The world's increasing need for economically purified water and the advent of 50 to 100 million gallons per day reverse osmosis (RO) plants producing potable water demand the simplest possible pretreatment processes.

We are driven to innovate by the current realities that fouling of membranes is widely accepted despite sometimes elaborate pretreatment schemes. Need for stoppage of production to clean periodically seems universal. Efforts at prolonging membrane service life in difficult waters to beyond 2-3 years underlies much efforts at resolution of fouling problems. Numerous RO plant problems were solved by retrofitting existing processes with the elimination of problematic pretreatment steps. This was made possible by the judicious selection of antiscalant and antifoulant and dosages used. Not only problems were resolved but the resulting cost savings have been substantial. Our successes in these efforts have led us to the conclusion that controlling the fouling potentials of scales and colloids in RO feedwaters with minimum dosages of chemicals is far better than the strategy involving the removal of these objectionable contaminants from the RO feedwater.

We wish to present in this paper an overview of the comparison of traditional pretreatments to remove contaminants compared to current capabilities of antiscalant and antifoulants in controlling the fouling tendencies by continuous injection into the feed at parts per million (mg/L) concentrations. The long-range goal of these developments is to eliminate membrane fouling entirely, and make purification of water by RO a truly continuous process with little or no maintenance cleaning and much prolonged membrane service life.