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"RE-CYCLE": AN ENVIRONMENTALLY SOUND SYSTEM FOR HOG

J.B. Koger, G.A. Wossink[1], B.A. Kaspers, and T. van Kempen

Introduction 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 . 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 "" 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 , 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 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 , recycles minerals, and avoids environmental eutrophication. The belt-based manure separation system is the first step for the “REcycle” program. Shown schematically in Fig. 1, the system is adapted to the partially slatted pen design used by some producers so that retrofitting existing structures is possible. The belt runs beneath the slatted portion of the pen, the usual flush area, where the animals naturally dung away from the feeding and sleeping quarters in the solid floored portion of the pen. The slanted belt allows urine to drain into a long, sloped gutter that directs it into a covered storage container. Feces are dried to 50-80% dry matter (DM) during their two to three day residence time on the belt. A demonstration, belt-based housing unit for 100 animals has been installed and is the subject of another report (Kaspers et al., 2001).

Figure 1. Schematic of the belt-based hog pen design.

The belt-based collection system offers many advantages over the flush method. With over 50% DM, rather than the 1% typical of lagoons, transportation is no longer cost-prohibitive. Moreover, this type of waste harvesting is expected to reduce odor and ammonia emissions by approximately 80% (Aarnink, 2000). Microbial metabolism, the source of much of the odor, is inhibited by the drier condition of the waste. The separation of the urine from the feces reduces ammonia formation since the fecal microbes are not allowed to convert urea to ammonia and . Ammonia emissions are further reduced by the fact that the urine is immediately directed to a closed container thereby greatly reducing its atmospheric contact. Roughly 70% of excreted nitrogen is in the urine and the fecal nitrogen compounds are slow to release ammonia, so curtailing ammonia emissions from the liquid waste stream dramatically reduces the overall ammonia release. Sequencing Batch Reactors Sequencing batch reactors are currently in use and continue to be investigated by other research groups. The characteristics of the liquid stream: 15 g/L BOD, 42 g/L COD, and 5% total suspended solids suggest that nitrification/denitrification should occur with a shorter residence time than for whole waste. The nitrogen nutrient load of this waste stream can thereby be converted to dinitrogen gas and released to the atmosphere. Use of this technology with the liquid waste eliminates its polluting potential without the sludge build-up that can occur when SBR is used with the whole waste stream. It is noteworthy, from the environmental standpoint, that the liquid waste can be successfully managed, but SBR research is not being done in this laboratory and will not be discussed further. Steam Reforming Gasification Steam reforming gasificationis the technology of choice for recovering the energy and mineral nutrients of fecal waste. Gasification is a yielding only energy and mineral ash while completely disposing of the waste with no dioxin formation and little or no odor production. A gasifier schematic, Figure 2, helps to explain the process. The feedstock is metered into the heated gasifier chamber (600-800°C) and, in the case of a fluidized bed gasifier, is mixed with a sand-like bed material that assists in heat transfer and mixing. Super heated steam helps to fluidize the bed and to thermally "crack" or decompose the organic compounds into low molecular weight gases as shown in equation 1 (Reed and Gaur, 1999): (1) CH1.4O0.6 + 0.35 O2à 0.4 CO + 0.6 H2 + 0.4 CO2 + 0.1 H2O + 0.2 C Gases and fine particulates percolate through the fluidized bed and are partially separated from one another in the disengagement zone and the subsequent cyclone (not shown). Particulates may be returned to the gasifier for further . The gases are collected, cooled, and scrubbed of any entrained particulates, sulfide, or ammonia that may be in the gas stream. The extreme temperatures guarantee the destruction of any pathogens, microbial populations, and bioactive molecules such as hormones.

Figure 2. Schematic of a steam reforming gasifier (Reed and Gaur, 1999). As a thermal cracking process, gasification is distinguished from combustion and by the reaction temperature and the amount of oxygen available. In combustion, are converted principally to carbon dioxide and water. Temperatures are in excess of 1500°C and oxygen is equal to or greater than the stoichiometric amount required for complete oxidation. Pyrolysis, by contrast, occurs at around 500°C in the absence of oxygen beyond what is available in the feedstock. It results in the formation of gases and charcoal. Gasification is intermediate between these first two processes. Biomass gasification is conducted at 600- 800°C in a low oxygen environment in order to maximize carbon conversion without fouling the gasifier. As a result of the low oxygen concentration, dioxin formation does not occur. When fluidized with super-heated steam, as opposed to air, the resulting product gas has a high hydrogen content, is not diluted with nitrogen, and thus has an energy value of 350-500 BTU per standard cubic foot (a medium energy gas, similar to ). These characteristics offer advantages for flexibility in end-use. Hog waste offers many advantages as a source of renewable energy. In the first place, it is continuously available rather than being seasonally limited, as is the case with crop sources. Being a waste material, it is a low to zero cost feedstock. The proximate and ultimate analyses of the fecal waste are shown in Table 1. The energy content of 14.3 BTU/g (6,500 BTU/lb) and the 45% carbon content suggest an excellent feedstock for thermal cracking processes. Moreover, hog fecal waste has a low amount of nitrogen and , minimizing concerns with NOx and SOx emissions. The low chlorine value is also important for avoiding agglomeration within the gasifier. Indeed, analysis of the bed material at the end of each of four gasification trials showed no formation of agglomerates.

