Wastewater treatment by high-growth bioreactor integrated with settling-cum-membrane separation Original Research Article

A different approach of wastewater treatment has been investigated in this study by operating bioreactor at low mixed liquor suspended solids (MLSS) concentrations, thereby maintaining high F/M ratio to target higher nutrient removal through higher biomass yield. A 10-L capacity laboratory-scale bioreactor followed by settling-cum-membrane separation employing hollow fiber membrane module (pore size: 0.1 μm) was set up and operated under batch mode at a hydraulic retention time (HRT) of 24 h using simulated domestic wastewater as feed. Average removal efficiencies of bioreactor were approximately 84% soluble chemical oxygen demand (SCOD), 95.5% total COD (TCOD), 90% NH4+–N, and 87% total Kjeldahl nitrogen (TKN). True yield coefficient (YT) and decay coefficient (Kd) for bioreactor were estimated at 0.397 kg VSS/kg SCOD and 0.0549 day− 1, respectively. Significant proliferation of non-flocculating microorganisms was observed in the system with decreasing solids retention time (SRT) and thereby deteriorating biomass settling property indicated by enhanced sludge volume index (SVI). Significant proliferation of non-flocculating microorganisms with better ability to access substrate from bulk solution through smaller mass transfer resistance most probably contributed to better organics removal. The modified approach of wastewater treatment can be a good basis to develop high-growth membrane bioreactor (MBR) as opposed to conventional MBR operation.