Experimental Assessment of Effects of Seasonal Variation and Weight Ratio on Mesophilic Biogas Production from Cow Manure

Biogas is a renewable energy resource that is not only economical but also fulfills the criteria of net-zero carbon emissions. This is highly favorable for agriculture-based developing countries with an abundance of animal and agricultural waste that can be effectively utilized for biogas production. A dual-stage reactor was designed and built to investigate the optimal conditions during the different seasons of winter and summer for mesophilic biogas production utilizing cow manure from local dairy farms. During the experiments, the pH was continuously monitored and automatically controlled between 6.8 and 7.2 over a period of fifteen days for each experiment using an Arduino Mega controller. The weight ratio (rw) of cow manure slurry was varied from 50% to 80%, and the optimal condition was found to be 70%, irrespective of the seasonal variations. However, the statistical analysis suggests that the optimal weight ratio is 66% for both seasons. A maximum reaction yield of 87% was achieved at a rw value of 60% during the summer, with an expected yield of over 95% at a rw value of 70% if similar extreme environmental conditions occur. Employing this apparatus for biogas production requires significant electrical energy to drive the stirrer and pumps, suggesting the use of a conventional underground setup for biogas production, integrated with an automatic pH control module.