30 March 2017
Posted in Center Information
High-Solids Anaerobic Digestion (HS-AD; aka Solid-State AD) is frequently used to process and produce bioenergy from the organic fraction of municipal solid waste (OFMSW), including yard waste, food waste and industrial organics. Compared with landfills or bioreactor landfills, HS-AD promotes faster OFMSW degradation, higher biogas methane content, reduced greenhouse gas (GHG) emissions and recovery of nutrients as compost. OFMSW diversion also saves landfill space and improves leachate quality at landfills. HS-AD of OFMSW has been rapidly increasing over the last decade in Europe and the US; however, no HS-AD facilities currently exist in Florida. The overall goals of this project were to evaluate the potential for HS-AD in Florida and improve methane production during HS-AD of the OFMSW. Specific objectives were to: 1) evaluate the most appropriate technologies for implementing HS-AD of OFMSW in Florida, 2) carry out fundamental research improve the biodegradability of lignocellulosic waste through co-digestion with pulp and paper mill waste anaerobic sludge (P&P), and 3) identify potential sites, collaborators and funding sources for a HS-AD demonstration in Florida.
State-of-the-Art of HS-AD: Current trends in Europe and the US suggest that single-stage HS-AD technologies are most appropriate for implementation in Florida due to their low cost, simplicity and reliability. The suitability of advanced HS-AD technologies, such as continuous and multi-stage systems, will depend on industry and legislative developments. Key factors affecting HS-AD economics include the quality, quantity, and proximity of OFMSW, markets for compost, energy, and renewable energy credits, and public-private partnerships. Source-separation of OFMSW is a critical factor affecting the economics of HS-AD, as it improves energy recovery and compost quality. However, more research is needed on the sustainability of source separation of putrescible waste in warm climates, such as Florida.
Enhancing Bioenergy Production: The potential to enhance methane production from yard waste via inoculation with P&P sludge, which contains microbial populations that are acclimated to a lignin-rich waste stream, was investigated. Side-by-side bench-scale HS-AD experiments were carried out under mesophilic conditions with yard waste inoculated with P&P sludge (bioaugmentation) and domestic wastewater anaerobic digester sludge. A 73% enhancement in methane yield was observed using the bioaugmentation strategy. Trends in volatile fatty acid concentrations suggested that increased methane production was due to acceleration of hydrolysis in the bioaugmented digesters. Additional experiments showed that enhancement could be sustained through digestate recirculation.
Potential for HS-AD Implementation in Florida: A detailed review of MSW management trends in Florida was conducted, with a focus on recent trends in OFMSW generation and management and relevant legislation. This information was used to identify locations where HS-AD may be promising based on potential for bioenergy production, GHG emissions reductions and nutrient recovery. Based on these criteria, the following counties were identified: Miami-Dade, Broward, Palm Beach, Hillsborough, Orange, Pinellas, Duval, Lee and Alachua. However, more research is needed to understand the compatibility of HS-AD with existing MSW infrastructure, particularly WTE. Florida universities may represent an opportunity for HS-AD demonstrations, as they generate large quantities of OFMSW, offer partnership and funding opportunities, and are a hub for education of future MSW professionals. Legislative incentives, as seen in Europe and California, would help foster implementation of HS-AD in Florida.