Minimising dairy shed effluent stream
The first step in managing or developing any effluent system is 'Minimisation'.
The amount of effluent generated at the dairy shed or intensive feeding facilities surprisingly is not related to the herd size or the size of the facility. Small herringbone dairies have been known to generate an effluent stream equivalent to large rotary operations.
The purpose of this information is to explore the various components that impact on a dairy effluent system and provide practical solutions and options to minimise their contribution to the total effluent volume.
Dairy shed and feedpad water use
Figure 1: Dairy water use survey (cleaning water versus herd size) McDonald 2005
Figure 2: Daily water use sources (large dairies) McDonald 2005
Daily water use in dairies
Understanding the daily water use in dairies and on feedpads is essential because it has many implications in relation to developing and managing a dairy effluent system.
- Storage capacity — The amount of water used over the day for milk harvest or on herd feeding facilities multiplied by the recommended storage requirement will determines pond size.
- Irrigation — The greater the water use, the greater volume that has to be irrigated back throughout the year. This has huge implications on the time spent irrigating and the scale of size in pump, pipes and irrigators.
- Total cost of effluent management — The more water and solids entering an effluent system the more money spent on building ponds, maintenance, labour and the irrigation system required to reapply the effluent water back to land.
Understanding where the water comes from (plant rinses, wash-down systems, cup and platform sprays) is important as it provides an opportunity to review and reduce the source. It also ensures the farm water reserves are sufficient to maintain the dairy or feedpad operation all year.
Water use in dairies alone can vary between 1000 litres to over 100,000 litres per day. It is this overall volume accumulated over the storage period, which requires management.
Flood washing dairy shed holding yards and feedpad alleyways is now a common practice throughout the dairy industry, with the main driver being as a time saver.
Floodwash tanks however require a significant water supply, with the most common tank capacity being 17,000 litres for the average sized dairy.
Unfortunately the common practice is to dump the tanks entire capacity, rather than the actual amount needed to successfully wash the yard.
Agriculture Victoria conducted a detailed survey of dairy water consumption in 2005. The averages (Tables 1 and 2) provide a general indication of total water volumes required to effectively operate dairy sheds without compromising milk quality.
Table 1 Daily water use averages for different shed types. (McDonald 2005)
| 60 unit|
| 50 unit|
| 44 unit|
| 32 unit|
| 24 unit|
| 20 unit|
| 18 unit|
| 16 unit|
| 12 unit|
| 10 unit|
Maintaining plant and yard hygiene is essential. Water minimisation at the dairy should not compromise milk quality or herd health.
Practical options to reduce water use may include:
- utilising recycled effluent from a multiple pond system to wash down holding yards
- mechanical breakdown of manure pats prior to hosing or floodwash dumping
- turning off cup and platform sprays immediate after cows have left the platform and reducing unnecessary volumes — (these two components contribute nearly 40% of total daily water use in rotary sheds)
- installing appropriate floodwash tanks to suit the yard washing requirement and positioned strategically to optimise performance
- repairing and replacing broken nozzles or leaking hoses
- strategically washing muddy udders and teats.
Recycling plate cooling water
Clearly the exclusion of plate cooling water from entering the effluent system directly will enable the size of any storage pond to be reduced significantly. Diverting plate cooler water into wash down tanks for yard cleaning or returning it to dam sources is best management practice.
Minimising effluent on farms relying on bore water for yard washdown can reduce the demand placed on groundwater. By so doing, farmers may be extending the life of their groundwater supply. Reducing groundwater extraction can also protect spring-fed dams from drying up, as well as protecting streams relying on groundwater flow.
A water consumption survey in 2005 found 49 per cent of Southwest farmers and 36 per cent of Gippsland farmers relied on bore water to supply the dairy. Poor bore water quality is also an important issue to address as it may increase the accumulation of salts in the ponds, affecting their performance.
Rainfall is another source of water that can enter the effluent system and unnecessarily fill storage ponds. Effluent storage ponds need to calculate 90th percentile rainfall contributions entering the system in order to prevent them from overflowing during heavy storm events.
Options to reduce rainfall entering the effluent system include:
- installing rainwater diversion off holding yards in high rainfall areas — trap doors and diversion pipes installed on spoon drains or off yards prior to the solids trap or sump or pump are common (See figure 3)
- ensuring that the nib walls around the yard is high enough to prevent surface runoff from surrounding areas entering the yard
- rainwater tanks capturing roof runoff — this will reduce the contribution and at the same time provide a reliable quality water supply
- levy banks or drain diversion around the pond — this will eliminate rainfall from surrounding paddocks and laneways entering the storage
Figure 3: Rainwater diversion device
Effluent solids and foreign material
Solids entering the effluent stream have the potential to cause problems with pumps, conveyance piping and within the ponds.
Separation of the liquid and solid effluent stream will be necessary at some stage within the overall effluent system. Some farmers opt to utilise sumps and traps with weeping walls prior to pondage while others prefer to use settling ditches and ponds before conveying the liquid fraction into storage ponds.
The amount of solids entering the effluent system can be reduced by:
- keeping laneways well drained and in good condition — this will prevent cows transferring stones and gravel into the holding yard
- placing foot baths immediately before the entry point to the yard
- installing a debris trap or screen below the yard and prior to any pond or pumps to collect fibrous material and other debris such as hair, tail tape, horns, and string
- installing weeping walls or weir type structures to remove solids from the liquid stream.
Facility and yarding design
The impact of the design of dairy sheds, yarding areas, entry laneways and feedpad facilities on minimising the generation of effluent is often underestimated.
Design criterion should take into account:
- cow flow
- operator ease
- stock handling management.
Design principles to reduce the amount of effluent being generated at the facility include:
- appropriate yard spacing per animal
- appropriate yarding width, length and slope to promote effective yard washing
- yard surfacing and patterning
- wide gateways to prevent cow bullying
- sprinklers and yard sprays to reduce heat stress
- avoidance of sharp angles for cows exiting the shed
- appropriate yard design and location of gates to enhance cow flow and effective drafting.
A dairy cow is capable of producing 7 to 8 per cent of her body weight in manure and urine every day. Depending on yarding time and shed design, most dairy herd will spend 10 to 15 per cent of their time each day at the dairy. Feedpads and intensive feeding areas can potentially accommodate the herd for longer.
A herd that is unsettled and stressed in their environment can deposit more manure than a herd that is content and comfortable.
Options to improve animal well being include:
- providing adequate shading and protective tree belts
- vector control (flies)
- establishing adequate drainage to keep the area dry
- maintaining sufficient water supplies
- ensuring manure and feed spoilage is removed from the area regularly.
Any strategy aimed at minimising nutrient losses from dairy farms should first examine the relationship between feed intake, milk production, and nutrient excretions in manure.
Manure management should start at the front, rather than the back end of the animal. Excessive feeding of crude protein and phosphorus to dairy cows increases nitrogen (N) and phosphorus loads in manure, which can exacerbate the potential nutrient loss.
Extensive research in dairy cow nutrition has shown a strong connection between supplementary feeding intakes and nutrient outputs in faeces and urine.
The manipulation and adjustment of feed rations without compromising herd productivity or herd health has the potential to reduce both phosphorus and nitrogen levels being deposited in the effluent stream.
This level of detail may be more applicable for the larger intensive herds operating on small acreages or on properties with extensive networks of watercourses and drainage lines.