Ultrafiltration - A Reliable Pretreatment Process for Reverse Osmosis Desalination

摘要

Since its theoretical inception in 1950s, reverse osmosis has come a long way and proved to be a mainstay in the field of desalination of brackish and sea water. The success of the process lies in its economics vis-a-vis other desalination processes, thermal desalination, in particular. Water cost in membrane process is a function of mainly the energy cost, the cost of the membranes and the cost of the dosing chemicals. The cost of the membranes and the chemicals, contributing about 40-45% of the water cost. It is imperative, hence, that, an increase in the life of the membranes and decreasing the chemical consumption would positively contribute to reduce the water cost further and make the process competitive even more. Stringent guidelines of turbidity and SDI of the feed water to membrane modules, set forth by the manufacturers are difficult at times to be obtained through the conventional pretreatment methods of clarification and filtration from raw surface feed water-sea water, for example forcing a considerable shut-down time of the plant and hence an increase in water cost. With a spectrum of membrane processes now available commercially in the market, it is possible to employ a membrane based pretreatment process, such as ultrafiltration working on the principle of size exclusion, as a precursor to the RO process. The paper discusses this ideology and describes an installation of UF-RO plant at Desalination Division, B.A.R.C., Mumbai.