Ethanol production from horticultural waste treated by a modified organosolv method

An overview of biomass conversion: exploring new opportunities

Recycling biomass is indispensable these days not only because fossil energy sources are gradually depleted, but also because pollution of the environment, caused by the increasing use of energy, must be reduced. This article intends to overview the results of plant biomass processing methods that are currently in use. Our aim was also to review published methods that are not currently in use. It is intended to explore the possibilities of new methods and enzymes to be used in biomass recycling. The results of this overview are perplexing in almost every area. Advances have been made in the pre-treatment of biomass and in the diversity and applications of the enzymes utilized. Based on molecular modeling, very little progress has been made in the modification of existing enzymes for altered function and adaptation for the environmental conditions during the processing of biomass. There are hardly any publications in which molecular modeling techniques are used to improve enzyme function and to adapt enzymes to various environmental conditions. Our view is that using modern computational, biochemical, and biotechnological methods would enable the purposeful design of enzymes that are more efficient and suitable for biomass processing.

Study on the Sequential Combination of Bioethanol and Biogas Production from Corn Straw

The objective of this study was to obtain two types of fuels, i.e., bioethanol and biogas, in a sequential combination of biochemical processes from lignocellulosic biomass (corn straw). Waste from the agricultural sector containing lignocellulose structures was used to obtain bioethanol, while the post-fermentation (cellulose stillage) residue obtained from ethanol fermentation was a raw material for the production of high-power biogas in the methane fermentation process. The studies on obtaining ethanol from lignocellulosic substrate were based on the simultaneous saccharification and fermentation (SSF) method, which is a simultaneous hydrolysis of enzymatic cellulose and fermentation of the obtained sugars. Saccharomyces cerevisiae (D-2) in the form of yeast cream was used for bioethanol production. The yeast strain D-2 originated from the collection of the Institute of Agricultural and Food Biotechnology. Volatile compounds identified in the distillates were measured using gas chromatography with flame ionization detector (GC-FID). CH₄ and CO₂ contained in the biogas were analyzed using a gas chromatograph in isothermal conditions, equipped with thermal conductivity detector (katharometer) with incandescent fiber. Our results show that simultaneous saccharification and fermentation enables production of bioethanol from agricultural residues with management of cellulose stillage in the methane fermentation process.

Effects of Organosolv Pretreatment Using Temperature-Controlled Bench-Scale Ball Milling on Enzymatic Saccharification of Miscanthus × giganteus

The effect of organosolv pretreatment was investigated using a 30 L bench-scale ball mill reactor that was capable of simultaneously performing physical and chemical pretreatment. Various reaction conditions were tried in order to discover the optimal conditions for the minimal cellulose loss and enhanced enzymatic digestibility of Miscanthus × giganteus (MG), with conditions varying from room temperature to 170 °C for reaction temperature, from 30 to 120 min of reaction time, from 30% to 60% ethanol concentration, and a liquid/solid ratio (L/S) of 10–20 under non-catalyst conditions. The pretreatment effects were evaluated by chemical compositional analysis, enzymatic digestibility test and X-ray diffraction of the treated samples. The pretreatment conditions for the highest glucan digestibility yield were determined as 170 °C, reaction time of 90 min, ethanol concentration of 40% and L/S = 10. With these pretreatment conditions, the XMG (xylan + mannan + galactan) fractionation yield and delignification were 84.4% and 53.2%, respectively. The glucan digestibility of treated MG after the aforementioned pretreatment conditions was 86.0% with 15 filter paper units (FPU) of cellulase (Cellic® CTec2) per g-glucan enzyme loading.

Biotransformation of lignocellulosic materials into value-added products-A review

In the past decade, with the key biotechnological advancements, lignocellulosic materials have gained a particular importance. In serious consideration of global economic, environmental and energy issues, research scientists have been re-directing their interests in (re)-valorizing naturally occurring lignocellulosic-based materials. In this context, lignin-modifying enzymes (LMEs) have gained considerable attention in numerous industrial and biotechnological processes. However, their lower catalytic efficiencies and operational stabilities limit their practical and multipurpose applications in various sectors. Therefore, to expand the range of natural industrial biocatalysts e.g. LMEs, significant progress related to the enzyme biotechnology has appeared. Owing to the abundant lignocellulose availability along with LMEs in combination with the scientific advances in the biotechnological era, solid-phase biocatalysts can be economically tailored on a large scale. This review article outlines first briefly on the lignocellulose materials as a potential source for biotransformation into value-added products including composites, fine chemicals, nutraceutical, delignification, and enzymes. Comprehensive information is also given on the purification and characterization of LMEs to present their potential for the industrial and biotechnological sector.

