Treatment and Disposal of Milk House and Milking Parlor Wastes

Land Surface Treatment

After the larger solids have been separated and remain in the settling tank, the relatively clear liquid discharging from the tank can be treated by applying it to the ground surface. The liquid must be spread over a large enough area so that it will seep into the soil and allow grass or other vegetation to grow and utilize the liquid during the growing season.

The surface soil will do an excellent job of treating the liquid wastes. As the liquid seeps into the soil, the fine solids are filtered out and become part of the organic matter of the soil. All of the phosphorus and most of the nitrogen will be trapped in the top soil for plant use. During the summer, water will either evaporate or be used by the plants.

A simple method to spread the liquid wastes over the soil area is to construct small terraces along the contour (figure 2). Space the terraces 8 to 16 feet apart depending upon the topography. The top of the terrace ridge should be level throughout its length and the ends of the terrace should be closed so that the liquid will flow evenly over the length of the ridge and into the soil area between it and the next terrace. Establish grass along the terrace ridge and allow grass or natural vegetation to grow between the terraces.

Figure 2. Surface spreading of liquid wastes with contour terraces

Discharge the liquid wastes on the ground above the top terrace to protect against erosion. As the top terrace fills, the liquid will flow over the top of the terrace and onto the ground surface down to the next terrace.

Allow grass or other vegetation to grow between and in the terraces. Do not remove the vegetation; it will protect the system against freezing during the winter. Fence the area to prevent farm animals from entering and construct a diversion above the area to prevent any surface runoff from entering.

Use 5 square feet of surface area for each gallon of liquid waste to be disposed of per day. The area should include the terrace bottoms as well as the area between the terraces provided the liquid is distributed evenly over the length of the terraces. For example, if 535 gallons of liquid waste are to be treated, the total area would be 2,675 square feet, or slightly larger than 50 feet by 50 feet.

Two methods can be used to prevent the discharge pipe from freezing when liquid wastes are pumped to the treatment area. The first is to install the discharge piping on a uniform slope back to the pump. No check valve is used and the pipe drains back when the pump stops (figure 3).

Figure 3. Pumping waste water to treatment area

The second method to prevent freezing is to use an ejector. The pressure pipe from the pump and the bottom of the ejector are buried below frost level. The liquid waste drains back down the 1¼-inch discharge pipe of the ejector after each pump operation. During the next pump operation the jet action sucks out the liquid stored in the bottom of the outside casing or standpipe (figure 4).

Figure 4. Ejector for waste water distribution and to prevent freezing

The pressure pipe between the pump and the ejector does not need to be on a uniform grade, but the pipe should be buried below frost depth. The liquid level of the pumping tank must be below the frost penetration elevation at the site of the ejector. A check valve may be used since the discharge pipe of the ejector will drain automatically (figure 4).

The ejector may be used for surface spreading for relatively small amounts of waste water. Turn the discharge nozzle one quarter turn every 3 to 4 days to prevent excessive wetting of the soil. The best location for the ejector is oil a slightly sloping area, below and at least 50 feet from the well and 200 feet from the house. Locate the ejector where runoff will lot discharge into any area accessible to livestock or into any lake or stream. Ejector discharge must not be allowed to pond in the milkhouse area to prevent fly breeding. The ejector can be used to apply the waste water over the ground surface in the area above the furrows previously described (figure 2).

The pump should deliver at least 10 gallons per minute to the ejector. A flow greater than 20 gallons per minute should not be used. A low head sump pump is usually adequate unless the surface treatment area is more than 15 feet above the bottom of the pumping tank. The pump can be a submersible sump pump located in the pumping tank as shown in figure 3 or the pump can be self-priming and located in the milkhouse (figure 5).

Pump at least 50 gallons of waste water per pump cycle at a rate of 10 gallons per minute to suck the waste water out of the standpipe from the previous cycle. Solids will plug the nozzle of the ejector. To flush the line from the pump before connecting it to the ejector. To avoid possible blockage of the ejector, remove the inner pipe of the ejector for a few days each fall before freeze-up. Then the pump can flush any sediment out of the pressure line.

The ejector is a method of surface spreading of wastes which has been used successfully for many years in Canada. Several installations are currently under trial in Minnesota. For more information write to Extension Agricultural Engineering, Department of Agricultural Engineering, University of Minnesota, St. Paul, MN 55108.

This ejector surface spreads the milkhouse liquid wastes from an 80-cow stall barn. The solid wastes are retained in a settling tank and the liquid wastes are pumped through the ejector. The farmer has his hand on the discharge elbow which must be rotated 90 degrees about every week to provide uniform surface spreading. It is essential that the ejector be protected by a fence to prevent physical damage from farm animals.

Gravity Drain

If the laid surface treatment area is below the dairy buildings, the liquid wastes can drain by gravity to the ground surface. Be sure to protect the open end of the pipe with ½-inch wire mesh or similar material to prevent small animals from entering. If the pipe goes under driveways or other areas where the snow is compacted or removed, insulate with 2-inch thick by 2-foot wide sheets of styrofoam laid in the trench above the pipe. If the pipe is laid less than 2 feet deep under driveways that are used by heavy vehicles, use strong pipe such as cast iron or extra thick plastic.

Pumping

When a suitable area for surface treatment of the liquid wastes is located higher than the dairy buildings, a submersible sump pump can be used. Don't install the pump in the settling tank; install it in another tank beyond the settling tank. The pumping tank should be large enough so that the liquid wastes from one milking are removed each time the pump runs.

A quality ½-horsepower submersible sump pump costs $150-$200. Pumps with built in switches cause problems, so use a separate mercury float switch to control the pump. Set the stop level of the float switch so the pump is not exposed but remains covered with liquid. Pump at least 75 gallons per pump operation to maximize pump life. The amount of liquid wastes pumped each time depends on the surface area of the pumping tank and the difference in the start-stop levels of the pump.

If the pumping tank is 4 feet by 4 feet inside dimensions, there are 16 square feet of surface area and 120 gallons per foot of depth (one cubic foot of liquid equals 7.5 gallons). So, if the start-stop difference is 18 inches, the pump will remove 180 gallons of liquid. Tank manufacturers will have information on the number of gallons per foot of depth.

The pipe from the pump to the treatment area should be 1½ or 2 inches in diameter and protected against freezing. The pipe can be laid 18" to 24" deep, but on a uniform grade draining back to the pumping tank (figure 3). A 1½-inch plastic pipe holds 10.5 gallons per 100 feet; a 2-inch pipe holds 18 gallons. If you use drainback to protect against freezing, be sure the pumping tank is large enough. Otherwise, your pump will soon wear out because of excessive starting and stopping.

Another type of installation which allows easy access to the pump for maintenance is a self-priming pump located in the milkhouse or milking parlor (figure 5). A suction pipe connects the pumping tank to the pump. Mercury floats located in the pumping tank connect to a relay to start and stop the pump. Locate the relay in the building near the pump. Never locate the relay in the pumping tank because it will quickly corrode and fail to operate.

Figure 5. Pumping station with self-pumping pump in milkhouse

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

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