Evaluation of Four Milk House Wastewater Treatment Systems in Minnesota

Abstract

This project evaluated and demonstrated effective techniques and/or systems to reduce environmental pollution contained in dairy milk house wastewater and disseminated the results to dairy producers in Minnesota. With federal Clean Water Act Section 319 funding, four new or modified milk house wastewater treatment systems were demonstrated and evaluated on sixteen farms in four counties in Minnesota. All of the treatment systems had a septic tank for primary treatment. The four types of systems installed included aeration, both aerobic treatment units and recirculating media filters with discharge to subsurface soil treatment systems, irrigation to cropland or pasture, and large soil surface infiltration areas covered with bark (bark beds). The systems were monitored for influent and effluent wastewater characteristics, water flow and overall system performance. Overall the systems removed 98-100% of BOD5 and TSS, 90 to 100% of the phosphorous and 75 - 90% of the nitrogen. Lessons learned from the installation and monitoring of these systems have led to design guidelines for the selection, design, and installation of these milk house wastewater treatment systems. In addition a milk house wastewater treatment estimator was developed to document the removal of contaminants after installation of a milk house wastewater treatment system. The estimator was tested on the impaired Carver Creek watershed in Carver County, Minnesota where seven farms have direct discharge of milk house wastewater to tile lines. The estimator showed the overall impact of installing milk house treatment systems on these seven farms will be an annual removal of 10,778 pounds of BOD5, 4003 pounds of TSS, 252 pounds of phosphorous and 336 pounds of nitrogen. Economically the removal of phosphorous per pound is much lower than many other potential practices, whereas nitrogen costs are more median; indicating watersheds facing nutrient impairment with small to mid-size dairies should focus improvements in this direction.