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 feedstockwater 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.
