WATER
Automatic scraper strainers protect critical membrane systems By Del Williams
M
embrane filtration is a valuable, commonly used means of filtering water and wastewater. The challenge is that membrane systems are delicate and can be easily damaged by large particulates in the water. A pre-filtration step eliminates this risk by removing oversized suspended solids to prevent damage, eliminate unnecessary maintenance, and reduce the cost of premature membrane replacement. Among the pre-filtering options available, automatic self-cleaning scraper strainers are increasingly popular because they are affordable, require very minimal maintenance or attention, and can remove solids down to 75 microns. The strainers allow for continuous, uninterrupted flows even during blowdown cycles and can save substantial costs on maintenance and membrane replacement.
WATER TREATMENT AND MEMBRANE SYSTEMS Although various filtration methods use membranes, the most mature is pressure-driven membrane filtration, which relies on a liquid being forced through a filter membrane with a large surface area. Depending on the size and type of the particles involved, the process could be categorized as reverse osmosis, nanofiltration, ultrafiltration, or microfiltration. In general, reverse osmosis is used to produce potable water or deionized water. Nanofiltration is used in wastewater treatment, as well as by the petrochemical industry to purify gas condensates, and the chemical industry for solvent recovery. Ultrafiltration and microfiltration are increasingly used in water and wastewater treatment. Numerous industries have high water usage that can require further treatment of water, including automotive, aerospace, oil & gas extraction, refining, textiles, and pulp & paper mills. Ultrapure water, which must meet strict limits of certain constituents in the water such as suspended and dissolved solids, dissolved gases, organic carbon, and biological organisms, is utilized in electronics and pharmaceutical manufacturing processes. In industrial applications, water treatment is also vital to protect downstream equipment from fouling, scaling, corrosion, and other forms of damage or premature wear due to contaminants present in the source water. For these reasons, cooling tower and boiler feed water are generally pre-treated. Membrane filtration is also utilized to treat non-potable water sources, such as greywater and reclaimed/recycled “purple pipe” water. Because the membranes are made using thin, porous sheets of material, failing to sufficiently pre-filter any large, suspended particles from the water can cause severe damage and fouling, leading to premature replacement and unnecessary mainte24 | February 2022
Automatic self-cleaning scraper strainers can remove solids down to 75 microns, protecting membrane systems.
nance. Most membrane filter manufacturers recommend that all influents be pre-screened from 100 to 500 microns to maintain membrane filter efficiency. Automatic scraper strainers are typically installed before the intake plenum of membrane filters, after the supply pumps. EXTENDING MEMBRANE LIFE As an alternative to sand filters, centrifugal separators and basket type strainers, automatic scraper strainers provide superior membrane protection while drastically reducing required maintenance. Automatic scraper strainers like those from Acme Engineering can provide continuous removal of suspended solids to comprehensively protect membrane systems. The units are motorized and designed to continually remove suspended particulates in industrial process water and wastewater to the specific size required, down to .003 inches (75 microns). Environmental Science & Engineering Magazine
