Water-Related News

Florida's first "Green City" St. Petersburg Plans to Convert Biosolids and Yard Wastes into Energy

As Florida's first "Green City," St. Petersburg wanted to recover the stored energy in biosolids and yard wastes and convert it into energy. Through a public-private partnership, St. Petersburg proposed to build, own and operate a facility that will use city-generated biostocks (such as biosolids, yard and wood waste, grit and screenings) to fuel a biomass gasification and energy facility. By doing so, the city not only would reduce its costs, but also generate renewable energy and eliminate the release of methane gas and the potential of groundwater pollution from landfills or land spreading.

To evaluate alternate methods of processing dewatered biosolids from its four water reclamation facilities and excess yard wastes, Brown and Caldwell performed detailed, quantitative analysis of 35 options, settling on nine possible solutions. The key was staying open to creative solutions; avoiding a traditional approach that would have been more costly for the city.

The BC team looked at higher quality biosolids (considering that the state was considering a ban on land application of Class B biosolids), more efficient operations and a reduced carbon footprint.

The solution? Upgrade a single plant (instead of all four) to a temperature-phased digestion process, and treat all biosolids at this plant, which will produce Class A biosolids. By pumping all biosolids to a single plant using existing pipelines, the city will save about $30 million over 20 years.