by Dana Kirk

Producers looking to generate renewable energy from animal manure have more technological choices today than ever before. Common renewable energy technologies include anaerobic digestion, direct combustion and gasification. As of 2008, there were 121 operating anaerobic digesters on livestock farms in the United States. Six of those are on Michigan farms, and another four are serving food processing facilities in the state. Michigan is also leading the development of livestock manure gasification. One of the first U.S. systems is scheduled to go into operation in the spring of 2009.

If you’re considering creating a renewable energy system on your farm, the first thing you should do is determine the energy needs of your farm (electric and heat) and think about other goals you want to accomplish. Besides producing renewable energy, the systems can reduce manure odor, volume and pathogen levels, and aid in nutrient management.

Next, determining the moisture content of your manure is critical. Knowing the moisture content will allow you to make the first cut of appropriate technologies. Technologies appropriate for a manure slurry (90 to 95 percent water), such as anaerobic digestion, may not work if the water content is significantly lower without pretreatment.

Evaluating the impact of a renewable energy system is the next critical step. Renewable energy systems are expensive and require a dedicated, skilled operator to be successful. The products generated by the energy conversion system may be quite different from untreated manure, so using them will change your manure management and utilization practices. The type of system adopted may also limit the management options available for a livestock or poultry production facility. For example, bedding and animal health products used at the production facility have a profound impact on biological systems such as anaerobic digestion.

To maximize the economic return from the system, energy produced should be used to replace as much of the facility’s purchased power as possible before you consider selling energy. Utilizing byproducts from the system will also improve its economic viability. Waste heat from the gas processing facility and nutrients and fiber contained in the effluent are the potentially valuable byproducts. Also, the value of the technology in solving environmental and nuisance issues should not be ignored. Rapidly advancing technologies such as algal production and manure-fiber-based wood composites may provide opportunities for utilizing the byproducts.

Learn more about this topic during the Manure $ense workshops. See the back page of this Scoop for more details. (click here for more details.)

Click here to read the full issue of the January 2009 Scoop.