The benefits of slurry separation were profiled at recent College of Agriculture Food and Rural Enterprise (CAFRE) events, hosted to highlight the value of all animal manures.
Research scientists at the Agri-Food and Biosciences Institute (AFBI) have assessed the most feasible way of separating slurry, and also how to best utilise the liquid and solid fractions produced.
Driving this work, is the growing recognition that slurry can be used in myriad ways to optimise crop growth.
AFBI’s Gary Lyons attended the slurry management event, hosted by CAFRE on the Banbridge dairy farm of Ian McClelland.
Lyons said: “The main driver of our research is to use mechanical separations in ways that allow for the better use of phosphorous (P) in both slurry and the digestate produced from anaerobic digestion systems.
“It is possible to remove some of the P contained in the solid fraction of these materials through a mechanical separation process.
“Driving improvements in water quality is the focal point of our work, looking at the mechanical separation of slurry.”
According to the AFBI representative, the environmental challenges associated with the algal blooms that developed on Lough Neagh last summer epitomise the problems associated with water quality in NI at the present time.
Water quality
Lyons also admitted that agriculture is not solely to blame for deteriorating water quality standards.
“Approximately 65% of P entering Lough Neagh is coming from agriculture. The remainder is accounted for by domestic sources.
“What is clear, is the need to start doing something about the problem now,” he said.
Lyons believes that it is financially feasible for most livestock farmers to invest in a screw press separation system.
“They have been grant aided by the Department of Agriculture in the past. Given current circumstances, I see no reason why investments in this form of technology would not be supported in the future,” he added.
Slurry separation
Slurry separation and management systems are being developed by AFBI on the basis that the solids are not put back onto the farmer’s land.
“The plan is the export the phosphorous in the solids off the farm.
“Slurry solids are regarded as concentrated energy sources in this context. Subsequent to the digestion process, there would be a requirement to separate out the slurry solids," he said.
Lyons pointed to the fact that separated digestate fibre can be applied as a valuable P source on tillage crops.
“This is already happening,” he confirmed.
“An AFBI team is currently looking at the option of using pellets as a solid fuel source. They have about 90% of the energy value contained in commercial wood pellets.
“However, the pellets would not be suitable for domestic use as they have high particulate gaseous emissions. They would be totally suited for use in power stations,” he added.
Currently, agriculture in NI is generating a P surplus of around 6,000t annually. This reflects P imported in feed and fertiliser relative to total crop requirements.
“The plan is to take as much of this surplus as possible out of agriculture altogether. This includes the sending of slurry solids to tillage areas in the Republic of Ireland.
“We are already supplying slurry solids generated at AFBI’s Hillsborough research farm in Co. Down to neighbouring arable farmers," Lyons said.
AFBI has carried out trial work using both screw press and decanter centrifuge separation technologies installed at its Hillsborough-based farm nutrient management centre.
For farms and those with anaerobic digesters and managing larger volumes of manure, screw press separation is possible.
However, if higher levels of P removal are required, the use of decanting centrifugation is a viable option.