Recent updates on different methods of pretreatment of lignocellulosic feedstocks: a review

Lignocellulosic feedstock materials are the most abundant renewable bioresource material available on earth. It is primarily composed of cellulose, hemicellulose, and lignin, which are strongly associated with each other. Pretreatment processes are mainly involved in effective separation of these complex interlinked fractions and increase the accessibility of each individual component, thereby becoming an essential step in a broad range of applications particularly for biomass valorization. However, a major hurdle is the removal of sturdy and rugged lignin component which is highly resistant to solubilization and is also a major inhibitor for hydrolysis of cellulose and hemicellulose. Moreover, other factors such as lignin content, crystalline, and rigid nature of cellulose, production of post-pretreatment inhibitory products and size of feed stock particle limit the digestibility of lignocellulosic biomass. This has led to extensive research in the development of various pretreatment processes. The major pretreatment methods include physical, chemical, and biological approaches. The selection of pretreatment process depends exclusively on the application. As compared to the conventional single pretreatment process, integrated processes combining two or more pretreatment techniques is beneficial in reducing the number of process operational steps besides minimizing the production of undesirable inhibitors. However, an extensive research is still required for the development of new and more efficient pretreatment processes for lignocellulosic feedstocks yielding promising results.

Organic solvent pretreatment of lignocellulosic biomass for biofuels and biochemicals: A review

Lignocellulosic biomass represents the largest potential volume and lowest cost for biofuel and biochemical production. Pretreatment is an essential component of biomass conversion process, affecting a majority of downstream processes, including enzymatic hydrolysis, fermentation, and final product separation. Organic solvent pretreatment is recognized as an emerging way ahead because of its inherent advantages, such as the ability to fractionate lignocellulosic biomass into cellulose, lignin, and hemicellulose components with high purity, as well as easy solvent recovery and solvent reuse. Objectives of this review were to update and extend previous works on pretreatment of lignocellulosic biomass for biofuels and biochemicals using organic solvents, especially on ethanol, methanol, ethylene glycol, glycerol, acetic acid, and formic acid. Perspectives and recommendations were given to fully describe implementation of proper organic solvent pretreatment for future research.

Pretreatment and conversion of lignocellulose biomass into valuable chemicals

Lignocellulose biomass can be utilized in many sectors of industry such as energy, chemical, and transportation. However, pretreatment is needed to break down the intricate bonding before converting it into wanted product.

An overview of key pretreatment processes for biological conversion of lignocellulosic biomass to bioethanol

Second-generation bioethanol can be produced from various lignocellulosic biomasses such as wood, agricultural or forest residues. Lignocellulosic biomass is inexpensive, renewable and abundant source for bioethanol production. The conversion of lignocellulosic biomass to bioethanol could be a promising technology though the process has several challenges and limitations such as biomass transport and handling, and efficient pretreatment methods for total delignification of lignocellulosics. Proper pretreatment methods can increase concentrations of fermentable sugars after enzymatic saccharification, thereby improving the efficiency of the whole process. Conversion of glucose as well as xylose to bioethanol needs some new fermentation technologies to make the whole process inexpensive. The main goal of pretreatment is to increase the digestibility of maximum available sugars. Each pretreatment process has a specific effect on the cellulose, hemicellulose and lignin fraction; thus, different pretreatment methods and conditions should be chosen according to the process configuration selected for the subsequent hydrolysis and fermentation steps. The cost of ethanol production from lignocellulosic biomass in current technologies is relatively high. Additionally, low yield still remains as one of the main challenges. This paper reviews the various technologies for maximum conversion of cellulose and hemicelluloses fraction to ethanol, and it point outs several key properties that should be targeted for low cost and maximum yield.

Complete chemical hydrolysis of cellulose into fermentable sugars through ionic liquids and antisolvent pretreatments

This work describes a relatively simple methodology for efficiently deconstructing cellulose into monomeric glucose, which is more easily transformed into a variety of platform molecules for the production of chemicals and fuels. The approach undertaken herein first involves the dissolution of cellulose in an ionic liquid (IL), followed by a second reconstruction step aided by an antisolvent. The regenerated cellulose exhibited strong structural and morphological changes, as revealed by XRD and SEM analyses. These changes dramatically affect the hydrolytic reactivity of cellulose with dilute mineral acids. As a consequence, the glucose yield obtained from the deconstructed-reconstructed cellulose was substantially higher than that achieved through hydrolysis of the starting cellulose. Factors that affect the hydrolysis reaction include the type of cellulose substrate, the type of IL used in pretreatment, and the type of acid used in the hydrolysis step. The best results were obtained by treating cellulose with IL and using phosphotungstic acid (0.067 mol L(-1) ) as a catalyst at 413 K. Under these conditions, the conversion of cellulose was almost complete (>99%), with a glucose yield of 87% after only 5 h of reaction.

