Transforming by-products into renewable energy: Biochemical analysis of anaerobic digestion of biowastes for bioreactors optimization supporting the low-carbon agroindustry

With the expansion in agro-industrial operations there is an urgent need to solve the challenge of dealing with the products waste. Today, an overwhelming portion of this waste ends up in industrial waste disposal sites. Wherefore, anaerobic co-digestion (ACoD) emerges as an effective technique for waste treatment, being environmentally and economically viable, since a microbial community converts by-products into renewable energy in the form of biogas, with high levels of hydrogen and other gases. ACoD has proven effective in the management of organic waste from agro-industry. However, mastering the biochemistry of the process, especially when varying the mixtures of waste used, is essential for controlling biological reactors and optimizing energy production. Even though separate studies have evaluated the anaerobic digestion of rice parboiling effluent and peach processing residue, co-digestion of both are scarcely investigated. The knowledge and mastery of the process parameters using this mixture are essential to ensure effective operational control of anaerobic reactors with maximum energy generation. Therefore, this research evaluated the biogas production from ACoD of rice parboiling effluent and waste of peaches processing. The experiment followed a batch regime based on a 2²-factorial arrangement. The factors used were the peach percentage in the substrate (P), which varied from 2.5 to 5%, and the substrate-inoculum ratio (S/I), which was alternated between 1.5 and 2.5 gCOD/gVSS. The average Chemical Oxygen Demand (COD) removal efficiency of the reactors was 82.1% and, after the digestion process, the pH of the reactors remained neutral, showing that anaerobic digestion is a suitable method for treating the assessed wastes. In the analyzed proportions, the higher the peach percentage in the substrate, the lower the total methane production, whereas the S/I demonstrated the opposite effect. Reactors III (S/I = 2.5 and P = 2.5%), presented the most durable and the highest production, being the best combination of the factorial studied. Finally, it can be said that for the state of Rio Grande do Sul, the largest rice and peach producer in Brazil, ACoD of the wastes assessed in this research represents a significantly relevant option, enabling the development of the circular economy, the industrial symbiosis, and the sustainable production in the State.