Optimizing the Conditions of Pretreatment and Enzymatic Hydrolysis of Sugarcane Bagasse for Bioethanol Production

The agricultural waste sugarcane bagasse (SCB) is a kind of plentiful biomass resource. In this study, different pretreatment methods (NaOH, H2SO4, and sodium percarbonate/glycerol) were utilized and compared. Among the three pretreatment methods, NaOH pretreatment was the most optimal method. Response surface methodology (RSM) was utilized to optimize NaOH pretreatment conditions. After optimization by RSM, the solid yield and lignin removal were 54.60 and 82.30% under the treatment of 1% NaOH, a time of 60 min, and a solid-to-liquid ratio of 1:15, respectively. Then, the enzymolysis conditions of cellulase for NaOH-treated SCB were optimized by RSM. Under the optimal enzymatic hydrolysis conditions (an enzyme dose of 18 FPU/g, a time of 64 h, and a solid-to-liquid ratio of 1:30), the actual yield of reducing sugar in the enzyme-treated hydrolysate was 443.52 mg/g SCB with a cellulose conversion rate of 85.33%. A bacterium, namely, Bacillus sp. EtOH, which produced ethanol and Baijiu aroma substances, was isolated from the high-temperature Daqu of Danquan Baijiu in our previous study. At last, when the strain EtOH was cultured for 36 h in a fermentation medium (reducing sugar from cellulase-treated SCB hydrolysate, yeast extract, and peptone), ethanol concentration reached 2.769 g/L (0.353%, v/v). The sugar-to-ethanol and SCB-to-ethanol yields were 13.85 and 11.81% in this study, respectively. In brief, after NaOH pretreatment, 1 g of original SCB produced 0.5460 g of NaOH-treated SCB. Then, after the enzymatic hydrolysis, reducing sugar yield (443.52 mg/g SCB) was obtained. Our study provided a suitable method for bioethanol production from SCB, which achieved efficient resource utilization of agricultural waste SCB.

Dark fermentation of pretreated hydrolysates of pineapple fruit waste for the production of biohydrogen using bacteria isolated from wastewater sources

In the present study, both acidic and alkaline hydrolysate of pineapple waste was utilised for the production of biohydrogen using locally isolated bacterial strains. The bacteria were isolated from different wastewater sources and were identified as Proteus mirabilis, Pseudomonas aeruginosa, Bacillus altitudinus, Bacillus subtilis, Paenibacillus alvei, and Lysinibacillus sphaericus. Experimental results showed that the highest biohydrogen yield of 836.33 ± 48.02 mL H2 was produced from alkaline hydrolysate with Bacillus altitudinis during the 96thhr of fermentation. Among the different bacterial strains, B. altitudinis showed higher H2 production. Comparatively alkaline hydrolysates exhibited a higher yield of hydrogen than acidic hydrolysates. The final pH of the experiment was found to be in acidic range. The total VFA concentration ranged between 930 ± 207.85 mg/L to 3050 ± 476.97 mg/L. Both sugar degradation and COD reduction were more than 80% in the acidic and alkaline hydrolysates while the lowest sugar degradation and COD reduction were observed for the untreated biomass. The rationale behind this study was to convert the waste biomass into energy by utilising the potential of native bacterial communities.

A review of the principles and biotechnological applications of glycoside hydrolases from extreme environments

It is apparent that Biocatalysts are shaping the future by providing a more sustainable approach to established chemical processes. Industrial processes rely heavily on the use of toxic compounds and high energy or pH reactions, factors that both contributes to the worsening climate crisis. Enzymes found in bacterial systems and other microorganisms, from the glaciers of the Arctic to the sandy deserts of Abu Dhabi, provide key tools and understanding as to how we can progress in the biotechnology sector. These extremophilic bacteria harness the adaptive enzymes capable of withstanding harsh reaction conditions in terms of stability and reactivity. Carbohydrate-active enzymes, including glycoside hydrolases or carbohydrate esterases, are extremely beneficial for the presence and future of biocatalysis. Their involvement in the industry spans from laundry detergents to paper and pulp treatment by degrading oligo/polysaccharides into their monomeric products in almost all detrimental environments. This includes exceedingly high temperatures, pHs or even in the absence of water. In this review, we discuss the structure and function of different glycoside hydrolases from extremophiles, and how they can be applied to industrial-scale reactions to replace the use of harsh chemicals, reduce waste, or decrease energy consumption.

Organosolv pretreatment: an in-depth purview of mechanics of the system

The concept of biorefinery has been advancing globally and organosolv pretreatment strategy has seen an upsurge in research due to its efficiency in removing the recalcitrant lignin and dissolution of cellulose. The high-performance organosolv system uses green solvents and its reusability contributes concurrently to the biorefinery sector and sustainability. The major advantage of the current system involves the continuous removal of lignin to enhance cellulose accessibility, thereby easing the later biorefinery steps, which were immensely restricted due to the recalcitrant lignin. The current system process can be further explored and enhanced via the amalgamation of new technologies, which is still a work in progress. Thus, the current review summarizes organosolv pretreatment and the range of solvents used, along with a detailed mechanistic approach that results in efficient pretreatment of LCB. The latest developments for designing high-performance pretreatment systems, their pitfalls, and advanced assessments such as Life Cycle Assessment along with Techno-Economic Assessment have also been deliberated to allow an insight into its diverse potential applicability towards a sustainable future.

