Olive pomace, a source of green energy using anaerobic digestion

Abstract

Organic waste generation is constantly increasing due to industrialization and various treatment processes. Nowadays, anaerobic digestion, as a green technology, is widely used to convert organic waste, into methane, and subsequently, into bioenergy. In this study, our main objective was to evaluate the feasibility of applying anaerobic digestion to treat Lebanese olive by-products, in particular olive pomace. Biochemical fractionation of our biomass showed high contents of cellulose (55.4% of total solids) and lignin (21.3% of total solids) which could limit the anaerobic digestion and result in low methane yield. Biochemical methane potential was assessed using anaerobic digesters in batch mode. These digesters containing the substrate and inoculum in a ratio substrate to inoculum of 1:3 (total solids basis) were incubated at 37°C. Results from anaerobic digestion showed that olive pomace is a great source of green energy. Alkaline pretreatment was effective in altering the lignocellulosic fractions of olive pomace. But when pretreated samples were subjected to anaerobic digestion, an inhibition occurred because of the formation of toxic compounds, mainly when higher NaOH dosages were used. Alkaline pretreatment also influenced the methane production rate constants and slowed down the anaerobic digestion process.