AWWA MTC61236

A two-month comparative pilot study was conducted to determine which submerged membrane would perform best for Kennewick's Water Filtration Plant (WFP) retrofit, how it should be configured, installation requirements, and to develop specific criteria to be used in the membrane procurement process. The most important issue to be resolved was whether pretreatment would be necessary, or beneficial, to the membrane operation. USFilter and Zenon are the only major manufacturers that offer low-pressure, submerged membranes. Both are relatively new to the membrane market, and there are few full-scale installations in the United States. Membranes from both companies were tested in this pilot study in an integrated pretreatment process, including coagulation followed by a plate settler. Settled water was fed into two submerged membrane units in parallel. After the first two months of parallel testing, the USFilter membrane was tested for another six months in direct filtration mode to asses the feasibility of operating without any pretreatment. In subsequent phases, small doses of coagulant and powdered activated carbon (PAC) were added inline to optimize organics removal. Overall, this study demonstrated that the new submerged membranes currently on the market are both robust and flexible. This paper provides valuable information on membrane performance and compares finished water quality characteristics for different treatment schemes, including direct filtration (no pretreatment) with a combination of various coagulant and PAC dosages. This paper also discusses membrane unit response when a short, but high spike of coagulated ferric flocs was accidentally released from the plate settler due to a chemical feed pump failure. Although this event was unplanned, it represents a realistic scenario which treatment plants should be prepared to handle and for which design criteria need to be developed. A set of pilot-study guidelines is provided for utilities considering the membrane retrofit option. Includes tables, figures.