Technological advances in membrane filtration systems and water quality concerns for granular systems that use sand and/ or anthracite are causing this paradigm shift. The concern over disinfectant-resistant pathogens, such as Cryptosporidium, has been a leading reason for the increased popularity of micro-filtration (MF) and ultra-filtration (UF) membrane systems.
Although such pathogens are not routinely present in source waters, treatment processes must be capable of removing or inactivating them to protect consumers against gastrointestinal illnesses. Such pathogens are larger than 2 microns in size and can be readily removed with membranes that have pores less than 0.5 microns in size. Granular media filtration systems may allow some of these organisms to pass.
New and cheaper MF/UF systems that use pretreatment filtration to prevent frequent membrane plugging and can be fabricated and plumbed to process millions of gallons of water daily (MGD) are now available. However, MF/UF systems may still be used in combination with other treatment methods, including chemical precipitation and granular media filtration of dissolved chemicals that would normally pass right through the membrane system.
Recent improvements in membrane technologies have allowed more versatile applications of drinking water treatment for small systems. Previously, more or less, membranes were used in drinking water treatment for desalting brackish water and seawater. Membranes are finding more applications in filtration and disinfection compliance.
Beside reverse osmosis (RO) engineers classify membranes in three additional categories: microfiltration (MF), ultrafiltration (UF), and unit operation remains dependent largely on the treatment source water, and whether the operations and maintenance personnel are adequately staffed and trained. Better understanding of membrane filtration for water treatment is required before universal application can be assumed.
Among the considerations for additional research include pretreatment and membrane fouling, precursor removal, and preoxidation issues. However, as the technology and systems continue to improve, membrane technology may offer an attractive alternative for treatment and should be considered in the overall evaluations.