Handling Milking Centre Washwater in an Environmentally-Responsible Manner

Agdex#:	720/410
Publication Date:	April 2004
Order#:	04-019
Last Reviewed:	April 2004
History:	Replaces OMAFRA Factsheet Milking Centre Washwater Disposal, Order No. 93-063
Written by:	Robert P. Stone - Engineer, Soil Management/OMAFRA

We are updating this page to reflect current regulations.

Information on this page about regulations under the Nutrient Management Act, 2002 and the Environmental Protection Act is out of date. On September 18, 2009 new regulations affecting those applying non-agricultural source materials on agricultural lands were filed. Please visit www.ontario.ca/nasm-omafra for more information.

Table of Contents

1. What is Milking Centre Washwater Disposal?
2. Quantity of Washwater Produced
3. Storage and Treatment Systems
   • Adding to Liquid Manure or Runoff Storage
   • Separate Storage
   • Sediment Tank and Treatment Trench System
4. Other Systems
   • Flocculator System
   • Vegetative Filter Strips (VFS)
   • Constructed Wetlands
   • Raised Bed Systems
5. Summary

What is Milking Centre Washwater Disposal?

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, washwater is exposed to high concentrations of chlorinated alkaline solutions, acidified waters, and heavy detergents that are not environmentally safe if improperly handled. Milking centre washwater must be handled in a manner that will not harm the environment. Included in this Factsheet are various proven techniques and new treatment methods for handling milking centre washwater.

Washwater contains phosphates from detergents and concentrated phosphoric acid that is used to clean and sanitize milk lines and equipment by trapping and dissolving oils and grease. Phosphorus is a main contaminant in surface water that leads to eutrophication. Eutrophication causes an increase in aquatic plant growth, a decrease in oxygen levels, minimizes transmittal of light and harms aquatic life.

Proper storage and handling of phosphorus in the milking centre washwater will protect 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.
Ultimately, milking centre washwater is a potential pollutant if not properly handled. This Factsheet describes acceptable options for the storage, handling or treatment of milking centre washwater.

Figure 1. Washwater from milking centres contains pollutants that must be disposed of properly.

Quantity of Washwater Produced

Milking centre washwater may result from dairy, goat and sheep operations. To select and design the best system for your farm, determine your approximate daily washwater production.

A survey of 300 Ontario dairy farms found the average washwater produced was approximately 14 L/cow/day (3.1 imp. gal/cow/day). This amount varied from a low of 6 L/cow/day (1.3 imp. gal/cow/day) to more than 28 L/cow/day (6.2 imp. gal/cow/day). For dairy operations with a pipeline milking system, the average daily washwater production was 14 L/cow/day (3.1 imp. gal/cow/day) and for operations with a milking parlour, it was only slightly higher at 17 L/cow/day (3.7 imp. gal/cow/day).

The amount of milking centre washwater produced by dairy milking cows is illustrated in Table 1.

For more milking cows than shown in Table 1, use the washwater production numbers outlined in Table 2.

The amount of washwater produced by goat and sheep milking herds is outlined in Table 3.

These numbers should only be used to obtain an estimated water use. It is important to accurately measure your specific water use to properly select and size the system that is best for you.

Measure your actual water use by installing a water flow meter or estimate it using a calibrated pail or the sink if you know its capacity and a stopwatch to time the water flow. If using an excessive amount of water, reduce this amount to make the disposal system work properly and reduce the amount of storage and handling required. To reduce water usage, use proper calibration, adjustment of 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.

Storage and Treatment Systems

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.

Three methods have been proven to be the most acceptable for handling milking centre washwater in Ontario:

• adding the milking centre washwater to a liquid manure storage or runoff storage
• collecting and storing it in a separate storage, or
• treating it through a sediment tank and treatment trench system.

Other systems have been developed more recently that are also capable of handling milking centre washwater. They include:

• flocculation of washwater through agitation and separation by the addition of a catalyst
• vegetated filter strips used to treat washwater
• constructed wetlands utilizing sedimentation and biological denitrification, or
• raised bed systems in situations where bedrock is close to the ground surface or high groundwater table.

Adding to Liquid 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 then be applied to the land along with the liquid manure or runoff material. Consider this alternative if:

• you already have a liquid manure or runoff storage with adequate additional capacity for the milking centre washwater or are planning to add one in the future
• you have a large herd or produce a large amount of washwater (> 80 cows or > 1120 L/day (246 imp. gal/ day))
• there are excessive solids in the washwater, or
• additional liquid is required in your manure storage for agitation and pumping.

