Recovery of High Purity Lignin and Digestible Cellulose from Oil Palm Empty Fruit Bunch Using Low Acid-Catalyzed Organosolv Pretreatment

Biovalorization of brewer's spent grain as single-cell protein through coupling organosolv pretreatment and fungal cultivation

Brewer's spent grain (BSG) is a clean byproduct from the food sector, comprising 85% of the brewing process solid byproducts. BSG is mainly used as low-quality animal feed and often ends up in landfills due to its short shelf life. However, considering its abundant availability and high nutritional content, BSG holds the potential for biorefineries to produce valuable products. The recalcitrant nature of BSG poses a challenge, requiring pretreatment steps. Therefore, this study focused on valorizing BSG obtained from organosolv pretreatment by producing food- and feed-grade single-cell protein (SCP). The BSG was subject to organosolv pretreatment at 180C for 2 h with 50% v/v ethanol as solvent. Filamentous fungi N. intermedia and A. oryzae were cultivated on as-received and different fractions of organosolv-treated BSG to evaluate the effect of factors such as pretreatment, fungal strain, pretreated fraction content, and substrate loading on fungal biomass yield, biomass composition (protein content), and metabolite production. A. oryzae cultivation on all tested substrates yielded 7%-40% more biomass than N. intermedia. Cultivating A. oryzae on organosolv liquor resulted in the highest biomass protein content (44.8% ± 0.7%) with a fungal biomass concentration of 5.1 g/L. A three-fold increase in the substrate loading increased the ethanol-to-substrate yield by 50%, while protein content was decreased by 23%. Finally, a biorefinery concept was proposed to integrate the organosolv pretreatment of BSG with fungal cultivation for maximum yield of SCP while obtaining other products such as lignin and ethanol, providing a sustainable rout for managing BSG.

Recent advancements in lignocellulose biomass-based carbon fiber: Synthesis, properties, and applications

A growing need to reduce the global carbon footprint has prompted all sectors to make significant efforts in this direction. For example, there has been much focus on green carbon fiber sustainability. For example, it was found that the polyaromatic heteropolymer lignin might act as an intermediary in synthesising carbon fiber. Biomass is seen as a potential carbon accommodated solid natural sources that protects the nature and has a big overall supply and widespread distribution. With growing environmental concern in recent years, biomass has gained appeal as a raw material for production of carbon fibers. Especially, the positives of lignin material include its reasonable budget, sustainability, and higher carbon content, which makes it a dominating precursor. This review has examined a variety of bio precursors that help produce lignin and have higher lignin concentrations. In addition, there has been much research on plant sources, lignin types, factors affecting carbon fiber synthesis, spinning methods, stabilization, carbonization, and activation the characterisation techniques used for the lignin carbon fiber to comprehend the structure and features. In addition, an overview of the applications that use lignin carbon fiber has been provided.

Microwave-assisted extraction of lignin from coconut coir using deep eutectic solvents and its valorization to aromatics

Lignin is a rich renewable source of aromatics present in lignocellulosic biomass (LCB). The extraction of lignin from the intricate LCB network is a challenging task for successful commercialization of sustainable biorefineries. In the present study, a series of choline chloride (ChCl)-carboxylic acid based deep eutectic solvents (DESs) were used for the extraction of lignin from coconut coir under microwave irradiation. Among the synthesized DESs, ChCl: lactic acid (LA) (1:4) gave the highest lignin yield of 82% with >95% purity. Interestingly, the severity factor (H factor) for the pretreatment process was found to be a significantly lower (55.5) as compared to reported studies due to efficient microwave heating. Moreover, the DES showed good recyclability for four recycle runs thus making it a promising candidate for the delignification of LCB. Finally, the extracted lignin was converted to aromatics via catalytic transfer hydrogenation (CTH) using Ru/C and isopropanol as in-situ hydrogen donor.

Simulation and optimization of organosolv based lignocellulosic biomass refinery: A review

Organosolv pretreatment can be considered as the core of the lignocellulosic biomass fractionation within the biorefinery concept. Organosolv facilitates the separation of the major fractions (cellulose, hemicelluloses, lignin), and their use as renewable feedstocks to produce bioenergy, biofuels, and added-value biomass derived chemicals. The efficient separation of these fractions affects the economic feasibility of the biorefinery complex. This review focuses on the simulation of the organosolv pretreatment and the optimization of (i) feedstock delignification, (ii) sugars production (mainly from hemicelluloses), (iii) enzymatic digestibility of the cellulose fraction and (iv) quality of lignin. Simulation is used for the technoeconomic optimization of the biorefinery complex. Simulation and optimization implement a holistic approach considering the efficient technological, economic, and environmental performance of the biorefinery operational units. Consequently, an optimized organosolv stage is the first step for a sustainable, economically viable biorefinery complex in the concept of industrial ecology and zero waste circular economy.

