Wastewater flow is the primary design parameter for all milk house treatment systems. Most milk house wastewater is generated during the cleaning of the milking units, milk pipelines, receiver, and bulk tanks. Depending on the milking schedule, the milking units and milk pipeline are cleaned two or three times per day. Bulk tanks are cleaned immediately after the tank has been emptied, typically once per day or once every other day. Water softener regeneration water also contributes to this waste stream.
Water flow meters provide the most accurate estimate of wastewater flow. Correct placement of these flow meters in the water supply line is critical and sometimes tricky. Often there are faucets in the milk house that are used for other purposes such as supplying water for mixing milk replacer for calves, washing of tractors and other farm implements, or filling of fertilizer or herbicide tanks. This water might be recorded by the flow meter but the water would not enter the wastewater treatment system. Farmers should document and subtract this usage to accurately determine the flows actually entering the wastewater handling system. Typically, the majority of water used in the milk house passes through a water softener so this is often the best location to install the flow meter. A minimum of two months of daily flow data provide adequate information for estimating design wastewater flows but continued flow monitoring should be part of the system operation and maintenance plan.
An alternative to a water meter are estimates based on average per cow water use data. A study conducted at the University of Minnesota on 16 milk house waste systems (Schmidt et al., 2005) found typical flows to be between 2 to 7 gal/cow/day with most farms using less than 5 gal/cow/day. Without any site specific data (water meter data), an estimate flow of 5 gal/cow/day should be used for designing the milk house wastewater treatment system. Note that this flow estimate is for milk house wastewater only and does not include any parlor washing or other wastewater.
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