Effluent system design - podcast transcription
Effluent system design
Greg: Welcome to Dairy News. Today I have with me Tony Dowman and my name is Greg Mills and today we’ll be looking at designing dairying effluent systems. So Tony, what’s the first things to consider when you’re looking at a dairy effluent system?
Tony: Firstly you need to understand what the legal ramifications are of effluent management control systems and they are all state specific. So if you’re interstate, not in New South Wales, you need to firstly talk to your local consenting authority to see what their requirements are.
In New South Wales 800 cow dairies have come under the consent of local council where the over 800 cow dairies require environmental impact statements and actually scheduled activities and licensed with state government. There is no actual requirement in the act to say what you must have. All it states is what are the environmental outcomes that you must achieve and these outcomes are that effluent must not enter any water course including underground water. It’s not to leave your property and go into your neighbours, it’s not to concentrate nutrients or water in the soil, it’s not to be offensive in sight, odour, noise, dust, vermin and lastly, there should be a one in 10 year wet weather management plan attached to the effluent system.
Greg: That last one, the 10 year climate information, does that make it very site specific?
Tony: Correct Greg. It has to be site specific and you need to source the weather data for the locality that you are designing the effluent management system for. These effluent systems are not just for the dairy, for the milking premises. It doesn’t matter where the cattle are congregating and what they’re doing, it’s any area where cattle are grouped together, it could be a loafing pad, it could be a feed pad, could be laneways, could be anywhere like that including the milking area that has to have an effluent management system attached.
Greg: Is there any significant differences between a feed pad and a dairy at all?
Tony: The type of dairy effluent generated on a feed pad compared to the milking area is subtly different. On a feed pad you’ll have a percentage of undigested food entering the effluent system which does put an extra loading on the system. But it’s nothing that can’t be catered for.
Greg: I have to get my climate data for my site. What other parameters about my dairy operation impact on an effluent system?
Tony: Well obviously the number of cows being milked or being contained. Secondly the milk production, the number of hours a day they spend in the confinement facilities, how much water you’re using for wash down, what is the surface area the cows are standing on, what’s the pumping capacity of the pumps that are transferring effluent firstly from the holding area to the pond, if you’re using a pond, and then also from the pond to the reuse area.
There are also other constraints as well such as are there solids separation going on and how big an area you would like to have to put the effluent onto to use up all the NP&K that’s in the effluent.
Greg: So that NP&K Tony, how do I work out the size of my reuse area?
Tony: It depends on the economic practises that you wish to carry out on that area. If you’re just going to grow a minimal amount of grass or do very sort of basic agricultural activities such as relying on base pastures to absorb all the NPK, you would then have to have a very large area to accommodate the nutrient loading.
If you are going to be grazing cattle at the same time, the dairy would even be bigger again because the cows that are grazing it are just recycling the NPK with the plant. So it’s absorbing from the soil.
So basically the farmer has to decide what agronomic practises he is prepared to put into the area and that will then determine how big that area has to be.
Greg: Given there’s a number of factors involved in this, is there some simpler way of calculating all of this?
Tony: There are a variety of effluent management calculators available for farmers to use. Most states have their own system. New South Wales Department of Primary Industries has an effluent management calculator which their staff can use to do all this number crunching for you. Contact those people or if you’re interstate, talk to Queensland DPI or Vic DPI to see whether they can assist you to design an effective effluent management system.
Greg: Tony does that mean everyone needs a pond as part of their effluent system?
Tony: No. A pond is not required but remember I said you have to have a one in 10 year wet weather management plan and we generally find that the softest option to meet that criteria is the effluent storage system which means a pond and those ponds will be designed based on what management strategy that you wish to adopt.
For example if you choose to store all the effluent that you generate in one year, put it into a pond and then deal with it another day, an effluent pond will be quite large because of all the water that you’re using for wash down. If you’re prepared to manage that pond almost on a daily basis and say recycle water, the ponds will be very, very small.
Again, depending on what management strategy you want to use, the pond will then be sized accordingly.
Greg: Tony, so these design systems, would they be suitable for any sized dairy operation?
Tony: Most of the calculators that are used today are really designed for the under 800 cow dairies or in areas which are not environmentally sensitive. If you require an environmental impact statement, any of these calculators really are not good enough. There needs to be very detailed documentation in those site specific areas because most of these calculators are using some generic information to do the calculation.
If you are in New South Wales over 800 cows you’ll need to employ consultants to do your environmental impact statement.
Greg: Thank you Tony.
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