Enhanced Volatile Fatty Acid Production from Oil Palm Empty Fruit Bunch through Acidogenic Fermentation—A Novel Resource Recovery Strategy for Oil Palm Empty Fruit Bunch

The glucan-rich fraction, hemicellulosic compounds-rich fraction, and a mixture of both fractions obtained from organosolv pretreatment of oil palm empty fruit bunch (OPEFB) were used as substrates to produce volatile fatty acids (VFAs) in acidogenic fermentation. In this study, the effects of medium adjustment (carbon to nitrogen ratio and trace elements supplementation) and methanogenesis inhibition (through the addition of 2-bromoethanesulfonate or by heat shock) to enhance VFAs yield were investigated. The highest VFA yield was 0.50 ± 0.00 g VFAs/g volatile solid (VS), which was obtained when methanogens were inhibited by heat shock and cultivated in a mixture of glucan-rich and hemicellulosic compounds-rich fractions. Under these conditions, the fermentation produced acetic acid as the only VFA. Based on the results, the mass balance of the whole process (from pretreatment and fermentation) showed the possibility to obtain 30.4 kg acetic acid and 20.3 kg lignin with a 70% purity from 100 kg OPEFB.

A review on enzymes and pathways for manufacturing polyhydroxybutyrate from lignocellulosic materials

Currently, major focus in the biopolymer field is being drawn on the exploitation of plant-based resources grounded on holistic sustainability trends to produce novel, affordable, biocompatible and environmentally safe polyhydroxyalkanoate biopolymers. The global PHA market, estimated at USD 62 Million in 2020, is predicted to grow by 11.2 and 14.2% between 2020-2024 and 2020-2025 correspondingly based on market research reports. The market is primarily driven by the growing demand for PHA products by the food packaging, biomedical, pharmaceutical, biofuel and agricultural sectors. One of the key limitations in the growth of the PHA market is the significantly higher production costs associated with pure carbon raw materials as compared to traditional polymers. Nonetheless, considerations such as consumer awareness on the toxicity of petroleum-based plastics and strict government regulations towards the prohibition of the use and trade of synthetic plastics are expected to boost the market growth rate. This study throws light on the production of polyhydroxybutyrate from lignocellulosic biomass using environmentally benign techniques via enzyme and microbial activities to assess its feasibility as a green substitute to conventional plastics. The novelty of the present study is to highlight the recent advances, pretreatment techniques to reduce the recalcitrance of lignocellulosic biomass such as dilute and concentrated acidic pretreatment, alkaline pretreatment, steam explosion, ammonia fibre explosion (AFEX), ball milling, biological pretreatment as well as novel emerging pretreatment techniques notably, high-pressure homogenizer, electron beam, high hydrostatic pressure, co-solvent enhanced lignocellulosic fractionation (CELF) pulsed-electric field, low temperature steep delignification (LTSD), microwave and ultrasound technologies. Additionally, inhibitory compounds and detoxification routes, fermentation downstream processes, life cycle and environmental impacts of recovered natural biopolymers, review green procurement policies in various countries, PHA strategies in line with the United Nations Sustainable Development Goals (SDGs) along with the fate of the spent polyhydroxybutyrate are outlined.

Effects of Organic Solvents on the Organosolv Pretreatment of Degraded Empty Fruit Bunch for Fractionation and Lignin Removal

Empty fruit bunch (EFB), which is one of the primary agricultural wastes generated from the palm oil plantation, is generally discharged into the open environment or ends up in landfills. The utilization of this EFB waste for other value-added applications such as activated carbon and biofuels remain low, despite extensive research efforts. One of the reasons is that the EFB is highly vulnerable to microbial and fungi degradation under natural environment owning to its inherent characteristic of high organic matter and moisture content. This can rapidly deteriorate its quality and results in poor performance when processed into other products. However, the lignocellulosic components in degraded EFB (DEFB) still largely remain intact. Consequently, it could become a promising feedstock for production of bio-products after suitable pretreatment with organic solvents. In this study, DEFB was subjected to five different types of organic solvents for the pretreatment, including ethanol, ethylene glycol, 2-propanol, acetic acid and acetone. The effects of temperature and residence time were also investigated during the pretreatment. Organosolv pretreatment in ethylene glycol (50 v/v%) with the addition of NaOH (3 v/v%) as an alkaline catalyst successfully detached 81.5 wt.% hemicellulose and 75.1 wt.% lignin. As high as 90.4 wt.% cellulose was also successfully retrieved at mild temperature (80 °C) and short duration (45 min), while the purity of cellulose in treated DEFB was recorded at 84.3%. High-purity lignin was successfully recovered from the pretreatment liquor by using sulfuric acid for precipitation. The amount of recovered lignin from alkaline ethylene glycol liquor was 74.6% at pH 2.0. The high recovery of cellulose and lignin in DEFB by using organosolv pretreatment rendered it as one of the suitable feedstocks to be applied in downstream biorefinery processes. This can be further investigated in more detailed studies in the future.