Table 1. Proximate and Ultimate Analyses of Hog Feces Weight Per Cent As Received Dry Basis Proximate Analysis Moisture 23.2 ------Ash 9.4 12.2 Volatile Matter 57.4 74.8 Fixed Carbon 10.0 13.0 HHV (Btu/g) 14.3 18.6 Ultimate Analysis Moisture 23.2 ------Carbon 34.6 45.0 Hydrogen 5.3 6.9 Nitrogen 3.1 4.0 Sulfur 0.3 0.4 Ash 9.4 12.2 Chlorine 0.2 0.3 Oxygen (by difference) 24.0 31.2

Mineral analysis of swine feces by inductively coupled plasma spectroscopy (ICP) suggests that the ash by-product of gasification could be useful as a feed additive. Results of the analysis are shown in Table 2. The calcium to phosphorus ratio of 1.5 is adequate when the phosphorus is highly bioavailable, as is expected to be the case in an ash material. This ratio promotes more efficient utilization of phosphorus (National Research Council, 1998). Ash from the trials conducted to date fails to demonstrate such a favorable composition. Contamination of the ash, presumably by the magnesium oxide bed material and the non-refractory lined test unit, results in an ash containing more magnesium than was supplied in the feedstock. The trials were run, however, in a very small test unit (0.5 lb/h) with no cyclone to remove particulates from the ash. It is expected that full-scale gasification will yield an ash product that more closely reflects the feedstock composition.

Table 2. Mineral analysis of hog fecal ash ppm Elementa Calcium 16,880 21,968 Copper 172 224 Iron 1,418 1,845 Phosphorus 12,820 16,684 Potassium 15,868 20,651 Sodium 2,901 3,776 Zinc 653 850 a Magnesium values are not reported as they far exceeded the feedstock input value. This is thought to have resulted from contamination of the ash by the magnesium oxide bed material.

The test system steam reformer used in these studies was owned and operated by ThermoChem (Manufacturing and Technology Conversion International, Inc., Baltimore, MD). Four trials were conducted to determine the fluidization medium and velocity best suited for conversion of swine waste to syngas with a 1.05: 1 ratio of H2: CO since this ratio is optimal for synthesis of ethanol, the chosen end-product. Bed temperature was maintained at 800°C +/- 15° based on earlier work with poultry litter (Manufacturing and Technology Conversion International, Inc., 2000). Fluidization with a mixture of steam and carbon dioxide gave the desired gas composition, but the loss in higher heating value (HHV), due to reduced hydrogen content, was unacceptable. When steam was used as the sole fluidization medium and oxygen source, a ratio of 2.1, H2: CO, was obtained and the product gas HHV was 382 BTU/scf. Composition of the resulting syngas, depicted in the first bar graph of Figure 3, showed that hydrogen constituted over 40% of the product with and carbon dioxide each constituting approximately 20%. Ethylene and are the only other hydrocarbons present at greater than 1% of the total. Nitrogen from the feedstock is emitted as ammonia is removed in the gas clean-up train. Nutrient distribution analysis indicated that virtually 100% of the input nitrogen appeared in the product gas. Potassium appeared both in the bed material (75%) and in the fines, and phosphorus was almost entirely in the bed material with none detected in the product gas.

Figure 3. Syngas composition from hog waste as a function of fluidization medium. Bars represent, from bottom to top: H2, CO, CO2, C2H4 (first column only), CH4, and "other". The product gas condensate was evaluated for volatile organic compounds (VOC) and semi- volatile organic compounds (SVOC). Quantities detected are presumed to represent the upper limit that would be obtained due to differences between the test system and a commercial unit. That is, a commercial system would have cyclones, lower freeboard heat losses, and higher gas residence times that would mitigate against such levels of VOC and SVOC. The condensate VOC loading was on the order of 0.099 mg/g of dry swine waste with acetone as the primary constituent. The SVOC’s indicated a gas condensate load of 0.038 mg/g dry feedstock and naphthalene and phenol were the principal components at 0.01 mg/g each. These components can be further reduced by design adjustments on the commercial scale, but the modest levels validate the technical feasibility of this approach.

