Estimating costs for integrated membrane systems

Abstract

Despite greater NF fouling rates, life cycle costs for membrane facilities appear to be reduced when membranes are operated at higher permeate fluxes and feedwater recoveries.Nanofiltration (NF) costs attributable to variations in chemical cleaning intervals (resulting from changes in permeate flux and feedwater recovery) were estimated based on membrane fouling rates, associated cleaning intervals, backwashing frequencies, permeate fluxes, and feedwater recoveries observed at pilot scale. Costs of integrated membrane systems using microfiltration (MF), ultrafiltration (UF), and conventional treatment to treat surface water prior to NF were compared. Costs of large systems (>3.8 ˇ 104 m3/d [10 mgd]) were also estimated and compared with extrapolations from cost surveys of existing membrane installations. Results suggest that the higher NF fouling rates observed following conventional treatment compared with MF and UF pretreatment may not translate into higher costs. Despite significant increases in fouling rates, membrane treatment costs decreased with increasing permeate flux and increasing feedwater recovery.