From odour mitigation to energy system

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In recent years, the New Zealand pig industry has been seeking solutions to odour emissions from open waste stabilisation ponds. One of the solutions is to integrate anaerobic digestion with biogas recovery into the effluent management system. A recent example is Taranaki pig farmer Steve Lepper.  

Steve wanted to reduce the odour emissions from the waste management system of his 450 sow farrow-to-finish piggery.

Odour minimisation was achieved by installing a custom designed covered anaerobic pond up front of the existing open waste stabilisation ponds. Anaerobic bacterial activity in the deep, stratified pond destroys the majority of biochemical oxygen demand (BOD5), volatile solids (VS) and odour causing compounds (volatile organic compounds / VOC) contained in the piggery effluent. This breakdown of effluent solids generates biogas, which is captured underneath the pond cover. The anaerobic treatment in the covered pond starkly reduces the loading of the existing waste stabilisation ponds and substantially reduced odour emissions from them.

With the primary goal achieved, attention turned to the use of the recovered biogas. The biogas could be flared for effective control of greenhouse gas (GHG) and odour emissions, or be used as an energy resource. The recovered biogas could be used either for boiler fuel, combined heat and electricity generation (CHP), or vehicle fuel.

In Steve’s case, the most practical option was the installation of a 50 kWe CHP plant with a hot water recovery system. The set-up is very flexible since biogas can be stored under the pond cover and used for electricity generation when needed. Thermal heat storage capacity in the hot water recovery system enables decoupling of the generators thermal and electrical load. In practice, this means that it possible to generate electricity during the day (when price / demand is highest), whilst heating the breeding unit at night.

Although it is not anticipated that the farm will become a net energy exporter, the majority of current energy requirements is expected to be provided by biogas in the not too distant future.

As 2009 draws to a close final work is being carried out to integrate the generator into the piggeries electricity system, and in the coming months the piggery will be progressively switching to using more of the reticulated hot water produced by the generator.

Mr Lepper would like to thankfully acknowledge the technical, financial and logistical support and advice provided by the Taranaki Regional Council, EECA, NIWA, Current Generation, Kerry Larsen and Jeff Kerr and during the planning and execution of this project.

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