Pretreatment of reverse osmosis feedwater by means of in line coagulation

Abstract

The possibilities of removing salts from Rhine water by means of reverse osmosis depend very considerably on the efficiency of the usable pretreatment techniques. Existing purification systems used for the preparation of drinking water are usually not oriented towards this task. Experiments carried out during the period from 1971 to 1977 with Rhine water show that this water can be so purified by coagulation with ferric salts that tubular membrane systems can be used. An additional treatment is necessary for spiral-wound and hollow fibre membranes. Experiments with one of the most promising techniques in this area, i.e. “in line coagulation” have shown that interesting results can be achieved with this. If, however, humic substances are present, this process is seriously disturbed because these compounds react with the cation-active polymer added. It has been shown that these humic substances can be conclusively removed by adjusting the addition of ferric salts in the preceding coagulation process to a sufficiently high level.