Reverse Osmosis Technology for Wastewater Reuse

Reverse osmosis technology has a great potential in the field of wastewater reclamation. A reverse osmosis plant includes the following processes: (1) feed water microfiltration and chemical conditioning, (2) membrane treatment, (3) permeate aeration, neutralization and disinfection, and (4) concentrate (liquid residue) treatment and disposal. The performance of reverse osmosis membranes depends on operating conditions and water quality parameters. Permeate productivity and contaminant removals increase with applied hydraulic pressure. Water quality parameters such as concentration, composition and pH also affect contaminant removal efficiencies. For example, the treatment of a simulated wastewater containing 10 mg/L of nitrate with a commercial polyamide-type reverse osmosis membrane resulted in membrane permeates containing approximately 0.05 mg/L of nitrate (or 99.5 percent removal) when sodium chloride was the major dissolved solid present in the feed water, and 1 mg/L (or 90 percent removal) when sodium sulfate was the predominant component. The removals of weak electrolyte contaminants are affected by feed water pH. For example, the removal of boron by a cellulose acetate-type membrane was reported to be greater than 99 percent at a pH of approximately 11, and less than 30 percent at a pH of 7. The practice of pre-treatment processes such as microfiltration and chemical conditioning can minimize performance deterioration resulting from membrane fouling by inorganic precipitates, organic macromolecules and microorganisms (biofouling).