Membrane regeneration for wastewater reclamation using reverse osmosis

One of the major problems in applying reverse osmosis to wastewater reclamation is the potential plugging and simultaneous product flux-decline of the membranes. At present two techniques are prevalently used to minimize these deleterious effects. These are periodic clearing and extensive pretreatment. A third, and as yet untried, technique is presented here. It involves the in situ replacement of degraded membranes at projected replacement costs far below those for spirally wound units.Results presented here demonstrate that in situ replacement of cellulose acetate reverse osmosis membranes is technically sound. The membrane replacement cycle was repeated six times with average water fluxes of about 13 gal ft⁻² day⁻¹ and salt rejections of between 78 and 85 per cent. The regenerable unit was also tested on primary and secondary sewage effluent. Average water fluxes were between 3 and 10 gal ft⁻² day⁻¹, respectively, while salt rejections were between 66 and 73 per cent. Projected membrane costs are reduced from $4.06 ft⁻² for a 6-in. dia. module to $0.08 ft⁻² for a 72-in. dia. module. Thus, large diameter units become economically very attractive. Design and cost computer parametrization is also presented.