Parlor Flush The parlor flush tanks located at the head of each milk alley generally have a capacity of 750-1000 gallons each. They are dumped after each milking with the released water cleaning the holding area also. This wastewater is either collected for reuse in one of the free-stall alley flush tanks or flows directly down one of the free-stall cow lanes. Clean water is required within the milk parlor for sanitation purposes. All other water usage for equipment cleaning, prep stalls or prewash systems is routed to the waste collection system. From a land application standpoint, unless extra water is needed for irrigation, water usage within the parlor should be held to a minimum.

Collection Flushed manure and wastewater are collected by a narrow channel across the end of the cow lanes and transported to a reinforced concrete tank with enough capacity to hold a 2-4 day accumulation. At Randleigh this 16,000- gallon tank has a reinforced roof with scrape-in ports such that manure could be scraped directly into the tank if desired. To remove the tank contents, adequate agitation capabilities are essential to get the manure solids into suspension. This requires either a solids handling centrifugal pump and propeller mixer or a liquid manure chopper-agitator impeller pump.

Solids Separation After agitation, tank contents are pumped into a liquids-solids separator. At Randleigh this 48-inch diameter vibrating screen separator has a 20-mesh stainless steel screen which rotates around its center of mass causing those manure solids larger than 0.033 inch to move to the outer edge of the screen and out a discharge spout. These fibrous solids are composed primarily of cellulose, hemicellulose and lignin and can be used as fiber supplements to feed rations or bedding for free stalls. Solids separation also removes those troublesome solids which tend to fill a lagoon or clog pumping and irrigation equipment making the slurry much easier to manage. About 80-90% of the fertilizer is retained in the slurry after solids removal.

Primary Lagoon The separator slurry is routed to a primary earthen lagoon. At Randleigh this holding lagoon serves to settle those fine solids not removed by the separator. Concentrated slurry can be irrigated or hauled to cropland. For this purpose the lagoon should have a maximum surface area of 100 feet by 100 feet with a depth of 12 feet. An alternate use of this holding lagoon would be for anaerobic digestion of the slurry for the purpose of biogas generation. The digestor would be deeper (up to 25 feet if site conditions permit) with a smaller surface area covered with a floating hypalon cover. Instead of the holding lagoon a larger primary lagoon might be used for biological treatment of the waste for odor control, nutrient reduction, and pathogen destruction. This lagoon design capacity would range from 1400-4200 cubic feet per cow.

Secondary Lagoon The secondary lagoon-retention pond has enough storage to handle a 180-day accumulation of lagoon liquid, lot rainfall runoff, and direct rainfall on the pond surface. Enough capacity is always maintained on the pond surface to store a 25-year, 24-hour storm (6-9") without overflow as required by EPA. Liquid for cow lane flushing is recycled from this pond using a flooded pump suction or a floating intake approximately 18 inches below the pond surface. The recycle pump is usually a 1/2 - 1 horsepower self-priming centrifugal pump. The recycle system can be fully automated by connecting this pump to an air precharge pressure tank similar to one used in a home water supply system.

Land Application To prevent the secondary lagoon from overflowing, excess lagoon liquid is periodically pumped onto pasture or cropland. Land application of this liquid is most economically achieved through irrigation as compared to liquid manure spreader. Wastewater is irrigated at rates not exceeding the nitrogen fertilizer requirement of the grass or crop and at rates below the soil infiltration capacity to prevent runoff.

Not Included: Flow Diagram for Dairy Manure Flush and Lagoon Treatment System

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