Enzymatic digestibility and pretreatment degradation products of AFEX-treated hardwoods (Populus nigra)

Multifaced application of AFEX-pretreated biomass in producing second-generation biofuels, ruminant animal feed, and value-added bioproducts

Lignocellulosic biomass holds a crucial position in the prospective bio-based economy, serving as a sustainable and renewable source for a variety of bio-based products. These products play a vital role in displacing fossil fuels and contributing to environmental well-being. However, the inherent recalcitrance of biomass poses a significant obstacle to the efficient access of sugar polymers. Consequently, the bioconversion of lignocellulosic biomass into fermentable sugars remains a prominent challenge in biorefinery processes to produce biofuels and biochemicals. In addressing these challenges, extensive efforts have been dedicated to mitigating biomass recalcitrance through diverse pretreatment methods. One noteworthy process is Ammonia Fiber Expansion (AFEX) pretreatment, characterized by its dry-to-dry nature and minimal water usage. The volatile ammonia, acting as a catalyst in the process, is recyclable. AFEX contributes to cleaning biomass ester linkages and facilitating the opening of cell wall structures, enhancing enzyme accessibility and leading to a fivefold increase in sugar conversion compared to untreated biomass. Over the last decade, AFEX has demonstrated substantial success in augmenting the efficiency of biomass conversion processes. This success has unlocked the potential for sustainable and economically viable biorefineries. This paper offers a comprehensive review of studies focusing on the utilization of AFEX-pretreated biomass in the production of second-generation biofuels, ruminant feed, and additional value-added bioproducts like enzymes, lipids, proteins, and mushrooms. It delves into the details of the AFEX pretreatment process at both laboratory and pilot scales, elucidates the mechanism of action, and underscores the role of AFEX in the biorefinery for developing biofuels and bioproducts, and nutritious ruminant animal feed production. While highlighting the strides made, the paper also addresses current challenges in the commercialization of AFEX pretreatment within biorefineries. Furthermore, it outlines critical considerations that must be addressed to overcome these challenges, ensuring the continued progress and widespread adoption of AFEX in advancing sustainable and economically viable bio-based industries.

Optimal Conversion of Organic Wastes to Value-Added Products: Toward a Sustainable Integrated Biorefinery in Denmark

It is crucial to leave behind the traditional linear economy approach. Shifting the paradigm and adopting a circular (bio)economy seems to be the strategy to decouple economic growth from continuous resource extraction. To this end, producing bio-based products that aim to replace a part, if not all, of the fossil-based chemicals and fuels is a promising step. This can be achieved by using multi-product integrated biorefineries that convert organic wastes into chemicals, fuels, and bioenergy to optimize the use and close the materials and energy loops. To further address the development and implementation of organic waste integrated biorefineries, we proposed the open-source organic waste to value-added products (O2V) model and multi-objective optimization tool. O2V aims to provide a quick and straightforward holistic assessment, leading to identifying optimal or near-optimal design, planning, and operational decisions. This model not only prioritizes economic benefits but also takes on board the other pillars of sustainability. The proposed tool is built on a comprehensive superstructure of processing alternatives that include all stages concerning the conversion of organic waste to value-added products. Furthermore, it has been framed and formulated in a “plug-and-play” format, where, when required, the user only needs to add new process data to the structured information database. This database integrates data on (i) new processes (e.g., different conversion technologies), (ii) feedstocks (e.g., composition), and (iii) products (e.g., prices), among others. Due to Denmark’s high availability of organic waste, implementing a second-generation integrated biorefinery in Denmark has been chosen as a realistic showcase. The application of O2V efficiently led to the identification of trade-offs between the different sustainability angles. Thus, it made it possible to determine early-stage decisions regarding product portfolio, optimal production process, and related planning and operational decisions. Henceforth, it has been demonstrated that applying O2V aids in shifting the fossil to bio-based production, thereby contributing to the switch toward a circular bioeconomy.

A New Method to Overcome Carboxyamide Formation During AFEX Pretreatment of Lignocellulosic Biomass

Lignin-carbohydrate complexes (LCCs) in the plant cell wall are responsible for providing resistance against biomass-degrading enzymes produced by microorganisms. Four major types of lignin-carbohydrate bonds are reported in the literature, namely, benzyl ethers, benzyl esters, phenyl glycosides, and acetyl ester linkages. Ester’s linkages in the plant cell wall are labile to alkaline pretreatments, such as ammonia fiber expansion (AFEX), which uses liquid or gaseous ammonia to cleave those linkages in the plant cell wall and reduce biomass recalcitrance. Two competing reactions, notably hydrolysis and ammonolysis, take place during AFEX pretreatment process, producing different aliphatic and aromatic acids, as well as their amide counterparts. AFEX pretreated grasses and agricultural residues are known to increase conversion of biomass to sugars by four- to five-fold when subjected to commercial enzyme hydrolysis, yielding a sustainable feedstock for producing biofuels, biomaterials, and animal feed. Animal feed trials on dairy cows have demonstrated a 27% increase in milk production when compared to a control feedstock. However, the presence of carboxamides in feedstocks could promote neurotoxicity in animals if consumed beyond a certain concentration. Thus, there is the need to overcome regulatory hurdles associated with commercializing AFEX pretreated biomass as animal feed in the United States. This manuscript demonstrates a modified pretreatment for increasing the digestibility of industrial byproducts such as Brewer’s spent grains (BSG) and high-fiber meal (HFM) produced from BSG and dry distillers grains with soluble (DDGS), while avoiding the production of carboxamides. The three industrial byproducts were first treated with calculated amounts of alkali such as NaOH, Ca(OH)2, or KOH followed by AFEX pretreatment. We found that 4% alkali was able to de-esterify BSG and DDGS more efficiently than using 2% alkali at both 10 and 20% solids loading. AFEX pretreatment of de-esterified BSG, HFM, and DDGS produced twofold higher glucan conversion than respective untreated biomass. This new discovery can help overcome potential regulatory issues associated with the presence of carboxamides in ammonia-pretreated animal feeds and is expected to benefit several farmers around the world.

