Effect of driving pressure and recovery rate on the performance of nanofiltration and reverse osmosis membranes for the treatment of the effluent from MBR

Abstract

This research was carried out to evaluate the suitable operating condition for both nanofiltration (NF) and reverse osmosis (RO) membranes for the reuse of wastewater effluent from membrane bioreactor (MBR). Various parameters such as pH, conductivity, total dissolved solids, UV254, dissolved organic carbon, total nitrogen and total phosphorus were analysed for the permeate from the NF and RO to compare the membrane performance. Batch experiments were conducted using a lab-scale NF and RO systems. Effluent from the MBR system treating synthetic wastewater was used as feed water to NF and RO. Filtration tests were performed at the operating pressure ranging from 0.2 to 1.0 MPa. Flux was measured at every 5 min, and the permeate was collected at the end of each experiment. Although the permeate flux and salt rejection increased in proportion to the operating pressure for NF, the increase in salt rejection was tapered off at a certain range of the operating pressure over 0.6 MPa for RO. As a result, an optimum operating pressure should be considered when using RO for treating the effluent from MBR. On the other hand, a better performance would be expected at higher operating pressure when using NF. The removal rates for various components in the feed slightly decreased by less than 5% as the recovery rate increased from 50 to 80%. Therefore, the optimization of the operating pressure and recovery rate should be considered when NF and RO systems were applied effectively to wastewater reuse purpose.