Temperature and pH Effects on High-Methane Biogas Production

Objective: Biomass is a renewable, widely available, and economically viable energy source for use in anaerobic digestion processes to produce biogas and methane (CH₄). To harness this potential, various technologies have been improved to better reuse organic waste, such as those from the agroindustry, to generate renewable energy and also to contribute to minimizing the environmental risks caused by the improper disposal of these materials. The objective of this study was to define the best operational conditions for the production of biogas and CH₄ from the anaerobic co-digestion of bovine manure, cassava wastewater, and coffee husk. Methods: All tests showed significant biogas production with at least 80% methane. The statistical tool of experimental design made it possible to identify an inversely proportional relationship between pH and temperature, within the conditions analyzed for these factors. Results: Thus, it was defined that the combination of an initial pH above 9.5 and a temperature below 35 °C is capable of resulting in a biogas volume > 600 cm³ and CH₄ > 500 cm³. For example, the best experimental performance was obtained with an initial pH of 10.0 and a temperature of 30 °C, which resulted in 798.72 cm³ of biogas and 638.98 cm³ of CH₄ accumulated after 15 days of hydraulic retention time. These best experimental conditions enabled 58.53% removal of chemical oxygen demand and a final pH close to neutrality (6.3). Conclusion: This represents good fermentation conditions for methanogenic bacteria and confirms the feasibility of using co-digestion of the three evaluated residues.