Recent Developments and Current Status of Commercial Production of Fuel Ethanol

Ethanol produced from various biobased sources (bioethanol) has been gaining high attention lately due to its potential to cut down net emissions of carbon dioxide while reducing burgeoning world dependence on fossil fuels. Global ethanol production has increased more than six-fold from 18 billion liters at the turn of the century to 110 billion liters in 2019, only to fall to 98.6 billion liters in 2020 due to the pandemic. Sugar cane and corn have been used as the major feedstocks for ethanol production. Lignocellulosic biomass has recently been considered as another potential feedstock due to its non-food competing status and its availability in very large quantities. This paper reviews recent developments and current status of commercial production of ethanol across the world with a focus on the technological aspects. The review includes the ethanol production processes used for each type of feedstock, both currently practiced at commercial scale and still under developments, and current production trends in various regions and countries in the world.

Acid Hydrotropic Fractionation of Lignocelluloses for Sustainable Biorefinery: Advantages, Opportunities, and Research Needs

This Minireview provides a comprehensive discussion on the potential of using acid hydrotropes for sustainably fractionating lignocelluloses for biorefinery applications. Acid hydrotropes are a class of acids that have hydrotrope properties toward lignin, which helps to solubilize lignin in aqueous systems. With the capability of cleaving ether and ester bonds and even lignin-carbohydrate complex (LCC) linkages, these acid hydrotropes can therefore isolate lignin embedded in the plant biomass cell wall and subsequently solubilize the isolated lignin in aqueous systems. Performances of two acid hydrotropes, that is, an aromatic sulfonic acid [p-toluenesulfonic acid (p-TsOH)] and a dicarboxylic acid [maleic acid (MA)], in terms of delignification and dissolution of hemicelluloses, and reducing lignin condensation, were evaluated and compared. The advantages of lignin esterification by MA for producing cellulosic sugars through enzymatic hydrolysis and lignin-containing cellulose nanofibrils (LCNFs) through mechanical fibrillation from the fractionated water insoluble solids (WIS), and for obtaining less condensed lignin with light color, were demonstrated. The excellent enzymatic digestibility of maleic acid hydrotropic fractionation WISs was also demonstrated by comparing with WISs from other fractionation processes. The recyclability and reusability of acid hydrotropes were also reviewed. Finally, perspectives on future research needs to address key technical issues for commercialization were also provided.

Pretreatment of lignocellulosic biomass: A review on recent advances

Depleting fossil reserves and growing energy needs have raised the demand for an alternative and clean energy source. The use of ubiquitously available lignocellulosic biomass for developing economic and eco-friendly large scale biorefinery applications has provided the much-needed impetus in this regard. The pretreatment process is a vital step for biomass transformation into added value products such as sugars, biofuels, etc. Different pretreatment approaches are employed to overcome the recalcitrance of lignocellulosic biomass and expedite its disintegration into individual components- cellulose, hemicellulose, and lignin. The conventional pretreatment methods lack sustainability and practicability for industrial scale up. The review encompasses the recent advances in selective physical and chemical pretreatment approaches such as milling, extrusion, microwave, ammonia fibre explosion, eutectic solvents etc. The study will allow a deeper understanding of these pretreatment processes and increase their scope as sustainable technologies for developing modern biorefineries.

Scale-up strategy for yeast single cell oil production for Rhodotorula mucilagenosa IIPL32 from corn cob derived pentosan

This work was aimed to strategically scale-up the yeast lipid production process using Reynolds number as a standard rheological parameter from 50 mL to 50 L scale. Oleaginous yeast Rhodotorula mucilaginosa IIPL32 was cultivated in xylose rich corncob hydrolysate. The fermentation process for growth and maturation was operated in fed-batch with two different C/N ratios of 40 and 60. The hydrodynamic parameters were used to standardize and represent the effect of rheology on the fermentation process. The growth pattern of the yeast was found similar in both shake flask and fermenter with the maximum growth observed at 48 h. The lipid yield increased from 0.4 g/L and 0.5 g/L to 1.3 g/L and 1.83 g/L for 50 mL to 50 L for C/N ratio 40 and 60 respectively. The increase in productivity during the growth phase and lipid accumulation during the maturation phase showed that the scale-up strategy was successful.

Recent advances on ammonia-based pretreatments of lignocellulosic biomass

Ammonia-based pretreatments have been extensively studied in the last decade as one of the leading pretreatment technologies for lignocellulose biorefining. Here, we discuss the key features and compare performances of several leading ammonia-based pretreatments (e.g., soaking in aqueous ammonia or SAA, ammonia recycled percolation or ARP, ammonia fiber expansion or AFEX, and extractive ammonia or EA). We provide detailed insight into the distinct physicochemical mechanisms employed during ammonia-based pretreatments and its impact on downstream bioprocesses (e.g., enzymatic saccharification); such as modification of cellulose crystallinity, lignin/hemicellulose structure, and other ultrastructural changes such as cell wall porosity. Lastly, a brief overview of process technoeconomics and environmental impacts are discussed, along with recommendations for future areas of research on ammonia-based pretreatments.