Optimization of OPEFB lignocellulose transformation process through ionic liquid [TEA][HSO4] based pretreatment

Research on the transformation of Oil Palm Empty Fruit Bunches (OPEFB) through pretreatment process using ionic liquid triethylammonium hydrogen sulphate (IL [TEA][HSO₄]) was completed. The stages of the transformation process carried out were the synthesis of IL with the one-spot method, optimization of IL composition and pretreatment temperature, and IL recovery. The success of the IL synthesis stage was analyzed by FTIR, H-NMR and TGA. Based on the results obtained, it showed that IL [TEA][HSO₄] was successfully synthesized. This was indicated by the presence of IR absorption at 1/λ = 2814.97 cm^-1, 1401.07 cm^-1, 1233.30 cm^-1 and 847.92 cm^-1 which were functional groups for NH, CH₃, CN and SO₂, respectively. These results were supported by H-NMR data at δ (ppm) = 1.217-1.236 (N-CH₂-CH₃), 3.005-3.023 (-H), 3.427-3.445 (N-H⁺) and 3.867 (N⁺H₃). The TGA results showed that the melting point and decomposition temperature of the IL were 49 °C and 274.3 °C, respectively. Based on pretreatment optimization, it showed that the best IL composition for cellulose production was 85 wt%. Meanwhile, temperature optimization showed that the best temperature was 120 °C. In these two optimum conditions, the cellulose content was obtained at 45.84 wt%. Testing of IL [TEA][HSO₄] recovery performance for reuse has shown promising results. During the pretreatment process, IL [TEA][HSO₄] recovery effectively increased the cellulose content of OPEFB to 29.13 wt% and decreased the lignin content to 32.57%. The success of the recovery process is indicated by the increasing density properties of IL [TEA][HSO₄]. This increase occurs when using a temperature of 80-100 °C. The overall conditions obtained from this work suggest that IL [TEA][HSO₄] was effective during the transformation process of OPEFB into cellulose. This shows the potential of IL [TEA][HSO₄] in the future in the renewable energy sector.

A Whole-Slurry Fermentation Approach to High-Solid Loading for Bioethanol Production from Corn Stover

Corn stover is the most produced byproduct from maize worldwide. Since it is generated as a residue from maize harvesting, it is an inexpensive and interesting crop residue to be used as a feedstock. An ecologically friendly pretreatment such as autohydrolysis was selected for the manufacture of second-generation bioethanol from corn stover via whole-slurry fermentation at high-solid loadings. Temperatures from 200 to 240 °C were set for the autohydrolysis process, and the solid and liquid phases were analyzed. Additionally, the enzymatic susceptibility of the solid phases was assessed to test the suitability of the pretreatment. Afterward, the production of bioethanol from autohydrolyzed corn stover was carried out, mixing the solid with different percentages of the autohydrolysis liquor (25%, 50%, 75%, and 100%) and water (0% of liquor), from a total whole slurry fermentation (saving energy and water in the liquid–solid separation and subsequent washing of the solid phase) to employing water as only liquid medium. In spite of the challenging scenario of using the liquor fraction as liquid phase in the fermentation, values between 32.2 and 41.9 g ethanol/L and ethanol conversions up to 80% were achieved. This work exhibits the feasibility of corn stover for the production of bioethanol via a whole-slurry fermentation process.

Optimization of lignin extraction from alkaline treated mango seed husk by high shear homogenization-assisted organosolv process using response surface methodology

Lignin valorisation into materials such as resins is essential to increase the value obtained from biomass. However, biomass recalcitrance limits the selective isolation of lignin for economic gains. This study developed a new process for fractionating alkaline treated mango seed husk into high purity lignin and cellulose-rich pulp, using high shear homogenization-organosolv (HSHO) process. The HSHO process conditions (ethanol concentration (50-70%), temperature (130-150 °C) and homogenizing time (10-20 min)) were optimized using response surface methodology to maximize the solubilised lignin with high purity while obtaining a fibrillated cellulose-rich pulp. Optimum process conditions of 60% ethanol, 148.41 °C, and 15 min homogenization, yielded 70.23% lignin of 96.18% purity, higher than those of the non-assisted process (68.58% and 94.74%, respectively). Nuclear magnetic resonance spectroscopy showed syringyl and guaiacyl lignin units with a molecular weight of 3247 g/mol and thermal degradation temperature of 298 °C. Sulphur and nitrogen contents in the resulting lignin were lower than 0.15%. Fibrillated cellulose pulp with diameters of <1-10 μm were obtained. This study has established the proficiency of an HSHO process for biomass fractionation and more so, for the extraction of lignin with >90% purity suitable for varied applications.