Catalytic Liquefaction Catalytic liquefaction, or the synthesis of liquid compounds such as ethanol from gaseous starting materials, is the method of choice for conversion of the syngas to fuel-grade ethanol. The process is preferred to the biological, fermentative route for reasons of synthetic and product-purification ease. While the catalytic method suffers from some lack of specificity, the conversion efficiency is excellent, mass transfer problems are greatly reduced, and there is no residual waste requiring disposal. Metal complexes, such as molybdenum sulfide, cause the carbon monoxide and hydrogen in syngas to form that then undergoes a condensation reaction producing higher alcohols. Ecalene ä produced in this way by Power Energy Fuels (Laramie, WY) is 75% ethanol and 25% higher alcohols (propanol to hexanol). Various catalysts are available and estimates of ethanol yield from one ton of hog waste range from 95 to 190 gallons. Currently, ethanol production facilities using this catalytic technology are steam reforming natural gas to syngas for ethanol synthesis.

Economic Analysis Economic Analysisof the “REcycle” system has been undertaken. The results, summarized in Table 3, are presented as the “Best Case” (maximum anticipated profits and minimum anticipated costs) and “Worst Case” (maximum costs, minimum profits) scenarios. The model system used for the analysis is a gasifier installation serving approximately 500,000 animals. For example, in a county such as Duplin, NC, there are roughly two million hogs in a 900 square mile area. Locating four gasifier installations in that county would provide each with 250 tons of fecal dry matter per day for processing assuming all producers were feeding into the system. Each gasifier would ideally serve farms within a 7.5 mile radius, hence a reasonable transportation distance. Based on the lower estimates of ethanol production (90 gallons of ethanol per ton of waste), a profit can be made in even the worst case scenario, as shown in Table 3 and calculated per pig place. When multiplied by the number of pig places in North Carolina, ethanol yields are sufficient to fuel 70,000 vehicles burning E-85 (85% ethanol fuel) at the average rate of approximately 40 gallons per week as indicated in Table 4. The potential profit for the system can be up to $60 million on the state level. National figures are roughly 6- fold greater as can be seen from the animal numbers. Achieving the higher ethanol yield, or combining hog waste with other animal and biomass wastes, could increase production and profits even further.

Table 3. Annual profit potential per pig place. Worst Case Best Case Revenues Ethanol and Ash $23.36 $27.55 Costs Housing $8.36 $7.35 Technologies $11.95 $11.40 Transportation $2.92 $1.46 Profit $0.11 $7.34

Table 4. Annual state and national ethanol production and profit potential. North Carolina USA (millions) (millions) Number of pig places 8 50 Fecal Dry Matter (tons) 1.5 9.2 Potential ethanol yield 140 870 (gallons) Potential profit (US Dollars) $37 $222

Implications The “REcycle” system promises to reduce the threat of agricultural while providing a clean source of renewable energy and returning minerals to the production cycle. The feedstock is constantly available, so off-season storage is not required. Using waste to provide renewable energy addresses two problems at once: environmentally sound disposal of a waste material, and a sustainable, renewable domestic energy supply.

References Aarnink, A. J. A., 2000. Institute for Environmental and Agritechnology, Wageningen, The Netherlands, personal communication. Kaspers, B. A., 2001. A Conveyor Belt Waste System for Swine. Poster, International Symposium Addressing Animal Production and Environmental Issues. Sheraton RTP, Oct. 3-5, Research Triangle Park, NC. Manufacturing and Technology Conversion International, Inc., 2000. Cost-Effective, Clean and Modular Biomass Power System for the Utilization of Farm Animal Waste. Phase I Final Report. Prepared for the US Department of Energy, Award #DE-FG02-99-ER82822, Small Business Innovation Research Program, pp 1-1 to 2-43. National Research Council. 1998. Nutrient Requirements of Swine, 10th Revised Edition; p. 51. National Academy Press, Washington, DC. Reed, T. B., and S. Gaur, 1999. “Current Status of Biomass Gasification” A Survey of Biomass Gasification 2000. The National Renewable Energy Laboratory and The Biomass Energy Foundation (Golden, CO), pp 1-1 to 1-32.

[1] Dept. of Agricultural and Resource Economics, Box 8109, NCSU, Raleigh, NC 27695-8109