Investigation of a thermostable multi-domain xylanase-glucuronoyl esterase enzyme from Caldicellulosiruptor kristjanssonii incorporating multiple carbohydrate-binding modules

BACKGROUND

Efficient degradation of lignocellulosic biomass has become a major bottleneck in industrial processes which attempt to use biomass as a carbon source for the production of biofuels and materials. To make the most effective use of the source material, both the hemicellulosic as well as cellulosic parts of the biomass should be targeted, and as such both hemicellulases and cellulases are important enzymes in biorefinery processes. Using thermostable versions of these enzymes can also prove beneficial in biomass degradation, as they can be expected to act faster than mesophilic enzymes and the process can also be improved by lower viscosities at higher temperatures, as well as prevent the introduction of microbial contamination.

RESULTS

This study presents the investigation of the thermostable, dual-function xylanase-glucuronoyl esterase enzyme CkXyn10C-GE15A from the hyperthermophilic bacterium Caldicellulosiruptor kristjanssonii. Biochemical characterization of the enzyme was performed, including assays for establishing the melting points for the different protein domains, activity assays for the two catalytic domains, as well as binding assays for the multiple carbohydrate-binding domains present in CkXyn10C-GE15A. Although the enzyme domains are naturally linked together, when added separately to biomass, the expected boosting of the xylanase action was not seen. This lack of intramolecular synergy might suggest, together with previous data, that increased xylose release is not the main beneficial trait given by glucuronoyl esterases.

CONCLUSIONS

Due to its thermostability, CkXyn10C-GE15A is a promising candidate for industrial processes, with both catalytic domains exhibiting melting temperatures over 70 °C. Of particular interest is the glucuronoyl esterase domain, as it represents the first studied thermostable enzyme displaying this activity.

Lignocellulosic Biomass: Understanding Recalcitrance and Predicting Hydrolysis

Lignocellulosic biomass (LB) is an abundant and renewable resource from plants mainly composed of polysaccharides (cellulose and hemicelluloses) and an aromatic polymer (lignin). LB has a high potential as an alternative to fossil resources to produce second-generation biofuels and biosourced chemicals and materials without compromising global food security. One of the major limitations to LB valorisation is its recalcitrance to enzymatic hydrolysis caused by the heterogeneous multi-scale structure of plant cell walls. Factors affecting LB recalcitrance are strongly interconnected and difficult to dissociate. They can be divided into structural factors (cellulose specific surface area, cellulose crystallinity, degree of polymerization, pore size and volume) and chemical factors (composition and content in lignin, hemicelluloses, acetyl groups). Goal of this review is to propose an up-to-date survey of the relative impact of chemical and structural factors on biomass recalcitrance and of the most advanced techniques to evaluate these factors. Also, recent spectral and water-related measurements accurately predicting hydrolysis are presented. Overall, combination of relevant factors and specific measurements gathering simultaneously structural and chemical information should help to develop robust and efficient LB conversion processes into bioproducts.

Lignin-Enzyme Interactions in the Hydrolysis of Lignocellulosic Biomass

Lignin is central to overcoming recalcitrance in the enzyme hydrolysis of lignocellulose. While the term implies a physical barrier in the cell wall structure, there are also important biochemical components that direct interactions between lignin and the hydrolytic enzymes that attack cellulose in plant cell walls. Progress toward a deeper understanding of the lignin synthesis pathway - and the consistency between a range of observations over the past 40 years in the very extensive literature on cellulose hydrolysis - is resulting in advances in reducing a major impediment to cellulose conversion: the cost of enzymes. This review addresses lignin and its role in the hydrolysis of hardwood and other lignocellulosic residues.

Lignin-carbohydrate complexes: properties, applications, analyses, and methods of extraction: a review

The complexity of lignin and hemicellulose segmentation has been known since the middle of the ninetieth century. Studies confirmed that all lignin units in coniferous species and 47-66% of lignin moieties in deciduous species are bound to hemicelluloses or cellulose molecules in lignin-carbohydrate complexes (LCC). Different types and proportions of lignin and polysaccharides present in biomass lead to the formation of LCC with a great variety of compositions and structures. The nature and amount of LCC linkages and lignin substructures affect the efficiency of pulping, hydrolysis, and digestibility of biomass. This review paper discusses the structures, compositions, and properties of LCC present in biomass and in the products obtained via pretreating biomass. Methods for extracting, fractionating, and analyzing LCC of biomass, pulp, and spent pulping liquors are critically reviewed. The main perspectives and challenges associated with these technologies are extensively discussed. LCC could be extracted from biomass following varied methods, among which dimethyl sulfoxide or dioxane (Björkman's) and acetic acid (LCC-AcOH) processes are the most widely applied. The oxidation and methylation treatments of LCC materials elucidate the locations and frequency of binding sites of hemicelluloses to lignin. The two-dimensional nuclear magnetic resonance analysis allows the identification of the structure and the quantity of lignin-carbohydrate bonds involved in LCC. LCC application seems promising in medicine due to its high anti-HIV, anti-herpes, and anti-microbial activity. In addition, LCC was successfully employed as a precursor for the preparation of spherical biocarriers.

