Which Membrane to Choose? A Comparison of Ceramic, PVDF, and PES Ultrafiltration Membranes and Surface Water Treatment

Since 1953, Halifax County Service Authority (HCSA) has treated the Dan River using flocculation, sedimentation, and conventional sand filtration at their Leigh Street Water Treatment Plant. HCSA is interested in replacing the existing sand filtration system with ultrafiltration (UF) membranes to provide consistent, high quality drinking water for their plant, regardless of variability in the feed source or pretreatment equipment. Additionally, HCSA has a goal to reduce operating costs and accommodate a higher capacity in the same footprint. To demonstrate ultrafiltration membrane technology and compare membrane modules HCSA has been operating a pilot onsite for the last 2-years. During this period, three different membrane modules have been utilized: 0.03 ?m Nanostone ceramic monolith, 0.01 ?m Toray PVDF outside-in hollow-fiber, and 0.02 ?m Dupont inge PES inside-out multibore. The stark differences in membrane material, flow-direction, and module type provide an interesting comparison of commercially-available ultrafiltration modules. This paper summarizes the pilot study results and methods used to evaluate the three different membrane module technologies for surface water treatment. Operating flux rates ranged from 40 – 85 gfd for polymeric membranes and 120 – 200 gfd for the ceramic membrane. Recovery ranged from 93 – 98.3%. Maintenance clean and CIP sequences were performed and the paper summarizes frequency and effectiveness for the membranes tested. In addition, energy consumption was evaluated at various flux rates and operating costs were considered. This data was used to provide a comparison for the 4.8 MGD full-scale plant to compare capital costs for the membrane equipment verses expected operating costs. The extensive pilot data will allow HCSA to select the optimal membrane and subsequent full-scale equipment design to provide an innovative, long-lasting membrane system, while lending comparison data and pilot methodology information to other utilities upgrading to membrane technology.

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