A novel loosely structured nanofiltration membrane bioreactor for wastewater treatment: Process performance and membrane fouling

A novel nanofiltration membrane bioreactor (NF-MBR) was constructed by integrating a loosely structured nanofiltration hollow fiber membrane into an aerobic activated sludge system. In order to verify the feasibility of loose NF membrane bioreactor, parallel experiments of conventional ultrafiltration membrane bioreactor (UF-MBR) and NF-MBR were conducted to investigate process performances, membrane fouling characteristics. The loose NF membrane showed a relatively high permeability at a level of around 10 L m-2 h-1 bar-1 (flux of 2.0 L m-2 h-1) under low operation pressure (10–30 KPa). The results showed that NF-MBR achieved a higher removal efficiency of chemical oxygen demand (CODCr) and dissolved organic carbon (DOC) due to high rejection of loose NF membrane for biopolymers and part of the humic substances. During long term operation in NF-MBR, loose NF membrane displayed low salt rejection, resulting in no obvious salts accumulation in bioreactor in comparison with UF-MBR. The average rising rates in TMP for the NF-MBR was 0.16 KPa/day, which was twice lower than that of UF-MBR. The results of fouling mechanism showed that reversible cake fouling was dominant for both NF and UF membranes, while the relatively small pore size of the NF membrane mitigated irreversible pore blockage. Further biofouling layer analysis demonstrated that humic substances, polysaccharides and proteins were the main organic foulants. The results of energy consumption revealed that NF-MBR had comparable total energy consumption compared with UF-MBR. The outcomes of this study show the feasibility of loose NF membrane bioreactor to provide a great potential as an advanced process for wastewater treatment.