BioCycle October 2004, Vol. 45, No. 10, p. 44
Solids utilization becomes significant income stream as dairy farmers discover range of benefits.
Steve Dvorak

THERE is a growing awareness among dairy farmers regarding the increased valuation of the separated biosolids from anaerobic digestion of dairy waste. Financial benefits for dairy farmers include purchased bedding replacement, biosolids sales off-farm, lowered dairy herd somatic cell counts, reduced dairy culling rates, and easier on-farm manure management.
Dr. Kenn Buelow, DVM, is the manager and partner at Holsum Dairy, near Green Bay, Wisconsin. Holsum Dairy, with a dairy herd of 2,900 lactating cows plus dry cows, installed a GHD, Inc. anaerobic digester system approximately two years ago. The total dairy waste, including parlor washdown water, is about 100,000 gallons/day. That waste stream, along with cattle waste from the barn and milking parlor, gravity flows into the anaerobic digester, which is operated at a mesophilic temperature (100°F). The system has 20 days of hydraulic retention time and is a plug flow based design with the addition of a proprietary biogas mixing system. Approximately 420,000 cubic feet/day of biogas are produced and utilized as fuel in both a Deutz and a Caterpillar engine to produce electricity for sale to the local power utility. Power for the dairy is bought back on a separate meter. Electricity sales are estimated at about $300,000/year with the recent addition of a second electrical generator.
SOLIDS SEPARATION
The biodigested waste is sent to a FAN solids separator, where solids at approximately 30 percent dry weight are automatically separated from the liquid waste stream. The biosolids are stored on a concrete pad and the liquid fraction gravity flows to a storage lagoon. Holsum Dairy utilizes the separated solids in its free stall dairy barn for cow bedding, resulting in an estimated bedding replacement savings of $9,000/month. Surplus solids, sold to five to eight area farmers per week, generate an additional $4,000/month in revenue to the dairy – opening options for the dairy’s manure management plan. Holsum Dairy currently has a backlog of farmers wishing to acquire biosolids for bedding, and is considering additional methods to increase solids production.
Buelow is also pleased that the somatic cell count of his milking herd has decreased from 350,000, when the dairy utilized wheat straw and rice hulls for bedding, to the current 145,000 count with the recycled biosolids. What makes this more remarkable is that Holsum Dairy never has tested or culled individual animals based on somatic cell counts (instead using culling based on criteria such as milk volume production, cow health). This naturally leads to a lower somatic cell count overall in the dairy herd when culling can be done based on individual somatic cell count per cow. Area farmers who are purchasing his biosolids also report similar herd improvements.
Holsum Dairy also has found that the digested liquid effluent, with the coarse solids removed, has led to improvements in its manure management and disposal. The dairy currently hauls about one-third of its liquid via semitankers to its most distant fields. Another third is used to irrigate fallow ground, and the remaining third is irrigated directly on crops during the summer growing season. Besides the lower costs of manure disposal via irrigation, alfalfa fields that Buelow directly applied liquid manure to achieved about 6 to 7 tons of alfalfa production per acre, without the application of commercial fertilizers.
Steve Dvorak is president of GHD, Inc. based in Chilton, Wisconsin. The company has installed its patented two-stage mixed plug-flow digester system across the Midwest (www.ghdinc.net).