Study on the effects of different pectinase/cellulase ratios and pretreatment times on the preparation of nanocellulose by ultrasound-assisted bio-enzyme heat treatment

With the development of science and technology, efficient, fast and green methods are increasingly being pursued. The production of nanocellulose by green methods, such as bio-enzymes-assisted ultrasound treatment, has been the focus of many studies. However, the yield of cellulose nanocrystals prepared by this method is very low. In this paper, by pretreatment of microcrystalline cellulose (MCC), nanocellulose was prepared by heating and stirring + pectinase/cellulase + ultrasonic treatment (HSt - P/C - Ultr). The effects of the ratios of pectinase and cellulase and the hydrolysis time on the yield of nanocellulose were studied. FTIR, XRD, SEM, TEM and TG were used to determine the structure, crystallinity, morphology and thermal stability of nanocellulose. The results showed that optimal hydrolysis conditions were determined as a pectinase : cellulase ratio of 1 : 1, 90 min and 50 °C. The yield of nanocellulose was about 32.0%. The yield of pectinase cellulase = 1 : 1 was higher than that of microcrystalline cellulose (MCC) treated by a single bio-enzyme. This indicated that the synergistic effects of pectinase and cellulase have a certain effect on the formation of nanocellulose. During the preparation, the crystalline form of cellulose did not change. It was still cellulose I with a crystallinity of 73.5%, which is 9.50% higher than that of microcrystalline cellulose (MCC), a width of 20-50 nm, a high aspect ratio and a winding network structure. Therefore, nanocellulose prepared by this method is an ideal toughening material for manufacturing composite materials.

Phosphoric acid pretreatment of poplar to optimize fermentable sugars production based on orthogonal experimental design

The recalcitrant structure of raw poplar limited the production of fermentable sugars when applied as the material in the pretreatment of biochemical conversions. Phosphoric acid pretreatment is an efficient method to destroy the compact lignocellulose matrix presence in the poplar. In this study, phosphoric acid pretreatment of poplar was optimised by an orthogonal experimental design [L₉(3³)] to improve enzymatic digestibility through investigating the effects of reaction temperature, time duration, and phosphoric acid concentration. The optimal conditions were selected based on the variance of chemical compositions, hemicellulose removal ratio, and delignification of the woody material after pretreatment. The optimum enzymatic hydrolysis yield of up to 73.44% was obtained when the phosphoric acid pretreatment performed at 190°C for 150 min under 1.5% of v/v phosphoric acid concentration.

Evaluation of the antimicrobial effects of Capsicum, Nigella sativa, Musa paradisiaca L., and Citrus limetta: A review

The extensive use of antibiotics and vaccines against microbial infections can result in long-term negative effects on humans and the environment. However, there are a number of plants that have antimicrobial effects against various disease-causing microbes such as bacteria, viruses, and fungi without negative side effects or harm to the environment. In this regard, four particular plants- Capsicum, Nigella sativa, Musa paradisiaca L., and Citrus limetta have been widely considered due to their excellent antimicrobial effect and ample availability. In this review, we discuss their antimicrobial effects due to the presence of thymoquinone, p-cymene, pinene, alkaloids, limonene, camphene, and melanin. These antimicrobial compounds disrupt the cell membrane of microbes, inhibit cellular division, and form biofilm in bacterial species, eventually reducing the number of microbes. Extraction of these compounds from the respective plants is carried out by different methods such as soxhlet, hydro-distillation, liquid-liquid extraction (LLE), pressurized liquid extraction (PLE), solid-phase extraction (SPE), supercritical fluid extraction (SFE), pulsed electric field (PEF), microwave-assisted extraction (MAE), enzyme-assisted extraction (EAE), ultrasound-assisted extraction (UAE), and high-voltage electrical discharge. Suitable selection of the extraction technique highly depends upon the associated advantages and disadvantages. In order to aid future study in this field, this review paper summarizes the advantages and disadvantages of each of these approaches. Additionally, the discussion covers how antimicrobial agents destroy harmful bacteria. Thus, this review offers in-depth knowledge to researchers on the antibacterial properties of Capsicum, Nigella sativa, Musa paradisiaca L. peels, and Citrus limetta.

Towards efficient and greener processes for furfural production from biomass: A review of the recent trends

As mentioned in several recent reviews, biomass-based furfural is attracting increasing interest as a feasible alternative for the synthesis of a wide range of non-petroleum-derived compounds. However, the lack of environmentally friendly, cost-effective, and sustainable industrial procedures is still evident. This review describes the chemical and biological routes for furfural production. The mechanisms proposed for the chemical transformation of xylose to furfural are detailed, as are the current advances in the manufacture of furfural from biomass. The main goal is to overview the different ways of improving the furfural synthesis process. A pretreatment process, particularly chemical and physico-chemical, enhances the digestibility of biomass, leading to the production of >70 % of available sugars for the production of valuable products. The combination of heterogeneous (zeolite and polymeric solid) catalyst and biphasic solvent system (water/GVL and water/CPME) is regarded as an attractive approach, affording >75 % furfural yield for over 80 % of selectivity with the possibility of catalyst reuse. Microwave heating as an activation technique reduces reaction time at least tenfold, making the process more sustainable. The state of the art in industrial processes is also discussed. It shows that, when sulfuric acid is used, the furfural yields do not exceed 55 % for temperatures close to 180 °C. However, the MTC process recently achieved an 83 % yield by continuously removing furfural from the liquid phase. Finally, the CIMV process, using a formic acid/acetic acid mixture, has been developed. The economic aspects of furfural production are then addressed. Future research will be needed to investigate scaling-up and biological techniques that produce acceptable yields and productivities to become commercially viable and competitive in furfural production from biomass.

