Investigating the Influence of Organic Loading Rate, Temperature and Stirring Speed on Biogas Production Using Agricultural Waste in South Africa

Biogas production offers an alternate method for managing agricultural waste and contributes to sustainable renewable energy generation. Anaerobic digestion (AD) enables the transformation of organic waste, including agricultural substrates, into biogas, mostly consisting of methane, carbon dioxide, and trace gases such as ammonia and hydrogen sulphide. The objective of this study was to employ a 30 L semi-continuous stirred tank reactor to evaluate the effects of organic loading rate, temperature, and speed of stirring on biogas production. The reactor was inoculated with 8.6 L and filled with 11.4 L of a mixed substrate including cattle manure, potato waste, potato starch waste, fruit waste, and expired dry dog food. The reactor was evaluated with organic loading rates (OLRs) of 11.2, 12.2, and 13.2 g VS/L d, and stirring speeds of 25.5, 35.5, and 45.5 rpm. The results indicated that the maximum yield was 12.2 g VS/L d at 45.5 rpm, and in thermophilic conditions, the biogas yield surpassed that of mesophilic conditions, measuring 105,860 NmL/g VS compared to 69,800 NmL/g VS. This study emphasises the significance of optimising operational parameters to improve biogas output, thereby contributing to sustainable energy resources and advancing the Sustainable Development Goals (SDGs).