A Western Australian dairyfarmer says his simple effluent management system is the most cost-effective and labour efficient for his farm.
Michael Twomey's 500-cow farm Dardanup, WA, was part of an effluent project this year environmental engineering honours student Laura Senge conducted an audit of the system and made recommendations for upgrades.
The aim of Ms Senge's research was to design a zero-waste discharge system for the farm. The total estimated cost for the system she designed was $168,000.
Mr Twomey said he had no criticism of Ms Senge's thesis and was happy for people to explore and come up with better ideas but, at this stage, he could not justify the expenditure to change a system that was operating effectively.
"Right at this point in time, where milk prices are going and what's going on here, I am not in a position to spend money on things that aren't broken," he said.
The two-pit solids trap system was installed at the farm about two years ago when a new dairy and yards were built when Mr Twomey returned to the farm after 13 years in the mining industry.
The farm's annual average rainfall is 770 millimetres, 90 per cent of which falls between May and September
Freshwater for the farm is supplied by a superficial bore (dam) and a bore into the Leederville aquifer, with a combined licence of 527,490 kilolitres annually. It is pumped to a 130,000-litre tank adjacent to the dairy shed for daily use.
The rotary dairy's under-platform area and yards drain into one end of a large concrete pit beside the yards.
A high-pressure washdown cannon is used and can be directed, if needed, into the effluent pit to break up floating solids.
Plastic plumbing with a low-level entry point picks up liquid from beneath floating solids and links via a T-piece to the adjacent smaller pit, which is monitored by high and low-level probes.
An electric pump pushes liquid waste from the second pit through a non-return valve ù to retain prime ù and out through a buried pipe to a modified 440-metre-diameter centre pivot irrigator in a nearby 20-hectare paddock.
A hose up the centre of the pivot tower and underslung along the pivot arm carries liquid waste to a simple 50 millimetre 'knocker' sprinkler, which can be moved along the pivot arm to alter the area of the paddock receiving water from the effluent pit. Each pivot tower has a cannon that spreads effluent about 10 metres.
"The system works pretty well, but it's not perfect ù there is no perfect system," Mr Twomey said. "I turn the pump on before I start milking and set the irrigator walking, but I can go a couple of days without having to do that. We currently use about 10,000 litres of water a day and the pits will hold 22,000 litres.
"Yes, the sprinkler does get blocked occasionally, we've also had to replace the packing (at the base of the pivot tower where the pipe enters) annually and every five to six months get into the (bigger) pit with the tractor and bucket to clean it out.
"At this stage, we've just been stockpiling the solids in one area to dry and we'll probably end up spreading it over paddocks."
Mr Twomey has refined the system this year to try to spread the effluent more evenly, particularly in winter when it drains into the pivot wheel ruts.
Droppers have been placed in the middle of the pivot span and a three-legged streel plate placed at the bottom of the dropper to help spread effluent to a diameter of about 5m.
"So I am spreading my effluent more evenly and it only cost me about $80 each to install," he said.
"I always knew there was a better way to spread it, we just had to get around to it. So I will see how that fares for a bit."
Ms Senge, who came to Australia from Germany three years ago to study, was awarded a scholarship by Western Dairy and WA's Department of Water (DoW) to design the zero-waste discharge effluent management system for the farm as her honours project.
She aimed to create an integrated dairy water supply and effluent system that eliminated soil and water pollution while minimising water demand and maximising outputs such as energy, soil nutrients and fit-for-purpose water recovery.
Her project will be incorporated into the Royalties for Regions-funded DairyCare project Western Dairy and DoW are undertaking to improve catchment water quality under the Regional Estuaries Initiative.
Ms Senge's study, which was presented at the 2017 Dairy Research Foundation 2017 Symposium at Port Macquarie, NSW, in July, involved an audit of water use in the effluent system and a study of nutrient movement through the system.
The findings were that 52,000 litres of freshwater was used per day (52 litres/cow/day), which was higher than industry benchmarks.
Ms Senge assessed four options for the system:
1. No action.
2. Single pond for storage.
3. Tank for storage.
4. Floodwash tanks for yard wash plus roof on yard for rainwater collection.
Option 3 was ruled out first, as the installation cost of a tank with a total capacity of the required 11 megalitres was estimated in the millions. Option 1 was also ruled out, as it did not achieve zero-waste discharge.
Option 4 was the preferred option, as it decreased the effluent volume significantly as well as the freshwater usage, increased productivity and reduced labour requirement.
The final proposed design was a hybrid of options 4 and 2, a roof and a floodwash system for the yard with a single pond for storage during the winter storage period.
In addition, a second pivot was suggested to be connected for effluent distribution, to allow for sufficient application area.
Due to the floodwash system, the pond size required was reduced to a total capacity of 8.7 megalitres, estimated at $42,000 maximum, including survey and geotechnical investigations.
The proposed improvements to the site included a roof, which would increase rainwater catchment, resulting in a reduction of freshwater use.
Although the cost of freshwater was not an issue for Twomey's farm, the lower volume of freshwater being used meant a reduction of contribution to the effluent stream.
The roof would also help reduce heat stress on the cows and thereby increase the volume of production at the farm.
If followed, the suggested solution of recycling wastewater after primary treatment would reduce labour costs and effluent discharge to the paddock, therefore providing a reduction of the size of the effluent application area necessary.
"With a total cost estimated at $168,000 and a payback period at 6.2 years, the system proposed was found to be a viable option," Mr Senge's study found.
Mr Twomey said he had no qualms about taking part in the study but he had to assess what was most practical and cost-effective for his farm.
"You could keep spending money on heaps of things," he said. "You've just got to try to keep things simple, the more you put in the more things can go wrong."
He said although the study had identified nutrient discharge from the system, this discharge was not leaving his property as it ran down to another part of his farm.
"Nothing is going to make the river system from my farm," he said. The 10,000 litres a day is pumped onto an area of 20ha, that then runs into the farm's own dam system.
The effluent paddock is on a gradient.
"When it is very wet I try to have the pivot on the top side in the drier areas ù so it puts it up there," Mr Twomey said.
He also said there would be little labour saved from changing the system, as the only labour currently involved was when a line blocked ù which did happen ù but that might be an hour a week.
"So if we built something bigger, we'd be assigning more labour to it," he said. "There's no foolproof or magic system but it's not bad."
DairyCare project Western Dairy regional manager Esther Jones said the project team was seeking expressions of interest from other WA dairyfarmers wanting to have their effluent system reviewed.
"Through our DairyCare project, we will be working closely with farmers in the Geographe, Hardy and Leschenault catchments to establish willingness to make a commitment to improved effluent management," Ms Jones said. "We have funds through the project to undertake 60 reviews ù a process that will give a real insight into the opportunities to improve the effectiveness of current systems."D
To volunteer for an effluent system review, contact Western Dairy project officer Dan Parnell, email Email email@example.com or phone 0467 556 542.
With Farm Weekly
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