Treatment and Disposal of Milk House and Milking Parlor Wastes

Lagoon Treatment

A lagoon (figure 6 and as shown on the cover) is a pond constructed to store the waste water, some of which evaporates and seeps into the surrounding soil. A lagoon may be used with a settling tank, or the waste may flow directly into the lagoon. The advantage of using and maintaining a settling tank is to reduce the amount of solids discharged into the lagoon.

Figure 6. Milking center waste lagoon

Gravity Drain

Milking parlor and milkhouse wastes can flow by gravity into a lagoon, eliminating the need for a settling tank. The pipe from the settling tank to the lagoon should be on a grade of at least 1 inch in 8 feet (1%). The outlet of the pipe must be higher than the surface of the lagoon.

One difficulty with a gravity drain is possible freezing. A trickle of water from the settling tank may freeze in the part of the pipe that extends out from the bank over the lagoon surface. Be sure the pipe which is exposed to the air over the lagoon has a slope of at least 1 inch in 8 feet. If trickle flows are common from your operation and the pipe begins to freeze shut, you may need to wrap insulation around the exposed part of the pipe. Heat tape also might be added as an extra precaution.

Pumping

On flat land where there isn't enough elevation for a gravity drain to the lagoon, use a pump. Always use a settling tank to retain the larger solids when pumping wastes to prevent pump problems. The pump can be a standard submersible sump pump. The pressure pipe can run all the way to the lagoon (figure 3), or it can run to a junction box at a high point from which the waste water flows by gravity into the lagoon (figure 7). When the pump stops, waste water in the pressure pipe drains back to the pumping tank to prevent freezing. All of the water also drains out of the gravity line. If a small amount of ice forms at the end of the gravity pipe, it is quickly melted by the water discharged during the next pump operation. Size the pumping tank and the amount of waste water pumped each time according to the guidelines previously described for surface treatment.

Figure 7. Pumping waste water to junction box

Lagoon Design

Lagoons for milkhouse and milking parlor wastes should be 3 feet deep and have 10 square feet of surface area for each gallon of waste discharged per day. This recommendation is based on average Minnesota precipitation and evaporation conditions, allowing for some bottom seepage. If the settling tanks are properly maintained, a major portion of the biological oxygen demand (BOD) will be retained in these tanks and removed by pumping. The lagoon will provide final treatment as well as ultimate disposal of the liquid. Table 3 presents lagoon bottom dimensions required to treat various waste water flows. Three different ratios of bottom widths to bottom lengths are presented in table 3.

The 3-foot lagoon depth should be maintained in summer to discourage growth of aquatic weeds. The construction area may be either flat or sloping. On level ground the excavated earth forms a dike of uniform height to contain the liquid. The bottom of the lagoon may be 3 to 4 feet below the general grade level, with the remaining part of the containment structure above ground. When the site is sloping, the height of the above-ground dike will vary with the topography.

The top of the dike should be about 4 feet above the maximum intended water level (figure 6). Dikes should have side slopes of 3:1 and a top width of 6 feet. To prevent overtopping the dike, an emergency spillway 1 foot deep and 4 feet wide should be built in undisturbed soil, if possible. It is important that the emergency spillway have an established and maintained grass cover to prevent erosion in case the lagoon overflows.

Liquid should be discharged into the lagoon through a 4-inch diameter pipe at the same elevation as the top of the dike, (1 foot above the emergency spillway). It is desirable to have the discharge point 20 or more feet from the bank; solids are less likely to build up and interfere with the inlet. If you do not extend the pipe this far, install 2" or larger rock rip rap. Observe the outlet frequently and take appropriate action if the solids build up. DO NOT INSTALL THE DISCHARGE PIPE BELOW THE WATER LINE; solids are likely to settle out and plug the pipe, and the pipe will be likely to freeze shut.

When possible, locate lagoons downwind and downhill from the farmstead. When this cannot be done, a minimum distance of 300 feet is recommended. Locate the lagoon downhill and at least 100 feet from the water supply well.

Lagoons should be located in relatively impervious soil when possible. Where the site has coarse sand or gravel, seal the bottom of the lagoon with 1 foot of clay soil packed in layers of 6 inches. In limestone areas be sure there is 3 feet of clay soil between the lagoon bottom and bedrock. The lagoon should always be protected against the entry of surface runoff. Construct appropriate diversion ditches as required.

Always build a fence around the lagoon to keep out children, who may enter because of curiosity, and cattle, which may damage the banks. Attach warning signs to the fence. Locate the fence to allow mowing of the dikes.

Lagoon banks should be kept mowed to maintain a good grass cover and keep weeds under control. Inspect dikes several times each spring and summer to be sure that no rodents are burrowing holes in the dike.

The liquid level should be maintained no higher than within one foot below the level of the emergency spillway. It may be necessary to periodically remove some liquid from the lagoon to prevent overflow during normal operation and possible contamination of surface waters or adjacent areas such as road ditches. This can be done with an irrigation pump and sprinkler or other suitable equipment.

For proper lagoon operation and to discourage aquatic weed growth, the liquid depth must be at least three feet. Thus, additional water may need to be added to maintain the minimum depth.

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

In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.

University of Minnesota Extension is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.