Analysis of energy return on investment of dry anaerobic digestion for low water alperujo with oxidative, thermal and alkaline pretreatments

Anaerobic digestion processes for biogas generation using alperujo have been the subject of intensive studies suggesting that phenolic compounds act as microbial inhibitors in anaerobic digestion. Pretreatments are needed to reduce the effects of phenolic compounds and improve biogas production, especially for dry anaerobic digestion. However, industrial-scale implementation of these pretreatments is challenging, and it is unclear whether the improvement in biogas production justifies the energy expended on pretreatment. This study examines the energy analysis of dry anaerobic digestion and three alternative pretreatments: alkaline, oxidative and thermal. Results indicate that thermal pretreatment at 80°C with added water reduces phenolic compounds in alperujo by 35.4%. Meanwhile, pretreated with hydrogen peroxide in alkaline medium had the highest methane productivity (205 mL CH₄/g_VS). Even so, thermal pretreatment was only one with an energy return on investment greater than 1, signifying the necessity for energy analysis to ensure the viability of pretreatment processes.