Science Centres: Energy

The pond cover incorporates methane-extracting pipes running underneath the cover around the edge. (Photo: Stephan Heubeck, NIWA)

NIWA research into biogas recovery from farm animal waste has taken another step forward with the successful design and installation of a cover for a large piggery effluent pond, and subsequent capture of methane produced by the pond.

A 1200-pig fattening unit in the Waikato had to control odour as part of its new resource consent conditions. NIWA’s Dr Rupert Craggs designed a 3000 m² polypropylene cover for the pond. A gas pump is used to suck the biogas from under the cover through a perforated pipe which runs around the pond perimeter. The biogas can be used to generate electricity or be purified and compressed for use in CNG or diesel  vehicles.

“The pond cover, including rainwater management, at a material cost of around $20 a square metre, has solved the piggery’s odour problem,” says Dr Craggs, “but the methane is potentially a valuable byproduct. We estimate that, if it was used to drive a generator and converted to electricity, the farmer could expect pay-back for his investment within three years.”

The seasonal variation in biogas production and quality is presently being monitored to determine the size of generator required by the farmer to most economically use all of the biogas.

Funding has come from the Foundation for Research, Science & Technology, Warratah Farms Ltd, and the NZ Pork Industry Board.

More information on the project can be found in our 'Biogas recovery from wastewater' section.