Life-cycle assessment of tobacco stalk utilization

Mild three-stage alkali-oxygen treatment preserving the native macromolecular structure of lignin for effective disassembling of tobacco stalk

Tobacco stalks, as one of the annual economic crops rich in biomacromolecules such as cellulose and hemicellulose, are more difficult to decompose into cellulose fibers due to their high degree of lignification compared to other ordinary straw feedstocks, resulting in their underutilization. In this study, we developed a mild three-stage alkali‑oxygen (AO) process to efficiently deconstruct the tobacco stalk cell walls. The process, involving alkaline dosages of 15 %, 10 %, and 3 % at each stage, effectively dissociated the cell walls and yielded cellulose fibers with high brightness (42.0 % ISO). The organics in the spent liquor, including lignin, hemicellulose, and small-molecular extracts, were isolated through acid/ethanol precipitation and organic solvent extraction. Lignin characterization by 2D HSQC NMR indicated that the majority of native β-aryl ether linkages were preserved after AO treatment, making it suitable for producing chemicals or biofuels via depolymerization. Additionally, the small-molecular extracts contained numerous depolymerized products from lignin and carbohydrates, as well as bioactive compounds derived from the tobacco stalk. Overall, this mild, efficient, and eco-friendly process offers a promising approach for the valorization of tobacco stalks and similar biomass resources.

A systematic review of life cycle assessment of solid waste management: Methodological trends and prospects

Solid waste disposal has led to increasing concerns over resource, health, and environmental problems. These issues have been investigated using the Life Cycle Assessment (LCA) technique which helps identify the roots of varying hazards and allows decision-makers to improve the environmental performance of waste management practices. However, there is a lack of review studies that conducted meta-analysis related to developments in critical methodological steps of LCA on solid waste management. To fill this gap, this review paper examines 15 elements comprising the preference of journals, 13 LCA method-related characteristics, and economic assessment. Insights on the limitations and current practices of LCA applications, along with trends for future research, are provided. 240 studies on the LCA of SWM from 2009 until 2020 were systematically reviewed and classified into two major year-groups (i.e., 2009-2014 and 2015-2020) to investigate the trend changes. Among the studied elements, it is found that energy-related applications are on the increase in LCA studies on solid waste management. Anaerobic digestion facilities nearly double in appearance in the second year-group (2015-2020). There is also a more frequent occurrence of certain characterization methods like ReCiPe and CML. Functional units become more diverse, but are overall mostly defined on a mass basis. A frequently identified issue of many LCAs on solid waste management is the ambiguity of data sources such as out-of-date literature or inconsistent geographical references. By addressing issues of methodological standardization, this review study provides a basis to further increase the reliability of results of future LCA studies on solid waste management.

Facile Synthesis of Magnetic Biochar Derived from Burley Tobacco Stems towards Enhanced Cr (VI) Removal: Performance and Mechanism

In this study, ferric-loaded magnetic burley tobacco stem biochar (MBTS) was synthesized via pyrolysis to improve the removal of Cr(VI). The results showed that MBTS had an adsorption capacity of 54.92 mg Cr(VI)/g, which was about 14 times higher than raw burley tobacco stem biochar (i.e., 3.84 mg/g). According to the findings obtained, a three-step mechanism of Cr(VI) removal by MBTS was further put forward, i.e., (1) Cr(VI) exchanged with hydroxyl groups on MBTS, (2) the reduction in Cr(VI) to Cr(III) mediated by oxygen-containing groups, and (3) the chelation of produced Cr(III) with the amino groups on MBTS. FTIR spectra further revealed that C-N, C-H, and C=C groups played an important role in Cr(VI) removal. Furthermore, the adsorption equilibrium and kinetics of Cr(VI) on MBTS could better be described by the Langmuir equation and pseudo-second-order rate equation. This study clearly demonstrated that ferric-loaded biochar derived from burley tobacco stems could serve as a cost-effective magnetic adsorbent for the high-efficiency removal of soluble Cr(VI) from wastewater. Tobacco stem-adsorbed Cr(VI) realized a green path for treating waste by waste.

