Water & Wastewater Treatment

24 | November 2015 | WWT | www.wwtonline.co.uk Project focus: Wastewater treatment and operation demonstrate its effectiveness for treatment of wet- weather flows and its relevance to communities around the world. For example: • The EHRT facilities are co- located at Springfield's main wastewater treatment plant. Yet the facility design and technologies are also suitable for decentralized facilities in the collection system. The wet-weather headworks design and equipment are more commonly used in collection system overflow structures and remote wet-weather facilities. • The automated CMF process is integrated into a supervisory control and data acquisition (SCADA) system for remote process control and does not need staff at the facility for startup or operations. • For treatment scenarios that require tertiary filtration, a dual- use CMF facility can be designed to provide secondary effluent filtration during dry-weather and then switched to a parallel auxiliary mode to treat wet-weather flows. Advanced clarification processes such as CMF serve as a viable parallel auxiliary treatment strategy. They offer effluent quality significantly better than primary equivalency, and are generally more cost effective than conventional secondary treatment alternatives in instances of peak wet- weather flows. As such, Springfield's new EHRT facilities should help to advance auxiliary treatment practices. high-rate disinfection and effluent pumping. The structures boast a number of innovative design features. • Wet-weather headworks: The system consists of a velocity control channel and "rock box" to remove large settleable solids such as grit, sand, gravel, and stones. Modulating gates at the end of the channel control the flow split between the new EHRT train and the existing treatment plant's conventional process trains. Horizontal rake bar screens located on the influent channel's overflow weir prevent screened material from flowing to the downstream CMF process. Placing the screens above the normal dry-weather influent channel serves to minimize screenings and grit handling while providing appropriate preliminary treatment for downstream processes. • Compressible media filters: The project represents the first full-scale wet-weather installation of this type of CMF technology located on the same site as the dry-weather wastewater treatment facility. The technology features a unique cell filter design that maximizes the solids loading capacity of the filter bed and reduces backwash requirements. • High-rate disinfection: Sodium hypochlorite is mixed rapidly into the CMF effluent, which then flows through a contact basin that is 33 percent smaller than conventional design standards. This provides significant capital cost savings. Construction began in August 2013, with commissioning in October 2014. Process control programming and functionality testing of the CMF system started with secondary effluent then switched to raw influent for process performance testing. Challenges inevitably arise when emerging technologies are integrated into existing facilities and Springfield was no exception. Issues included odour control, which was resolved by recirculating influent in the rock-box chamber, to keep lighter organics and solids suspended and flowing to the main headworks. The CMF cells in the facility are the largest of their kind, which required construction materials, fabrication details and installation procedures to be carefully scrutinized by the equipment supplier and contractor prior to installation. Adjustments to control programme settings and override protections were suggested aˆer a significant first-flush load overwhelmed the initial system programming. By June 2015, wet-weather events were sizeable enough to require operation of the EHRT facilities on 21 days. Flows from five of those events were small enough in magnitude and duration to be completely captured by the new facilities. Performance was consistent with design criteria and pilot results. The CMF system has achieved excellent turbidity and removal of suspended solids and associated organics. The Springfield facility is unique, being among the first of its kind and the largest capacity CMF installation to date. Findings from its design Enhanced high-rate treatment (top) and wet-weather headworks (bottom) facilities at the Springfield, Ohio, Wastewater Treat- ment Plant (Photo credit: City of Springfield)

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