Influence of filtration conditions on the performance of nanofiltration and reverse osmosis membranes in dairy wastewater treatment

Filtration performance and fouling of nanofiltration (NF) and reverse osmosis (RO) membranes in the treatment of dairy industry wastewater were investigated. Two series of experiments were performed. The first one involved a NF membrane (TFC-S) for treating the chemical–biological treatment plant effluents. The second one used a RO membrane (TFC-HR) for treating the original effluents from the dairy industry. The permeate flux was higher at higher transmembrane pressures and higher feed flowrates. The curves of permeate flux exhibited a slower increase while the feed flowrate decreased and the pressure increased. Membrane fouling resulted in permeate flux decline with increasing the feed COD concentration. Furthermore, the flux decline due to the COD increase was found higher at higher pressures for both NF and RO membranes.

The effect of hydrodynamic conditions and fouling on the filtration performance of the NF and RO membranes in dairy wastewater treatment was investigated. The following conclusions can be drawn from this work: C The RO and NF membranes showed excellent performance by removing at 99.7% and 98% of the COD, respectively, from a feed COD concentrations of 40 and 450 mg/l for NF feedwater and 5,000 and 10,000 mg/l for RO feedwater. C The permeate flux in the NF membrane increased by about 45% while the flowrates increased by 40%. On the other hand, the flux showed a slower increase at higher feed COD concentrations and NF flux declined in the range of 33–52% while the feed COD and the transmembrane pressure increased from 40 to 450 mg/l and 5 to 12 bar, respectively. C The decrease in the filtration can be attributed to the increase both in the fouling layer and the concentration polarization layer. Similarly, a 27% increase in the permeate flux through the RO membrane was achieved with increasing the feed flowrate by about 50%. Besides, RO flux decline also varied between 15–31% while COD values ranged from 5,000 to 10,000 mg/l and pressure ranged from 6 to 18 bar. Consequently, the flux decline in the RO membrane because of increasing the feed COD was lower than that in the NF membrane.