Removal of inhibitory furan aldehydes in lignocellulosic hydrolysates via chitosan-chitin nanofiber hybrid hydrogel beads

Biohydrogen fermentation from pretreated biomass in lignocellulose biorefinery: Effects of inhibitory byproducts and recent progress in mitigation strategies

Lignocellulosic biomass (LCB) is expected to play a critical role in achieving the goal of biomass-to-bioenergy conversion because of its wide distribution and low price. Biomass fermentation is a promising method for the sustainable generation of biohydrogen (bioH2) from the renewable feedstock. Due to the inherent resistant structure of biomass, LCB needs to be pretreated to improve its digestibility and utilization. However, certain intermediates by-products generated during the pretreatment process, such as phenolic compounds, furan derivatives, and aldehydes, have been identified as potent inhibitors of subsequent anaerobic fermentation due to their disruptive effects on the physiological and metabolic functions of hydrogen-producing microbiota. To counteract the negative effects of these inhibitors on bio-H2 fermentation, various detoxification strategies for LCB hydrolysates have been explored. This review presents a comprehensive analysis of fermentation-inhibitory by-products commonly generated by modern pretreatment protocols and their negative impacts on biohydrogen fermentation. Furthermore, the underlying mechanisms of inhibition upon hydrogen-producing microbes and their impacts on microbial community dynamics are exhibited. State-of-the-art strategies for detoxifying pretreated LCB have been also discussed, along with alternative pretreatment strategies designed to minimize or eliminate the formation of inhibitory by-products. Additionally, this review addresses the significant gap in the economic viability assessments of these processes, offering a detailed evaluation of both the technological and economic feasibility of biomass fermentation. Given the limitations of previous studies, strategies for cost-effective pretreatment and detoxification should be developed in the future to overcome the inhibition of fermentation inhibitors in the bioconversion of biomass to hydrogen.

Crosslinked hydrogel-derived carbons activated by trace amounts of aqueous potassium carbonate for carbon dioxide adsorption

A new method for green synthesis of activated carbon using chitosan-based hydrogel precursors is reported. Chitosan-based hydrogel materials are designed to absorb trace amounts of non-toxic and non-corrosive activating agent K2CO3 from dilute aqueous solution. The K2CO3 impregnated hydrogels are further freeze-dried and converted to activated carbons with tuneable pore structure by a single-step pyrolysis. Activated carbon with highest pore volume of 0.76 cm3/g and surface area of 2026 m2/g is obtained by using K2CO3 as low as 0.23 g per gram of chitosan hydrogel. It can adsorb maximum CO2 of 4.2 mmol/g at 25 °C and 1 bar. This study demonstrates that biopolymer hydrogels impregnated with trace amounts of K2CO3 are excellent precursor materials to design high surface area carbons for CO2 capture.

Promoting microbial fermentation in lignocellulosic hydrolysates by removal of inhibitors using MTES and PEI-modified chitosan-chitin nanofiber hybrid aerogel

To further enhance the removal efficiency for furanic and phenolic compounds in lignocellulosic hydrolysates, a new detoxification strategy was proposed, which retained fermentable sugars and promoted the growth and metabolism of subsequent bacteria. The best adsorbent (P/M-CCA) was prepared by hybrid chitosan-chitin nanofiber, graft modification with polyethylenimine, and silanization with methyl triethoxylsilane in order. Taken corn cob hydrolysate as object, the removal rates of HMF and furfural were 85.1 % and 99.0 %, respectively. The removal rates of six out of nine phenolic inhibitors were 100 %, and the other three were more than 65 %. Even better, the retention rates of glucose and xylose were both 100 %. In contrast to no growth in undetoxified hydrolysates, Bacillus coagulans grew normally in detoxified hydrolysates, and lactic acid reached 19.1 g/L after 12 h fermentation. P/M-CCA achieves both removal of multiple inhibitors and retain sugars, which would promote the valorization of highly toxic lignocellulosic hydrolysates.

Removal of Fermentation Inhibitors from Sugarcane Bagasse Hydrolysate via Post-cross-linked Hydrophilic-Hydrophobic Interpenetrating Polymer Networks

The efficient and economical removal of fermentation inhibitors from the complex system of biomass hydrolysate was one of the basics and keys in bio-chemical transformation. In this work, post-cross-linked hydrophilic-hydrophobic interpenetrating polymer networks (PMA/PS_pc IPNs and PAM/PS_pc IPNs) were proposed to remove fermentation inhibitors from sugarcane bagasse hydrolysate for the first time. PMA/PS_pc and PAM/PS_pc IPNs can obviously enhance the adsorption performance towards fermentation inhibitors due to their higher surface area and hydrophilic-hydrophobic synergetic surface properties, especially PMA/PS_pc IPNs has higher selectivity coefficients of 4.57, 4.63, 4.85, 16.0, 49.43, and 22.69, and higher adsorption capacity of 24.7 mg/g, 39.2 mg/g, 52.4 mg/g, 9.1 mg/g, 13.2 mg/g, and 144.9 mg/g towards formic acid, acetic acid, levulinic acid (LA), 5-hydroxymethylfurfural (HMF), furfural, and acid-soluble lignin (ASL), respectively, in a lower total sugar loss of 2.03%. The adsorption kinetics and isotherm of PMA/PS_pc IPNs were studied to elucidate its adsorption behavior towards fermentation inhibitors. In addition, the cyclic utilization property of PMA/PS_pc IPNs was stable. Synthesizing PMA/PS_pc IPNs is a new strategy to provide an efficient adsorbent for the removal of fermentation inhibitors from lignocellulosic hydrolysate.

