Abstract
Industrial hemp stands out as a promising candidate for clean and sustainable biomass-to-bioenergy systems due to its multipurpose, high biomass yield and resource efficiency features. In this study, different hemp biomass residues (HBRs) were evaluated as a potential feedstock for renewable biomethane production through anaerobic digestion (AD). The biochemical methane potential (BMP) of the raw and pretreated fibers, stalks, hurds, leaves and inflorescences was investigated by means of batch anaerobic tests. The highest BMP was obtained with the raw fibers (i.e., 422 ± 20 mL CH4·g VS−1), while hemp hurds (unretted), making up more than half of the whole hemp plant dry weight, showed a lower BMP value of 239 ± 10 mL CH4·g VS−1. The alkali pretreatment of unretted hurds and mechanical grinding of retted hurds effectively enhanced the BMP of both substrates by 15.9%. The mix of leaves and inflorescences and inflorescences alone showed low BMP values (i.e., 118 ± 8 and 26 ± 5 mL CH4·g VS−1, respectively) and a prolonged inhibition of methanogenesis. The latter could be overcome through NaOH pretreatment in the mix of leaves and inflorescences (+28.5% methane production).
Highlights
Bioenergy and food security are strongly interlinked and globally relevant issues, both relying on limited resources such as arable land, fresh water and chemical fertilizers [1,2,3]
Among the substrates tested in this study, the untreated hemp fibers showed the highest biochemical methane potential (BMP) value, reaching a final biomethane production of 422 ± 20 mL CH4 ·g VS−1
CH4 ·g VS−1 produced by the unretted hurds
Summary
Bioenergy and food security are strongly interlinked and globally relevant issues, both relying on limited resources such as arable land, fresh water and chemical fertilizers [1,2,3]. With the aim of rebalancing the energy–food nexus, non-food crops and agricultural residues have been proposed as a potential feedstock for the sustainable implementation of second-generation biorefineries [5,6]. In such context, the rediscovery of versatile and resource efficient crops such as industrial hemp (Cannabis sativa L.) offers the opportunity to reconcile agricultural food and bio-commodity supply with bioenergy production. The high biomass productivity (up to 20 tons dry matter per hectare), together with the potential supply of seeds, fibers and other biobased raw materials to fit multiple applications is driving the rise of industrial hemp production [8,9,10]. Hemp has thousands of applications, each specific production chain generates high amounts of hemp biomass residues (HBRs), which are often regarded as waste [11]
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