Enhanced MPBR with polyvinylpyrrolidone-graphene oxide/PVDF hollow fiber membrane for efficient ammonia nitrogen wastewater treatment and high-density Chlorella cultivation

Abstract Membrane fouling always as the main obstacle hinders wide application of membrane bioreactor (MBR). Development of antifouling membranes is a promising strategy to overcome this issue. In this study, novel polyvinylpyrrolidone (PVP)-graphene oxide (GO)/PVDF hollow fiber membrane with enhanced hydrophilicity and antifouling property was synthesized by assembling PVP-GO nanocomposites via chemical grafting method. The PVP-GO/PVDF membrane was successfully applied into algae-membrane photo-bioreactor (MPBR) with solids retention times (SRTs) of 30 d for high ammonia-nitrogen wastewater treatment at hydraulic retention times (HRTs) of 24 h. The permeability, removal performance and influence on extracellular polymeric substance (EPS) of algae-MPBR with modified PVDF membrane were compared to a control traditional system operated in parallel. Compared with pristine PVDF membrane, PVP-GO/PVDF membrane exhibited improved hydrophilicity (contact angle decreased from 97 to 62°), better permeability (1.7 times) and attractive flux recover rate (96 %) in MPBR filtration, which was attributed to uniformly dispersed PVP-GO nanocomposites as spatial brushes for mitigating foulants on membrane surface. In terms of contaminants degradation, COD, NH4-N+ and NO3-N removal efficiency of algae-MPBR with modified membranes were kept above 97.8, 93.1 and 68.7 %, much higher than traditional MBR. Moreover, remarkable reduction in hydrophobic proteins amount of EPS on fouling layer was observed for PVP-GO/PVDF membrane. The biomass concentration was maintained around 780 mg/L after 16 days and average biomass production rate reached as high as 45 mg/L·d. These results indicated that PVP-GO/PVDF membrane exhibited superior antifouling performance for high-density microbes harvesting and efficient treatment for high ammonia-nitrogen wastewater.