The responses of activated sludge to membrane cleaning reagent H2O2 and protection of extracellular polymeric substances

Abstract

Hydrogen peroxide (H₂O₂) is evaluated as a potential replacement for chlorine to control biofouling in membrane bioreactors (MBRs). However, H₂O₂ might diffuse into the mixed liquor and damage microorganisms during membrane cleaning. This study comprehensively analyzed the impacts of H₂O₂ on microbes. Key enzymes involved in phenol biodegradation were inhibited with H₂O₂ concentration increased, and thus phenol degradation efficiency was decreased. Increase of lactic dehydrogenase (LDH) and intracellular reactive oxygen species (ROS) indicated more severe cell rupture with H₂O₂ concentration increased. At the same H₂O₂ concentration, Extracellular polymeric substances (EPS) extraction further led to inhibiting the activity of key enzymes, decreasing phenol degradation efficiency, and enhancing LDH release and ROS production, demonstrating that the existence of EPS moderated the adverse impacts on microbes. Spectroscopic characterization revealed the increase of H₂O₂ decreased tryptophan protein-like substances, protein-associated bonds and polysaccharide-associated bonds. Hydroxyl and amide groups in EPS were attacked, which might lead to the consumption of H₂O₂, indicated EPS protect the microorganism through sacrificial reaction with H₂O₂.

Keywords: Extracellular polymeric substances; Hydrogen peroxide; Membrane bioreactor; Metabolism behaviors; Phenol wastewater.