Fractionation of hemp hurds by organosolv pretreatment and its effect on production of lignin and sugars

Fractionation of hemp hurds into its three main components, cellulose, hemicellulose, and lignin, was carried out using organosolv pretreatment. The effect of processing parameters, such as temperature, catalyst concentration, reaction time, and methanol (MeOH) concentration, on the dissolution and recovery of hemicellulose and lignin was determined. More than 75% of total hemicellulose and 75% of total lignin was removed in a single step with low amounts of degradation products under the following conditions: 165 °C, 3% H2 SO4 , 20 min reaction time, and 45% MeOH. Enzymatic hydrolysis of the residual pretreated biomass yielded up to 60% of cellulose-to-glucose conversion. The maximum recovery of the main components was obtained at a combined severity factor value of around one. Characterization of pretreated biomass and isolated lignin was carried out with FTIR and 2D (13) C-(1) H correlation HSQC NMR spectroscopy, the latter technique providing detailed structural information about the obtained methanol organosolv lignin (MOSL). Results suggested that xylopyranoside is the major carbohydrate associated with hemp lignin. The chemical properties of MOSL samples in terms of their phenolic group content and antioxidant capacity were also investigated. The results showed that MOSL samples have a high phenolic group content and antioxidant capacity relative to Klason lignin.

Simultaneous fermentation of glucose and xylose to butanol by Clostridium sp. strain BOH3

Cellulose and hemicellulose constitute the major components in sustainable feedstocks which could be used as substrates for biofuel generation. However, following hydrolysis to monomer sugars, the solventogenic Clostridium will preferentially consume glucose due to transcriptional repression of xylose utilization genes. This is one of the major barriers in optimizing lignocellulosic hydrolysates that produce butanol. Unlike studies on existing bacteria, this study demonstrates that newly reported Clostridium sp. strain BOH3 is capable of fermenting 60 g/liter of xylose to 14.9 g/liter butanol, which is similar to the 14.5 g/liter butanol produced from 60 g/liter of glucose. More importantly, strain BOH3 consumes glucose and xylose simultaneously, which is shown by its capability for generating 11.7 g/liter butanol from a horticultural waste cellulosic hydrolysate containing 39.8 g/liter glucose and 20.5 g/liter xylose, as well as producing 11.9 g/liter butanol from another horticultural waste hemicellulosic hydrolysate containing 58.3 g/liter xylose and 5.9 g/liter glucose. The high-xylose-utilization capability of strain BOH3 is attributed to its high xylose-isomerase (0.97 U/mg protein) and xylulokinase (1.16 U/mg protein) activities compared to the low-xylose-utilizing solventogenic strains, such as Clostridium sp. strain G117. Interestingly, strain BOH3 was also found to produce riboflavin at 110.5 mg/liter from xylose and 76.8 mg/liter from glucose during the fermentation process. In summary, Clostridium sp. strain BOH3 is an attractive candidate for application in efficiently converting lignocellulosic hydrolysates to biofuels and other value-added products, such as riboflavin.

Bioethanol production from leafy biomass of mango (Mangifera indica) involving naturally isolated and recombinant enzymes

The present study describes the usage of dried leafy biomass of mango (Mangifera indica) containing 26.3% (w/w) cellulose, 54.4% (w/w) hemicellulose, and 16.9% (w/w) lignin, as a substrate for bioethanol production from Zymomonas mobilis and Candida shehatae. The substrate was subjected to two different pretreatment strategies, namely, wet oxidation and an organosolv process. An ethanol concentration (1.21 g/L) was obtained with Z. mobilis in a shake-flask simultaneous saccharification and fermentation (SSF) trial using 1% (w/v) wet oxidation pretreated mango leaves along with mixed enzymatic consortium of Bacillus subtilis cellulase and recombinant hemicellulase (GH43), whereas C. shehatae gave a slightly higher (8%) ethanol titer of 1.31 g/L. Employing 1% (w/v) organosolv pretreated mango leaves and using Z. mobilis and C. shehatae separately in the SSF, the ethanol titers of 1.33 g/L and 1.52 g/L, respectively, were obtained. The SSF experiments performed with 5% (w/v) organosolv-pretreated substrate along with C. shehatae as fermentative organism gave a significantly enhanced ethanol titer value of 8.11 g/L using the shake flask and 12.33 g/L at the bioreactor level. From the bioreactor, 94.4% (v/v) ethanol was recovered by rotary evaporator with 21% purification efficiency.

