Advanced treatment for actual hydrolyzed polyacrylamide-containing wastewater in a biofilm/activated sludge membrane bioreactor system: Biodegradation and interception

Abstract

This study deeply investigated the overall performance, nitrogen transformation, membrane fouling and cleaning, extracelluar polymeric substances (EPS) and microbial function in a biofilm/activated sludge membrane bioreactor (BF-AS-MBR) for treating actual hydrolyzed polyacrylamide (HPAM)-containing oilfield wastewater. The removal efficiencies of HPAM, COD, viscosity, TOC and TN achieved 97.5%, 98.5%, 74.8%, 98.5% and 96.2%, respectively. Nitrogen transformation revealed nitratation became the main reaction in the process of aerobic amide group bioconversion and surpassed denitrification, nitritation and ammonification in BF-AS-MBR system. Scanning electron microscopy (SEM) showed the morphology of new, contaminated and washed membranes. The membrane permeability was recovered to 92% and 87% after the first and second cleaning, respectively. Tryptophan protein-like, aromatic protein-like, simple aromatic protein-like and fulvic acid-like organics presented in loosely bound EPS (LB-EPS) of sludge. Polysaccharide-like and tyrosine protein-like organics presented in tightly bound EPS (TB-EPS) of sludge. Tryptophan protein-like organics existed solely in TB-EPS of cake sludge, and played an essential role in membrane fouling. HPAM-degrading microorganisms and nitrifiers were deeply discussed to explore its correlations with HPAM removal, EPS and membrane fouling. The viscosities of HPAM solution re-prepared with different effluent were compared, and the order was: supernatant after biodegradation < effluent after membrane filtration ≈ clean water. This study offered a technical support and theoretical foundation for treating actual HPAM-containing oilfield wastewater, and improved water reuse.