SPOKANE SOLIDS HANDLING UPGRADE

The City of Spokane, Washington is upgrading its advanced wastewater treatment plant (SAWTP) and improvements to solids thickening, dewatering, odor control and sidestream treatment are being made to provide capacity for growth, to meet more stringent water quality requirements, replace facilities beyond their useful life and respond to neighbor interest in reducing odors from the SAWTP. Solids are treated by anaerobic digestion prior to land application on dry land grains. The City of Spokane has operated the land application program including site acquisition, permitting, hauling, biosolids application and monitoring since the early 1980s. The City wished to continue its land application program for biosolids. This paper describes the evaluation of thickening, dewatering, odor control and sidestream treatment alternatives for the SAWTP. Recommended thickening alternative is cothickening of primary and waste activated solids using gravity belt thickeners. Recommended dewatering alternative is belt filter presses. Recommended odor control alternative is use of enclosures for GBTs and BFPs to minimize the volume of odorous air produced and to provide the optimum environment for operations and maintenance staff and biofilters for odorous air treatment. The initial project of installing new BFPs and a biofilter for treatment of odorous air from dewatering is complete. The organic media biofilter is removing greater than 99% of hydrogen sulfide, greater than 95% of ammonia and greater than 97% of odors based on odor panel testing.