Statistical Optimization of Fermentation Process Parameters by Taguchi Orthogonal Array Design for Improved Bioethanol Production

The statistical optimization of different fermentation process parameters in SSF of mixed MAA and organosolv pretreated 1% (w v−1) wild grass, namely, recombinant Clostridium thermocellum hydrolytic enzymes’ volume (GH5 cellulase, GH43 hemicellulase), fermentative microbes’ inoculum volume (Saccharomyces cerevisiae, Candida shehatae), pH, and temperature, was accomplished by Taguchi orthogonal array design. The optimized parameters in 100 mL of fermentation medium were (%, v v−1) as follows: 1.0, recombinant GH5 cellulase (5.7 mg−1, 0.45 mg mL−1); 2.0, recombinant GH43 hemicellulase (3.7 U mg−1, 0.32 mg mL−1); 1.5, S. cerevisiae (3.9 × 108 cells mL−1); 0.25, C. shehatae (2.7 × 107 cells mL−1); pH, 4.3; and temperature, 35∘C. pH with p-value 0.001 was found to be the most significant factor affecting SSF. The ethanol titre obtained in Taguchi optimized shake flask SSF was 2.0 g L−1 implying a 1.3-fold increase as compared to ethanol titre of 1.5 g L−1 in unoptimized shake flask SSF. A 1.5-fold gain in ethanol titre (3.1 g L−1) was obtained with the same substrate concentration in lab scale bioreactor on scaling up the shake flask SSF with Taguchi optimized process parameters.

Naturally occurring phenolic sources: monomers and polymers

Phenolic compounds sourced from agro-based feedstock, viz. cashew nut shell liquid, lignin, tannin, palm oil, and coconut shell tar, have come up as sustainable alternatives to petro-based feedstock. This review explores their utility as green polymer feedstock with citation of ~ 600 references.

An overview of key pretreatment processes employed for bioconversion of lignocellulosic biomass into biofuels and value added products

The hunt for alternative sources of energy generation that are inexpensive, ecofriendly, renewable and can replace fossil fuels is on, owing to the increasing demands of energy. One approach in this direction is the conversion of plant residues into biofuels wherein lignocellulose, which forms the structural framework of plants consisting of cellulose, hemicellulose and lignin, is first broken down and hydrolyzed into simple fermentable sugars, which upon fermentation form biofuels such as ethanol. A major bottleneck is to disarray lignin which is present as a protective covering and makes cellulose and hemicellulose recalcitrant to enzymatic hydrolysis. A number of biomass deconstruction or pretreatment processes (physical, chemical and biological) have been used to break the structural framework of plants and depolymerize lignin. This review surveys and discusses some major pretreatment processes pertaining to the pretreatment of plant biomass, which are used for the production of biofuels and other value added products. The emphasis is given on processes that provide maximum amount of sugars, which are subsequently used for the production of biofuels.

Microbial cocktail for bioconversion of green waste to reducing sugars

Green waste has been identified as a sustainable resource to convert into reducing sugars and subsequently for production of ethanol. In this study, enhancement of reducing sugar production from green waste by the different combination of pure strains was investigated. The best-defined microbial cocktail for high reducing sugars production, consisting of one fungus (Pseudallescheria sp. D42) and three bacteria (Microbacterium sp. F28, Tsukamurella sp. C35, and Bacillus sp. F4), was successfully constructed. The maximum reducing sugars yield by this fungal-bacterial cocktail was 165.2 mg/g-green waste within 24 h, which is approximate 10 times higher than the selected individual microbial strains. Without extraction and purification of specific enzymes, whole-cell-bioconversion by a defined microbial cocktail is proven as a potential alternative process for lignocellulose hydrolysis and reducing sugars production.

Xylitol production from D-xylose and horticultural waste hemicellulosic hydrolysate by a new isolate of Candida athensensis SB18

This paper describes the production of xylitol from d-xylose and horticultural waste hemicellulosic hydrolysate by a new strain of Candida athensensis SB18. Strain SB18 completely consumed 250 and 300 g L(-1) D-xylose and successful converted it to xylitol in the respective yield of 0.83 and 0.87 g g(-1), resulting in 207.8 and 256.5 g L(-1) of xylitol, respectively. The respective volumetric productivity were 1.15 and 0.97 g L(-1) h(-1). Approximately 100.1 g L(-1) of xylitol was obtained from the bioconversion of detoxified horticultural waste hemicellulosic hydrolysate using strain SB18. The yield and productivity were 0.81 g g(-1) xylose and 0.98 g L(-1) h(-1), respectively. Strain C. athensensis SB18 was able to completely utilize glucose, mannose, xylose and partially arabinose. This work demonstrates that stain C. athensensis SB18 is a promising strain for high-titer and high-yield xylitol production and it has great potential in bioconversion of hemicellulosic hydrolysate.