Evaluation of biogas production potential of shrimp (Penaeus monodon Fabricius, 1798) aquaculture sludge with cow dung inoculum

Abstract

Shrimp aquaculture generates substantial quantities of organic waste, particularly bottom sludge, which poses both environmental and management challenges. This study evaluated the biogas production potential of shrimp aquaculture sludge through anaerobic digestion, focusing on the effect of varying substrate-to-inoculum (S/I) ratios on methane yield, methane content, and the digestate’s solid reduction. Batch anaerobic digestion trials were conducted under mesophilic conditions for 30 days using cow dung as inoculum. Treatments included S/I ratios of 0.5:1, 1.0:1, 1.5:1, and 2.0:1 based on volatile solids (VS), along with an inoculum-only control (Blank). Results showed that the S/I = 1.5:1 S/I achieved the highest methane yield of 8.82 mL CH₄/g VS and reached a peak methane content of 78.76%. This indicates that increasing the organic loading rate enhances biogas and methane production up to an optimal point, beyond which further increase does not proportionally improve methane yield. Conversely, the lowest S/I ratio (0.5:1) achieved the greatest reduction in solids, with 90.12% TS and 94.03% VS reduction. Despite its lower methane output, this ratio resulted in effective substrate stabilization, which is favorable for waste treatment objectives. These findings suggest a trade-off between energy recovery and waste stabilization, emphasizing the importance of selecting appropriate S/I ratios based on intended outcomes. Overall, the results demonstrate that shrimp aquaculture sludge is a promising substrate for anaerobic digestion, offering dual benefits of renewable energy generation and organic waste treatment. Optimizing the S/I ratio is essential to balance methane production with effective waste stabilization.