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Michigan State University
215 Farrall Hall
East Lansing, MI 48824
Phone: 517-355-4720
Fax: 517-432-2892
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Bark Beds – An Option for Treating Milking Center Wastewater?
By: Dr. William Northcott
Assistant Professor in Biosystems Engineering
Milkhouse center wastewater is a problem that every dairy, regardless of size, must deal with on a daily basis. The wastewater originates from the water that is used to clean milking handling and storage equipment and the parlor itself. A typical 150 cow dairy will produce somewhere around 1,000 gallons of this wastewater per day. The wastewater consists of a number of different constituents including detergents and disinfectants as well as some waste milk, manure, and undigested feed. Milking center wastewater is fairly dilute, with a solids content of about 0.5% solids however the strength of this wastewater can be as much as 10 times the strength of domestic wastewater with relatively low nutrient content when compared with straight dairy manure. A new multi-agency project spearheaded by the Biosystems and Agricultural Engineering Department is researching and developing a low cost, low maintenance, environmentally friendly method for treating and disposing of milking center wastewater utilizing shredded tree bark and wood chips, byproducts from a lumber mill. The system is being installed in Gratiot County on a 150 cow dairy farm own by Mr. Joe Ensz and is being fully funded by the Michigan Department of Environmental Quality. The overall goal of this project is to develop and test this low cost technology, show that it works and develop it into a standard that the NRCS (Natural Resource Conservation Service) can provide cost sharing to farmers. So far, there has been a very positive response to this project and we have had a number of cooperators from many agencies and organizations volunteer their time to add input into this project as it has developed. They include:
- Michigan Department of Environmental Quality
- Michigan State Natural Resources Conservation Service
- Michigan Department of Agriculture
- Michigan State University – Department of Biosystems and Agricultural Engineering
- Michigan State University – Department of Crop and Soil Sciences
- Michigan State University Extension
- Michigan Milk Producers Association
- Clinton County Soil and Water Conservation District
- Gratiot County Natural Resources Conservation Service
- Foster Trenching
- Ensz Dairy
Currently under Michigan DEQ regulations, the only option that producers have is to pump their milking center wastewater off to a manure storage structure for later land application. At a volume of 1,000 gallons per day, 365 days a year, that requires a storage volume of 365,000 gallons. When it comes to land application time, this converts into about 50 7,500 tanker loads of wastewater that must be applied to the land for disposal. Besides the potential for runoff and environmental impact of the land applied wastewater there is the cost in the storage structure, machinery, fuel and time for land application. This project involves a full scale system on a dairy farm testing a number of biological (shredded bark and wood chips) and non-biological (recycled Styrofoam pellets) filters to act as a filter mound prior to discharge into a soil based treatment system. Disposing of milking center wastewater via a normal soil treatment system (septic leach field) has been tried in the past and generally fails in a short time due to biological clogging caused by the high strength of the waste water. In this project we are working to avoid that by providing some primary treatment from the filter mound. This project grew out of a student senior design project where BE students performed an experiment by dosing milking center wastewater through a four foot column of landscape woodchips. The students found that they were able to reduce the strength of the wastewater by 70% percent and removed the offensive odor. In this new study, we are building a full scale system to treat 1,000 gallons per day of milking center wastewater. The treatment system itself merges the technologies of biological filtering and small-scale wastewater treatment.
The system is conceptually simple in design. First, the milking center wastewater is drained through a series of 3 1,500 gallon septic tanks. The primary goal of so many septic tanks is to promote a long residence time to remove as many of the wastewater solids, fats, greases, and oils by settling or forming a floating scum layer. By removing as much as possible prior to discharge to the filter mound will decrease the chances of clogging within the filter mound and soil. Next, the wastewater is drained into a pump chamber where it will be pressure dosed out into the filter mound by a screened pump. Through the filter mound, four perforated distribution lines will pulse the wastewater into the mound on a timed basis where it will trickle through the media. The media will act as a site for bacteria to attach and grow where it can feed on the contaminants in the wastewater. After passing through the woodchip/bark media, the wastewater will infiltrate into the ground where it will receive further treatment. Figure 1 shows one of the treatments we will be evaluating in this project.
The filter mound will be built in a small pasture down slope from the milking parlor on the farm. Since this treatment system is going to be full scale and treat around 1,000 gallons per day, it will be taking up a lot of space. The treatment system will be approximately 200 feet long by 18 feet wide. We will be breaking the system up into 4 – 50 foot sections to test different media types and options. These include wood chips, shredded bark, shredded bark with passive aeration, and recycled Styrofoam chips. The evaluated the effectiveness of the system, we will be sampling the wastewater at a number of locations within the treatment process.
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