Like many cities in the Florida Keys, Marathon, Florida had historically used septic systems to treat wastewater. The community added secondary treatment several years ago, but the facility was unable to prevent nitrogen and phosphorous contamination of sensitive Gulf of Mexico coastal waters. Under orders to improve the quality of its effluent, the community opted out of a $181 million plan for one large treatment facility and connecting sewers, choosing instead to build five smaller decentralized plants, each treating between 200,000 and 400,000 gallons per day.
After a competitive review process, Marathon hired Weiler Engineering (Punta Gorda, FL) to design a treatment solution. According to Zully Hemeyer, Marathon utilities director, "we chose a decentralized network of collection systems and small, advanced treatment plants serving various sections of the community." "That proved to be the most cost-effective option." After visiting a few plants, the city decided on the OMNIPAC® SBR to achieve a cost effective solution in a small footprint with a design to installation timeline of 12 months for each system.
The OMNIPAC SBR system is a factory-built, Davco™ field-erected aboveground structure composed of pre-fabricated steel rings utilizing OMNIFLO® SBR technology. The outer diameters of the four units at Marathon range from 60 to 105 feet. Each unit contains three SBR basins with jet aeration systems to mix and aerate the mixed liquor. Each basin includes a solids-excluding floating decanter for effluent withdrawal, as well as an influent manifold for even distribution of influent into the sludge blanket. Waste sludge pumps for sludge withdrawal are also located in each basin.
The OMNIPAC SBR field-erected treatment systems were key in getting treatment in place quickly and cost effectively. The systems enabled Marathon to meet new discharge parameters well ahead of a 2016 deadline, while reducing their capital costs. In dry seasons, 20-40 percent of treated water is recycled for community use. The remainder of treated water is pumped into injection wells. No effluent is discharged to the Gulf of Mexico.
Results like these plus the cost effectiveness and timely installation of the treatment plants have earned Marathon a number of awards, including the 2012 Plant Operations Excellence Award from the FL Dept. of Environmental Protection, and the 2013 Environmental Project of the Year for projects over $75 million from the American Public Works Association.