GAINESVILLE---No way around it: Manure happens. But when it happens in dairy farms near residential areas, the odors can provoke protests that threaten the dairy's survival. Now, however, a team of University of Florida researchers, led by Professor Ann Wilkie, seeks a solution that not only eliminates the odors, but also produces methane gas for energy, conserves the fertilizer value of the manure and recycles valuable water. "What is the cost of odor reduction?" asks Wilkie, research assistant professor in soil and water science at the Institute for Food and Agricultural Sciences. "It may be the cost of staying in business." Dairy farms in Florida use water extensively for cleanup and flushing because it is sanitary, saves labor and is inexpensive. In addition, many dairies have incorporated fan and sprinkler cooling systems. The most commonly used manure-management system in the newer dairies in Florida utilizes short-term holding ponds for flushed-manure wastewater storage, with subsequent pumping to sprayfields to supply fertilizer nutrients and irrigation water for production of forage crops. Although effective for nutrient recycling, these systems can produce strong odors. Spreading of manure slurry on land is the single largest cause of complaints from the public, but odors also arise from buildings and waste storage facilities. Odor complaints can place great pressure on farmers. Anaerobic digestion, a biological process in which complex organic compounds are decomposed by microorganisms in the absence of oxygen, offers a holistic solution. During storage of manure, malodorous compounds are formed as a result of incomplete microbial fermentations. In contrast, when anaerobic digestion is used under controlled conditions, most of the digestible organic matter is biodegraded with a less-offensive effluent and energy byproduct, methane gas. Using this concept, Wilkie and her graduate research assistants are developing an anaerobic digester, known as a fixed-bed reactor, for treating the dairy wastes. Unlike aerobic systems that require energy input, anaerobic treatment is energy producing. The fixed-bed anaerobic reactor immobilizes bacteria on a matrix or medium within the reactor, thereby preventing washout of the microbial substance. Wastewater is passed through a column filled with packing, usually a honeycomb-like structure made of plastic or other material. The packing material acts as a surface for the attachment of microorganisms and also as a trap for unattached organisms. The end result is methane and carbon dioxide. The fixed-bed anaerobic reactor is capable of treating larger volumes of wastewater than conventional systems. Where it would take conventional anaerobic digesters about 20 days to handle the waste, a fixed-bed reactor can often do the job in as little as two days. Thus the fixed-bed reactor is appropriate technology for Florida dairy farms given the large amounts of water used. Wilkie has been using four, 400-liter pilot plants, but is now building a full-scale plant at the IFAS Dairy Research Unit in Hague. The reactor is an 86,000-gallon steel tank, 25 feet in diameter and 23 feet tall. The plant is expected to handle the waste from a 350-cow operation. Perhaps the biggest challenge involves the medium which makes up the honeycomb-like structure, to which the bacteria cling. The problem is matching up the proper type of bacteria to the proper surface -- an issue best dealt with on the microscopic level -- and finding the proper hydraulics, including the proper flow rate of waste, explains Kelly J. Riedesel, one of Wilkie's graduate research assistants. "That's where you make it work," she said. "If you don't get the cells attached, you can't treat the waste." Solving the problem gives Wilkie's work a global perspective. "We have similar conditions in climate and humidity," research assistant Hector Castro says about his native Uruguay and its dairy industry. "We have no real treatment right now. But this (Wilkie's anaerobic digester) will be directly applicable for us." The benefits to the dairy industry are likely to be significant. But for some, the appeal goes beyond the elimination of odor. Truth be told, Wilkie and her colleagues are thrilled about developing a holistic system that takes on several problems and unites them into one solution. As they see it, an anaerobic digester functions as an integral part of the total waste-management system; advantages and disadvantages should be reviewed in the context of the overall system. In addition to eliminating odor, the potential benefits from anaerobic digestion include improving water quality, improving handling and fertilizer value of the wastes and production of biogas for general farm use. Farms, with their many pumps, fans and other devices driven by small motors, are a natural place for methane conversion and use. Methane generally is considered the second most significant greenhouse gas, after carbon dioxide. Anaerobic digestion cuts uncontrolled methane release. Then there is the conservation of water, a particularly precious resource in Florida. Water has numerous uses on a dairy farm, including cleaning and cooling. "We use copious amounts of water," Wilkie says. " But, adds another research assistant, Kevin Cubinski: "Ultimately, you could have a closed-loop dairy where you recycle all your water." Wilkie says their role is one of applying their expertise in environmental microbiology to the solution of real-world problems, with the ultimate goal of preserving valuable natural resources.
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