Milkhouse Treatment Areas
Vegetated infiltration areas and septic type systems designed to treat milkhouse waste.
Milkhouse waste contains high concentrations of phosphorus (P) and total solids due to the common use of phosphate-containing cleaning agents, as well as the contributions of manure, feedstuffs and residual milk in waste. Treatment areas remove particulate P by settling the solids from waste and decrease dissolved P by promoting contact of wastewater with P binding materials.
How Does This Practice Work?
Milkhouse treatment areas serve to trap solid constituents of milkhouse waste by distributing flow evenly to promote infiltration of wastewater and deposition of solids, or by intercepting solids with surface vegetation. Septic-type systems remove solids with a settling tank and by filtration in the leachfield or filter strip.
Dissolved P is removed by putting wastewater in contact with soil or other fill material that has a high P binding capacity. In vegetated filter strips, growing vegetation promotes infiltration and takes up some of the P. Harvesting of treatment area vegetation helps to recover plant-available P from the soil, removing a fraction of the P applied in wastewater.
Where This Practice Applies and Its Limitations
Milkhouse treatment areas are suited to better-drained sites where local hydrology and wastewater-dosing regimes will not cause saturation of the soil. The slope of the land should be less than 15 percent to induce infiltration and reduce runoff. Treatment areas should be located in soil or fill material with high P binding capacity, and be of sufficient area to meet hydraulic loading requirements and the long-term phosphorus binding requirements. Because of risks to groundwater contamination, treatment areas should not be sited on highly permeable soils or near wells. Neither should treatment areas be located near tile inlets, due to the risk of routing wastewater flow to surface water.
The long-term efficacy of milkhouse treatment areas is dependent upon waste characteristics including volume, organic matter and P content, maintenance of treatment system and effective P binding capacity of the treatment medium. Ultimately, treatment areas will become saturated with respect to P binding potential and may need to be reconditioned. As such, minimizing P loading to the treatment area by controlling waste volume, eliminating P-containing reagents and minimizing waste milk, manure and feed inputs extends longevity.
The effectiveness of milkhouse treatment areas depends upon proper siting and maintenance. A study reported in 1989 found that a vegetative treatment area removed 90 percent of total P from milkhouse waste. In contrast, a 2006 study observed 60 percent of total P in milkhouse waste passed through a poorly sited and maintained treatment area. Another report in 2003 gave the average P trapping efficiency of all vegetated treatment areas as 61 percent and ranged from 31 percent in a 2-m area to 89 percent in a 15-m area. Treatment area length has been found to be the predominant factor affecting P trapping. The rate of inflow, type of vegetation and density of vegetation coverage had secondary influences on P removal.
Proper maintenance and design measures that prevent concentrated flow path formation are critical factors affecting performance. Proper hydraulic loading is also important for preventing failure. A 1992 study found that when channelized flow occurred, no significant reduction in P concentrations was observed, and only 12 percent of the total mass of P entering the strip was retained.
A common problem of septic systems is that fatty solids from the milk rapidly clog leach fields and infiltration trenches. As a result, septic tanks must be pumped regularly to extend the effective life of the leach field. Appropriately sized settling tanks reduce the frequency with which tanks must be pumped and maximize the hydraulic retention time to promote solids removal. Mechanically aerated septic tanks may also facilitate the breakdown of the fatty milk solids.
Cost of Implementing the Practice
The cost of establishing treatment areas depends upon the method installed. Septic systems are typically more expensive to install and maintain, given the frequent pumping required and replacement of leachfields.
Generally, the use of a treatment area or organic filter bed to treat the leachate from the septic tank reduces the long-term maintenance costs. However, treatment areas must be properly sited and graded, isolated from livestock or intensive tillage operations, and equipped with flow distribution systems that promote infiltration (e.g., gravel infiltration ditch) and sheet flow (e.g., perforated pipe). Gravity-fed treatment areas, where a perforated pipe distributes the flow, are comparatively inexpensive, but do not provide control of the dosing regime. A pump-fed distribution to treatment areas is intermediate in cost, due to the need to install a pump and liquid level controls and provide electricity.
Operation and Maintenance
The operation of a septic tank and treatment area system, even with pump distribution, is relatively automatic unless some different dosing cycle is required. Pumping of septic tanks should be done annually or a minimum of once every three years, depending on wastewater characteristics. The maintenance of treatment areas, such as routine repairs to distribution pipes or removing milk solids that are reducing infiltration and/or affecting flow are critical to minimizing concentrated flows through the treatment area.
Abu-Zreig M., Ramesh P. Rudra, Hugh R. Whiteley, Manon N. Lalonde and Narinder K. Kaushik. 2003. Phosphorus Removal in Vegetated Filter Strips. J. Environ. Qual. 32: 613-619.
Faulkner, J.W., W. Zhang, L.D. Geohring, T.S. Steenhuis. 2011. Tracer movement through paired vegetative treatment areas receiving silage bunker runoff. J. Soil Water Conserv. 66(1):18-28
Kim, Y.J., L.D. Geohring, J.H. Jeon, A.S. Collick, S.K. Giri, T.S. Steenhuis. 2006. Evaluation of the effectiveness of vegetated filter strips for phosphorus removal with the use of a tracer. J. Soil Water Conserv. 61(5):293-302
Schellinger, G.R. and J.C. Clausen. 1992. Vegetative filter treatment of dairy barnyard runoff in cold regions. J. Environ. Qual. 21: 40-45.
Schwer, C.B. and J.C. Clausen. 1989. Vegetative filter treatment of dairy milkhouse wastewater. J. Environ. Qual. 18: 446-451.
Wright, P.E. and R.E. Graves. 1998. Guideline for milking center wastewater. NRAES-115, BE Regional Ag Engineering Service, Cornell Coop. Ext., Ithaca, NY.
For Further Information
Contact your local soil and water conservation district, USDA-NRCS or Cooperative Extension Service office. To find your local USDA Service Center, visit https://www.nrcs.usda.gov/contact/find-a-service-center.
University of Vermont
Editing and Design
NC State University
University of Tennessee
Faulkner, J., P. Kleinman, Geohring, T. Steenhuis. 2023. Milkhouse Treatment Area. SERA17 Phosphorus Conservation Practices Fact Sheets. https://sera17.wordpress.ncsu.edu/milkhouse-treatment-areas/