Improvement of Nicotine Removal and Ethanol Fermentability From Tobacco Stalk by Integration of Dilute Sulfuric Acid Presoak and Instant Catapult Steam Explosion Pretreatment

The nicotine from tobacco stalk showed obvious inhibitory effect on the activity of cellulase and fermentability of microorganisms, which seriously hinders the utilization of tobacco stalk. Dilute sulfuric acid presoak of tobacco stalk was used to enhance the performance of instant catapult steam explosion (ICSE) for tobacco stalk pretreatment. The presoak was beneficial to break the recalcitrant structure of tobacco stalk, reduce nicotine content to relieve the inhibition on the activity of cellulase and metabolism of microorganisms, and promote the performance of enzymatic hydrolysis and ethanol fermentation. The optimized 0.8% sulfuric acid (w/w) presoak-integrated ICSE pretreatment resulted in 85.54% nicotine removal from tobacco stalk; meanwhile, the total sugar concentration from enzymatic hydrolysis of pretreated tobacco stalk increased from 33.40 to 53.81 g/L (the ratio of dry tobacco stalk to water was 1:8, w/w), ethanol concentration increased 103.36% from 5.95 to 12.10 g/L in flask, compared with separate ICSE pretreatment. Finally, the ethanol concentration achieved the highest 23.53 g/L in a 5-L fermenter with the ethanol yield from the glucose of tobacco stalk hydrolysate achieving 71.40% by increasing the solid loading of the tobacco stalk in the enzymatic hydrolysis process (the ratio of dry tobacco stalk to water was 1:4, w/w). These results achieved the expected purpose of efficient utilization of discarded tobacco stalk.

Micro- and nanocelluloses from non-wood waste sources; processes and use in industrial applications

In addition to renewability and abundance, nanocellulose materials have tremendous (and variable) properties for different applications, ranging from bulk applications, such as paper and packaging reinforcement, to emerging high added-value applications, such as substrates for optoelectronics. Lignocellulosic biomass from agricultural and industrial waste sources is readily available and shows great promise as an inexpensive and sustainable raw material for nanocellulose production. However, the understanding of the potential of using non-wood based biowaste sources is not established and systematic comparisons of versatile agricultural and industrial waste sources can elucidate this complex topic. Here we present an overview of the most studied and most promising sources from agro-industrial waste, the processes to convert them into nanocellulose, some of the established and emerging applications, and discuss the advancements that are still needed for large-scale production. Sugarcane bagasse and oil palm empty fruit bunch have been the most researched waste-based sources for nanocellulose production and demonstrate the most promise due to availability and access. Industrial sources seem to have advantages over agricultural sources in collectability and ease of access. This work gives insight on the potential and the challenges of nanocellulose production from waste sources and discusses how the criteria set for nanocellulose materials in different applications can be met, thus opening new routes for circular economy.

Sustainable Agri-Food Processes and Circular Economy Pathways in a Life Cycle Perspective: State of the Art of Applicative Research

This study aims at providing a systematic and critical review on the state of the art of life cycle applications from the circular economy point of view. In particular, the main objective is to understand how researchers adopt life cycle approaches for the measurement of the empirical circular pathways of agri-food systems along with the overall lifespan. To perform the literature review, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol was considered to conduct a review by qualitative synthesis. Specifically, an evaluation matrix has been set up to gather and synthesize research evidence, by classifying papers according to several integrated criteria. The literature search was carried out employing scientific databases. The findings highlight that 52 case studies out of 84 (62% of the total) use stand-alone life cycle assessment (LCA) to evaluate the benefits/impacts of circular economy (CE) strategies. In contrast, only eight studies (9.5%) deal with the life cycle costing (LCC) approach combined with other analyses while no paper deals with the social life cycle assessment (S-LCA) methodology. Global warming potential, eutrophication (for marine, freshwater, and terrestrial ecosystems), human toxicity, and ecotoxicity results are the most common LCA indicators applied. Only a few articles deal with the CE assessment through specific indicators. We argue that experts in life cycle methodologies must strive to adopt some key elements to ensure that the results obtained fit perfectly with the measurements of circularity and that these can even be largely based on a common basis.

