Z-Filter a new tool for effluent management?

For a long time the dairy industry has been trying to find fit-for-purpose systems to deal with effluent in a manner that maintains profitability and reduces environmental impacts. Now an initiative by Augusta Margaret River Clean Community Energy Incorporated (AMRCCE) may be one step closer to an alternative solution with big benefits both on- and off-farm.

With an eye on protecting the iconic Hardy Inlet from pollution and reducing greenhouse gas emissions, the AMRCCE surveyed local dairy farmers in 2018 to see whether it would be possible to collect effluent from farms to feed a potential biogas waste facility. However, after finding that local dairy farms produce approximately 315,000 m3 of effluent annually, they realised that effluent would first need to be processed on farm to separate liquids from solids to reduce transport costs.

In August 2019, the group partnered with local farmer Brad Boley, the University of Southern Queensland (USQ) and the Department of Water and Environmental Regulation’s Regional Estuaries Initiative, in cooperation with Lower Blackwood Land Conservation District Committee, to trial the Z-Filter, a machine that can separate effluent into a liquid filtrate and transportable solid.

With the trial up and running, project partners came together to host an event at the farm in Scott River where the trial is taking place.

The Z-filter at Boley Farm drops dry cake onto a conveyor belt

Dr Stephan Tait from the Centre of Agricultural Engineering, USQ, said that the project aimed to recover valuable water, nutrients and energy from effluent, which would protect waterways, reduce fertiliser costs and contribute towards farm profitability. He said that spreading raw effluent repeatedly onto paddocks near the milking shed can lead to a big oversupply of nutrients, increasing the likelihood of nutrients entering waterways.

His study has found that the filtrate (liquid) extracted by the Z-Filter has a similar nutrient content to raw effluent, while the solid cake has a higher proportion of nutrients due to the reduction in moisture content.

Host farmer Brad Boley agreed that in his previous effluent management system, using raw effluent had caused a big over-supply of soil phosphorus in some paddocks. With the help of the Z-Filter, he is able to pump filtrate through irrigation systems without clogging the equipment and allowing him to spread the diluted filtrate (4% filtrate) over a much larger portion of the farm. He said that over a 14-day period he applies the equivalent of 20 kg of super potash 1:1 and 10 kg of urea, an equivalent value of $70,000 to $80,000 of fertiliser per year. In addition to this, approximately 8-10 tonne of dry cake is being produced per week.

Maintenance is significant and estimated to be two hours per day for two people and as such the cost of the system may not be viable for all farms, particularly those smaller in size.

The filter works by gravity drainage on an incline, then bending sludge through a serpentine shape with rollers and a final compression sequence to result in a liquid filtrate and a dry cake which is roughly 24% dry matter and much more transportable. Directing waste to biogas facilities has been increasingly adopted by the piggery industry with the help of USQ with the reduction in energy and carbon credit sales resulting in a capital payback period of less than three years. However, Mr Boley said he would prefer to keep the nutrient source on the paddock if it can be used effectively.

Mr Boley said he wanted to see the trial run through before making any commitments, but at this stage is “pretty positive”.

This project is a part of Royalties for Region’s Regional Estuaries Initiative which aims to protect the health of six key south-west estuaries.

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