If you are planning for an additional manure and runoff storage, it must be designed and constructed following the Nutrient Management Act, (NMA) Ontario Regulation 267/03, as amended, if your farm is phased in under the Regulation. It is a good practice to follow the requirements of the NMA, regardless of whether your farm is phased in or not. The municipality that administers the Ontario Building Code will also have requirements that must be met before obtaining a building permit.

Liquid manure systems require 240 days (with exceptions) of storage. Concrete, earthen and steel storage facilities are commonly used methods of containing liquid manure or runoff. Any concrete or steel storage that is adequate for liquid manure will also be adequate for storing milking centre washwater. Earthen storages may require a greater clay content to store milking centre washwater as opposed to liquid manure because the washwater may not have the amount of solids to promote sealing of the clay. Further information on the siting, sizing and design of manure and runoff storages is available in NMA, Reg. 267/03, as amended.

Adding milking centre washwater adds very little fertility value to the manure but diluting manure solids makes agitation and pumping easier. When land applying the manure and washwater be sure to follow procedures and practices that prevent ground and surface water pollution. For requirements on land application of manure and washwater see NMA, Reg. 267/03, as amended.

Figure 2. Washwater can be added to a manure runoff storage.

Separate Storage

Milking centre washwater may also be collected and stored in a separate storage (Figure 3). This storage should have capacity for a minimum of 240 days of washwater production. Consider this alternative if:

• your liquid manure storage cannot hold additional liquid
• a treatment trench system is not feasible due to heavy clay soil, a high water table or shallow soil, or
• you can locate a separate storage such that odours will not be a problem.

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. Check with your municipality regarding siting of the manure storage to meet the Minimum Distance Separation Formula II and any other municipal requirements.

Figure 3. Washwater can be stored separately.

Sediment Tank and Treatment Trench System

A sediment tank and treatment trench system is the third method of handling milking centre washwater. This system requires a building permit and is regulated under the Ontario Building Code (OBC), Part 8 under the Building Code Act. The design, construction, operation and maintenance of these systems must meet the minimum requirements set out by this regulation. The following conditions for installing a sediment tank and treatment trench system must be met:

• each individual system must have a design capacity to a maximum of 10,000 litres per day or less
• the system(s) and building(s) that they serve must be located entirely within the boundaries of the lot or parcel of land, and
• the first rinse from the wash cycle of milking operations is not allowed to enter the sediment tank and treatment trench system unless treated to an equivalent of domestic sanitary sewage prior to entering the treatment system. Removal of the first rinse before entering the sediment tank and treatment trench system is the most common and acceptable solution for dealing with this concern.

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 Ontario Building Code must be followed.

The sediment tank and treatment trench system should only be considered if the following can be adhered to:

• you do not have or are not planning to build a liquid manure or runoff storage
• the soil around the farm is deep and has good drainage characteristics
• your washwater is relatively free from solids
• you are willing to restrict the water that enters the system to a minimum, and
• you are willing to prevent milk from entering the system.

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 like phosphates are trapped and degraded by the soil.

The success of the sediment tank and treatment trench system depends on the principal of treated water draining away from the distribution pipes. Therefore, this system works best in well-drained soil types. Where finer soils exist, it may be better to use another option. It is important to follow the design details outlined in OMAFRA Publication 28, Milking Centre Washwater Disposal Manual, Chapter 9 for this system to work satisfactorily.

The treatment trench area should be seeded to grass and also fenced 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 (100 ft.) from the treatment trench area. Remove other trees and shrubs if they are within 15 m (50 ft.) of the treatment trench.

The sediment tank must be large enough to retain the wastes until the solid particles can 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 also provide space for 6 months or more of accumulated solids. An approved 2-compartment septic tank with a minimum capacity of 3600 L (800 imp. gal.) is satisfactory for operations producing up to 680 L (150 imp. gal.) 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.