Yeast biomass ornamented macro-hierarchical chitin nanofiber aerogel for enhanced adsorption of cadmium(II) ions

There is an urgent need to develop sustainable, renewable, and environment-friendly adsorbents to rectify heavy metals from water. In the current study, a green hybrid aerogel was prepared by immobilizing yeast on chitin nanofibers in the presence of a chitosan interacting substrate. A cryo-freezing technique was employed to construct a 3D honeycomb architecture comprising the hybrid aerogel with excellent reversible compressibility and abundant water transportation pathways for the accelerated diffusion of Cadmium(II) (Cd(II)) solution. This 3D hybrid aerogel structure offered copious binding sites to accelerate the Cd(II) adsorption. Moreover, the addition of yeast biomass amplified the adsorption capacity and reversible wet compression of hybrid aerogel. The monolayer chemisorption mechanism explored by Langmuir and pseudo-second-order kinetic exhibited a maximum adsorption capacity of 127.5 mg/g. The hybrid aerogel demonstrated higher compatibility for Cd(II) ions as compared to the other coexisted ions in wastewater and manifested a better regeneration potential following four consecutive sorption-desorption cycles. Complexation, electrostatic attraction, ion-exchange and pore entrapment were perhaps major mechanisms involved in the removal of Cd(II) revealed by XPS and FT-IR. This study unveiled a novel avenue for efficient green-synthesized hybrid aerogel that may be sustainably used as an excellent purifying agent for Cd(II) removal from wastewater.

Microbial tolerance engineering for boosting lactic acid production from lignocellulose

Lignocellulosic biomass is an attractive non-food feedstock for lactic acid production via microbial conversion due to its abundance and low-price, which can alleviate the conflict with food supplies. However, a variety of inhibitors derived from the biomass pretreatment processes repress microbial growth, decrease feedstock conversion efficiency and increase lactic acid production costs. Microbial tolerance engineering strategies accelerate the conversion of carbohydrates by improving microbial tolerance to toxic inhibitors using pretreated lignocellulose hydrolysate as a feedstock. This review presents the recent significant progress in microbial tolerance engineering to develop robust microbial cell factories with inhibitor tolerance and their application for cellulosic lactic acid production. Moreover, microbial tolerance engineering crosslinking other efficient breeding tools and novel approaches are also deeply discussed, aiming to providing a practical guide for economically viable production of cellulosic lactic acid.

Subcritical Water Pretreatment for Anaerobic Digestion Enhancement: A Review

This work reviews hydrothermal subcritical water pretreatment to enhance biogas production through anaerobic digestion. The complexity of the lignocellulosic structure has been the main limitation contributing to unsatisfactory biogas production throughout the anaerobic digestion. The high resistance of the structure to biological hydrolysis has increased the interest in applying pretreatment prior to anaerobic digestion to facilitate hydrolysis. Hydrothermal subcritical water technology, an environmentally friendly pretreatment that uses water as the main medium, is gaining prominence in biogas enhancement. However, the subcritical water pretreatment influence on structural properties, biogas production, and the production of anaerobic process inhibitors signifies a knowledge gap and needs an evaluation. This review presents the need for pretreatment reaction and properties in the subcritical water region, biogas production from subcritical water pre-treated waste, production of inhibitors, and its challenges are discussed. This pretreatment could be a promising option and further enhance biogas production throughout the anaerobic digestion process.

Inhibitor formation and detoxification during lignocellulose biorefinery: A review

For lignocellulose biorefinery, pretreatment is needed to maximize the cellulose accessibility, frequently generating excess inhibitory substances to decline the efficiency of the subsequent fermentation processes. This mini-review updates the current research efforts to detoxify the adverse impacts of generated inhibitors on the performance of biomass biorefinery. The lignocellulose pretreatment processes are first reviewed. The generation of inhibitors, furans, furfural, phenols, formic acid, and acetic acid, from the lignocellulose, with their action mechanisms, are listed. Then the detoxification processes are reviewed, from which the biological detoxification processes are noted as promising and worth further study. The challenges and prospects for applying biological detoxification in lignocellulose biorefinery are outlined. Integrated studies considering the entire biorefinery should be performed on a case-by-case basis.