BENCH-SCALE STUDIES PROVIDE INSIGHT INTO PASTEURIZATION SYSTEM DESIGN

Based on comprehensive qualitative and quantitative analyses of multiple biosolids management options, the Oxnard Wastewater Treatment Plant (OWTP) decided to pursue the additional treatment of its current Class “B” biosolids to meet Class “A” Exceptional Quality standards through thermal pasteurization. Bench-scale studies were conducted during the pasteurization system design to provide insight into critical design issues. Biosolids pasteurization tests examined the disinfection efficiency of pasteurization with the OWTP sludge, the potential for grease deposition on pasteurization equipment and pipes, and the viscosity of OWTP sludge at pasteurization temperatures.The disinfection tests confirmed that pasteurization of the OWTP sludge would reduce the fecal coliform and Salmonella concentrations to below the analytical limit, allowing the pasteurized biosolids to meet the Kern County requirements for Class “A”, Exceptional Quality biosolids. Grease deposition testing showed a tendency for a grease residue to buildup on stainless steel during the pasteurization process, which could affect the heat transfer properties, cause clogging of the heat exchanger channels, and increase the equipment cleaning frequency. Sludge viscosity testing showed that the apparent viscosity varied over a wide range, especially at low shear rates and temperatures, which could affect the design and operation of the pasteurization facility.