Life-Cycle Modeling Of Nutrient And Energy Recovery Through Mixed Waste Processing Systems

There is increasing interest in recovering nutrients and energy from the organic fraction of municipal solid waste (OFMSW). Given the costs associated with separate collection of OFMSW, and the potential difficulty in finding clean feedstocks, there are potential benefits in beneficial recovery of OFMSW as part of residual MSW. Therefore, this study compared the life-cycle impacts associated with management alternatives for recovering energy and/or nutrients from the OFMSW through mixed waste processing systems. The considered treatment alternatives include landfilling, mass burn waste-to-energy, gasification and syngas combustion (GC) for electricity production, gasification Fischer-Tropsch (GFT) for transportation fuel production, aerobic composting (AC), and anaerobic digestion (AD). Seven environmental impacts include global warming potential (GWP), cumulative energy demand, acidification, eutrophication, photochemical oxidation, ecotoxicity, and human toxicity were assessed for five sets of state and one U.S. national waste compositions. The mass burn waste-to-energy and GC scenarios generally have the lowest environmental impacts, while landfilling and GFT have the greatest impacts. Separating out organics for AC increased environmental impacts compared to sending them to GC, while sending them to AD decreased GWP and increased the other impacts. Sensitivity analyses suggest that these conclusions are generally robust to uncertainty in input values.