July 25, 2007 | General

Converting Waste Streams To Energy And Other Valuable Commodities

BioCycle July 2007, Vol. 48, No. 7, p. 62
Iowa DNR prepares interactive mapping tool as part of outreach to link codigestible feedstocks and industries that are large energy users to achieve widespread benefits.
Jim Bodensteiner

LIVESTOCK and food processing industries in Iowa provide tremendous economic benefit to the state. However, managing waste streams from these industries economically, while mitigating environmental risks and negative societal perceptions, is a growing challenge.
Recognizing the enormous opportunity for implementation of large-scale anaerobic digester systems in Iowa, the Department of Natural Resources (DNR) set about promoting the digester concept to Iowa communities having large concentrations of livestock production, large volumes of organic wastes, and large energy users.
Through anaerobic digestion processes, manure, food processing waste, and other industrial organic waste streams can be converted to renewable energy and valuable fertilizers. The methane recovered can be used to fuel large industrial processes or to generate electricity and thermal energy for community use. Digested biosolids can be used as fertilizers, soil amendments and livestock bedding.
According to a survey conducted by the U.S. Environmental Protection Agency, Iowa has the second highest methane production potential from swine production in the nation (Table 1). Methane recovered from Iowa’s swine industry alone could be used to generate 677,000 MWh of electricity per year, enough to power 63,469 average American homes. Recovered methane could also be used to heat 130,000 average American homes or to power three 100 million-gallon/year ethanol production facilities (boilers, evaporators, and dryers). Energy-intensive Iowa industries, such as ethanol production facilities, can benefit as end users of this renewable energy resource.
Methane is the main component of natural gas. It is also a component of biogas, which is generated during the decay of organic (living or once-living) materials in an anaerobic, or oxygen-free, environment. Oxygen-free conditions occur in natural systems such as the bottom layers of wetlands and bogs, and in artificial systems like landfills, anaerobic lagoons, and specially designed tanks called anaerobic digesters.
Figure 1 illustrates the process of converting waste to energy and nutrients with a community-scale anaerobic digester system.
Anaerobic digesters that produce the most methane are those designed as codigestion systems. Livestock manure is essential to the process, but the addition of organic feedstocks to the mix increases gas production dramatically. Good feedstocks or substrates for codigestion include: cattle manure; pig manure; poultry manure; sewer sludge; vegetable processing residues; dairy processing residues; brewer sludge; restaurant waste; fish oil and processing residues; bleaching clay; milk processing residues; crushed oil waste; glycerin from biodiesel; and thin stillage from ethanol.
Not all systems will look or operate the same. System designs or models can include community-based digestion with a centralized organics collection facility; integrated systems that incorporate municipal wastewater treatment with the anaerobic treatment of livestock manure and other organics; industrial park models where industries with problematic waste streams build and use a digester collectively; and self-sustaining closed-loop systems, that integrate livestock production and anaerobic digestion to fuel ethanol production.
Closed loop systems increase the efficiency of ethanol production significantly. The digested manure and thin stillage from the ethanol process feed the digester, the biogas off the digester fuels the ethanol plant, and the wet distillers grains from ethanol production feed the livestock – typically beef or dairy cattle. Biogas offsets the natural gas that fuels most ethanol production, and the feeding of wet distiller’s grains onsite eliminates the need for fuel to dry the grains and the use of transportation fuels to ship them offsite.
Economic benefits include: Recovery of a renewable energy resource – biogas; Capture of valuable, nutrient measurable, and more environmentally benign crop fertilizers; Production of soil amendments, compost, fiber, and animal bedding; Carbon credit trading to monetize the environmental benefits of methane recovery; Elimination or reduction of fees and other costs associated with livestock mortality disposal and organic waste management; and Creation of community economic development opportunities, including jobs, business development, increased tax receipts, and green energy investment opportunities.
Environmental benefits include: Improved air quality through the recovery of methane, a greenhouse gas 21 times more damaging to the atmosphere than carbon dioxide; Improved water quality, as captured organic nutrients are converted to inorganic fertilizers that are taken up by plants more quickly, reducing the risk of stream and groundwater contamination; and Increased production of a renewable energy resource that reduces fossil fuel use and the emissions associated with fossil fuels.
Societal benefits include: Reduction of odors associated with livestock production and land application of manure by 90 percent or more; Reduced dependence on foreign oil and the reduction of the security risks associated with that dependence; Promotion of good environmental stewardship and corporate responsibility; and Improved community perception of participating industries.
The Iowa Anaerobic Digester Asset Mapping Tool was designed to assist the DNR and its partners with identification of Iowa sites that have large quantities of codigestible feedstocks as well as industries that are large energy users. Mapping data sets available, to date, include wastewater treatment plants, confined feeding operations, open feedlots, food manufacturing facilities, rendering facilities, municipal gas and electric utilities biodiesel production facilities, and ethanol production facilities (in house, under construction, operational).
To use DNR’s GIS-based interactive mapping tool, go to http://www.iowadnr.gov; click on the “Mapping (GIS Interactive)” link in the left menu near the bottom; and select the “Anaerobic Digester Map” link to open the map.
Jim Bodensteiner is Biomass Program Manager for the Iowa Department of Natural Resources based in Des Moines. He can be contacted via e-mail at jim.bodensteiner@dnr.state.ia.us. Phone contact is (515) 281-8416.

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