Handling Milking Centre Washwater
The introduction of the pipeline milking system in the late 1960s was a welcome improvement for dairy farmers everywhere. At the same time, a new problem was created what to do with the large quantity of water required to clean and sanitize the milking equipment and pipeline.
Equipment used during the milking of livestock must be rinsed, washed, acid rinsed and sanitized. Through this process, milking centre washwater is exposed to high concentrations of chlorinated alkaline solutions, acidified waters and heavy detergents that are not environmentally safe if improperly handled (Figure 1).
This Factsheet describes acceptable options for the storage, handling or treatment of milking centre washwater.
Washwater contains phosphates from detergents and concentrated phosphoric acid that is used to remove dissolving oils and greases and sanitize milk lines and equipment. Phosphorus is a main contaminant in surface water that leads to eutrophication a process that causes an increase in aquatic plant growth, a decrease in oxygen levels and a reduction in light penetration, all of which harm aquatic life.
Figure 1. Washwater from milking centres contains pollutants that must be disposed of properly.
Proper storage and handling of the milking centre washwater containing phosphorus protects surface waters from eutrophication. Phosphate-free soaps are not an acceptable alternative to proper storage and treatment since the phosphates are usually replaced with nitrates. Nitrates from soap and manure can lead to contamination of surface and groundwater.
Milk in the washwater is also a contaminant. Decomposing milk uses oxygen, while associated bacteria are known to transmit disease.
Milking centre washwater comes from dairy cow, goat and sheep operations. To select and design the best system for the farm, determine the daily washwater production.
A survey of 300 Ontario dairy farms found the average washwater produced was approximately 14 L/cow/day. This amount varied from a low of 6 L/cow/day to more than 28 L/cow/day. For dairy operations with a pipeline milking system, the average daily washwater production is 14 L/cow/day, and for operations with a milking parlour, it is only slightly higher at 17 L/cow/day.
Table 1 shows the minimum amount of milking centre washwater produced by dairy milking cows. Use the washwater production numbers in Table 3 for operations with more milking cows than shown in Table 1.
Robotic milking systems use different methods to wash the cow's teats prior to cleaning. The most common systems clean the teats with rotating brushes or with a water bath inside a special teat cup. Table 2 shows the washwater produced for robotic milking systems.
These numbers should only be used to obtain an estimated water use. It is important to accurately measure the specific water used to properly select and size the system that is best suited for the operation.
Table 4 shows the amount of washwater produced by goat and sheep milking herds.
Measure the actual water used by installing a water flow meter or estimate using a calibrated pail or the sink (if its capacity is known) and a stopwatch to time the water flow. If using an excessive amount of water, reduce this amount to improve the performance of the disposal system and to reduce the amount of storage and handling required. To reduce water usage, use proper calibration and adjust the pipeline and bulk tank wash cycles. Also, use recaptured washwater for cleaning floors and direct clean water, such as the overflow from heat reclaimers, away from the floor drains. Ensure that any steps taken to reduce washwater do not adversely affect the cleaning of the milking system.
*One robotic milking system milks 60 cattle.
* Based on: dry parlour (parlour floor scraped instead of washed), bulk tank cleaned out once a week, and no preparation on does.
Storage and treatment systems must be properly designed, installed and operated to be economical, compatible with current washwater and manure handling systems on the farm, and effective in preventing pollution of surface or groundwater.
The storage systems are either a separate storage designed for the quantity of washwater produced or a combined storage for both the manure and the washwater. The stored washwater is disposed of through land application or as a liquid ingredient for anaerobic digesters. The storage of milking centre washwater is regulated under the Nutrient Management Act (NMA), 2002, Ontario Regulation 267/03 as amended.
Farm operations are now required to comply with requirements under Part VII.I of the Regulation for managing milking centre washwater (MCW) when:
In addition, farm operations that have a nutrient management strategy (NMS) are required to comply by January 1, 2016, or when they undertake a project that involves one of the three scenarios listed above, whichever comes first.
An existing dairy producer who is not required to prepare an NMS under the Regulation and does not apply for a building permit for the three scenarios listed is not affected by the new regulation, assuming there is no negative effect to the environment. However, operators should always follow best management practices and dispose of milking centre washwater in an environmentally safe manner.