Lignocellulose biohydrogen towards net zero emission: A review on recent developments

This review mainly determines novel and advance physical, chemical, physico-chemical, microbiological and nanotechnology-based pretreatment techniques in lignocellulosic biomass pretreatment for bio-H2 production. Further, aim of this review is to gain the knowledge on the lignocellulosic biomass pretreatment and its priority on the efficacy of bio-H2 and positive findings. The influence of various pretreatment techniques on the structure of lignocellulosic biomass have presented with the pros and cons, especially about the cellulose digestibility and the interference by generation of inhibitory compounds in the bio-enzymatic technique as such compounds is toxic. The result implies that the stepwise pretreatment technique only can ensure eventually the lignocellulosic biomass materials fermentation to yield bio-H2. Though, the mentioned pretreatment steps are still a challenge to procure cost-effective large-scale conversion of lignocellulosic biomass into fermentable sugars along with low inhibitory concentration.

Investigating the Impact of Polymer Length, Attachment Site, and Charge on Enzymatic Activity and Stability of Cellulase

The thermophilic cellulase Cel5a from Fervidobacterium nodosum (FnCel5a) was conjugated with neutral, cationic, and anionic polymers of increasing molecular weights. The enzymatic activity toward an anionic soluble cellulose derivative, thermal stability, and functional chemical stability of these bioconjugates were investigated. The results suggest that increasing polymer chain length for polymers compatible with the substrate enhances the positive impact of polymer conjugation on enzymatic activity. Activity enhancements of nearly 100% were observed for bioconjugates with N,N-dimethyl acrylamide (DMAm) and N,N-dimethyl acrylamide-2-(N,N-dimethylamino)ethyl methacrylate (DMAm/DMAEMA) due to proposed polymer-substrate compatibility enabled by potential noncovalent interactions. Double conjugation of two functionally distinct polymers to wild-type and mutated FnCel5a using two conjugation methods was achieved. These doubly conjugated bioconjugates exhibited similar thermal stability to the unmodified wild-type enzyme, although enzymatic activity initially gained from conjugation was lost, suggesting that chain length may be a better tool for bioconjugate activity modulation than double conjugation.

Comparison of various delignification/desilication pre-treatments and indigenous fungal cellulase for improved hydrolysis of paddy straw

The efficient removal of lignin and silica from paddy straw is essential for its volarization into biofuels and other value-added products. In this work, different chemical pre-treatments viz. acid/alkali, organosolv and deep eutectic solvents were carried out to assess the extent of delignification and desilication of paddy straw. Maximum lignin and silica removal of 96.08 and 95.51% was observed with two step acid (0.5% sulphuric acid) followed by alkali (4% sodium hydroxide) pre-treatment with significantly low total lignin (2.30%) and silica content (0.80%) of the treated straw residue. The treated straw residue contained significantly high holocellulose (91.65%), cellulose (75.01%) and hemicellulose content (16.64%). Among the four indigenous fungal isolates, Penicillium mallochii (JS17) cellulase showed better accessibility for the treated straw residue with maximum release of 504.18 mg g^-1 of reducing sugars and saccharification efficiency of 56.90%. The two-step acid/alkali pre-treatment of paddy straw was highly effective for removing lignin and silica from paddy straw, thereby, resulting in enhanced enzymatic accessibility of the substrate and more efficient hydrolysis of cellulose into fermentable sugars.

Enzymatic Glucose and Xylose Production from Paper Mill Rejects

Recycled paper fiber rejects have shown potential as a source of waste-to-resource carbohydrates for renewable chemicals production. This study examined three classes of recycled paper fines (old corrugated containers, old newspaper, and mixed office waste) and two industrial papermaking rejects streams from different recycling mills (one mill processes linerboard and the other old corrugated cardboard). The effect of chemical pretreatment using dilute sodium hydroxide, hot water and dilute sulfuric acid on enzymatic glucose and xylose yields was evaluated. Enzymatic hydrolysis results indicated that recycled fiber streams with more old corrugated cardboard have higher potential to produce carbohydrates. The recycled cardboard rejects produced more glucose and xylose per kilogram of rejects than the linerboard rejects under all untreated and pretreated conditions. The highest producing rejects sample was sodium hydroxide pretreated cardboard rejects with 373 g glucose and 61 g xylose produced per kilogram of rejects. However, a simple hot water pretreatment showed similar results, with 335 g glucose and 58 g xylose produced per kilogram of rejects. The hot water pretreatment is recommended due to its comparable yield and lower chemical addition.

Production of Different Biochemicals by Paenibacillus polymyxa DSM 742 From Pretreated Brewers' Spent Grains

Brewers' spent grains (BSG) are a by-product of the brewing industry that is mainly used as feedstock; otherwise, it has to be disposed according to regulations. Due to the high content of glucose and xylose, after pretreatment and hydrolysis, it can be used as a main carbohydrate source for cultivation of microorganisms for production of biofuels or biochemicals like 2,3-butanediol or lactate. 2,3-Butanediol has applications in the pharmaceutical or chemical industry as a precursor for varnishes and paints or in the food industry as an aroma compound. So far, Klebsiella pneumoniae, Serratia marcescens, Clostridium sp., and Enterobacter aerogenes are being used and investigated in different bioprocesses aimed at the production of 2,3-butanediol. The main drawback is bacterial pathogenicity which complicates all production steps in laboratory, pilot, and industrial scales. In our study, a gram-positive GRAS bacterium Paenibacillus polymyxa DSM 742 was used for the production of 2,3-butanediol. Since this strain is very poorly described in literature, bacterium cultivation was performed in media with different glucose and/or xylose concentration ranges. The highest 2,3-butanediol concentration of 18.61 g l-1 was achieved in medium with 70 g l-1 of glucose during 40 h of fermentation. In contrast, during bacterium cultivation in xylose containing medium there was no significant 2,3-butanediol production. In the next stage, BSG hydrolysates were used for bacterial cultivation. P. polymyxa DSM 742 cultivated in the liquid phase of pretreated BSG produced very low 2,3-butanediol and ethanol concentrations. Therefore, this BSG hydrolysate has to be detoxified in order to remove bacterial growth inhibitors. After detoxification, bacterium cultivation resulted in 30 g l-1 of lactate, while production of 2,3-butanediol was negligible. The solid phase of pretreated BSG was also used for bacterium cultivation after its hydrolysis by commercial enzymes. In these cultivations, P. polymyxa DSM 742 produced 9.8 g l-1 of 2,3-butanediol and 3.93 g l-1 of ethanol. On the basis of the obtained results, it can be concluded that different experimental setups give the possibility of directing the metabolism of P. polymyxa DSM 742 toward the production of either 2,3-butanediol and ethanol or lactate.

