• Energy Research

Among agricultural residues, lignocellulosic materials (LMs) are highly attractive substrates for anaerobic digestion (AD), given their high availability, low cost and no direct competition with food and feed production. Hemp (Cannabis sativa L.) is a multipurpose crop, and its cultivation has boosted again in the last years. Nevertheless, due to contrasting legislation, in some European Countries the harvesting and manufacturing of plant components (e.g. leaves and inflorescences) has stopped, resulting in a massive amount of lignocellulosic biomass to be diversely disposed. This research explores the valorization of hemp biomass (whole stalk, bast fiber, decorticated hurds, and a mixture of leaves and inflorescences) by AD, as a first major step for the establishment of a wider, future biorefinery platform. Both physical (grinding) and chemical (acid and alkali) pretreatments have been investigated to break down the lignocellulosic matrix of different hemp biomass components. Their biomethane yield has been then evaluated through batch biochemical methane potential (BMP) tests performed in 100 mL serum bottles under controlled mesophilic (37°C) conditions for 45 days. The highest cumulative biomethane production (422 mL CH4/g VS) was obtained with the raw bast fiber, while the BMP of the raw whole stalk and decorticated hurds reached 271 and 240 mL CH4/g VS, respectively. The alkali pretreatment with NaOH increased the BMP of the hurds by 15% obtaining a final biomethane yield of 277 mL CH4/g VS. The mixture of leaves and inflorescences resulted in the lowest BMP values, with the NaOH-pretreated material reaching approximately 150 mL CH4/g VS.

Abstract In the emerging context of circular bioeconomy, industrial hemp (Cannabis Sativa L.) biomass is a valuable resource for the sustainable implementation of second-generation biorefineries. Potentially, all the main hemp components can find application within different biorefinery approaches, adding value to the conventional production of hemp fibres and seeds. Hurds, leaves and inflorescences, constituting most of the hemp plant biomass, and often considered as low-value residues, can indeed play a key role in the sustainable production of both bioenergy and high-value bioproducts. The present article reviews the advances and outlines the potential future perspectives of hemp-based biorefineries. After critically overviewing some of the most established applications of hemp, spanning from soil bioremediation to bioenergy and biofuel production, particular attention is given to novel valorisation schemes to synthetize highly demanded bioproducts such as microbial protein and biopolymers. Our preliminary calculations show that hemp biomass can sustain high biodiesel yield (1.6 g/g VS (volatile solids)) and related revenues (510–868 €/ha•year), while bioethanol production can yield 0.10–0.33 mL/g VS, profiting between 75–325 €/ha•year. Moreover, hemp suits biomethane production by yielding and profiting 98–426 mL/g VS and 60–380 €/ha•year, respectively. High yields of polyhydroxybutyrate (0.13 g/g VS) can be obtained, albeit high production costs might restrain their marketability. Finally, the biomethane-to-microbial protein pathway can yield and profit 0.03–0.15 g/g VS and 141–893 €/ha•year, respectively, while the volatile fatty acids-to-microbial protein pathway 0.04 g/g VS and 91–362 €/ha•year.

Biogas production via anaerobic digestion is a constantly growing technology all around the world. Lignocellulosic materials (LMs) present several features that make them particularly attractive among the organic substrates commonly employed in anaerobic bioreactors. However, their recalcitrance to biological conversion still hinders their application for commercial production of biogas and requires a pretreatment step to improve their microbial degradability. Among the several pretreatments proposed for LMs, cellulose solvents and organosolv pretreatments are arising as the most effective in disrupting the bonds among cellulose, hemicellulose, and lignin, thus increasing the accessible surface area of the biodegradable matter for microbes. Here, the solvents that have been employed as pretreatment to enhance the biogas production yields from the anaerobic digestion of LMs are reviewed, examining the dissolution mechanisms involved, as well as the main advantages and drawbacks for their full-scale applica...

