Transition from Biosolids Slurry to Dewatered Product for Clackamas County Water Environment Services

Many agencies in the Pacific Northwest have considered shifting from a slurry-based biosolids land application program to a dewatered product. As rural residential development has progressed in agricultural areas, haul distances have often increased along with operating costs. By producing a mechanically dewatered product it is possible to control transportation related operating costs. Costs for dewatering equipment and operation can be fully or partially offset by savings on transportation. After reviewing options, Water Environment Services made the decision to construct new thickening and centrifuge dewatering facilities for this reason. New gravity belt thickener and centrifuge equipment installation will be complete by September 2002 as part of design/build improvements at the Tri-City Water Pollution Control Plant in Oregon City. New solids application and handling equipment will be procured by that time. New equipment includes ram-eject haul trailers, a conveyor system for off loading haul trailers in the field, and a low ground pressure application vehicle with side-delivery spreader. The Biosolids Management Plan has been amended to reflect these modifications. Concurrent with the improvements, staff is participating in development of a Biosolids Environmental Management System (EMS) as part of the National Biosolids Partnership (NBP) initiative. Progress with all these efforts will be reported in the presentation along with the economic rationale for moving in this direction.