Production of single cell oil by Yarrowia lipolytica JCM 2320 using detoxified desiccated coconut residue hydrolysate

Nowadays, the replacement of petro-diesel with biodiesel has raised the concern among the community for the utilization of improper feedstocks and the cost involved. However, these issues can be solved by producing single cell oil (SCO) from lignocellulosic biomass hydrolysates by oleaginous microorganisms. This study introduced Yarrowia lipolytica JCM 2320 with a desiccated coconut residue (DCR) hydrolysate (obtained from the 2% dilute sulphuric acid pretreatment) as a carbon source in generating SCO. However, common inhibitors formed during acid pretreatment of biomass such as five-hydroxymethylfurfural (HMF), furfural, acetic acid and levulinic acid resulting from the sugar degradations may have detrimental effects towards the fermentation process. To visualize the effect of inhibitors on Y. lipolytica, an inhibitory study was conducted by adding 0.5-5.0 g/L of potential inhibitors to the YPD (yeast, peptone and D-glucose) medium. It was found that the presence of furfural at 0.5 g/L would increase the lag phase, which beyond that was detrimental to Y. lipolytica. Furthermore, increasing the five-hydroxymethylfurfural (HMF) concentration would increase the lag phase of Y. lipolytica, whereas, for acetic acid and levulinic acid, it showed a negligible effect. Detoxification was hence conducted to remove the potential inhibitors from the DCR hydrolysate prior its utilization in the fermentation. To examine the possibility of using adsorption resins for the detoxification of DCR hydrolysate, five different resins were tested (Amberlite® XAD-4, Amberlite® XAD-7, Amberlite® IR 120, Amberlite® IRA 96 and Amberlite® IRA 402) with five different concentrations of 1%, 3%, 5%, 10% and 15% (w/v), respectively. At resin concentration of 10%, Amberlite® XAD-4 recorded the highest SCO yield, 2.90 ± 0.02 g/L, whereas the control and the conventional overliming detoxification method, recorded only 1.29 ± 0.01 g/L and 1.27 ± 0.02 g/L SCO accumulation, respectively. Moreover, the fatty acid profile of the oil produced was rich in oleic acid (33.60%), linoleic acid (9.90%), and palmitic acid (14.90%), which indicates the potential as a good biodiesel raw material.

Valorization of Brewers’ Spent Grains: Pretreatments and Fermentation, a Review

Brewers’ spent grains constitute a valuable byproduct of the beer industry. They are characterized by a rich nutritional composition consisting of around 70% lignocellulosic fibrous material, 20% proteins, 10% lipids, in addition to vitamins, minerals, amino acids, and phenolic compounds. These spent grains are produced in large amounts all through the year, are cheap, and lack economically feasible applications. Nowadays, 70% of these spent grains are used as animal feed, 10% are used for biogas production, and the remaining 20% are disposed in landfills. Due to the aforementioned facts, alternative uses of the brewers’ spent grains are highly sought-after. In fact, this nutrient-rich industrial by-product makes it a very good candidate for valorization through biotechnological processing, particularly microbial fermentation. After applying the needed pretreatments, using brewers’ spent grains as a substrate in submerged and solid-state fermentation of different microorganisms leads to the production of various value-added compounds such as organic acids, amino acids, volatile fatty acids, enzymes, vitamins, second-generation biofuels and other products.

Acid-based lignocellulosic biomass biorefinery for bioenergy production: Advantages, application constraints, and perspectives

The production of chemicals and fuels from renewable biomass with the primary aim of reducing carbon footprints has recently become one of the central points of interest. The use of lignocellulosic biomass for energy production is believed to meet the main criteria of maximizing the available global energy source and minimizing pollutant emissions. However, before usage in bioenergy production, lignocellulosic biomass needs to undergo several processes, among which biomass pretreatment plays an important role in the yield, productivity, and quality of the products. Acid-based pretreatment, one of the existing methods applied for lignocellulosic biomass pretreatment, has several advantages, such as short operating time and high efficiency. A thorough analysis of the characteristics of acid-based biomass pretreatment is presented in this review. The environmental concerns and future challenges involved in using acid pretreatment methods are discussed in detail to achieve clean and sustainable bioenergy production. The application of acid to biomass pretreatment is considered an effective process for biorefineries that aim to optimize the production of desired products while minimizing the by-products.

