Life cycle assessment of nutrient recovery from the liquid fraction of pig manure digestate via struvite precipitation

In this work, the environmental performance of a prototype designed by Centro Ricerche Produzioni Animali – CRPA, which allows the nutrient recovery (N and P) from the liquid fraction of pig manure digestate, has been monitored through a Life Cycle Assessment (LCA). The process is born to solve the problem of the surplus of nutrients in zones rich in livestock and its expensive transportation to more needful areas. The reduction of nutrients in the effluents allows farmers to spread higher amounts of manure on the crop with lower emissions and ecosystem contamination. The recovered fraction consists of a Struvidic mud (MgNH4PO4∙6H2O), which can be used as a fertiliser replacing synthetic fertiliser, decreasing the impact due to their production. The impact categories analysed are Climate Change, Eutrophication, and Acidification for the prototype system and the control system. The second one represents the already existing manure management system in the livestock. The environmental analysis shows an impact of 18.60 kg CO2 eq, 0.034 kg PO43- eq and 0.211 kg SO2 eq for these categories regarding the prototype system, measured with respect to 1 m3 of liquid fraction. Regarding the same FU, the control system’s impact result is 27.66 kg CO2 eq, 0.035 kg PO43- eq and 0.177 kg SO2 eq. The chemical analysis results show that a more nutrient-concentrated fraction was obtained during the process, and the reduction of nutrients in the others leads to a decrease in GHGs and contaminants emissions during the storage period.