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From Farmland to Flower Beds: Mountain City, Tenn.’s WWTP Improves Quality of Biosolids
Challenge A few years ago, the Mountain City, Tenn. wastewater treatment plant (WWTP), operating at full capacity, found itself unable to handle additional wastewater. As a result, the state imposed a moratorium on new sewer connections in the northeast Tenn. community.
The urgent need for a system upgrade also affected the city’s practice of recycling wastewater into Class B biosolids. As the plant’s flow increased, the city struggled with limited drying bed capacity, which affected activated sludge waste rates. This, in turn, made the biosolids process control difficult, creating inefficient plant operations.
The city staff hauled the biosolids to a 300-acre dairy farm where it was land-applied. Because of the biosolids’ Class B status, the city had limited options for cost-effective distribution of the material. Federal regulations do not allow Class B biosolids to be applied to hillside farms due to concerns of water runoff.
In addition to improving and expanding its WWTP, Mountain City needed a more efficient alternative to producing biosolids that also provided a larger capacity and could yield more beneficial uses.
Solution With the plant expansion, Mountain City upgraded its 0.9 million gallons per day (mgd) WWTP to 1.2 mgd. This retrofit project included a 50,000-gallon aerobic digester, which added to 125,000 gallons of existing digester capacity, and a 50-cubic foot J-Vap® unit. The latter is a patented one-step biosolids dewatering and drying process that has the capacity and flexibility to produce Class A biosolids.
When Mountain City’s J-Vap® system first began operation in May 2000, it was processing eight batches of sludge per day due to high solids loading in the digester. Six months later, the unit had reduced the solids loading in the digester, and only one or two batches per day were required.
Results The WWTP processes average flows of 800,000 gallons per day. The J-Vap® unit has proven more cost-effective than other dewatering/drying systems, helping to reduce labor costs. The environmentally friendly unit conserves energy by drying materials at low temperatures and does not require additional air quality permits due to the minimal air exhaust from the system.
Overall, the more efficient solids processing with the J-Vap® system has enabled the city to improve its treatment plant operations. Yielding dried cake at greater than 75 percent solids in a single, fully automated process, the J-Vap® system is capable of delivering cake at levels as high as 95 percent solids. This gives the city more control of its end-product and meets U.S. EPA standards for Class A biosolids.
USFilter’s J-Vap® system has also helped Mountain City facilitate the community’s growth and prosperity, with plans to eventually offer the WWTP’s Class A biosolids to the community for use as a fertilizer. Since Mountain City’s flow is primarily domestic wastewater, the biosolids product is low in metals, making it suitable for flower and vegetable gardens.
Robert W. Mau
Phone: (616) 748-7612
Fax: (616) 772-4516