Net Energy Analysis and Techno-Economic Assessment of Co-Production of Bioethanol and Biogas from Cellulosic Biomass

Co-production is a process based on the biorefinery concept that maximizes the benefit of biomass by reusing residue from the production of one product to produce others. In this regard, biogas is one of the most researched second products for the production of ethanol from cellulosic biomass. However, operating this scheme requires additional investment in biogas processing equipment. This review compiles data from research studies on the co-production of bioethanol and biogas from lignocellulosic biomass to determine which is more worthwhile: leaving the residue or investing more to benefit from the second product. According to previous research, ethanol stillage can be converted to biogas via anaerobic digestion, increasing energy output by 2–3 fold. Techno-economic studies demonstrated that the co-production process reduces the minimum ethanol selling price to a level close to the market price of ethanol, implying the possibility of industrializing cellulosic ethanol production through this scheme.

Perspective on the Therapeutic Applications of Algal Polysaccharides

Abstract

Algae are an enormous source of polysaccharides and have gained much interest in human flourishing as organic drugs. Algal polysaccharides have aroused interest in the health sector owing to the various bioactivities namely anticancer, antiviral, immunoregulation, antidiabetic and antioxidant effects. The research community has comprehensively described the importance of algal polysaccharides regarding their extraction, purification, and potential use in various sectors. However, regardless of all the intriguing properties and potency in the health sector, these algal polysaccharides deserve detailed investigation. Hence, the present review emphasizes extensively on the previous and latest developments in the extraction, purification, structural properties and therapeutic bioactivities of algal polysaccharides to upgrade the knowledge for further advancement in this area of research. Moreover, the review also addresses the challenges, prospective research gaps and future perspective. We believe this review can provide a boost to upgrade the traditional methods of algal polysaccharide production for the development of efficacious drugs that will promote human welfare.

Graphic Abstract

Nanocellulose Production Using Ionic Liquids with Enzymatic Pretreatment

Nanocellulose has gained increasing attention during the past decade, which is related to its unique properties and wide application. In this paper, nanocellulose samples were produced via hydrolysis with ionic liquids (1-ethyl-3-methylimidazole acetate (EmimOAc) and 1-allyl-3-methylimidazolium chloride (AmimCl)) from microcrystalline celluloses (Avicel and Whatman) subjected to enzymatic pretreatment. The obtained material was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM), and thermogravimetric analysis (TG). The results showed that the nanocellulose had a regular and spherical structure with diameters of 30-40 nm and exhibited lower crystallinity and thermal stability than the material obtained after hydrolysis with Trichoderma reesei enzymes. However, the enzyme-pretreated Avicel had a particle size of about 200 nm and a cellulose II structure. A two-step process involving enzyme pretreatment and hydrolysis with ionic liquids resulted in the production of nanocellulose. Moreover, the particle size of nanocellulose and its structure depend on the ionic liquid used.

Lignocellulosic Waste Pretreatment Solely via Biocatalysis as a Partial Simultaneous Lignino-Holocellulolysis Process

Human endeavors generate a significant quantity of bio-waste, even lignocellulosic waste, due to rapid industrialization and urbanization, and can cause pollution to aquatic ecosystems, and contribute to detrimental animal and human health because of the toxicity of consequent hydrolysis products. This paper contributes to a new understanding of the lignocellulosic waste bio-pretreatment process from a literature review, which can provide better biorefinery operational outcomes. The simultaneous partial biological lignin, cellulose and hemicellulose lysis, i.e., simultaneous semi-lignino-holocellulolysis, is aimed at suggesting that when ligninolysis ensues, holocellulolysis is simultaneously performed for milled lignocellulosic waste instead of having a sequential process of initial ligninolysis and subsequent holocellulolysis as is currently the norm. It is presumed that such a process can be solely performed by digestive enzyme cocktails from the monkey cups of species such as Nepenthes, white and brown rot fungi, and some plant exudates. From the literature review, it was evident that the pretreatment of milled lignocellulosic waste is largely incomplete, and ligninolysis including holocellulolysis ensues simultaneously when the waste is milled. It is further proposed that lignocellulosic waste pretreatment can be facilitated using an environmentally friendly approach solely using biological means. For such a process to be understood and applied on an industrial scale, an interdisciplinary approach using process engineering and microbiology techniques is required.

Advanced Bioethanol Production: From Novel Raw Materials to Integrated Biorefineries

The production of so-called advanced bioethanol offers several advantages compared to traditional bioethanol production processes in terms of sustainability criteria. This includes, for instance, the use of nonfood crops or residual biomass as raw material and a higher potential for reducing greenhouse gas emissions. The present review focuses on the recent progress related to the production of advanced bioethanol, (i) highlighting current results from using novel biomass sources such as the organic fraction of municipal solid waste and certain industrial residues (e.g., residues from the paper, food, and beverage industries); (ii) describing new developments in pretreatment technologies for the fractionation and conversion of lignocellulosic biomass, such as the bioextrusion process or the use of novel ionic liquids; (iii) listing the use of new enzyme catalysts and microbial strains during saccharification and fermentation processes. Furthermore, the most promising biorefinery approaches that will contribute to the cost-competitiveness of advanced bioethanol production processes are also discussed, focusing on innovative technologies and applications that can contribute to achieve a more sustainable and effective utilization of all biomass fractions. Special attention is given to integrated strategies such as lignocellulose-based biorefineries for the simultaneous production of bioethanol and other high added value bioproducts.

