RE-CYCLE – AN ENVIRONMENTALLY SOUND SYSTEM FOR HOG WASTE MANAGEMENT
North Carolina State University Swine Nutrient Management Research from 2002. Animal production provides significant agricultural receipts for many state economies, but the environmental impact of animal industries is coming under increasing scrutiny. In North Carolina, hog production accounted for $1.3 billion in cash receipts or nearly 20% of the 1999 agricultural receipts. However, the nearly 10 million hogs in this state annually produce 65,000 metric tons of nitrogen, 20,000 of phosphorus, and 26,000 of potassium. The current waste management strategy of flushing waste from houses, storing it in lagoons, and ultimately applying it to dedicated spray fields has led to public outcry concerning environmental eutrophication, potential pathogen spread, and emissions of odor and ammonia. A new strategy must be developed which addresses these concerns if the industry is to remain a viable, strong contributor to the economy. REcycle is a closed system of integrated technologies that addresses all these identified concerns. The first component of this system is a belt-based waste harvesting system that separates the liquid from the solid waste and partially dries the fecal portion with normal ventilation air. Feces are trucked to a centralized gasification/steam reforming facility for thermal decomposition to a medium Btu gas and a sterile mineral ash. The product gas, or “syngas” as it is called, has many potential end-uses giving the entire system additional flexibility for adjusting to changing power markets. It can be converted to liquid fuels such as ethanol, by a process known as catalytic liquefaction, or it can be used to generate electricity, produce steam, or synthesize chemicals. The ash, a by-product, can be used to produce fertilizer pellets or it may possibly be processed directly into animal feed. The liquid waste, on the other hand, is then directed to an enclosed vessel for processing in a sequencing batch reactor (SBR). The SBR returns the nitrogen to the atmosphere as dinitrogen gas, which normally constitutes 80% of our atmosphere. The treated effluent can then be used as irrigation water. These technologies together recover nutrients for use in the production cycle, yet have no open storage of waste streams or over-application of nutrients to a limited land area. Thus, the “REcycle” system eliminates lagoons, provides “green” or renewable energy, recycles minerals, and avoids environmental eutrophication.