Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | November 2015 | 23 Project focus: Wastewater treatment the Mad River were approximately 3.8 billion litres a year in 2000. Under federal and state regulations, the city of Springfield developed a long-term control plan, to increase its wet-weather flow capacity and its control of untreated CSOs to the Mad River. The plan recommended the addition of EHRT facilities as part of a range of treatment plant improvements. Dynamic influent characterisation and full-plant dynamic process modelling was conducted to predict performance and evaluate impacts to the existing liquid and biosolids treatment facilities during wet- weather events. Alternatives were evaluated for the new EHRT facilities, and equipment bids were solicited for solids contact high-rate clarification, ballasted flocculation and CMF. Conceptual facility designs for the technology alternatives were developed and evaluated for economic and non-economic factors. It was determined that lifecycle costs were within 7 percent of each other. As a result, CMF technology was selected largely because of non- economic factors, including: • Operations can be monitored and controlled remotely without additional staff at the treatment the media bed. While in filtration mode, a perforated plate compresses the media from the top using an electrically actuated screw drive. The FlexFilter operates similarly except that it uses a down-flow configuration, and the media bed is compressed transversely to the liquid flow through sidewall bladders using influent hydrostatic pressure instead of external mechanical or electrical actuators. The CMF system selected for Springfield was the WWETCO FlexFilter. The technology originated in Japan and has been in use for more than a decade in full-scale wet- weather treatment applications. Considered an innovative technology by the U.S. Environmental Protection Agency, CMF can operate at higher flow rates and provide cleaner effluent compared to conventional clarification technologies. It can be used to treat storm sewer, combined sewer and sanitary sewer overflows, and provide polishing of plant effluent during normal, dry-weather conditions. A key advantage of CMF is automation. Process control uses robust flow and level meters and timers without needing additional human operators. It also requires no chemicals for most applications. Another advantage of CMF, and most high-rate filtration technologies, is that chemicals are generally not required for wet-weather treatment applications. High-rate filters like CMF also can serve as a safety net downstream of secondary clarifiers, to allow existing biological facilities to be maximised during smaller wet- weather events with less risk of losing biomass. Springfield's EHRT facilities have two structures: a wet-weather headworks for preliminary treatment, and a separate common wall structure for the CMF process, facility during an event • Simplicity of process, equipment and maintenance • No need for clarification coagulants or specialty polymers and associated makeup and feed equipment • No constraints concerning process start-up time or turn-down • Potential for dual function during dry weather conditions An on-site demonstration pilot unit was operated from October 2010 to June 2011. Approximately 150 tests were run on dry and wet-weather flows. In addition to filtration performance, effluent disinfection dose response was tested, using E. coli as an indicator. Results of the pilot confirmed the influent characteristics, process design criteria, and process performance during a variety of dry- and wet- weather conditions. CMF FlexFilter choice CMF uses a bed of synthetic fibre balls to capture influent suspended solids and colloidal particles. Two types are available in the United States: the Fuzzy Filter and the FlexFilter. The Fuzzy Filter is usually configured with influent flowing up through Horizontal raked bar screens along a side-exiting overflow weir on the velocity control channel of the wet-weather headworks prevent screened material flowing downstream to the CMF process • Innovations ● CMF technology is fully automated and does not require clarification chemicals ● The wet-weather installation is located on the same site as the dry-weather wastewater treatment facility ● Contact basin is 33 percent smaller than conventional design standards, providing cost savings

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