Options for management of MCW in the Regulation include:
Figure 2. Washwater added to a manure runoff storage.
Adding MCW to Liquid Manure, Solid Manure or Runoff Storage
A proven means of handling milking centre washwater is to add it to liquid manure or manure runoff storage (Figure 2). The milking centre washwater can be applied to the land along with the liquid manure or runoff material. Consider this alternative if:
Liquid manure systems require 240 days storage (with exceptions as defined in the regulations). Concrete, earthen and steel storage facilities are commonly used for containing liquid manure or runoff. Any concrete or steel storage that is adequate for liquid manure is also adequate for storing milking centre washwater. Further information on the siting, sizing and design of manure, runoff and washwater storages is available in NMA, 2002, O.Reg. 267/03 as amended.
Adding milking centre washwater to a solid manure storage facility adds very little fertility value to the manure but may eliminate the need for liquid storage and handling. To store washwater in a solid manure storage:
When applying the manure and washwater to land, follow procedures and practices that prevent surface and groundwater pollution. For requirements on land application of manure and washwater, see NMA, 2002, O. Reg. 267/03 as amended.
Milking centre washwater can be collected and stored in a separate storage (Figure 3). The storage should have capacity for a minimum of 240 days of washwater production. Consider this alternative if:
Milking centre washwater can produce offensive odours during warm summer weather. It is wise to locate open storages at considerable distances from neighbours' dwellings and from the farm family's living area. Follow the setback distances for manure storages outlined in NMA, 2002, O.Reg. 267/03 as amended. An approved NMS is required prior to construction for any concrete, steel or earthen storage facility. Also, check with the municipality regarding siting of the manure storage to meet the Minimum Distance Separation Formula II and any other municipal requirements.
Figure 3. Store washwater separately.
Sediment Tank and Treatment Trench System
A sediment tank and treatment trench system is an approved method for handling milking centre washwater (Figure 4). This system requires a building permit and is regulated under the Building Code, Part VIII. The design, construction, operation and maintenance of these systems must meet the minimum requirements set out by this code.
Installing a sediment tank and treatment trench system is only allowed if:
Setbacks from landscape features have different requirements for both the distribution pipes in the treatment trenches and the sediment tanks. The setback distances contained in the Building Code must be followed.
Figure 4. The sediment tank and treatment trench system is an alternative for handling milking centre washwater.
Consider the sediment tank and treatment trench system only if:
A sediment tank and treatment trench system consists of a sediment tank and several treatment trenches. The purpose of the sediment tank is to collect solids that are washed down drains and to prevent floating material from blocking the treatment trench lines. The treatment trenches distribute the liquid from the sediment tank over a large area to allow it to percolate into the soil. Bacteria attached to the stone in the treatment trench help to remove contaminants in the milking centre washwater; other contaminants, such as phosphates, are trapped and degraded by the soil.
The success of the sediment tank and treatment trench system depends on the principle of treated water draining away from the distribution pipes. Therefore, this system works best in well-drained soil types. Where finer soils exist, consider another option.
Seed the treatment trench area to grass, and fence it to prevent heavy traffic and livestock from damaging the system. Remove all water-loving trees, such as willow, soft maple, elm and poplar for a distance of 30 m from the treatment trench area. Remove other trees and shrubs if they are within 15 m of the treatment trench.
The sediment tank must be large enough to retain the wastes until the solid particles separate out. A minimum retention time of 4 days is recommended, but 6 days is preferable. The retention time is equal to the capacity of the sediment tank divided by the daily washwater use. The tank must provide space for 6 months or more of accumulated solids. An approved two-compartment septic tank with a minimum capacity of 3,600 L is satisfactory for operations producing up to 680 L of washwater per day.
The disposal field includes distribution piping and treatment trenches. Use connecting pipe from the sediment tank to the distribution pipes in the treatment trenches. If the connecting pipe must go under a roadway, replace it with galvanized steel pipe to prevent damage due to heavy vehicles or frost.
Make the sediment tank and treatment bed large enough to accommodate any future herd expansion. Have a licensed engineer/contractor knowledgeable in milking centre washwater disposal systems install the treatment system.
