Valorization of industrial by-products for the production of biogas

The present work aims at the evaluation of the possibility to use different agro-industrial by-products as substrates to produce renewable energy through anaerobic digestion. Their valorization would reduce the social, environmental and economic burdens related to different alternative managements. AD performance for potato peels, rejected fresh potatoes and concentrated fat generated during the potato processing and post-processing stage at a local industry was assessed by a biochemical methane potential (BMP) batch assay under thermophilic conditions (50 °C). The purpose was to assess if those substrates are suitable to produce methane-rich biogas, which then could be fed into the energy grid, and to investigate potential inhibitory phenomena and kinetics of methane production. After a 42-days incubation period, potato peels reported the highest methane yield among the substrates tested, equal to 366.62 mLCH4/gVS added, and the maximum first-order kinetic constant for biogas production (0.130 day-1), making them the most promising substrate among the ones tested. Rejected fresh potatoes reported a lower methane yield, equal to 317.22 mLCH4/gVS added, and pH inhibition phenomena due to high organic loading were observed for a substrate concentration of 23.22 gVS/L. The BMP assay for concentrated fat lasted 94 days and led to the lowest methane yield measured, equal to 288.74 mLCH4/ gVS added, and the lowest first order kinetic constant for biogas production (0.036 day-1), reflecting the reduced bioavailability of lipid-rich substrates. In conclusion, biogas production from potato processing by-product streams through anaerobic digestion is a suitable and more sustainable alternative to its conventional disposal pathways, with potato peels offering the most promising results. Optimization, scale-up and co-digestion strategies are required to enhance methane yields while simultaneously avoiding inhibitory phenomena.