Impact of centrifugation treatment on enzymatic hydrolysis of cellulose and xylan in poplar fibers with high lignin content

Centrifugation is very common in the production and treatment of lignocellulose for applications like pretreatment for enzymatic hydrolysis, but it is not certain whether it affects applications of lignocellulose and almost no one realizes this problem. This study investigated the effects of centrifugation on the characteristics and enzymatic hydrolysis of poplar fibers with high lignin content. The results showed that centrifugation inhibited the enzymatic hydrolysis of fiber, but fiber characteristics and enzymatic digestibility fluctuated with increasing centrifugation time. Centrifugation for about 15 min had the least effect on fiber properties while centrifugation for 30 min had the least effect on enzymatic hydrolysis. The water retention value was closely related to the enzymatic digestibility, but the pore characteristics and crystallinity index could not reflect the enzymatic accessibility of the fiber. This article will provide useful references for the enzymatic hydrolysis of lignocellulose and other high-value applications to improve production efficiency furtherly.

Effect of sequential pretreatment combinations on the composition and enzymatic hydrolysis of hazelnut shells

Hazelnut shells, a high lignin containing biomass, were subjected to individual and sequential liquid hot water (LHW), alkaline (AP) and dilute acid pretreatments (DAP). Among the single pretreatments, LHW demonstrated the highest cellulose recovery of 98.1%, DAP resulted in the highest hemicellulose solubilization of 56.0%, and AP of the highest lignin removal of 49.6%. Employing two-step pretreatment on hazelnut shells, in general, demonstrated an enhanced action of the second pretreatment; therefore, the sequence of the pretreatment methods had a significant impact on both substrate characteristics and enzymatic hydrolysis efficiency of biomass. In terms of delignification, AP-LHW achieved 60.7% lignin removal, while LHW-DAP showed the highest hemicellulose removal of 93.8% and DAP-LHW resulted in the highest cellulose recovery of 94.0%. Structural properties of raw and pretreated hazelnut shells were observed by FTIR. The maximum glucose recovery of 54.9% was observed in DAP-LHW pretreated samples. For this pretreatment combination, almost 1.8 MJ total energy was required to recover 10.2 g glucose. The findings indicated that complete removal of the physical barrier of lignin and hemicellulose might not be essential; partial relocation of lignin and alteration of cellulose structure may also be efficient in increasing the sugar recovery from the lignocellulosic biomass.

Comparative Study on Pretreatment Processes for Different Utilization Purposes of Switchgrass

Switchgrass (Panicum virgatum, L., Poaceae) with the advantages of high cellulose yield, and high growth even under low input and poor soil quality, has been identified as a promising candidate for production of low-cost biofuels, papermaking, and nanocellulose. In this study, 12 chemical pretreatments on a laboratory scale were compared for different utilization purposes of switchgrass. It was found that the pretreated switchgrass with sodium hydroxide showed considerable potential for providing mixed sugars for fermentation with 11.10% of residual lignin, 53.85% of residual cellulose, and 22.06% of residual hemicellulose. The pretreatment with 2.00% (v/v) nitric acid was the best method to remove 78.37% of hemicellulose and 39.82% of lignin under a low temperature (125 °C, 30 min), which can be used in the production of nanocellulose. Besides, a completely randomized design analysis of switchgrass pretreatments provided the alternative ethanol organosolv delignification of switchgrass for the papermaking industry with a high residual cellulose of 58.56%. Finally, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR) were carried out to confirm the changes in functional groups, crystallinity, and thermal behavior of the three materials, respectively, from the optimal pretreatments.

The Effect of Mechanocatalytic Pretreatment on the Structure and Depolymerization of Willow

In this study, the effect of a mechanocatalytic pretreatment on the structure of willow and sugar release from pretreated willow was explored. In the mechanocatalytic approach, the pretreatment consists of solvent-free impregnation with sulfuric acid and a mechanical treatment with ball milling. Willow sawdust and pretreated samples were analyzed with field emission scanning electron microscope and X-ray diffraction. The products in the sugar solution were determined as the total reducing sugars with the 3,5-dinitrosalicylic acid method and monosaccharides with capillary electrophoresis. According to the results, milling increased the sugar production, depending on the sulfuric acid load. The milling parameters, such as the rotation speed of the mill, the catalyst-to-willow ratio, and the milling time influenced the amount of sugars in the hydrolysate and the composition of the sugar solution produced. Changes were observed in the surface of the willow particles as well as changes in the crystalline structure. Glucose and xylose yields increased after 15 min of milling and reached their maximum level after 45 min of milling with the 0.5 mmol/g sulfuric acid load.

Pretreatment and fermentation of lignocellulosic biomass: reaction mechanisms and process engineering

At a time of rapid depletion of oil resources, global food shortages and solid waste problems, it is imperative to encourage research into the use of appropriate pre-treatment techniques using regenerative raw materials such as lignocellulosic biomass.

Life Cycle Assessment for Bioethanol Production from Oil Palm Frond Juice in an Oil Palm Based Biorefinery

A study was conducted to estimate the possible environmental impacts arising from the generation of bioethanol from oil palm frond sugar juice in a theoretical oil palm based biorefinery model. A life cycle assessment (LCA) with the gate-to-gate approach was performed with the aid of SimaPro version 8.0 whereby ten impact categories were evaluated. The scope included frond collection and transportation, frond sugar juice extraction, and bioethanol fermentation and purification. Evaluation on the processes involved indicated that fermentation contributed to the environmental problems the most, with a contribution range of 52% to 97% for all the impact categories. This was due to a substantial usage of nutrient during this process, which consumes high energy for its production thus contributing a significant burden to the surrounding. Nevertheless, the present system offers a great option for biofuel generation as it utilizes sugar juice from the readily available oil palm waste. Not only solving the issue of land utilization for feedstock cultivation, the enzymatic saccharification step, which commonly necessary for lignocellulosic sugar recovery could also be eliminated.

