Comparative Bibliometric Analysis of Biomethane Production from Anaerobic Digestion of Pig Slurry and Slaughterhouse Wastewater: Research Trends and Gaps

This bibliometric study evaluates scientific production between 2015 and 2025 inclusive on anaerobic digestion of pig slurry and slaughterhouse wastewater for biomethane generation. A total of 1.414 documents were identified for pig slurry and 250 for slaughterhouse wastewater, reflecting a marked imbalance in research attention. For pig slurry, the literature shows strong consolidation, with consistent focus on biogas yield optimization, emission mitigation, and agricultural valorization of digestate. By contrast, slaughterhouse wastewater research is comparatively limited, fragmented across technical case studies, and often concerned with process inhibition, pretreatment strategies, and integrated treatment systems. Despite this disparity, both residues are recognized as important feedstocks for renewable energy recovery, with co-digestion offering particular promise in terms of process stability and biomethane enhancement.