PRETREAMENT OF SECONDARY EFFLUENT FOR REUSE AS POWER PLANT MAKEUP WATER

摘要

When source water is taken from secondary effluent, effective treatment is a must. Variability in water quality parameters such as turbidity and Total Organic Carbon make operation of conventional clarification and filtration systems problematic. When secondary effluent is used for high purity applications such as boiler feedwater or cooling tower makeup, pretreatment is even more of a concern, since reverse osmosis and deionization equipment and processes can be jeopardized by poor feedwater quality. Immersed hollow fibre membranes are now recognized as the preferred technology for treating high turbidity feed water on variable supplies. This paper will discuss experiences at a power plant on the US east coast. This plant was designed to use secondary effluent from the sewage treatment facility of a nearby town as cooling tower makeup and boiler feedwater makeup. The power plant is located 12 miles away from the sewage plant. Pretreatment for the plant's feedwater facility is located at the sewage treatment facility, and initially consisted of vertical disk cloth media filters. It was soon found that during periods of high turbidity from the wastewater plant, the cloth media filters would load with solids very rapidly. As a result, the filters were not able to meet the makeup flow demand. The power plant required a solution that would augment flow from the cloth media filters during high turbidity and produce water with less than 5 mg/L Total Suspended Solids (TSS). In response, an immersed hollow fibre ultrafiltration (UF) system was installed in August 2003. This paper will discuss the UF technology and its usage in this particular application.