment with endogenous lysozyme (EL) and biosurfactant rhamnolipid (RL). The employed lysozyme was produced by the strains isolated from the ES. The ES hydrolysis performance was strengthened in EL + RL system as the RL dosage increased from 0 to 0.5 g/gSS, and the optimized synergistic effect was achieved at 0.3 g/gSS RL dosage. The additional released SCOD, protein and polysaccharide in EL + RL pretreatment system over those of sole RL pretreatment system reached around 2796.1, 1174.4 and 277.7 mg/L at 8 h, respectively. Moreover, the bacteria and archaea decomposition degree reached around 80.3% and 93.4%. Both sole EL pretreatment and EL + RL pretreatment were conducive to the production of volatile fatty acids (VFAs), with the highest VFAs concentrations reaching 2.5 and 3.0 fold of control, respectively. Although sole EL pretreatment was more appropriate for the survival of volatile fatty acids (VFAs) producing bacteria, the EL + RL pretreatment gained more VFAs generation. Tepidiphilus with a relative abundance of 59.8%-76.7%, replaced Dechloromonas and became the predominant bacteria.