Never dispose of waste milk, milk from treated cows or waste colostrum through the sediment tank and treatment trench system. This system is not designed to "treat" milk. In the event of a milk spill, pump out the sediment tank and properly dispose of the material immediately.
Collect the first 1015 L of the first rinse cycle, composed of a high percentage of milk, before it enters the sediment tank and treatment trench system. Even a small amount of milk going down the drain every day will eventually plug the system. One method of disposing of this first rinse is to feed it to calves. There is not enough milk in this rinse water to contribute significantly to the nutritional requirements of young calves, but it can be fed to older calves, already weaned, or used as the liquid to reconstitute milk replacers. For calves one month of age, add the first rinse to milk to provide additional liquids.
If this system is used to treat water from a milking parlour, do not wash manure from the parlour into the sediment tank, as this could completely fill the system with solids in a week or less. Shovel all manure solids into manure alleys or gutters of adjoining barns before washing walls and floors into the washwater system. To wash solids from the milking parlour through the floor drain system, connect the system to a liquid manure storage tank and not to the sediment tank and treatment trench system.
With proper design, management and soil conditions, these systems work quite well. Failures are often due to the disposal of excess milk and water through the system. It is illegal to dispose of human wastes through any of these washwater systems. If installing a toilet, it must be connected to a separate septic tank system approved by the local regulatory agency.
Vegetated Filter Strip System (VFSS)
Vegetated filter strip systems are strips or areas of vegetation designed to remove sediment, organic matter, nutrients and other pollutants from washwater (Figure 5). VFSSs use a number of treatment processes, thereby reducing pollution and protecting the environment.
Figure 5. Distribution pipe for a vegetated filter strip system.
The washwater is treated by overland sheet flow through vigorous dense vegetation, by settling and some infiltration. The strip is not intended to treat concentrated flows. It is an excellent method for reducing the total solids, sediment, biochemical oxygen demand and total phosphorus in the washwater.
The VFSS must be sited correctly to ensure the treatment system works effectively. Solids removal must occur prior to entering the VFSS to ensure that it does not clog. This is accomplished through a sediment tank, as previously described. It must meet all appropriate setbacks and soil conditions. A VFSS should be designed by a professional engineer and approved under the Ontario Water Resources Act, 1990, through the Ontario Ministry of the Environment, prior to construction.
Pollutants in milking centre washwater can be removed through the use of natural processes and systems such as sedimentation and engineered wetlands (Figure 6). Wetlands have always been valued as nature's natural filter. Using engineered wetlands to remove phosphorous, nitrogen, pathogens and soluble organic material is becoming more common and is considered an acceptable way of treating and recycling milking centre washwater.
Figure 6. This 3-celled engineered wetland treats milking centre washwater from a dairy goat operation as well as runoff from the adjacent 280-m2 solid manure storage.
Given Ontario's cool climate and that milkhouse washwater is produced year-around, it is recommended that sub-surface engineered wetlands be used to treat milkhouse washwater. Subsurface engineered wetlands are constructed so that water flow is below ground and contained within an impermeable membrane or liner, ensuring that the system does not freeze in the winter months.
Subsurface engineered wetlands use gravel, water depth and aquatic plant life to reduce the presence of pollutants in the washwater. By forcing the milking centre washwater to flow through a subsurface gravel medium, bacteria growing on the surface area of the gravel feed on the nutrients and compete with pathogenic bacteria in the milking centre washwater as it passes through the wetland. The longer the residence time, the greater the reduction or conversion of pathogens and nutrients. In the subsurface flow, additional bacteria may thrive. Additional bacteria will increase the rate at which soluble nutrients are degraded. The intent of an engineered wetland is to improve water quality so the discharge does not impair surface and groundwater sources.
An engineered wetland should be designed by a professional engineer and approved under the Ontario Water Resources Act, 1990, through the Ontario Ministry of the Environment, prior to construction.
Several alternatives for disposing of milking centre washwater are described in this Factsheet. Any of these options will work well if installed correctly and managed properly. The choice of the best system depends on the current operation and its future plans. Further instructions for constructing an environmentally safe and secure storage facility are available in NMA, 2002, O.Reg. 267/03 as amended and associated protocols.
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