Influence of Elemental Composition of Geothermal Waters and Succulent Feedstocks on Cryo-mesophilic Biogas Production from Mt. Suswa, Kenya

Abstract

Background: Dependence on charcoal and firewood in the Mt. Suswa region creates environmental and health concerns and supports the need to evaluate locally available feedstocks for renewable biogas production. This study investigated the elemental composition of geothermal waters and three succulent feedstocks and examined their biogas production under cryo-mesophilic conditions.  Methods: Steam-vent water, water-pan samples, and Agave sisalana, Echinocactus grusonii, and Opuntia ficus-indica were analysed by Microwave Plasma Atomic Emission Spectroscopy. Biogas production was monitored for 132 h in 26 laboratory-scale batch digesters operated at 20–24.5°C with different feedstock-water combinations, with or without cow dung inoculum.  Results: Agave sisalana contained 3,765.53 ± 0.00 g/L potassium, 1.23 ± 0.00 g/L cobalt, and 1.08 ± 0.03 g/L nickel. Region II steam-vent water had 50,268.93 ± 29.19 ppm potassium, 1,317.85 ± 1.10 ppm nickel, 1,184.54 ± 5.76 ppm cobalt, and the lowest measured arsenic concentration among the steam-vent regions. The highest cumulative biogas yield was 62 mL in D6, containing A. sisalana, water-pan sample, and cow dung. Most O. ficus-indica treatments yielded 12–24 mL, although D10 reached 50 mL. Conclusion: Biogas performance varied with feedstock, water source, and inoculation. A. sisalana-based treatments and cow dung inoculation showed the most favourable overall performance under the tested conditions.