The Stewartstown Sewage Treatment Plant (STP) is owned by the Stewartstown Borough Authority of Stewartstown, PA. The plant experiences flow at an average rate of 0.625 MGD (millions of gallons per day) plant with MBR (membrane bioreactor) treatment. Sludge is dewatered with a 1.5m belt filter press that produces 16-17% solids. Before working with the Bioset process, the Stewartstown Sewage Treatment Plant's disposal strategy typically consisted of processing liquid sludge at a neighboring facility. Alternatively, dewatered sludge was hauled to a landfill.
Upon recommendation of their consulting engineer, the Borough investigated Class A technology to take advantage of more disposal options. A thermophilic digestion process was considered. However, given the relatively small size of the plant, this option was rejected for requiring the investment of too much capital and manpower. The Bioset process offered a low-cost Class A option that could be integrated into the plant operation. Alkaline stabilization was designed into an overall plant upgrade and put out for tender in 2007.
The layout flexibility of the process was again crucial as the mixer, pump, power unit, and reactor were engineered to fit into a single garage bay, with reactor discharge pumping to an adjacent garage bay to load the truck. The process was operational by the end of 2007.
Today, using the Bioset process, the Class A biosolids are disposed of at two agricultural sites. The farmers are responsible for spreading the product. The farmers have reported positive results with their crop yields and have not had any odor-related complaints. Pennsylvania regulations permit spreading Class A biosolids year-round, so there is no need for material storage through the winter.