Dairy Effluent Management: Right Amount at the Right Time
Good effluent management on a dairy farm combines a well-designed system with proper processes to ensure the right amount of effluent gets applied to pasture at the right time.
The system was installed by John Scandrett of Dairy Green Ltd with Fortuna Group Ltd.
The ground-breaking project implementing a prototype methane recovery system on a 950-cow farm in Southland has demonstrated for the first time commercial viability of this technology within a cool climate, says Dairy Green in its award entry.
“Performance has exceeded forecasts, providing 30kW electricity and 60kW hot water, providing for most of the farm’s energy needs, including running an electric farm bike entirely from waste product.
“Dairy effluent storage ponds are known to produce methane, a greenhouse gas more than 21 times worse than carbon dioxide in effect. Despite this the dilute nature of dairy shed effluent means it is not suitable for supplying conventional biogas digesters.
“The Fortuna Group’s Glenarlea Farms 950-cow property in western Southland has successfully demonstrated biogas can be harvested and used to meet a significant portion of the electricity needs and all the hot water needs of a dairy shed.
“The science behind the project was developed by NIWA and monitoring of a Southland dairy shed effluent pond for NIWA by Dairy Green Ltd staff confirmed the commercial viability of methane recovery.”
Dairy Green Ltd was contracted by the Fortuna Group to implement methane recovery and electricity and hot water generation at the Glenarlea Farms property. Scandrett designed the water cooling system.
Venture Southland arranged EECA involvement and funding NIWA’s initial involvement, completing a feasibility study. EECA provided a subsidy.
The project involved building a biogas recovery pond, gas collection and transfer piping and condensate removal. This was followed by filtering and compression and storage so the generator could be run on a standby basis.
Scandrett says five farms in the South Island are interested in the system. They are at the stage of putting a package together for commercial development.
Because of economies of scale the system will suit larger farms better. But possibly two or three farms could come together and have one setup between them.
Scandrett says about 7% of methane losses from the farm are from the effluent pond but a farm with a wintering home probably has about 15% of its methane footprint from stored effluent.
“So covering the effluent and capturing the methane could be capturing 7-15% of the methane from the farm. It is certainly significant as well as being an energy source.”
The nutrients in the effluent are not being affected at all, so there are “a whole lot of pluses” to the system, he says.
