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The design included two new grit washer-classifiers, new grit pumps and piping, and a new screenings handling unit that grinds, washes, and compacts the screenings. |
The Sanitary District of Decatur owns and operates a 41-mgd (125 peak mgd) wastewater treatment facility. The facilities include two independent headworks facilities, each with mechanical bar screens and Dorr-Oliver grit removal facilities. The service area includes a collection system that is partially combined. The headworks area of the plant had been chronically plagued with reliability problems and the District’s goal for the project was to improve overall system reliability at the headworks.
Plugging of the screens had been a recurring problem during the fall months, and clogging of the grit pumping systems frequently occurs after significant rainfall events. In addition, the District has experienced maintenance and reliability problems with certain headworks equipment. Donohue evaluated several alternative methods for resolving these problems and completed a study, design and construction project to accomplish the project goals.
The reliability study investigated the headworks system’s various deficiencies and evaluated options for correcting those deficiencies. Four program options were considered for upgrading the headworks. The study recommended that the District separate the screenings and grit removal functions, replace one of the existing grit and screenings materials handling systems, one of the existing catenary bar screens with fine screens, the grit pumping system, and add an emergency bar screen bypass structure. Another short-term modification was to increase the speed of the grit rake arm to more quickly move grit from the grit removal tank to the grit processing facilities.
The design included two new grit washer-classifiers, new grit pumps and piping, and a new screenings handling unit that grinds, washes, and compacts the screenings. During design, particular attention was paid to minimizing plugging of the grit pumping and dewatering application. The upgrade also included a new masonry grit loading building and a new flow control vane gate on one of the headworks’ influent channels systems, to assist in equalizing flows and solids loadings between the two channels.
Brought on-line in 2004, the new grit removal and dewatering system removed significantly more grit from the system. Grit pump and piping systems saw significantly less plugging problems. Odors from the dewatered grit were greatly reduced, as the new ventilation system maintained a good working environment in the grit handling area.
This project was received a Engineering Excellence Merit Award from ACEC of Illinois. |
