Acidification of pig slurry before separation to improve slurry management on farms

ABSTRACT

Pig slurry, rich in plant nutrients such as nitrogen (N) and phosphorus (P), is generally applied to soil as organic fertilizer. However, costs related to slurry transport may limit its utilization to fields close to the farm, leading to significant N losses, namely ammonia (NH₃) emissions. Slurry acidification, to minimize NH₃ emissions, is a potential solution to this problem, while solid–liquid separation leads to a solid fraction (SF) – rich in organic matter (OM) and phosphorus – and a liquid fraction (LF) rich in soluble nutrients. We hypothesized that a combination of acidification and separation could affect the quality of the resulting fractions depending on the separation technique used. After acidification, the two most common techniques for separation, centrifugation (CF) and screw-press (SP), were applied. The main characteristics of the slurry fractions in terms of nutrient concentrations and speciation as well as the potential N mineralization (PNM) were analysed. Our results show SFs with improved properties, mostly N and PNM when acidification is performed before separation with both techniques. The PNM was significantly increased in LFs from both techniques after acidification. The concentration increased in LFs from SP with acidification; therefore, slurry acidification is recommended to avoid any N losses during the separation process with SP, while CF may not require such pretreatment. Acidification could allow the use of a cheaper technique such as SP relative to CF since it prevents NH₃ emissions during the separation process and leads to more equilibrated fractions in terms of nutrient composition.

KEYWORDS:

• Slurry acidification
• mechanical separation
• potential N mineralization
• ammonia emission
• nutrients distribution

Acknowledgements

The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Program FP7/2007-2013/under REA grant agreement n° [289887]. This document reflects only the author's view and the Union is not liable for any use that may be made of the information contained therein.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Iria Regueiro http://orcid.org/0000-0002-1311-4088

João Coutinho http://orcid.org/0000-0002-6303-9549