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ARS Home » Southeast Area » Florence, South Carolina » Coastal Plain Soil, Water and Plant Conservation Research » Research » Publications at this Location » Publication #324547

Title: Livestock waste-to-energy opportunities

item Ro, Kyoung

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/16/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The use of animal manure and other organic-based livestock wastes as feedstocks for waste-to-energy production has the potential to convert the livestock waste treatment from a liability into a profit center that can generate annual revenues and diversify farm income. This presentation introduces two prominent livestock waste-to-energy technologies; anaerobic digestion (AD) and pyrolysis. Biochemical and thermochemical platforms are the two basic platforms exist for converting organic biomass into energy. Biochemical conversion processes use living organisms or their products to convert organic material to fuels. AD is the most dominant waste-to-energy technology which produces combustible biogas. AD breaks down complex organic wastes and produces biogas, chiefly methane (60-70%) and carbon dioxide (30-40%), by a community of anaerobic microorganisms. Potential benefits of AD are odor control, potential pathogen kill, reduction of wastewater strength, preservation of plant nutrients for use as a high quality fertilizer, and production of a renewable energy source- biogas (Cantrell et al., 2008). The biogas can be used to meet on-farm heating needs or to meet electrical demands with the excess electricity having the potential to be sold to a local utility company. Unfortunately, in the case of farm-scale dairy manure anaerobic digestion, the energy savings and potential revenue (i.e., current selling price of electricity) were mostly not enough to provide a positive cash-flow (Wright et al., 2004). Contrasting to slow biological-based conversion processes requiring an extended amount of reaction time (days, weeks or even months), thermochemical conversion processes (TCC) can quickly (seconds to hours) convert livestock wastes into combustible gas and value-added products. Pyrolysis is one of main TCC processes for converting livestock wastes-to-energy, which breaks down chemical bonds of biomass feedstock with heat in the absence of air. The end product of biomass pyrolysis is some combinations of combustible gas, oil, and carbonaceous solids called biochar. Biochar could be used as a soil amendment to improve soil quality. The distribution of the end products depends on the operating temperature, pressure, heating rate, and residence time. When swine manure, chicken litter, and a mixture of swine manure with rygrass were pyrolyzed, swine manure produced gas with the highest heating value followed by the mixture of swine manure with rye grass and chicken litter (Ro et al., 2010). Biochar yield ranged from 43 to 49% based on dry weight with about 53% of carbon recovery. While the heating value of the chicken litter biochar was slightly below that of low rank coals, swine manure based biochars had heating values between high and low rank coals. Approximately 50% of the feedstock energy was retained in biochar and 25% in produced gases. Manure-based biochars contained higher concentrations of phosphorus (P) and potassium (K) than that of original manure feedstocks. Consequently these could be used as a low-grade fertilizer to improve soil fertility and crop yields. Extremely high energy (232.3 million Joules per kilogram, MJ/kg) was required to make 1 kg of biochar from wet swine manure with 97% moisture content (MC), making the process energetically not sustainable. Dewatered swine manure with 75% MC required substantially lower external energy by 19 folds. However, the pyrolysis process with dewatered swine manure was still energetically unsustainable. Co-pyrolyzing swine manure with high energy density spent plastic mulch (SPM) film eliminated the need for external energy (Ro et al., 2014). The heating value of the product gas from the co-pyrolysis was found to be much higher than that of natural gas; furthermore, the gas had no detectable toxic fumigants. Energetically sustainable swine manure pyrolysis could be achieved by