Dairy Unit Fieldtrip
On Tuesday May 20, 2008 the Bioenergy Summer School interns took a trip to the UF Dairy Unit (DU), formerly known as the Dairy Research Unit, located in Hague, Florida. The DU is a fully operational 800 acre dairy farm run by the Institute of Food and Agricultural Sciences where research on all facets of the dairy industry, such as livestock and manure management, takes place.
Animal manure handling represents a huge problem for every livestock operation. Whether the method of livestock management is free grazing, where manure is left on pastures, or barn confinement, which is the Dairy Unit’s method, where manure control means energy and water intensive management. Either way letting animal manure pile up at farms is dangerous due to potential leaching and contamination of the water supply.
In her efforts to make the dairy industry “more environmentally benign”, Dr. Wilkie had worked on a project which focused on manure management and nutrient recovery. That project turned out to be one of her proudest accomplishments – a 100,000-gallon industrial size, fixed film anaerobic digester. In order to impart the importance of such projects onto the students, Dr. Wilkie gave her interns a guided tour of every operational part of the facility.
Roughly 500 cows are held at the dairy unit and when they are not being milked several times a day they rest and feed in barns. These animals consume a highly nutritious feed made up of corn, citrus peels, alfalfa beans and other ingredients.
The cows are kept in the barn where each cow has a slot with sand bedding. The slot is constructed so that it is only big enough for the cow’s size and most of the solid waste goes into one main trough. Such trough is made from sloped floors where all animal dropping are flushed out with water and following several processes the nutrients end up in the anaerobic digester. Once the waste is flushed out with the sand, which is a natural filter, the sand is settled out and reused for bedding. Water is filtered out and reused. Then the solid waste follows a path where before it becomes an influent it is separated from all the indigestible material which is mainly fiber, a low nutrient material that is later used as a preventative measure for soil erosion on the land surrounding the farm. Next, the effluent is fed into the fixed film digester, where the bacteria grow as biofilm on the plastic media inside the digester. The fixed film media reduces sludge build up and provides a surface area for the microbial cultures, making the digester extremely efficient with a retention time of only three days. In comparison, the retention time for a normal suspended growth drum digester holding about 100 gallons is around 30 days.
The resultants of anaerobic digestion are effluent and biogas. The effluent contains recovered nutrients and is a great fertilizer for the acres of land surrounding the farm. The interns also got to test the gas for its quality - sulfide and the methane content. Sulfides make up dangerous greenhouse gasses and should be kept to a minimum when producing biogas. Methane comprises 80 to 90% of the biogas generated by this biodigester. This high quality biogas can be stored and used to power the facility, currently it is used specifically to heat water and milk. However, the potential for biogas involves much more utility such as power generation and use in vehicles.
Projects such as the anaerobic digester carry out several environmentally responsible and economical purposes for the farm. It reuses water, recovers nutrients, generates energy, and significantly reduces the amount of odor with its closed system. The installation of the digester has also provided the farm with a mechanism for a closed loop cycle allowing it to become a much more sustainable facility. The cows generate waste, which is used to produce energy for the farm and fertilizer for the surrounding land used to grow food for the animals, while water, sand and, nutrients are recycled. Overall, “manure matters when it comes to making the dairy industry more environmentally benign” said Dr. Wilkie while explaining her patented designs.
Before the interns left, they gathered some manure to take with them back to the lab to use as soil fertilizer in their food and energy gardens. What completed the day was a quick stop at the “kindergarten” where baby calves spend their young days. At the end of it the tired interns had declared the trip a success while leaving the DU with a truck full of manure and a head full of knowledge. The next glass of milk they enjoyed had never tasted sweeter.