Selective precipitation and characterization of lignin-carbohydrate complexes (LCCs) from Eucalyptus

Six types of lignin-carbohydrate complex (LCC) fractions were isolated from Eucalyptus. The acidic dioxane treatment applied significantly improved the yield of LCCs. The extraction conditions had a limited impact on the LCC structures and linkages. Characterization of the lignin-carbohydrate complex (LCC) structures and linkages promises to offer insight on plant cell wall chemistry. In this case, Eucalyptus LCCs were extracted by aqueous dioxane, and then precipitated sequentially by 70% ethanol, 100% ethanol, and acidic water (pH = 2). The composition and structure of the six LCC fractions obtained by selective precipitation were investigated by sugar analysis, molecular weight determination, and 2D HSQC NMR. It was found that the acidic (0.05-M HCl) dioxane treatment significantly improved the yield of LCCs (66.4% based on Klason lignin), which was higher than the neutral aqueous dioxane extraction, and the extraction condition showed limited impact on the LCC structures and linkages. In the fractionation process, the low-molecular-weight LCCs containing a high content of carbohydrates (60.3-63.2%) were first precipitated by 70% ethanol from the extractable solution. The phenyl glycoside (PhGlc) bonds (13.0-17.0 per 100Ar) and highly acetylated xylans were observed in the fractions recovered by the precipitation with 100% ethanol. On the other hand, such xylan-rich LCCs exhibited the highest frequency of β-O-4 linkages. The benzyl ether (BE) bonds were only detected in the fractions obtained by acidic water precipitation.

Physico-Chemical Conversion of Lignocellulose: Inhibitor Effects and Detoxification Strategies: A Mini Review

A pretreatment of lignocellulosic biomass to produce biofuels, polymers, and other chemicals plays a vital role in the biochemical conversion process toward disrupting the closely associated structures of the cellulose-hemicellulose-lignin molecules. Various pretreatment steps alter the chemical/physical structure of lignocellulosic materials by solubilizing hemicellulose and/or lignin, decreasing the particle sizes of substrate and the crystalline portions of cellulose, and increasing the surface area of biomass. These modifications enhance the hydrolysis of cellulose by increasing accessibilities of acids or enzymes onto the surface of cellulose. However, lignocellulose-derived byproducts, which can inhibit and/or deactivate enzyme and microbial biocatalysts, are formed, including furan derivatives, lignin-derived phenolics, and carboxylic acids. These generation of compounds during pretreatment with inhibitory effects can lead to negative effects on subsequent steps in sugar flat-form processes. A number of physico-chemical pretreatment methods such as steam explosion, ammonia fiber explosion (AFEX), and liquid hot water (LHW) have been suggested and developed for minimizing formation of inhibitory compounds and alleviating their effects on ethanol production processes. This work reviews the physico-chemical pretreatment methods used for various biomass sources, formation of lignocellulose-derived inhibitors, and their contributions to enzymatic hydrolysis and microbial activities. Furthermore, we provide an overview of the current strategies to alleviate inhibitory compounds present in the hydrolysates or slurries.

Mushroom Crop in Agricultural Waste Cleanup

The environment is a life support system and it significantly influences the living organisms and their genes. Decomposers and microorganisms play a major role in maintaining the sustainability of the environment by converting toxic products into a mineralized form and maintaining the nutrient cycle. It is estimated that 62% of the 22 million tons of surplus rice straw is burnt in the field every year and contributes significantly to the black carbon emission from biomass burning. This alarming situation calls for a sustainable approach in crop residue management. Mushroom cultivation offers one such approach. Mushroom farms can act as disposal sites of agriculture residue and at the same time produce quality protein to meet the increasing protein demand. The macro fungi can play a major role in synthesis of non-toxic metal nano-particles from their salts and degradation of diverse crop residues through various enzymes present in them such as ligninases, cellulases, and laccases. Their role also extends to degrading the pesticides and persisting chemicals. This chapter explains the recent advances in mushrooms for effective crop residue utilization.

Formulation of an optimized synergistic enzyme cocktail, HoloMix, for effective degradation of various pre-treated hardwoods

In this study, two selected hardwoods were subjected to sodium chlorite delignification and steam explosion, and the impact of pre-treatments on synergistic enzymatic saccharification evaluated. A cellulolytic core-set, CelMix, and a xylanolytic core-set, XynMix, optimised for glucose and xylose release, respectively, were used to formulate HoloMix cocktail for optimal saccharification of various pre-treated hardwoods. For delignified biomass, the optimized HoloMix consisted of 75%:25% protein dosage, CelMix: XynMix, while for untreated and steam exploded biomass the HoloMix consisted of 93.75%:6.25% protein dosage. Saccharification by HoloMix (27.5mgprotein/gbiomass) for 24h achieved 70-100% sugar yields. Pre-treatment of the hardwoods (especially those with a higher proportion of lignin) with a laccase, improved saccharification by HoloMix. This study provided insights into enzymatic hydrolysis of various pre-treated hardwood substrates and showed the same lignocellulolytic cocktail comparable to/if not better than commercial enzyme preparations can be used to efficiently hydrolyse different hardwood species.

