Influence of Molasses and Caesalpinia spinosa Meal Inoculums on Biogas Production from Cattle Manure

The management of organic waste through anaerobic digestion is an alternative to energy recovery. This research focused on evaluating the production of biogas with different inoculums. For this purpose, two types of systems were implemented—one used a heating system controlled by an STC-1000 thermostat, while the other used a solar heating system under a polycarbonate parabolic trough. The experiment was carried out at laboratory level with 3 L PET bottle biodigesters and the biogas produced was collected with the water displacement technique in 3 L bottles, calibrated every 50 mL, over 43 days. Inoculums of the following manure concentrations were used: water (1:5, 1:2, 1:3) mixed with Caesalpinia spinosa meal and molasses. The results determined that the thermostat-controlled heating system generated 69.6 mL/day of biogas while the other system produced 610.9 mL/day. On the other hand, the T1 treatment with a manure:water ratio of 1:5 and molasses and Caesalpinia spinosa meal inoculums in both systems had a higher average biogas volume. In terms of methane (CH₄), the highest value of 76.9% was obtained through the T1 treatment under the controlled heating system. This allows the production of biogas with a high concentration of methane, which in future applications can be utilized for residential or industrial purposes, promoting economic, social and environmental development. Since the main challenge in the production of biogas is to reduce the digestion time, which is influenced by the temperature of the site, two types of inoculums with a low cost and easy access were used.