AFBI leading on managing nutrients from slurry

Date published: 05 April 2018

Areas of Expertise: Sustainable Livestock, Grassland and Plant Science, Environmental Protection

The Nutrient Management Centre at the Agri-Food and Biosciences Institute (AFBI), Hillsborough, funded by the Department of Agriculture, Environment and Rural Affairs (DAERA) is currently being commissioned with a key goal to explore technologies which offer opportunities for better nutrient management of slurry and digestate.

Screw Press Separation and Centrifugation are the two established technologies currently being investigated for their impact and effectiveness in removing, off farm, large quantities of solids from farm slurries and digestates i.e. feedstock. Separation of feedstock produces a solids fraction containing a high proportion of phosphorus (P) which is more economical to transport off farm for both agricultural and non-agricultural purposes. This is especially important for Northern Ireland, since oversupply of P to grassland has increased soil P levels beyond crop requirement optimum, leading to increased risk of P runoff to water courses and a negative impact on water quality.

$Screw Press separator separating anaerobic digestate in to solid and liquid fractions$

At AFBI Hillsborough, it is planned that separated solids will be exported off farm to other agricultural land where P supply is low, and the separated liquid fraction, with its reduced solids and P content, will be applied to AFBI grassland as a bio-fertiliser. The Screw Press Separation technology has the potential to reduce total P from slurry or digestate by 20-40%. Results during the commissioning phase of the Screw Press indicate that 25% of the total P, 15% of the total nitrogen (N) and 10% of the total potash (K2O) in digestate was removed in the separated solids fraction, with a DM content of 24.5% (i.e. suitable for dry handling). It is expected that greater removal of P should be possible once the system is fully commissioned.

Use of centrifugation should result in even higher levels of P removal, with potential for >60% of P being removed in the solid fraction. Therefore, the technology appears to have appreciable potential to address the challenge of better management and recycling of the nutrients in slurry and digestate, contributing to more effective nutrient management and reduced environmental impact.