Biorefining of Lignocellulosic Feedstock by a Modified Ammonia Fiber Expansion Pretreatment and Enzymatic Hydrolysis for Production of Fermentable Sugars

Wheat straw was pretreated and afterwards enzymatically hydrolyzed using a modified ammonia fiber expansion (AFEX) process under different reaction conditions to produce fermentable sugars. Instead of liquid ammonia, aqueous ammonia (25 % w/v) was used to test its influence on the sugar concentration and yield of the sugars. It is shown that a protein extraction after the pretreatment can distinctly improve the result obtained for the enzymatic hydrolysis. This modified AFEX process using aqueous ammonia represents a simpler and less expensive variant of the AFEX process usually described in literature. Thus, the described process can be used for the primary refining of lignocellulosic feedstocks in the sense of a roadmap for biorefinery.

Necessity of enzymatic hydrolysis for production and functionalization of nanocelluloses

Nanocellulose (NC) from cellulosic biomass has recently gained attention owing to their biodegradable nature, low density, high mechanical properties, economic value and renewability. They still suffer, however, some drawbacks. The challenges are the exploration of raw materials, scaling, recovery of chemicals utilized for the production or functionalization and most important is toxic behavior that hinders them from implementing in medical/pharmaceutical field. This review emphasizes the structural behavior of cellulosic biomass and biological barriers for enzyme interactions, which are pertinent to understand the enzymatic hydrolysis of cellulose for the production of NCs. Additionally, the enzymatic catalysis for the modification of solid and NC is discussed. The utility of various classes of enzymes for introducing desired functional groups on the surface of NC has been further examined. Thereafter, a green mechanistic approach is applied for understanding at molecular level.

Assessment of bacterial and fungal (hemi)cellulose-degrading enzymes in saccharification of ammonia fibre expansion-pretreated Arundo donax

This study reports enzymatic hydrolysis of the biomass of the giant reed (Arundo donax L.) after ammonia fibre expansion (AFEX) pretreatment. In particular, the capacity of the arabinofuranosidase from the fungus Pleurotus ostreatus recombinantly expressed in Pichia pastoris rPoAbf, its evolved mutant rPoAbf F435Y/Y446F and the endo-cellulase from Streptomyces sp. G12 CelStrep recombinantly expressed in Escherichia coli to enhance the hydrolysis of AFEX-treated A. donax was investigated, using the corn stover as reference feedstock. The investigated enzymes were assayed using a mixture of purified cellulases (CBHI, CBHII, EGI and βG), endoxylanases (LX3, LX4) and accessory hemicellulases (LarbF and LβX) as reference enzyme mixture and substituting EGI with rCelStrep and LarbF with rPoAbf or rPoAbf F435Y/Y446F. The use of rPoAbf F435Y/Y446F in the substitution of LarbF led to improvements in sugar conversion, giving a glucan, xylan and arabinan conversion after 72 h of around 62, 63 and 80 %, respectively, similar or higher than those (44, 66 and 55 %) achieved by 72 h hydrolysis with commercial enzymes Novozymes Cellic®, Ctec3 and Htec3. The enzymes rPoAbf, rPoAbf F435Y/Y446F and rCelStrep were also investigated for their effect on hydrolysis of AFEX-pretreated A. donax by addition to commercial enzyme mixture Novozymes Cellic®, Ctec3 and Htec3, and it was shown that the addition of rPoAbf and its evolved mutant rPoAbf F435Y/Y446F enhanced both xylan and arabinan conversions, which achieved 80 % after 6 days of saccharification with rPoAbf F435Y/Y446F.

Insights into plant cell wall structure, architecture, and integrity using glycome profiling of native and AFEXTM-pre-treated biomass

Cell walls, which constitute the bulk of plant biomass, vary considerably in their structure, composition, and architecture. Studies on plant cell walls can be conducted on both native and pre-treated plant biomass samples, allowing an enhanced understanding of these structural and compositional variations. Here glycome profiling was employed to determine the relative abundance of matrix polysaccharides in several phylogenetically distinct native and pre-treated plant biomasses. Eight distinct biomass types belonging to four different subgroups (i.e. monocot grasses, woody dicots, herbaceous dicots, and softwoods) were subjected to various regimes of AFEX™ (ammonia fiber expansion) pre-treatment [AFEX is a trademark of MBI, Lansing (http://www.mbi.org]. This approach allowed detailed analysis of close to 200 cell wall glycan epitopes and their relative extractability using a high-throughput platform. In general, irrespective of the phylogenetic origin, AFEX™ pre-treatment appeared to cause loosening and improved accessibility of various xylan epitope subclasses in most plant biomass materials studied. For most biomass types analysed, such loosening was also evident for other major non-cellulosic components including subclasses of pectin and xyloglucan epitopes. The studies also demonstrate that AFEX™ pre-treatment significantly reduced cell wall recalcitrance among diverse phylogenies (except softwoods) by inducing structural modifications to polysaccharides that were not detectable by conventional gross composition analyses. It was found that monitoring changes in cell wall glycan compositions and their relative extractability for untreated and pre-treated plant biomass can provide an improved understanding of variations in structure and composition of plant cell walls and delineate the role(s) of matrix polysaccharides in cell wall recalcitrance.

