Influence of filtration conditions on the performance of NF membranes in the filtration of paper mill total effluent

Nanofiltration membranes were studied and their suitability for treatment of paper mill total effluent was evaluated. The membrane flux, its decline and retentions of various components were studied on a laboratory scale using a flat sheet module under different operation conditions. The results showed that during short filtrations temperature, pressure and flow velocity had minor effects on the retention of the measured components. Only the retention of monovalent ions (chloride) was significantly dependent on the flow velocity and the ionic concentration on the surface of the membrane. With the Desal-5 membrane, however, temperature, pressure and flow velocity were found to have a considerable effect on the permeate flux. The critical flux of the membranes was dependent on the flow velocity. The higher the flow velocity, the higher the pressure that could be used without a decrease in permeate flux. pH had a considerable effect on the ability of the membranes to retain various species. Increasing the pH of the solutions improved retention ability of the membranes. An increase in salt concentration (Na2SO4and NaCl) decreased the flux and led to a decrease in the retentions of COD and chloride. With the RO membrane (TFC ULP) changes in salt concentration did not significantly alter the retentions. Adjustment of the filtration conditions is one way to improve the efficiency of NF membranes. Appropriate pretreatment of the waste water can also improve the flux and filtering efficiency. The permeates from the NF membranes were adequately clean to be reused, for example, as shower waters.