Evaluation of biogas production potential in arid and semi – arid regions of developing countries: A case study of Tiaty East, Kenya

Energy poverty remains the main challenge in arid and semi-arid lands (ASALs), where communities primarily rely on firewood and charcoal for cooking and heating. Biogas offers a sustainable alternative but low degradability of some organic substrates limits biogas production. Co – digestion improves nutrient balance, microbial activity, and substrate biodegradability and therefore improving biogas yield. This study investigated anaerobic digestion (AD) of Opuntia ficus-indica (OFI), Euphorbia scarlatina (ES), and cow dung (CD to determine their biogas production potential under mono and co – digestion process. Batch anaerobic digestion experiments were conducted under mesophilic conditions (37.5 °C) for 60 days without pretreatment to reflect practical rural conditions. Biogas daily production was monitored, measured and gas analysis conducted to quantify the methane content. Physicochemical characterization results showed that cow dung had the highest total solids (25.44%), while E. scarlatina had the highest volatile solids (95.45%FM). The methane yields from mono-digestion were 113.66, 86.77, and 41.27 mLCH 4 /gVS for CD, ES, and OFI, respectively. Co-digestion significantly enhanced methane production, with the optimum blend comprising of 16.67% OFI, 33.33% ES, and 50% CD produced 154.67 mLCH 4 /gVS. Modified Gompertz model offered an excellent fit to the experimental methane production data for all substrates (R 2 > 0.99). Under the model, cow dung had the highest methane production potential of (P = 201.81 mL CH 4 /gVS), while E. scarlatina showed the highest methane production rate (R m = 12.249 mL CH 4 /gVS/day). The findings demonstrated that co-digestion of drought-tolerant biomass with cow dung provides a practical, low-cost, and sustainable approach for decentralized biogas production in ASAL regions, reducing dependence on traditional biomass while improving energy security.