Production of cellulase enzyme by Trichoderma reesei Cefl9 and its application in the production of bio-ethanol

The present study aimed at the production of cellulase enzyme from the cellulolytic fungi Trichoderma reesei CEF19 and subsequent application of the cellulase for the fermentation of ethanol. For the same, the cellulolytic fungi, Trichoderma reesei CEF19 was isolated and was allowed to produce cellulase enzyme using optimized conditions. The cellulase enzyme was extracted and purified with the help of ammonium sulphate precipitation, dialysis followed by ion exchange chromatography with DEAE-Sephadex column. The purified cellulase enzyme was characterized using SDS-PAGE analysis. The saccharification of the cellulosic substrates was done using the cellulase enzyme. The fermentation of saccharified cellulosic substrates into ethanol was carried out using Saccharomyces cerevisiae. From the results obtained, rice straw was found to be the better source for the ethanol production when compared to the other substrates.

Reactors for High Solid Loading Pretreatment of Lignocellulosic Biomass

The review summarized the types, the geometry, and the design principle of pretreatment reactors at high solid loading of lignocellulose material. Among the reactors used, the explosion reactors and the helical stirring reactors are to be considered as the practical form for high solids loading pretreatment operation; the comminution reactors and the extruder reactors are difficult to be used as an independent unit, but possible to be used in the combined form with other types of reactors. The principles of the pretreatment reactor design at high solid loading were discussed and several basic principles for the design were proposed. This review provided useful information for choosing the reactor types and designing the geometry of pretreatment operation at the high solids loading.

By-products resulting from lignocellulose pretreatment and their inhibitory effect on fermentations for (bio)chemicals and fuels

Lignocellulose might become an important feedstock for the future development of the biobased economy. Although up to 75 % of the lignocellulose dry weight consists of sugar, it is present in a polymerized state and cannot be used directly in most fermentation processes for the production of chemicals and fuels. Several methods have been developed to depolymerize the sugars present in lignocellulose, making the sugars available for fermentation. In this review, we describe five different pretreatment methods and their effect on the sugar and non-sugar fraction of lignocellulose. For several pretreatment methods and different types of lignocellulosic biomass, an overview is given of by-products formed. Most unwanted by-products present after pretreatment are dehydrated sugar monomers (furans), degraded lignin polymers (phenols) and small organic acids. Qualitative and quantitative effects of these by-products on fermentation processes have been studied. We conclude this review by giving an overview of techniques and methods to decrease inhibitory effects of unwanted by-products.

Current challenges in commercially producing biofuels from lignocellulosic biomass

Biofuels that are produced from biobased materials are a good alternative to petroleum based fuels. They offer several benefits to society and the environment. Producing second generation biofuels is even more challenging than producing first generation biofuels due the complexity of the biomass and issues related to producing, harvesting, and transporting less dense biomass to centralized biorefineries. In addition to this logistic challenge, other challenges with respect to processing steps in converting biomass to liquid transportation fuel like pretreatment, hydrolysis, microbial fermentation, and fuel separation still exist and are discussed in this review. The possible coproducts that could be produced in the biorefinery and their importance to reduce the processing cost of biofuel are discussed. About $1 billion was spent in the year 2012 by the government agencies in US to meet the mandate to replace 30% existing liquid transportation fuels by 2022 which is 36 billion gallons/year. Other countries in the world have set their own targets to replace petroleum fuel by biofuels. Because of the challenges listed in this review and lack of government policies to create the demand for biofuels, it may take more time for the lignocellulosic biofuels to hit the market place than previously projected.

Hydrogen peroxide presoaking of bamboo prior to AFEX pretreatment and impact on enzymatic conversion to fermentable sugars

Bamboo is a fast growing plant found worldwide that has high potential as an energy crop. This project evaluated the effectiveness of AFEX pretreatment for converting moso bamboo (Phyllostachys heterocycla var. pubescens) to fermentable sugars, both with and without pre-soaking in hydrogen peroxide. Pretreatment conditions including temperature, water loading, residence time, ammonia loading, and hydrogen peroxide loadings were varied to maximize hydrolysis yields. The optimal conditions for AFEX were 150°C, 0.8 or 2.0 (w/w) water loading, 10-30 min residence time, and 2.0-5.0 (w/w) ammonia loading. The optimal conditions for H-AFEX were same AFEX conditions with 0.7-1.9 (w/w) 30% (wt) hydrogen peroxide solutions loading. Using 15 FPU/g glucan cellulase and under optimal conditions, AFEX pretreatment achieved a theoretical sugars yield of 64.8-72.7% and addition of hydrogen peroxide presoaking increased the yield to 83.4-92.1%. It is about 5-fold and 7-fold increase in sugars yield for AFEX-treated and H-AFEX-treated bamboo respectively.

Performance of AFEX™ pretreated rice straw as source of fermentable sugars: the influence of particle size

BACKGROUND

It is widely believed that reducing the lignocellulosic biomass particle size would improve the biomass digestibility by increasing the total surface area and eliminating mass and heat transfer limitation during hydrolysis reactions. However, past studies demonstrate that particle size influences biomass digestibility to a limited extent. Thus, this paper studies the effect of particle size (milled: 2 mm, 5 mm, cut: 2 cm and 5 cm) on rice straw conversion. Two different Ammonia Fiber Expansion (AFEX) pretreament conditions, AFEX C1 (low severity) and AFEX C2 (high severity) are used to pretreat the rice straw (named as AC1RS and AC2RS substrates respectively) at different particle size.

