A Two-stage Fluidized Bed Combustor for Treatment of Waste from Livestock Operations

There is a growing concern for adverse effects of untreated discharge from confined animal feedlot operations (CAFOs) in the Midwestern states. Ample data exists to show that the waste discharge from livestock operations is a major contributor to the contamination of surface water systems. The United States Environmental Protection Agency (US EPA) estimates that 41 percent of the total non-point source (NPS) pollution results from agricultural sources, and a third of that is attributable to large CAFOs. Water quality concerns such as the spread of pathogens, residual antibiotics, and pesticides are becoming serious. In addition noxious odors emitted from the waste is a major nuisance in the vicinity of such operations. Clearly effective and economical treatment technologies are required to reduce the discharge volume, destroy pathogens and other harmful components such as residual pesticides, and eliminate or reduce odor. A two-stage fluidized bed combustion system was designed and fabricated in our laboratory for treatment of the waste from livestock operations. The system includes a biomass concentrator and a two-stage fluidized bed combustor. Both combustor stages are equipped with 8000 BTU/pound solid-fuel burners. The fuel for the burner is derived from the livestock wet-waste slurry (15-20% solids). The slurry is fed into the fluidized bed dryer maintained at approximately 650oC (1200oF). The hot combustion gases are used to remove excess moisture from the waste stream in a fluidized bed dryer. The dry solids from the first stage are fed into the second solid-fuel burner. The disinfected solids from the first stage can be used as fuel or fertilizer. The flue gases from the fluidized bed are combusted in a secondary burner generating an odor-free off gas, which is released through a cyclone-equipped stack. The system yielded high disinfection efficiency; pathogens such as salmonella and E. coli were effectively eliminated from the treated residues. High destruction efficiencies were obtained for selected insecticides such as organophosphates and carbamates.