Ideal feed pretreatment for reverse osmosis by continuous microfiltration

• Published in: Desalination 1997-08, Vol.110 (1), p.143-149
• Main Authors: Chakravorty, B., Layson, A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Continuous microfiltration; Drinking water and swimming-pool water. Desalination; Exact sciences and technology; Marine; Pollution; Pretreatment; Reverse osmosis; Water treatment and pollution
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/S0011-9164(97)00093-3

Investigations have established that majority of failure/inefficient operation of RO is due to improper/inadequate feed pretreatment. The conventional feed pretreatment techniques such as, sand filters, cartridge filters, chlorination, flocculation, etc are not capable to remove suspended solids, bacteria, colloids, etc completely which results in RO membrane fouling. From the performance of many installations of continuous microfiltration (CMF) technology it appears that this is the most satisfactory feed pretreatment process capable of ensuring highest degree of reliability for the RO system. The technology is fairly simple where the feed is allowed to pass through a barrier of 0.2 micron polypropylene membrane in continuous mode under a pressure gradient of 100 kpa. The filtrate thus obtained on the low pressure side is virtually free from any suspensions, bacteria, colloids, etc. Typically the SDI of the filtrate is lower than 3 which is far below the specified SDI by RO membrane manufactures. This fully automatic system works almost unattended and unlike conventional filters the quality of the filtrate is independent of feed quality variations. The rate of filtration is maintained for long term operations through an innovative backwash system using compressed air at 600 kpa. The paper describes the technology in details besides few case studies.