Impact of resuscitation promoting factor (Rpf) in membrane bioreactor treating high-saline phenolic wastewater: Performance robustness and Rpf-responsive bacterial populations

Enhancement of bacterial activity in membrane bioreactor (MBR) is crucial to overcome the low efficiency of biological process for treating phenolic wastewater with high salinity. It is predicted that resuscitation promoting factor (Rpf) from Micrococcus luteus may improve the degradative performance of bacterial populations. In this study, a control MBR (c-MBR) and a treatment MBR (t-MBR) with Rpf addition were operated for assessing the influences of Rpf. The potential bacterial populations in response to Rpf addition were investigated by both culture-dependent and culture-independent techniques. Results showed that Rpf significantly enhanced phenol removal under high salinity stress. In the MBR system, a higher efficiency for phenol removal in the effluent was observed in t-MBR compared to that in c-MBR (nearly zero versus 221-272 mg/L) under phenol concentration of 1800 mg/L and 30 g/L NaCl in the influent. Batch tests further demonstrated that, at the initial phenol concentration of 1500 mg/L and 60 g/L NaCl, sludge from t-MBR could achieve almost 100% phenol removal within 100 h, while it was only 54.7% for the sludge from c-MBR. High-throughput 16S rRNA analysis indicated that the genus Rhizobium in Alphaproteobacteria was greatly enriched in the t-MBR. The genus Pseudomonas in Gammaproteobacteria was identified as the dominant resuscitated bacteria. These findings suggested that Rpf-responsive bacterial species belonging to Alphaproteobacteria and Gammaproteobacteria were key populations contributed to better phenol-degrading capabilities under high salinity condition.