Biological nutrients & micro-pollutants removal and microbial community structure in a membrane bioreactor
Biological nutrient removing (BNR) performance was evaluated at different operating conditions using an innovative system, sequencing anoxic/anaerobic-aerobic membrane bioreactor (SAM). The SAM was operated at: internal recycling rate of 1.0, 1.5, 2.5; and 3.0 time of influent flow; SRT of 20, 40, and 100 days; low and moderate influent COD at hydraulic retention time of 4 hrs and 8 hrs; and fed with substrate composed of two different combinations of volatile fatty acids (acetate-dominant and propionate-dominant). Microbial quinone profile analysis was also conducted using the sludge from the SAM fed with acetate-dominant substrate. In addition, removal pathway of two model micropollutants was also investigated. The internal recycling rate 2.5 times of influent flow was suitable for better BNR performance. Membrane fouling was much higher at a short SRT (20 days) as compared to longer SRTs (100days). BNR performance was improved when the SAM was operated at short HRT (4 hrs) due to increase in organic loading
rates. Addition of external carbon source might be helpful in enhancing the treatment performance in case of low strength wastewater. The acetate-dominant substrate as an external carbon source found suitable to achieve good BNR performance. Quinone profile results revealed that the β-subclass of Proteobacteria was dominant. The γ- subclass of Preteobacteria were also contributing in phosphate removal performance. The removal pathway of two micro-pollutants was mainly through biodegradation.