As the world looks to agriculture for renewable fuels from crops, University of Florida researchers have developed a process that produces energy, extracts valuable nutrients for fertilizer, cuts greenhouse gas emissions, and stops offensive odors. And it’s all done with manure.

It’s an environmentally friendly, profitable replacement for an unpleasant farming task. It’s not often that one new technology can solve several major problems at once, but this innovative animal manure management system is a sustainable option for dairies and other livestock operations that produces renewable energy and protects the environment.

The growing number of big dairy and swine livestock farms — along with urban sprawl in rural areas — has resulted in greater awareness and concern about the proper storage, treatment and utilization of manure. Without proper management, animal manure can get into groundwater supplies, and odor problems can irk nearby residents.

The key to this new waste management system is a natural biological process called anaerobic digestion. It relies on microorganisms to transform animal manure into methane gas. These critters process waste under oxygen-free conditions, making them very different than conventional aerobic systems that use oxygen to treat the waste. Anaerobic digesters can process five to ten times more waste than aerobic systems. Also, the waste is enclosed to keep oxygen out, so anaerobic digestion keeps odors in. Odors, flies, and pathogens are reduced by as much as ninty-five percent.

With anaerobic digestion, the methane produced can be used to heat water or generate electricity, eliminating greenhouse gas emissions that contribute to global warming. About forty cubic feet of methane per day can be produced from the waste of each dairy cow. Each cubic foot of methane contains about 1,000 BTUs of energy, which adds up to a huge amount of usable energy.

Nutrients such as nitrogen and phosphorus can be recovered and used to fertilize crops. The by-products of anaerobic digestion — liquid fertilizer and compost — reduce the need for synthetic fertilizers and soil conditioners that are ordinarily produced using less sustainable methods, providing a cost savings as well as environmental benefits.

The waste treatment system is in place at the University of Florida’s Dairy Research Unit in Alachua.
To demonstrate the technology at a working dairy farm, a large-scale anaerobic digester at the University of Florida’s 500-cow Dairy Research Unit is now generating bio-gas from manure flushed from animal barns and milking parlors.

The fixed-film anaerobic digester tank produces methane gas from flushed manure, and the flare stack burns off excess amounts of gas produced by the system. Some of the gas is used to heat water on site. The patented waste treatment technology is being made available for licensing by UF’s Office of Technology Licensing. Methane technology can solve important energy and environmental problems on dairy farms.

This system takes advantage of the fact that it is less expensive to move liquid containing manure than moving dry manure solids. The anaerobic digester processes manure from the large volumes of water used to flush waste from animal holding areas at the dairy. Because manure flushed from these areas is so diluted by water, only two types of anaerobic digesters are practical for most dairies — covered lagoons and fixed-film digesters.

Covered lagoons require large land areas, gas-tight covers, and careful sealing to prevent nutrients from leaching into groundwater. By contrast, the fixed-film anaerobic digester at Hague is a 100,000-gallon tank that has a relatively small footprint, which can be a real plus when local land-planning issues are a concern.

In covered lagoons, which are less efficient than fixed-film anaerobic digesters, the digestive bacteria float around, making only random contact with the manure particles. In fixed-film digesters, the bacterial growth occurs on the surfaces of the internal media that the waste must flow over, thereby assuring frequent contact. In this way, higher volumes of waste-water can be processed.

A fixed-film digester can process flushed manure in two to three days compared to thirty to forty days for a covered lagoon. Generally, the fixed-film design is suitable for any livestock manure that is diluted with water for transport or processing, such as dairy and swine waste.

Anaerobic digestion reduces the potential for global warming in two ways. First, by capturing bio-gas, anaerobic digestion can reduce natural emissions of methane, a potent greenhouse gas. Second, when anaerobic digestion produces renewable fuel to replace fossil fuels such as coal, oil and natural gas, production of carbon dioxide from burning those fossil fuels is avoided.

Another advantage of anaerobic digestion is that it produces very little sludge. Sludge requires further processing and disposal. With aerobic treatment, less than half of the organic matter from the waste is converted to sludge. The anaerobic digester also lowers the levels of pathogens; starvation and competition with other microorganisms help kill pathogens that might be in the manure.

The fixed-film anaerobic digester has been operating successfully for five years, and some of the methane produced is used to heat water for the milking parlor. The digester is also “farmer friendly” because it is easy to operate and maintain.