Assessment of the Methanogenic Potential of Biogas Produced by Anaerobic Co-digestion of Three Mixing Ratios of Seaweed Waste (Sargassum spp.) and Pig Manure

Abstract

Objective: The aim of this study was to evaluate the methanogenic potential of biogas produced by anaerobic co-digestion using three different mixing ratios of seaweed waste (Sargassum spp.) and pig manure. Methodology: Biogas production was carried out using an experimental water-displacement system. Three experimental set-ups were prepared using three mixing ratios of the substrate and co-substrate. The first bioreactor was fed with a mixture comprising 30 % of seaweed waste and 70 % of pig manure (30:70). The second set-up was fed with 50 % of seaweed waste and 50 % of pig manure (50:50), and the third comprised 70 % of seaweed waste and 30 % of pig manure (70:30). The fermentation process lasted 32 days and was carried out in batch mode. The composition of the biogas produced from each mixture was analysed, and flammability tests were performed. Results: The results showed that the cumulative volume of biogas for the 30:70, 50:50 and 70:30 ratios was 16.5 L, 17.8 L and 5.4 L, respectively. The biogas produced at the 30:70 ratio exhibited the highest methane content, at 60 %, while those produced at the 50:50 and 70:30 ratios had methane contents of 45 % and 36 %, respectively. In addition, the biogas flammability test showed a blue flame for the biogas produced at the 30:70 ratio, whereas no blue flame was observed for the biogas produced from the other two mixtures. Conclusion: The biogas produced from the mixture containing 30 % seaweed waste and 70 % pig manure therefore showed the highest observed methane fraction. This study suggests a possible route for recovering energy from seaweed strandings while addressing coastal waste management.