Pelletization of Post-Harvest Tobacco Waste and Investigation of Flue Gas Emissions from Pellet Combustion

The paper presents the results of the pelletization (agglomeration) tests of post-harvest tobacco waste as a feedstock for fuel pellet production. The experiment was conducted on a prototype pelleting–briquetting device with a flat matrix. The influence of the tobacco waste moisture content (17, 21 and 25wt.%) and the rotational speed of the agglomerating rolls (120, 170 and 220 rpm) on the power demand and on the pellet’s kinetic durability and density were determined. It was found that the moisture content has a significant impact on the pellet’s density but slightly affects its kinetic durability. The obtained pellets were characterized by a high density above 1000 kg·m−3 and kinetic durability above 97%. In order to examine the exhaust composition, the obtained pellets were combusted in a 25 kW fixed great boiler. High amounts of CO, SOx, NO and HCl were obtained, which suggests that the selection of a different technology for tobacco waste pellet combustion should be made.

Effect of organic loading, feed-to-inoculum ratio, and pretreatment on the anaerobic digestion of tobacco stalks

This work firstly investigated the suitable organic loading (OL) and feed to inoculum (F/I) ratio of three kinds of tobacco stalks (TS116, TS99, and TS85) during anaerobic digestion (AD) via response surface methodology (RSM). The highest experimental methane yield (EMY) of 148.1 mL/g VS was achieved from TS116 at OL of 20.2 g VS/L and F/I ratio of 1.1. To further increase EMY, various pretreatments including alkaline hydrogen peroxide (AHP), NaOH, KOH, Ca(OH)2, HCl, and oxalic acid (H2C2O4) were implemented on TS116. Results showed that AHP was most effective, and the maximal EMY of 350.7 mL/g VS and biodegradability (Bd) of 81.4% were obtained from 7% AHP pretreated TS116, which increased by 105.6% than untreated. XRD, FTIR, and SEM analyses evidenced that the structure of AHP pretreated TS116 was strongly disrupted. This study lays the foundation for applying this waste into AD in future applications.

Effect of various pretreatments on improving cellulose enzymatic digestibility of tobacco stalk and the structural features of co-produced hemicelluloses

Hereon, tobacco stalk was deconstructed by lyophilization, ball-milling, ultrasound-assisted alkali extraction, hydrothermal pretreatment (HTP), and alkali presoaking, respectively, followed by dilute alkali cooking to both improve its enzymatic digestibility and isolate the hemicellulosic streams. It was found that a maximum cellulose saccharification rate of 93.5% was achieved from the integrated substrate by ball-milling and dilute alkali cooking, which was 4.4-fold higher than that from the raw material. Interestingly, in this case, 76.9% of hemicelluloses were simultaneously recovered during the integrated treatment. Structural determination indicated that the hemicelluloses released from tobacco stalk by dilute alkali cooking were mixed polysaccharides, and the (1 → 4)-linked β-D-Xylp backbone branched with L-Araf units at O-2/O-3 and 4-O-Me-α-D-GlcpA units at O-2 of the xylose residues was the main structure. In comparison, ultrasound-assisted alkali extraction, ball-milling, and HTP favored the extraction of hemicelluloses with less branched structure and lower molecular weights in the following alkali cooking.

Sustainability evaluation and implication of a large scale membrane bioreactor plant

Membrane bioreactor (MBR) technology is receiving increasing attention in wastewater treatment and reuse. This study presents an integral sustainability evaluation of a full scale MBR plant. The plant is capable of achieving prominent technical performance in terms of high compliance rate, low variation in effluent quality and high removal efficiency during long term operation. It is also more responsive to the new local standard with rigorous limits. However, electricity consumption is found to be the dominant process resulting in elevated life cycle environmental impacts and costs, accounting for 51.6% of the costs. As such, it is suggested to optimize energy use in MBR unit and implement sludge treatment and management. The prolonged membrane life span could also contribute largely to reduced life cycle environmental concerns and expenses. This study is of great theoretical significance and applicable value in guaranteeing the performance and sustainability of large scale MBR schemes.