AWWA MTC57640

As freshwater supply options become fewer and more difficult to access, municipal water suppliers have begun turning to supplies of lesser quality. These supplies include hard, colored, and brackish waters that require advanced treatment, such as reverse osmosis (RO) and nanofiltration (NF). Groundwater sources have been, overwhelmingly, the sources of choice due to more consistent and predictable water quality. However, more recently, many have been looking at treating low quality surface water supplies with RO or NF. Treating surface water with RO and NF poses certain challenges associated with system design and membrane fouling. Due to the wide variations seen in surface water temperature, turbidity, and organic carbon concentrations, engineers must be particularly careful when designing surface water RO and NF systems. Adequate pumping design, intake type and location, and pretreatment are paramount to controlling system operation, finished water quality, and treatment cost. Pilot tests are a useful tool for developing design criteria for surface water RO treatment processes. However, appropriate consideration must be given to scheduling pilot tests to capture the water quality events that bear significant impact to the operation of the RO process. Such events include seasonal variations in temperature, turbidity, algae, taste and odors, synthetic organic compounds, etc. While much pilot data is available, few surface water RO or NF treatment systems have actually been built in the United States. This paper presents a review of the few facilities that currently exist or are in the planning or construction phases. These facilities include: Granbury, Texas; Barrow, Alaska; Wichita, Kansas; and, West Jordan, Utah. A review of existing and planned treatment facilities indicates that intake type and pretreatment required bear significant impact on treatment costs. Surface intakes typically require advanced pretreatment processes that may include ultrafiltration (UF) or microfiltration (MF). However, some may operate well when using conventional processes and media filtration. Types of intake structures and siting intake facilities, operation of conventional pretreatment processes before RO or NF, and considerations that may lead to the implementation of advanced pretreatment processes are presented and discussed. Riverbank filtration can be used to reduce the seasonal impacts of particulate matter, organics, algae and algae related taste and odor problems. Interest in riverbank filtration is increasing due to the recently proposed Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), which may grant this process log-removal credits for microbial pathogens such as Giardia and Cryptosporidium. Criteria for evaluation of hydrogeologic conditions that indicate the feasibility of riverbank filtration are summarized. Includes 10 references, tables, figures.