Experimental Comparison Between Over Ground and Underground Solar Thermostatic Biogas Digesters in Biogas-Producing Performances

摘要

With the aim of developing the solar thermostatic biogas digester that is more suitable for public adoption, this study used pig manure and maize straws as test substrates for anaerobic digestion, and conducted tests on both above ground and underground solar thermostatic biogas digesterscomparing operational temperature variation and biogas generation. Over an 89 day digestion, the ambient air temperature fluctuated within a range of –18.3–26.4 °C, and for both digesters, the fermentation temperature remained approximately constant (26±2.6) °C,despite adverse weather conditions. Under different weather conditions, the fermentation in the aboveground biogas digester varied within a temperature range of 1.8 °C, while the fermentation in underground biogas digester varied within a temperature range of 2.6 °C, suggesting thatthe former exhibited a more favorable performance with respect to process stability. During digestion, the average volume fractions of biogas produced from above ground and underground thermostatic biogas digesters reached up to 59.6% and 58.8% represent volume biogas production rates of 0.43m~(3)/(m~(3)·d) and 0.41 m~(3)/(m~(3)·d), respectively. It is apparent both digester designs can produce high-quality fuel gas, but the above ground biogas digester was found to be superior to the underground system in terms of biogas-producingperformances. Additionally, in comparison with the underground biogas digester, the aboveground thermostatic digester exhibited other advantages, such as shorter construction period, broader application range, and more discharge efficiency. In conclusion, both solar thermostatic biogas digesterscan efficiently recycle rural organic wastes and achieve stable biogas production; in particular, the aboveground solar constant-temperature biogas digester shows good potential for public adoption.