Biosolids- and Yard-Waste-to-Energy Feasibility Study in St. Petersburg, FL

The City of St. Petersburg, FL (City) produces an average of 41,000 wet tons per year (WTpY) of Class-B biosolids and 40,000 WTpY of yard waste. The City operates four Water Reclamation Facilities (WRFs): Albert Whitted WRF, NEWRF, NWWRF, and SWWRF. Plans are underway to decommission the Albert Whitted WRF and pump that service area's wastewater to the SWWRF for treatment. The Biosolids- and Yard-Waste-to-Energy Feasibility Study (Study) was driven by the State of Florida's “effective ban” on Class-B biosolids land application (Florida Administrative Code Chapter 62-640) and the City's desire to produce renewable power from currently under-used resources.During the feasibility study, the team (City of St. Petersburg and Brown and Caldwell staff) investigated over 35 options and determined that a 2-phase approach could save the city up to $33 million over the next 20 years. The two phases consist of:Phase 1. Consolidate all solids processing at the SWWRF through a combination of sludge forcemains and the existing collection system. Add primary clarifiers to “catch” the conveyed solids and other settleable solids at the SWWRF and upgrade the digestion at that plant to Class-A, temperature-phased, anaerobic digestion (TPAD). Digester gas would be used to fuel new engines for production of 1.2MW of power and the heat needed for Class-A digestion. Additional thickening and dewatering capacity would also be required.Phase 2. Develop a yard-waste-fueled thermal process to produce additional power; this is currently envisioned as gasification with syngas-to-internal-combustion-engine power generation. Depending on the selected thermal process and its final configuration, biosolids may also be burned in this system.The Phase 1 improvements are moving forward while the Phase 2 efforts have been deferred until certain technical and economic conditions have been met. The two phases have been coordinated so that all Phase 1 improvements will have benefit/be integrated into the Phase 2 improvements.