RESULTS

Hydrolysis of AC1RS substrates showed declining sugar conversion trends as the size of milled and cut substrates increased. Hydrolysis of AC2RS substrates demonstrated opposite conversion trends between milled and cut substrates. Increasing the glucan loading to 6% during hydrolysis reduced the sugar conversions significantly in most of AC1RS and AC2RS except for AC1RS-2 mm and AC2RS-5 cm. Both AC1RS-2 mm and AC2RS-5 cm indicated gradual decreasing trends in sugar conversion at high glucan loading. Analysis of SEM imaging for URS and AFEX pretreated rice straw also indicated qualitative agreement with the experimental data of hydrolysis. The largest particle size, AC2RS-5 cm produced the highest sugar yield of 486.12 g/kg of rice straw during hydrolysis at 6% glucan loading equivalent to 76.0% of total theoretical maximum sugar yield, with an average conversion of 85.9% from total glucan and xylan. In contrast, AC1RS-5 cm gave the lowest sugar yield with only 107.6 g/kg of rice straw, about 16.8% of total theoretical maximum sugar yield, and equivalent to one-quarter of AC2RS-5 cm sugar yield.

CONCLUSIONS

The larger cut rice straw particles (5 cm) significantly demonstrated higher sugar conversion when compared to small particles during enzymatic hydrolysis when treated using high severity AFEX conditions. Analysis of SEM imaging positively supported the interpretation of the experimental hydrolysis trend and kinetic data.

An economic and ecological perspective of ethanol production from renewable agro waste: a review

Agro-industrial wastes are generated during the industrial processing of agricultural products. These wastes are generated in large amounts throughout the year, and are the most abundant renewable resources on earth. Due to the large availability and composition rich in compounds that could be used in other processes, there is a great interest on the reuse of these wastes, both from economical and environmental view points. The economic aspect is based on the fact that such wastes may be used as low-cost raw materials for the production of other value-added compounds, with the expectancy of reducing the production costs. The environmental concern is because most of the agro-industrial wastes contain phenolic compounds and/or other compounds of toxic potential; which may cause deterioration of the environment when the waste is discharged to the nature. Although the production of bioethanol offers many benefits, more research is needed in the aspects like feedstock preparation, fermentation technology modification, etc., to make bioethanol more economically viable.

Cellulose solvent- and organic solvent-based lignocellulose fractionation enabled efficient sugar release from a variety of lignocellulosic feedstocks

Developing feedstock-independent biomass pretreatment would be vital to second generation biorefineries that would fully utilize diverse non-food lignocellulosic biomass resources, decrease transportation costs of low energy density feedstock, and conserve natural biodiversity. Cellulose solvent- and organic solvent-based lignocellulose fractionation (COSLIF) was applied to a variety of feedstocks, including Miscanthus, poplar, their mixture, bagasse, wheat straw, and rice straw. Although non-pretreated biomass samples exhibited a large variation in enzymatic digestibility, the COSLIF-pretreated biomass samples exhibited similar high enzymatic glucan digestibilities and fast hydrolysis rates. Glucan digestibilities of most pretreated feedstocks were ∼93% at five filter paper units per gram of glucan. The overall glucose and xylose yields for the Miscanthus:poplar mixture at a weight ratio of 1:2 were 93% and 85%, respectively. These results suggested that COSLIF could be regarded as a feedstock-independent pretreatment suitable for processing diverse feedstocks by adjusting pretreatment residence time only.

Pseudo-lignin formation and its impact on enzymatic hydrolysis

Pseudo-lignin, which can be broadly defined as aromatic material that yields a positive Klason lignin value and is not derived from native lignin, has been recently reported to form during the dilute acid pretreatment of poplar holocellulose. To investigate the chemistry of pseudo-lignin formation, GPC, FT-IR and 13C NMR were utilized to characterize pseudo-lignin extracted from dilute-acid pretreated α-cellulose and holocellulose. The results showed that pseudo-lignin consisting of carbonyl, carboxylic, aromatic and aliphatic structures was produced from dilute acid pretreated cellulose and hemicellulose. Pseudo-lignin extracted from holocellulose pretreated at different conditions had similar molecular weights (Mn∼1000 g/mol; Mw∼5000 g/mol) and structural features (carbonyl, carboxylic, aromatic and methoxy structures). These characterizations have provided the pseudo-lignin formation mechanisms during pretreatment. The presence and structure of pseudo-lignin is important since pseudo-lignin decreases the enzymatic conversion.

Chromatographic detection of lignin-carbohydrate complexes in annual plants by derivatization in ionic liquid

The opportunity for detecting the presence and the amount of lignin-carbohydrate complexes (LCCs) in renewable feedstocks is a major issue for the complete utilization of biomass. Indeed, LCCs are known to shield cellulose from enzymatic hydrolysis, reducing the efficiency of the digestion processes needed for the production of biobased products. This study is focused on the chromatographic characterization of lignocellulose from agricultural residues (rice husk, wheat straw) and herbaceous energy crops ( Arundo donax , Miscanthus sinesis ) and their fractionation products (hemicellulose, cellulose, and lignin). Exploiting alternative chemical derivatizations on the aforementioned samples, it was possible to discern the connectivity among the various lignocellulosic components. The complete acetylation and benzoylation of the milled native substrates in ionic liquid media, and the systematic comparison between their GPC-UV chromatograms collected at different wavelengths has revealed itself as a straightforward technique in the detection of LCCs. This novel approach proved an extensive connectivity between the lignin and the hemicellulosic for all the analyzed specimens, whereas the cellulosic fraction was conceived as a substantially unbound moiety, accounting for the sample composition at higher molecular weights. Moreover, the collected lignin fractions were extensively characterized by means of (31)P NMR and 2D-HSQC techniques.

