EVOLUTION OF THE KING COUNTY BIOSOLIDS PROGRAM: EVALUATING CLASS A COST AND FEASIBILITY

The King County biosolids recycling program was initiated in the early 1970s after the passage of the Clean Water Act, which prohibited disposal of wastewater solids in water bodies. Like many municipalities at the time, King County began exploring alternatives for beneficial use of biosolids. The initial focus was on the forest, a readily available land base in the Puget Sound area. A pioneering research effort was launched in partnership with the University of Washington, College of Forest Resources to document environmental effects and benefits from silvicultural application. Operational methods and equipment were developed over time to improve distribution of biosolids and improve economy of the practice. In the early 1990s, in response to farmer demand, an agricultural program was developed east of the Cascade Mountains. While the haul distance to agricultural land was greater, site management and application costs were less and public acceptance was strong. In recent years agricultural land application has received a greater percentage of total product because of operational simplicity, storage capacity and unrelenting demand from farmers. However, local use has been preserved through the multi-partner Mountains to Sound Greenway Trust biosolids forestry program and the privatized production of GroCo compost.Recently, interest in increasing Class A biosolids production has emerged due, in part, to the EMS principle of “continual improvement” and the desire to prepare the program for future markets. Because of the success of the county's Class B program, planning for Class A upgrades has not been a priority. The county's policy is to continue Class B production and explore technologies that could generate Class A cost-effectively or improve biosolids marketability. For an agency this size, conversion to Class A processing is clearly a major undertaking. A study has been implemented to identify and evaluate Class A technologies that are most appropriate for the county's two wastewater plants and its current and future biosolids markets. This paper reviews the existing program, including technologies previously evaluated by King County, and analyzes alternatives for production of a Class A biosolids.