Dairy effluent is a useful resource with value as a fertiliser and soil conditioner. The quantity, characteristics and nutrient concentration of dairy waste will vary from each farm depending on factors such as the degree of treatment, herd size and the quantity of water used for dairy shed cleaning and yard wash-down.
Dairy shed waste largely consists of the manure and urine in washdown water. However, it also includes detergents, gravel from the cows hooves, suspended soil particles, cow hair, milk, string, paper and other debris that can collect around the dairy. Before dairy shed effluent can be used, the waste needs to be collected and the gravel and other debris need to be separated out.
In order to re-use dairy effluent the property must have a system that provides for continuous wastewater disposal or wastewater storage/treatment prior to application by irrigation (ie not just a hose left on the ground) to land.
Pollution of waterways and groundwater or erosion must not occur whilst maximising benefits to land.
- Rigorously follow a detailed maintenance program to ensure a minimum of component breakdowns.
- Careful consideration of wastewater nutrient concentrations and application rates should be undertaken.
- Site features need careful consideration when considering hydraulic loading or the amount of effluent able to be supplied that is consistent with the soil profile.
- Hydraulic loading rates should be calculated using rainfall, evapotranspiration evaporation and transpiration rates of the pasture or crops/vegetation to be irrigated.
Effluent Management Systems:
Effluent management system options include spray irrigation, pond systems or a combination. Whatever system is used needs to be effectively managed.
- Effluent is sprayed directly onto pasture or crops:
Provision should be made to store the effluent during extended periods of wet weather when spray irrigation of effluent should not take place. Application of effluent to pastures by a spray irrigator requires regular manual or automatic shifting of the irrigator to avoid excessive application so the soil is not overloaded and the pasture is palatable to cows at the next grazing.
- Ponds and Storage Tanks:
Once ponds and storage tanks are installed, effluent may be stored during the wetter months and sprayed onto pastures or crops in dry periods. Storage needs to be sized according to the amount of manure, washwater and rain entering the waste system during the wetter months of the year. Ponds for storage or treatment need to be adequately designed, sealed and managed properly to prevent soakage into groundwater and so they have adequate storage capacity to handle future expansion. Above ground, hillside and turkey's nest storage can be used as well as excavated ponds. Run-off into the ponds should be avoided.
- Two (or more) ponds:
Effluent is treated in an anaerobic settling pond and (generally) one aerobic treatment/storage pond. Ponds need to be correctly sized. Treated effluent is applied to pastures or crops by gravity or spray irrigation or recycled for yard washdown.
There is a trend to use a single pond or tank for storage of effluent and application to pasture at appropriate times rather than a multi-pond treatment system. Two (or more) pond systems need to be effectively managed to ensure the effluent is treated to reduce its pollution potential. Anaerobic ponds will require periodic de-sludging. The frequency of the task is greatly reduced if the pond is sized correctly and the solids content is reduced before entry using an effective solids trap.
The treated effluent from pond systems can be recycled for yard washdown.
The design of an effective effluent wastewater management system will be farm specific. Gravity should be used to advantage to minimise the need for pumping.
- Minimal storage (to cater for emergency pump or irrigator breakdown) and pumping through an effluent irrigator,
- Anaerobic and aerobic ponds treatment prior to application to land through an effluent irrigator or shandied with clean water and application through a centre pivot irrigator,
- Pond(s) and solids trench/'green water' storage and application to land through an effluent irrigator or shandied with clean water and application through a centre pivot irrigator, and
- Screw press or static screen solids separation with storage of 'green water' and application to land through an effluent irrigator or shandied with clean water and application through a centre pivot irrigator and use of solids as a soil conditioner, sale to nurseries, etc.
The Bottom Line:
Dairy farming results in effluent and wastewater in quantities at the farm dairy that requires a well-planned and well-designed effluent management system.
Farmers who ignore the need for effective effluent management may be prosecuted.
Minimise Health Risks:
Dairy effluent management must seek to minimise health risks associated with the reuse of wastewater. Bacteria that cause diseases, such as Johnes disease, salmonellosis, leptospirosis, mastitis and enzootic bovine leucosis, can be found in manure, urine and milk. Worm eggs, coccidial eggs, clostridial organisms and tetanus spores are also passed in manure. A program must be implemented to protect against transfer of disease-causing organisms. Veterinary advice should be sought on health matters concerning the herd.
- Young stock should not graze areas treated with effluent for at least the first 12 months of their life.
- Adult stock should not graze areas where waste has been applied for at least 10 - 14 days in summer and several weeks in winter.
- Do not allow drains from treated areas to flow into areas where young stock are being kept. (This will help to reduce the risk of infection with Johnes disease.)
- Do graze areas just prior to effluent application to allow increased sunlight penetration to kill organisms and to extend the period before the area is ready to be regrazed.
- Do spread effluent during the warmer, drier months to reduce survival chances of disease organisms.
Associated Environmental Issues:
- Dairy effluent management systems must strive to avoid problems.
- Wastewater should be spread at rates to allow changes in temperature, pH, moisture and sunlight to help destroy harmful organisms.
- Veterinary requirements on disease control should be observed. For example, isolate infected animals.
A single application of dairy waste at a rate of about 25 mm/ha will not apply excess nutrients. This application rate should also reduce the risk of effluent run-off and of nitrates leaching to groundwater. At this application rate, one to three applications can be made per year, preferably at times when the pasture is actively growing and will use the nutrients and water.
Every megalitre should irrigate about 4 ha with one irrigation. If the crop or pasture is to be irrigated more than once in a year, then the following points need to be considered:
- Normal fertiliser applications should be altered (in the case of potassium, eliminated) on the paddocks to which waste is applied.
- Timing of applications.
- Withholding periods.
- Grazing management of wastewater treated areas.
Dairy shed waste must be managed in such a way that it remains on the farm and does not contaminate waterways or sub-surface (ground) water with nutrients or bacteria.
For more information including the Code of Practice, visit the DPIPWE website.