As part of the District’s mission of resource recovery, Nine Springs Wastewater Treatment Plant (NSWWTP) utilizes a phosphorus recovery process to produce a commercial struvite product for beneficial reuse as a fertilizer. Removal of phosphorus from the waste stream allows the District to produce a beneficial product for reuse and reduces the labor and cost involved with removing nuisance formations of struvite in the solids handling processes. The struvite harvesting process takes place in the Struvite Harvesting Building dedicated to this use at NSWWTP. The Struvite Harvesting Building was constructed in 2013 as part of the 11th Addition Project, which was primarily focused on solids handling at NSWWTP. The struvite harvesting process is fed digested sludge filtrate and waste activated sludge filtrate from a series of gravity belt thickeners. The filtrate is fed through two parallel process trains. The filtrate is screened and fed into the reactors. Magnesium chloride is added to provide additional magnesium to maximize struvite production, and sodium hydroxide is added to maintain pH to optimize precipitation of the struvite. Precipitated struvite produced in the reactors is then fed to the vibrating dryers where it is heated with the plant hot water loop. The exhaust passes through a cyclone system to remove fine particles before being discharged out the side of the building. During the time the struvite harvesting process has been in operation, some issues have been observed with these first-generation drying and seeding processes which will be addressed under this project to improve reliability, safety, and production capacity.
