Putting Biogas to Work

Many farmers have stood next to their dairy effluent ponds and watched the biogas bubble up and disappear into the air.

“We all know this is a wasted resource, but hardly anyone uses it,” says Dr Andy Shilton, director of Massey University’s Centre for Environmental Engineering and Technology.

Shilton is enthusiastic about using the biogas resource to lower on-farm energy costs.

He leads the Innovative Anaerobic Pond Design — a group of Massey University researchers and collaborators, which includes Rupert Craggs, of the National Institute of Water and Atmospheric Research, and Graeme Attwood, of AgResearch.

The group has two-year Dairy InSight “innovation funding” of $395,000 to design and build a treatment system to capture and use the biogas from effluent treatment ponds.

“There is a real opportunity to make New Zealand’s dairy sheds energy self-sufficient by harnessing the energy potential (of) the cow manure,” Shilton says.

At the moment, most waste goes back on the land as manure fertiliser. But its energy potential could be captured better and used to run dairy sheds.

“There’s nothing new about the idea of making biogas from manure,” says Shilton. “The trick, however, is developing a practical and efficient system that farmers would realistically invest in and use.”

The project has two levels. The first involves using best international practice to develop a smart but simple optimised anaerobic pond.

“The second is where we lift the bar by looking long and hard at what makes a cow such an efficient grass digester, and then adapting this into an improved engineering design for the new treatment system,” Shilton says.

“It’s a bit like trying to engineer another, final cow’s stomach for biogas production,” he adds.

Work has just begun in the Centre for Environmental Engineering and Technology laboratories in Palmerston North to assess process parameters and optimise biogas yields.

Several factors have converged to make the use of dairy effluent as an energy source on the farm increasingly viable, he says.

“Herd sizes are bigger, making it easier to justify investment in a system to use biogas,” he says. “The cost of gas engines for electricity production has come down. In Europe, there are tens of thousands of on-farm biogas systems going in.”

That has made the gas-to-energy conversion-equipment technology cheaper and better, he says.

“However, the way they produce the actual biogas is still pretty complicated and expensive, and this is where our approach differs.

“But perhaps the major driver in the coming decade (will be) the price of energy. Ask anyone what the price of electricity is doing. It is going up.”

A biogas system has the potential to generate enough electricity to run an energy-efficient dairy shed; and the by-product of heat from the electricity generation could be used to meet all the shed’s hot-water requirements, Shilton says.

The project aims to develop an on-farm system that will be relevant to all dairy farms, and to have a demonstration model up and running on Massey’s No. 4 dairy farm this year.

Shilton says the strategic significance of the project for the New Zealand dairy farmer is substantial.

“Instead of emitting tonnes of this severe greenhouse gas from ponds, we have the potential to turn it around to insulate our farmers from escalating energy costs.

“It’s a real win-win where the key is being smart in the science but keeping it practical in its delivery.”

Manawatu Standard

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