Evaluation of membrane pre-treatment to further wastewater reuse

Sep 18, 2006

CDM recently completed an in-depth, two-phase study to assess the potential for membrane technologies to expand the reuse of secondary effluent. Commissioned by the Water Environment Research Foundation, CDM, in collaboration with the University of North Carolina at Chapel Hill, conducted research that will guide utilities and regulatory agencies in expanding wastewater reuse. Since rapid urbanization and severe regional droughts make it clear that fresh water supplies cannot continue to indefinitely meet water demands, wastewater reuse will be needed to ensure water sustainability.

Phase 1, a review of the best combination of membrane technologies to meet the water quality requirements of agricultural, non-potable, indirect potable, industrial, and environmental reuse applications, guided the phase 2 pilot studies. The overall objective of phase 2 was to evaluate membrane pretreatment techniques to minimize fouling of high-pressure membranes. Low-pressure membranes have been shown to be superior to chemical coagulation/granular media filtration, but the choice between microfiltration (MF) and ultrafiltration (UF) remains unclear. Field research, including this pilot plant study, is essential in guiding the wastewater treatment industry in designing facilities that better protect membranes against fouling.

Conducted at the North Buffalo water reclamation facility in Greensboro, North Carolina, the pilot plant results showed very clearly that high-pressure membranes pretreatment by UF had less decline in specific flux than those receiving MF pretreatment. Supplementary testing including virus challenge tests, two-fiber bench tests, and membrane autopsy, supported the operational results.

Though further research is needed to fully understand why UF provides better pretreatment than MF for high-pressure membranes, it was determined that UF pretreatment reduced the rate of fouling and required less energy consumption for the utility, implying that UF pretreatment should be a more cost-effective method when treating secondary wastewater effluent.

CDM is a consulting, engineering, construction, and operations firm delivering service to public and private clients worldwide.

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