Bioethanol production from waste lignocelluloses: A review on microbial degradation potential

Tremendous explosion of population has led to about 200% increment of total energy consumptions in last twenty-five years. Apart from conventional fossil fuel as limited energy source, alternative non-conventional sources are being explored worldwide to cater the energy requirement. Lignocellulosic biomass conversion for biofuel production is an important alternative energy source due to its abundance in nature and creating less harmful impacts on the environment in comparison to the coal or petroleum-based sources. However, lignocellulose biopolymer, the building block of plants, is a recalcitrant substance and difficult to break into desirable products. Commonly used chemical and physical methods for pretreating the substrate are having several limitations. Whereas, utilizing microbial potential to hydrolyse the biomass is an interesting area of research. Because of the complexity of substrate, several enzymes are required that can act synergistically to hydrolyse the biopolymer producing components like bioethanol or other energy substances. Exploring a range of microorganisms, like bacteria, fungi, yeast etc. that utilizes lignocelluloses for their energy through enzymatic breaking down the biomass, is one of the options. Scientists are working upon designing organisms through genetic engineering tools to integrate desired enzymes into a single organism (like bacterial cell). Studies on designer cellulosomes and bacteria consortia development relating consolidated bioprocessing are exciting to overcome the issue of appropriate lignocellulose digestions. This review encompasses up to date information on recent developments for effective microbial degradation processes of lignocelluloses for improved utilization to produce biofuel (bioethanol in particular) from the most plentiful substances of our planet.

Biochemical conversion of sweet sorghum bagasse to succinic acid

Succinic acid, an important intermediate in the manufacture of plastics and other commodity and specialty chemicals, is currently made primarily from petroleum. We attempted to biosynthesize succinic acid through microbial fermentation of cellulosic sugars derived from the bagasse of sweet sorghum, a renewable feedstock that can grow in a wide range of climates around the world. We investigated pretreating sweet sorghum bagasse (SSB) with concentrated phosphoric acid at mild conditions (40-85°C) at various residence times and biomass concentrations. We then subjected the pretreated SSB to enzymatic hydrolysis with a commercial cellulase to release glucose. The highest glucose yield was obtained when SSB was pretreated at 50°C for 43 min at 130 g/L biomass concentration on dry basis. Fermentation was carried out with Actinobacillus succinogenes 130Z, which readily converted 29.2 g/L of cellulosic glucose to 17.8 g/L of succinic acid in a 3.5-L bioreactor sparged with CO₂ at a rate of 0.5 vvm, thus reducing the carbon footprint of the process. Overall, we demonstrated, for the first time, the use of SSB for production of succinic acid using practices that lower energy use, future equipment cost, waste generation, and carbon footprint.

Two-Stage Pretreatment to Improve Saccharification of Oat Straw and Jerusalem Artichoke Biomass

Pretreatment is a necessary step when lignocellulosic biomass is to be converted to simple sugars; however single-stage pretreatment is often insufficient to guarantee full availability of polymeric sugars from raw material to hydrolyzing enzymes. In this work, the two-stage pretreatment with use of acid (H2SO4, HNO3) and alkali (NaOH) was applied in order to increase the susceptibility of Jerusalem artichoke stalks (JAS) and oat straw (OS) biomass on the enzymatic attack. The effect of the concentration of reagents (2% and 5% w/v) and the order of acid and alkali sequence on the composition of remaining solids and the efficiency of enzymatic hydrolysis was evaluated. It was found that after combined pretreatment process, due to the removal of hemicellulose and lignin, the content of cellulose in pretreated biomass increased to a large extent, reaching almost 90% d.m. and 95% d.m., in the case of JAS and OS, respectively. The enzymatic hydrolysis of solids remaining after pretreatment resulted in the formation of up to 45 g/L of glucose, for both JAS and OS. The highest glucose yield was achieved after pretreatment with 5% nitric acid followed by NaOH, and 90.6% and 97.6% of efficiency were obtained, respectively for JAS and OS.

Enhancement of bioethanol production from Gracilaria verrucosa by Saccharomyces cerevisiae through the overexpression of SNR84 and PGM2

A total monosaccharide concentration of 47.0 g/L from 12% (w/v) Gracilaria verrucosa was obtained by hyper thermal acid hydrolysis with 0.2 M HCl at 140°C for 15 min and enzymatic saccharification with CTec2. To improve galactose utilization, we overexpressed two genes, SNR84 and PGM2, in a Saccharomyces cerevisiae CEN-PK2 using CRISPR/Cas-9. The overexpression of both SNR84 and PGM2 improved galactose utilization and ethanol production compared to the overexpression of each gene alone. The overexpression of both SNR84 and PGM2 and of PGM2 and SNR84 singly in S. cerevisiae CEN-PK2 Cas9 produced 20.0, 18.5, and 16.5 g/L ethanol with ethanol yield (Y_EtOH) values of 0.43, 0.39, and 0.35, respectively. However, S. cerevisiae CEN-PK2 adapted to high concentration of galactose consumed galactose completely and produced 22.0 g/L ethanol at a Y_EtOH value of 0.47. The overexpression of both SNR84 and PGM2 increased the transcriptional levels of GAL and regulatory genes; however, the transcriptional levels of these genes were lower than those in S. cerevisiae adapted to high galactose concentrations.

