Biomethane potential of lignocellulosic waste from industrial hemp production

As multipurpose, high biomass yielding and resource efficient crop, industrial hemp stands out as a promising source of biomass feedstock for anaerobic digestion (AD). Besides bioenergy cropping systems, the production of renewable biomethane can rely also on the large availability of hemp biomass residues (HBRs), which are generated by different hemp production chains. In the present study, the biochemical methane potential (BMP) of raw and pretreated fibers, stalks, hurds (retted and unretted) as well as of the mix of leaves and inflorescences was assessed through batch anaerobic tests. Untreated hemp fibers showed the highest BMP of 422 ± 20 mL CH4 · g VS-1 among the tested substrates. Retted and unretted hurds reached similar BMP values of 242 ± 13 and 239 ± 10 mL CH4 · g VS-1, respectively, while the mix of leaves and inflorescences showed a low BMP value of 118 ± 8 mL CH4 · g VS-1. Concerning HBRs pretreatments, dilute alkaline pretreatment through a NaOH solution enhanced the BMP of unretted hurds by 15.9%, while a 28.5% increase was obtained with the mix of leaves and inflorescences. Finally, dilute acid pretreatment with a H2SO4 solution showed no significant effect, while mechanical pretreatment through grinding increased the BMP of retted hurds by 15.9%.