Antimicrobial-Coated Granular Filter Media for Drinking Water Treatment
Coating Systems Laboratories, Inc., of Chandler, Arizona, has developed a quaternary ammonium chloride (QAC) coating with antimicrobial properties that may be attached to common granular filter media such as sand and zeolite. The potential for coating filter media to improve drinking water treatment with respect to both disinfection efficiency and the production of disinfection by-products could impact the majority of surface water treatment plants in the United States. Most surface water treatment plants use granular media filtration prior to disinfection. Antimicrobial-coated media can inactivate pathogens without the addition of energy or chemicals. This technology could be a sustainable component of both large and small treatment systems. Preliminary studies with point-of-use treatment filters using QAC-coated media have demonstrated that increases of 1 log removal or higher are possible for several different classes of pathogens in comparison to non-coated media. British abrasion testing has demonstrated that the coating is stable, and toxicity testing by the National Sanitation Foundation has verified that the coating is stable and does not pose a risk for leaching.
The primary objective of this Phase I project is to demonstrate the technical feasibility of QAC-coated media to sustain microbial inactivation in a continuous drinking water treatment filter that is loaded with solids and backwashed. This demonstration is necessary because the technology does not fit the classic mode for assessing disinfection efficiency by quantifying chemical or energy input. The efficacy of QAC-coated media will be assessed for the removal of different classes of pathogens, including emerging pathogens, during simulated drinking water treatment. Four granular media filters containing different granular media will be assembled and tested. The four different media will be sand, QAC-coated sand, zeolite, and QAC-coated zeolite. The filters will be operated at typical hydraulic loading and solid loading rates for conventional granular filter media filters at surface water treatment plants. Although zeolite might not be a typical filter media for drinking water treatment, the increased surface area as compared to sand could significantly increase antimicrobial activity. The filter run lengths and backwashing cycles also will simulate operation at a surface water treatment plant. The water applied will be spiked with known concentrations of pathogens (Cryptosporidium, Escherichia coli, Adenovirus, Echovirus, Cocksackievirus, and Calicivirus) to assess the removal efficiency during filtration. The potential to remove these difficult-to-disinfect pathogens without chemical or energy input will be evaluated.
* information listed above is at the time of submission.