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The Elk River Wastewater Treatment Plant (WWTP) processes solids via anaerobic digestion, and then provides further treatment and biosolids storage in facultative sludge lagoons (FSLs). Biosolids are harvested (dredged) from lagoons in the summer months and land-applied on 85 acres of land owned by the City of Eureka, California. The land base is inadequate to accommodate 100 percent of biosolids production. As a result, a solids inventory has accumulated in the lagoons and effective capacity is compromised.

A biosolids dewatering facility design is in progress to address this issue. After review of available technologies, the FKC® screw press was pilot-tested and a request for a price quote was issued. The FKC process can dewater FSL solids to facilitate transport to more distant agricultural land. The process includes an option to provide lime pasteurization and generate a more marketable Class A biosolids product. In addition to dewatering and lime pasteurization, a covered slab will be included in the upgrade to provide seasonal product storage and improve product marketing flexibility.

To allow rapid project implementation and relieve storage in the lagoons, a design/build procurement strategy was initially considered. However, the decision to stick with conventional procurement was subsequently made to retain greater control over facility design. To address the immediate solids inventory problem, additional application sites will be permitted on agricultural land within 10 miles from the WWTP.

The current direction for improvements is to implement dewatering only initially, and then upgrade to provide lime feed and heating. Potential markets for a Class A biosolids product include local compost and topsoil blending, as well as local soil improvement. Savings on future Class A product handling and transportation are expected to help offset increased processing costs.

Document Type: Research Article


Publication date: 2007-01-01

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