Treatment and Disposal of Milk House and Milking Parlor Wastes

Settling Tanks

A settling tank removes settleable and floatable solids and reduces treatment problems when liquid wastes are treated on the ground surface. The tank must be at least 50 feet from the well. For subsurface treatment and disposal of liquid wastes, separation of solids is absolutely necessary. A settling tank requires regular maintenance. Once the tank becomes filled with solids it is more difficult to empty than if serviced on a regular basis. Lack of service will cause premature failure of the rest of the system.

Wastes must flow slowly through the tank to permit the solids to settle. Waste water usually enters the tank twice a day in the relatively short periods during and immediately following each milking. Adequate tank size is necessary for effective separation of solids. The outlet baffle should be at least 5 feet away from the inlet baffle. Rectangular tanks should be twice as long as they are wide. The inlet pipe should be 3 inches above the liquid surface in the tank. An inlet baffle is necessary to dissipate the velocity of the incoming waste and all outlet baffle is necessary to hold floating material in the tank (figure 1). The settling tank must either be compartmented or there must be two or more tanks in series. The rate at which solids accumulate depends on the dairy operation. Measure the amount of accumulated solids each month through an inspection pipe or a manhole to determine the amount of solids in the tank. The tank should be pumped when it is about half full of solids. A vacuum system that allows backflushing the tank to suspend the solids is preferable. The wastes from the tank should be spread on suitable land for incorporation into the soil.

Figure 1. Settling Tank

A settling tank should have a capacity of at least 10 gallons per cow. For a 50-cow herd this would be 2,000 gallons. This is the smallest size tank recommended although the herd size may be less than 50 cows.

There are two alternatives for treating the waste water from a properly managed settling tank. For daily volumes of waste water of approximately 500 gallons or less, it may be impractical to construct a lagoon and immediate land treatment should be used. For larger volumes, a lagoon may be used to store the waste water prior to land surface treatment.

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