Towards greenhouse gases mitigation for liquid pig slurry management with solid-liquid separation technologies

Solid-liquid separation (SLS) is considered an important strategy in animal slurry management for reducing the load on surrounding water bodies. However, a systematic study revealing the full impact of centrifugation-based SLS with different flocculants is lacking, e.g., the contributions and trade-offs of methane (CH₄), nitrous oxide (N₂O), and ammonia (NH₃) emissions from both the liquid fraction (LF) and solid fraction (SF) to greenhouse gas (GHG) emissions. After screening for suitable dosing rates of polyferric sulfate (PFS), polyacrylamide (PAM), tannic acid (TA), and polyaluminum ferric chloride (PAFC) for centrifugation separation (CE), this study monitored CH₄, N₂O, and NH₃ emissions during the storage of liquid fractions (LF) over 3 months and solid fractions (SF) over 4 months, and evaluated their nitrogen (N) loss and CO₂-equivalent (CO₂-e) emissions per kilogram of raw pig slurry. Standalone centrifugation increased GHG emissions by 23.7 % compared to raw slurry. Flocculated centrifugation had little impact on N losses but reduced GHG emissions by 17.7 %-74.2 % compared to CE, but only centrifugation with PFS and PAM achieved reductions of 68.1 % and 23.9 %, respectively, compared to raw slurry. This study demonstrated that, despite efficient CH₄ mitigation, the application of centrifugation may not guarantee GHG mitigation compared to raw pig slurry as it is highly dependent on the N₂O emissions during SF storage. Combining centrifugation and flocculation with PFS and PAM could reduce total GHG emissions, but might cause elevated N₂O emissions, indicating short-term benefits for CH₄ management but significant challenges for long-term climate stabilization. Therefore, optimizing solid fraction storage to suppress or avoid high N₂O emissions will be a key task in pig slurry management under current conditions.