Processing of undervalued dates biomass from common cultivar ( Phoenix dactylifera L. ) for sequential production of soluble sugars syrup and biogas

Date production is usually associated to a considerable loss either in common cultivars or in fruit picking and storage stages. This discarded biomass is not very well valued up to now especially in bioenergy production. The Tunisian second-grade cultivar ‘Kenta’ was biochemically characterized in the present study. ‘Kenta’ discarded flesh is rich in soluble sugars (79.5VS ± 0.8%VS) and fibers (7.4 ± 0.5%VS). The crude fibers were recovered after soluble sugars extraction. The biochemical composition analysis showed that this by-product contains mainly carbohydrates (33.2 VS ± 0.7%VS) and proteins (8.8 VS ± 0.1% VS) making it a suitable feedstock for biogas production. A biorefinery concept was therefore developed based on soluble sugars (date-syrup) aqueous extraction and biogas production via anaerobic digestion of the residual fibers. The proposed concept showed interesting results since it permitted the co-production of date syrup, as high-added value product, with 0.6 g sugars/gVS and biogas with maximum methane yield of 225 mL CH4/gVS fibers. This study presents a proof of a sustainable processing approach allowing an almost bioconversion of undervalued secondary date variety and integrates the concept of circular bio-economy.