This work evaluated for the first time the employment of hydrothermal alone (i.e. at 60, 80 and 100 °C) and combined ultrasonic–hydrothermal pretreatments on hazelnut shell (HS) to promote the energetic valorization of HS through anaerobic digestion. The highest cumulative biomethane yield of 137 mL CH4·g VS−1 was achieved performing biochemical methane potential tests under wet–mesophilic conditions with the hydrothermally (i.e. at 100 °C) and ultrasonically–pretreated HS. This CH4 yield was 2.3–fold higher than that obtained with the raw HS due to an enhanced hemicellulose polymerization and delignification after the sequential hydrothermal and ultrasonic pretreatment. Under the same pretreatment conditions, total volatile fatty acids peaked at 755 mg HAc L−1. The biomethane production followed the modified Gompertz model (R2 = 0.993–0.996) and a Pearson correlation test showed that it was mainly influenced by the soluble chemical oxygen demand (i.e. 0.983). A positive energy balance revealed that the produced biomethane can offset the energy needed for the pretreatment.

This study proposes the phytoremediation of phenanthrene (PHE)-, pyrene (PYR)-, and copper (Cu)-contaminated soil by Cannabis sativa L. The experimental campaign was conducted in 300 mL volume pots over a 50 d period using different initial polycyclic aromatic hydrocarbon (PAH) concentrations, i.e., 100 (PC1), 200 (PC2), and 300 (PC3) mg ƩPAHs kg−1 dry weight of soil, while maintaining a constant Cu concentration of 350 mg∙kg−1. PHE and PYR removal was 93 and 61%, 98 and 48%, and 97 and 36% in PC1, PC2, and PC3, respectively, in the greenhouse condition. The highest Cu extraction amounted to 58 mg∙kg−1. In general, the growth of C. sativa L. under the PC1, PC2, and PC3 conditions decreased by approximately 25, 65, and 71% (dry biomass), respectively, compared to the uncontaminated control. The present study is aimed at highlighting the phytoremediation potential of C. sativa L. and providing the preliminary results necessary for future field-scale investigations.

The effect of the sulfide concentration on the location of the metal precipitates within sulfate-reducing inversed fluidized bed (IFB) reactors was evaluated. Two mesophilic IFB reactors were operated for over 100 days at the same operational conditions, but with different chemical oxygen demand (COD) to SO(4)(2-) ratio (5 and 1, respectively). After a start up phase, 10mg/L of Cu, Pb, Cd and Zn each were added to the influent. The sulfide concentration in one IFB reactor reached 648 mg/L, while it reached only 59 mg/L in the other one. In the high sulfide IFB reactor, the precipitated metals were mainly located in the bulk liquid (as fines), whereas in the low sulfide IFB reactor the metal preciptiates were mainly present in the biofilm. The latter can be explained by local supersaturation due to sulfide production in the biofilm. This paper demonstrates that the sulfide concentration needs to be controlled in sulfate reducing IFB reactors to steer the location of the metal precipitates for recovery.

Abstract Lignocellulosic materials are the most abundant biomass on the planet, representing a great opportunity for energy valorisation. This work investigated the effect of methanol-organosolv pretreatment on the methane production from hazelnut skin (HS), spent coffee grounds (SCG), and almond shell (AS). The pretreatment on the three lignocellulosic materials was performed at 130, 160, and 200 °C for 60 min using a 50% (v/v) methanol solution, with and without the addition of sulfuric acid as a catalyst. The biomethane potential of raw and pretreated substrates was evaluated under wet-mesophilic conditions in batch reactors, achieving 17.3 (±32.3), 293.4 (±46.6), and 23.2 (±9.6) mL CH4/g VS for HS, SCG, and AS, respectively. The methanol-organosolv pretreatment was particularly effective on HS, increasing its biomethane potential up to 310.6 (±22.2) CH4/g VS. On the contrary, all pretreatment conditions were ineffective on SCG and AS in terms of cumulative methane production. Among the three substrates, only HS showed significant composition changes due to the pretreatment, with the lignin content decreasing from 39.66 to 34.73% and the amount of bioavailable sugars increasing. An energy assessment confirmed the pretreatment efficacy on HS, with a maximum net positive energy recovery of 1.35 kWh/kg VS.