Niwa engineer's design

The Lepper piggery biogas digester was designed and commissioned by Niwa research engineer Stephan Heubeck, of Hamilton.

He says Steve Lepper "is the first one doing this in New Zealand for 20 years. He has a real pioneering spirit and others will learn from him."

In the early 1980s, there were dozens of agricultural digesters in this country, mainly producing biogas for fuelling vehicles, but these systems couldn't compete when oil dropped to $10 a barrel. All but Fonterra's Tirau industrial plant were discontinued.

"However, there is renewed interest in these systems and I think we will see more built in the next few years," Mr Heubeck says.

"The scope for this technology is quite wide, but for the time being, it will be limited to situations where you can link the supply of manure feedstock to a local demand for power or heat. Often, you don't have both in the same place. It works in the Lepper case because the feedstock supply is immediately adjacent to the piggery's demand for heat and power.

"Piggeries are one of the best sites to do this, because they have a high waste output and a high demand for power and heat. The driver for the piggery is reduction in waste odour.

"Energy independence, GHG [greenhouse gas] emission reduction and improved effluent land application are all secondary benefits, but they are less tangible and not the main driver at this point in time.

"This is the first one of this kind I've been involved with," Mr Heubeck says.

"I've worked with heated mixed digesters in Europe and we have designed covered anaerobic ponds for other piggries, but they were mainly for odour control with the biogas flared off. Lepper is New Zealand's first full co-generation design based on simple covered anaerobic pond technology."

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