PLWC engaged Crist Engineers, Inc. to provide a preliminary engineering report and final design of a facility to stabilize dewatered biosolids to a Class A exceptional quality product by utilizing lime stabilization.

The project included the following components: Development of an Preliminary Engineering Report that evaluated sludge storage, thickening, dewatering, and stabilization. An evaluation of historical sludge production was evaluated to determine sludge storage and loading with a projection to 2030. Several screw press manufacturers were evaluated, sludge treatment for Class B and Class A stabilization as well as surface disposal. The report recommended sludge storage and handling facilities to treat a maximum daily sludge yield of 7,220 dry pounds per day. Sludge dewatering and treatment was targeted at a operational period of 35 hours per week, with one redundant unit for dewatering to year 2030.

Concluding the preliminary engineering report, design of the facility including the following major components:

• Demolition of the existing dewatering and drying equipment in the biosolids building. The building was repurposed for new dewatering and sludge treatment equipment.
• Developing bid documents for owner procured equipment; dewatering screw press, sludge feed pumps, sludge treatment (lime stabilization).
• Installation of two screw presses capable of dewatering 1,083 dry pounds of sludge per hour, with a solids capture rate of 90% producing a cake solids of 17%. Included polymer feed station for each screw press unit.
• Installation of submersible digester sludge pump station for each aerated sludge storage tank with firm capacity of 275 gpm utilizing screw centrifugal pumps.
• Installation of dewatered cake pumps for each screw press with a rated cake sludge pumping capacity of 19 gpm.
• Installation of lime stabilized reactor with a rated capacity of 1,000 dry pounds per hour to include lime storage silo and lime feed conveyors.
• Installation of decanters for the sludge storage tanks.
• Installation of positive displacement blowers for mixing aeration requirements in the sludge storage tanks.