Weakened adhesion force between extracellular polymeric substances of waste activated sludge caused by rhamnolipid leading to more efficient carbon release.

Rhamnolipid (RL), a biosurfactant produced by bacteria, is investigated to alter the physical characteristics of extracellular polymeric substance (EPS) of waste-activated sludge (WAS), and subsequently promotes hydrolysis and acidogenesis during anaerobic digestion for short chain fatty acids (SCFAs) production. The results revealed that RL could decrease the adhesion force of EPS from 13.46 nN to 1.08 nN, resulting in EPS disintegration layer by layer, decreasing the median particle size by 31.57 μm and releasing abundant soluble organic matter. The cell number of living bacteria remained stable after RL pretreatment (2.59 × 10 vs. 2.66 × 10), indicating that RL has a minimal impact on microbial cells (only ~2% bacterial lysis was observed). The kinetic studies of ammonia nitrogen release and SCFA production suggested that, in the RL-pretreated WAS, the reaction rate constants for hydrolysis and acidogenesis were respectively 2-fold and 1.5-fold higher than those of the control group.