Excavate the treatment trenches with a backhoe in parallel lines at least 2.4 m (8 ft.) on centre. The trenches should be 18-30 m max. (60-100 ft. max) in length. Install a minimum of 2 treatment trench lines per system. Excavate trenches 0.5-1 m (20-40 in.) wide and at least 0.75-0.9 m (30-36 in.) deep. The minimum depth from the bottom of the treatment trench to the top of bedrock or high groundwater table must be 0.9 m (3 ft.). Partly fill the trenches to a depth of 0.3 m (12 in.) with 19 mm (¾ in.) septic stone or 19-53 mm (¾-2 in.) clean, screened gravel to make an aerated treatment bed. Lay the distribution pipe at a uniform slope of 0.3%-0.5% away from the tank, with the holes facing down in the 4-6-8 o'clock positions. Add more septic stone or gravel to provide 50 mm (2 in.) of cover on the pipe and a layer of filter cloth to keep soil out of the stone bed. Backfill to the top of the trench with the excavated topsoil (Figure 4). DO NOT use plastic drainage tile, as the perforations are not large enough and will quickly become plugged. Tables 4 and 5 provide minimum treatment trench dimensions for milking dairy cows (Table 4) and goats/sheep (Table 5).

Figure 4. The sediment tank and treatment trench system is an alternative for handling milking centre washwater.

* Part 8, OBC requires a minimum total length of distribution piping of 40m (131 ft.) regardless of daily flow to the system.

* Part 8, OBC requires a minimum total length of distribution piping of 40m (131 ft.) regardless of daily flow to the system.

Make your sediment tank and treatment bed large enough to accommodate any foreseeable future herd expansion. Have a licensed engineer/contractor knowledgeable in milking centre washwater disposal systems install the treatment system.

Waste milk, milk from treated cows or waste colostrum must never be disposed of 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 immediately.

The first 10-15 L (2-3 imp. gal.) of the first rinse cycle composed of a high percentage of milk must be collected before it enters the sediment tank and treatment trench system, as 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, the first rinse can be added 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 can work quite well. Historically, many systems have failed, however, the cause of failure was often related 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.

Other Systems

Flocculator System

The flocculator system is a relatively new technology used to treat milking centre washwater. Currently, the flocculator system is being used by farmers across Canada and is encouraged as a means of technology to maintain environmental quality.

The flocculator cleans washwater through agitation by separating the waste and leaving clean usable water behind. Figure 5 illustrates the basic model of the flocculator system.

A binder is added to the washwater and agitated to form solid particles (floc), then is allowed to separate into a water and solid layer. The processed water is removed from the top of the flocculator and typically sent to a trench system while the solids are removed through the bottom and transferred to a manure storage tank.

Vegetative Filter Strips (VFS)

Vegetative filter strips (VFS) are strips or areas of vegetation designed to remove sediment, organic matter, nutrients and other pollutants from washwater. VFS utilize a number of treatment processes, thereby, reducing pollution and protecting the environment.

Figure 5. Basic model of a flocculator 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 VFS must be sited correctly to ensure the treatment system works effectively. Solids removal must also occur prior to entering the VFS to ensure that the VFS does not clog. It must meet all appropriate setbacks and soil conditions. If you are planning on constructing a VFS, it should be designed and constructed by a Professional Engineer and approval must be obtained under the Ontario Water Resources Act through the Ministry of the Environment.

Constructed Wetlands

Pollutants in milking centre washwater can be removed through the use of natural processes and systems such as sedimentation and constructed wetlands. Wetlands have always been valued as nature's natural filter. Hence, the use of constructed wetlands to remove phosphorus, nitrogen, pathogens and soluble organic material is becoming more widely used and is considered an acceptable method to treat and recycle milking centre washwater.

Constructed wetlands use gravel, water depth and aquatic plant life to reduce the presence of pollutants in the washwater. Through the incorporation of gravel in the subsurface flow, additional bacteria may thrive. Additional bacteria will increase the rate at which soluble nutrients are degraded. The intent of constructed wetlands is to improve water quality so it does not impair surface and groundwater sources.
A Professional Engineer should design constructed wetlands and an Ontario Water Resources Act Approval must be obtained through the Ministry of the Environment.

Raised Bed Systems

In areas with bedrock close to the surface or where the soil is saturated close to the surface, it may still be possible to use a sediment tank and treatment trench system installed in a raised bed or a mound. These systems work but the design and installation of the system is critical. Consult an experienced professional, to find out if this system is likely to work on your operation.

Summary

Several alternatives for disposing of milking centre washwater have been 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 your present operation and future plans. Further information on milking centre washwater storage and treatment system design can be found in OMAFRA's Publication 28, Milking Centre Washwater Disposal Manual, 1999. Further instructions for constructing an environmentally safe and secure storage facility are available in NMA, Reg. 267/03, as amended and associated protocols.