Utilizing Sargassum polycystum as Co-Feedstock to Enhance Methane Yield from Pig Dung in Anaerobic Digestion

Anaerobic digestion (AD) is a promising technology for biogas production, but optimizing feedstock composition is still a key challenge. The present study investigated invasive macroalgae Sargassum polycystum as co-feedstock source combined with pig dung to enhance methane production. Three feedstock groups were assessed: (1) mechanically pretreated S. polycystum + pig dung, (2) untreated S. polycystum + pig dung, and (3) pig dung alone. Seaweed feedstocks were collected in Dahican beachline, and pig manure was sourced from a livestock auction market in the City of Mati, Davao Oriental, the Philippines. Feedstocks were loaded and inoculated in improvised biodigester. Methane concentrations were measured using a gas analyzer, and flammability test was conducted to evaluate biogas quality. Kruskal-Wallis test revealed significant differences in methane production across treatments (H(2) = 9.116, p = 0.010). The pretreated group exhibited the highest methane concentration (>9,999.00 ppm), followed by the untreated group (8,931.75 ppm), while the control group produced the lowest yield (3,644.25 ppm). Post hoc analysis confirmed a significant difference in methane yield in the pretreated group compared to the control (p = 0.010). Only biogas from pretreated group ignited, producing a blue flame indicating methane-rich, high-quality biogas. These findings highlight the dual benefit of using Sargassum macroalgae as co-feedstock, mitigating seaweed overgrowth in coastal areas and improving biogas production efficiency in pig manure. The study underscores the potential of seaweed-based co-digestion as an accessible, sustainable energy solution. Future research may explore long-term process stability, gas composition analysis, and the economic viability of large-scale applications.