Enhanced Enzymatic Hydrolysis of Pennisetum alopecuroides by Dilute Acid, Alkaline and Ferric Chloride Pretreatments

In this study, effects of different pretreatment methods on the enzymatic digestibility of Pennisetum alopecuroides, a ubiquitous wild grass in China, were investigated to evaluate its potential as a feedstock for biofuel production. The stalk samples were separately pretreated with H₂SO₄, NaOH and FeCl₃ solutions of different concentrations at 120 °C for 30 min, after which enzymatic hydrolysis was conducted to measure the digestibility of pretreated samples. Results demonstrated that different pretreatments were effective at removing hemicellulose, among which ferric chloride pretreatment (FCP) gave the highest soluble sugar recovery (200.2 mg/g raw stalk) from the pretreatment stage. In comparison with FCP and dilute acid pretreatment (DAP), dilute alkaline pretreatment (DALP) induced much higher delignification and stronger morphological changes of the biomass, making it more accessible to hydrolysis enzymes. As a result, DALP using 1.2% NaOH showed the highest total soluble sugar yield through the whole process from pretreatment to enzymatic hydrolysis (508.5 mg/g raw stalk). The present work indicates that DALP and FCP have the potential to enhance the effective bioconversion of lignocellulosic biomass like P. alopecuroides, hence making this material a valuable and promising energy plant.

Nanoengineered cellulosic biohydrogen production via dark fermentation: A novel approach

The insights of nanotechnology for cellulosic biohydrogen production through dark fermentation are reviewed. Lignocellulosic biomass to sugar generation is a complex process and covers the most expensive part of cellulose to sugar production technology. In this context, the impacts of nanomaterial on lignocellulosic biomass to biohydrogen production process have been reviewed. In addition, the feasibility of nanomaterials for implementation in each step of the cellulosic biohydrogen production is discussed for economic viability of the process. Numerous aspects such as possible replacement of chemical pretreatment method using nanostructured materials, use of immobilized enzyme for a fast rate of reaction and its reusability along with long viability of microbial cells and hydrogenase enzyme for improving the productivity are the highlights of this review. It is found that various types of nanostructured materials e.g. metallic nanoparticles (Fe°, Ni, Cu, Au, Pd, Au), metal oxide nanoparticles (Fe₂O₃, F₃O₄, NiCo₂O₄, CuO, NiO, CoO, ZnO), nanocomposites (Si@CoFe₂O₄, Fe₃O₄/alginate) and graphene-based nanomaterials can influence different parameters of the process and therefore may perhaps be utilized for cellulosic biohydrogen production_. The emphasis has been given on the cost issue and synthesis sustainability of nanomaterials for making the biohydrogen technology cost effective. Finally, recent advancements and feasibility of nanomaterials as the potential solution for improved cellulose conversion to the biohydrogen production process have been discussed, and this is likely to assist in developing an efficient, economical and sustainable biohydrogen production technology.

Lignin-first biomass fractionation using a hybrid organosolv - Steam explosion pretreatment technology improves the saccharification and fermentability of spruce biomass

For a transition to a sustainable society, fuels, chemicals, and materials should be produced from renewable resources. Lignocellulosic biomass constitutes an abundant and renewable feedstock; however, its successful application in a biorefinery requires efficient fractionation into its components; cellulose, hemicellulose and lignin. Here, we demonstrate that a newly established hybrid organosolv - steam explosion pretreatment can effectively fractionate spruce biomass to yield pretreated solids with high cellulose (72% w/w) and low lignin (delignification up to 79.4% w/w) content. The cellulose-rich pretreated solids present high saccharification yields (up to 61% w/w) making them ideal for subsequent bioconversion processes. Moreover, under high-gravity conditions (22% w/w) we obtained an ethanol titer of 61.7 g/L, the highest so far reported for spruce biomass. Finally, the obtained high-purity lignin is suitable for various advanced applications. In conclusion, hybrid organosolv pretreatment could offer a closed-loop biorefinery while simultaneously adding value to all biomass components.

Effects of acids pre-treatment on the microbial fermentation process for bioethanol production from microalgae

BACKGROUND

Microalgae are one of the promising feedstock that consists of high carbohydrate content which can be converted into bioethanol. Pre-treatment is one of the critical steps required to release fermentable sugars to be used in the microbial fermentation process. In this study, the reducing sugar concentration of Chlorella species was investigated by pre-treating the biomass with dilute sulfuric acid and acetic acid at different concentrations 1%, 3%, 5%, 7%, and 9% (v/v).

RESULTS

3,5-Dinitrosalicylic acid (DNS) method, FTIR, and GC-FID were employed to evaluate the reducing sugar concentration, functional groups of alcohol bonds and concentration of bioethanol, respectively. The two-way ANOVA results (p < 0.05) indicated that there was a significant difference in the concentration and type of acids towards bioethanol production. The highest bioethanol yield obtained was 0.28 g ethanol/g microalgae which was found in microalgae sample pre-treated with 5% (v/v) sulfuric acid while 0.23 g ethanol/g microalgal biomass was presented in microalgae sample pre-treated with 5% (v/v) acetic acid.

CONCLUSION

The application of acid pre-treatment on microalgae for bioethanol production will contribute to higher effectiveness and lower energy consumption compared to other pre-treatment methods. The findings from this study are essential for the commercial production of bioethanol from microalgae.

Application of genetic algorithm in modelling and optimization of cellulase production

The aim of this work was to study the application of genetic algorithm (GA) in modelling and optimization of cellulose production by Trichoderma reesei from pea hull. Enzyme activity of cellulase was determined using Filter Paper Activity (FPA) assay. Optimization of process parameters was performed using mathematical (MO) and genetic optimizers to obtain combination of variables for highest possible enzyme activity. GA generated a higher value of cellulase activity (0.353 U/mL) as compared to MO (0.302 U/mL). The values of independent variables in set (GA, MO) were: agitation speed (127, 120 rpm), %H2O2 concentration (10.36, 5.0), cultivation time (112, 91 h). The investigation highlights that GA could be used as a potential optimizer for processes involving waste utilization.