NZ Farmer - Effluent pond methane powers Southland dairy farm shed

 Methane generated from an effluent pond is heating and lighting up a cowshed in Southland.

In what could only be described as an environmental game-changer, Glenarlea Farm, one of Fortuna Group's farms in Southland, is converting effluent methane into electricity.

Dairy Green agricultural and engineering consultant John Scandrett says the new system has been 13 years in the making and is now generating enough electricity to power the cowshed and heat the shed hot water.

The pond on Glenarlea Farm where the covered effluent pond is producing methane under the black lining which is then converted into electricity.

"It's all powered by poo," he says. "David has always been an innovator thinker and early adopter. He had this big idea of producing biogas years ago and now here we are."

He is talking about David Dodunski, who with wife Kay established the Fortuna Group in 2012.

It all started when Dodunski changed his effluent system and irrigator to a low-rate K-line developed by Dairy Green and built a new pond.

"The downside of the new system was the smell being emitted from the pond," Scandrett says.

"David asked what could be done about the smell so we consulted Niwa scientists who told us that regardless of what we did or added, there was no beating Mother Nature – it would always go back to its original state."

The scientists recommended the best course of action was to cover the pond to stop the smell permeating the air.

"And as a result of that, they said we would be able to capture the methane produced underneath the cover."

Producing methane is a two-step bacterial process. The first stage of breaking down solids happens quite quickly and unfortunately some of the breakdown can produce quite an odour.

The second stage of converting those breakdown products to methane happens more slowly and also stinks, especially in a new pond.

"We undertook to do some field work for Niwa to see how well the methane-forming process would work in Southland and the results agreed with the expected theoretical output of gas, based on the amount of food going into the pond for the bacteria.

"The process is slower in Southland because of the colder climate. But if it works in Southland, it can work anywhere in New Zealand.

"So the idea was to cover the pond, capture the methane and use it in a motor-driven generator and produce power to run the shed and heat the water. David was keen."

They approached the Energy Efficiency and Conservation Authority (EECA) with the help of Venture Southland, and they were keen to see the trial go ahead and helped with some funding.

"The thing is, no-one had done this in this part of the country using a diluted waste like dairy effluent.

"So it was very much experimental. The system is a prototype but has shown it is a commercially viable operation. It is not the first methane recovery plant in New Zealand, but is the only trial I know of that has been successful to date, but I am sure there will be others soon."

The 900-cow dairy farm has been converting methane gas captured from the dairy effluent pond into electricity and hot water for the dairy shed since spring last year.

Waste from the dairy shed, including manure, urine and wash water, goes into a sand trap, then a pump sump, which is a storage tank, before it ends up in the biogas pond.

Methane then naturally develops and collects under the black lining before it is piped through to the generator to power the shed and heat the water for plant washing.

"It has been working exceptionally well and producing more than what is needed or predicted," Scandrett says.

"The plant worked for 16 hours a day during spring and generated 30KW each hour plus an excess of hot water."

He said they have now tweaked the system so that the plant only produces what electricity is needed.

"The system now senses the load required and produces electricity accordingly.

"If 25KW is needed, that is what it will produce. If more or less is required, then it will generate it."

The obvious benefit is the saving in power bills.

"The generator will save about $25,000 of the annual power bill for the shed.

"That's money saved which over time, will pay for the initial set-up and installation.

The system cost $180,000 to $200,000 and included the covered pond, generator, hot water system, electrical system, biogas reticulation and a shed to house the generator.

"At that rate, it will take about 10 years to pay for it so may not be suitable for small farms. But there could be options available and the potential is huge for larger farms.

"There has been a lot of interest in this, which is not surprising considering all the environmental issues facing our farmers and the increasing costs of compliance."

There is also a significant reduction in greenhouse gas emissions as the methane is converted to carbon dioxide, which in this case is carbon neutral.