Impact of syringaldehyde on the growth of Clostridium beijerinckii NCIMB 8052 and butanol production

While lignocellulosic biomass excels as a cheap, renewable resource for biofuel production, it does present some challenges such as generation of microbial inhibitory compounds. The mode of selective inhibition of acetone–butanol–ethanol (ABE) production (as opposed to cell growth) by syringaldehyde on Clostridium beijerinckii NCIMB 8052 was examined. C. beijerinckii 8052 grown in syringaldehyde-supplemented P2 medium had a comparable growth rate (μ = 0.34) at acidogenic growth phase to that of C. beijerinckii 8052 grown in control P2 medium (μ = 0.30). The addition of syringaldehyde into P2 medium inhibited solvent production by C. beijerinckii 8052 and increased butyric and acetic acid accumulation in the fermentation broth. Analysis of coenzyme A transferase (CoAT) using cell-free extracts of C. beijerinckii 8052 showed decreased expression and activity in the presence of syringaldehyde. These results indicate that C. beijerinckii 8052 CoAT is negatively affected by syringaldehyde and thus, hampers the ability of the microorganism to metabolize butyric and acetic acid for ABE production as evidenced by the accumulation of butyric and acetic acid in the fermentation broth.

Surface and ultrastructural characterization of raw and pretreated switchgrass

The US Department of Energy-funded Biomass Refining CAFI (Consortium for Applied Fundamentals and Innovation) project has developed leading pretreatment technologies for application to switchgrass and has evaluated their effectiveness in recovering sugars from the coupled operations of pretreatment and enzymatic hydrolysis. Key chemical and physical characteristics have been determined for pretreated switchgrass samples. Several analytical microscopy approaches utilizing instruments in the Biomass Surface Characterization Laboratory (BSCL) at the National Renewable Energy Laboratory (NREL) have been applied to untreated and CAFI-pretreated switchgrass samples. The results of this work have shown that each of the CAFI pretreatment approaches on switchgrass result in different structural impacts at the plant tissue, cellular, and cell wall levels. Some of these structural changes can be related to changes in chemical composition upon pretreatment. There are also apparently different structural mechanisms that are responsible for achieving the highest enzymatic hydrolysis sugar yields.

Comparative study on enzymatic digestibility of switchgrass varieties and harvests processed by leading pretreatment technologies

Feedstock quality of switchgrass for biofuel production depends on many factors such as morphological types, geographic origins, maturity, environmental and cultivation parameters, and storage. We report variability in compositions and enzymatic digestion efficiencies for three cultivars of switchgrass (Alamo, Dacotah and Shawnee), grown and harvested at different locations and seasons. Saccharification yields of switchgrass processed by different pretreatment technologies (AFEX, dilute sulfuric acid, liquid hot water, lime, and soaking in aqueous ammonia) are compared in regards to switchgrass genotypes and harvest seasons. Despite its higher cellulose content per dry mass, Dacotah switchgrass harvested after wintering consistently gave a lower saccharification yield than the other two varieties harvested in the fall. The recalcitrance of upland cultivars and over-wintered switchgrass may require more severe pretreatment conditions. We discuss the key features of different pretreatment technologies and differences in switchgrass cultivars and harvest seasons on hydrolysis performance for the applied pretreatment methods.

Using FTIR to predict saccharification from enzymatic hydrolysis of alkali-pretreated biomasses

Fourier transform infrared, attenuated total reflectance (FTIR-ATR) spectroscopy combined with partial least squares (PLS) regression accurately predicted 72-h glucose and xylose conversions (g sugars/100 g potential sugars) and yields (g sugars/100 g dry solids) from cellulase-mediated hydrolysis of alkali-pretreated lignocellulose. Six plant biomasses that represent a variety of potential biofuel feedstocks--two switchgrass cultivars, big bluestem grass, a low-impact, high-diversity mixture of 32 species of prairie biomasses, mixed hardwood, and corn stover--were subjected to four levels of low-temperature NaOH pretreatment to produce 24 samples with a wide range of potential digestibility. PLS models were constructed by correlating FTIR spectra of pretreated samples to measured values of gluose and xylose conversions and yields. Variable selection, based on 90% confidence intervals of regression-coefficient matrices, improved the predictive ability of the models, while simplifying them considerably. Final models predicted sugar conversions with coefficient of determination for cross-validation (Q(2)) values of 0.90 for glucose and 0.89 for xylose, and sugar yields with Q(2) values of 0.92 for glucose and 0.91 for xylose. The sugar-yield models are noteworthy for their ability to predict enzymatic saccharification per mass dry solids without a priori knowledge of the composition of the solids. All peaks retained in the final regression coefficient matrices were previously assigned to chemical bonds and functional groups in lignocellulose, demonstrating that the models were based on real chemical information. This study demonstrates that FTIR spectroscopy combined with PLS regression can be used to rapidly estimate sugar conversions and yields from enzymatic hydrolysis of pretreated plant biomass.

Reactions of dehydrodiferulates with ammonia

Lignocellulosic materials derived from forages and agricultural residues are potential sustainable resources for production of bioethanol or other liquid biofuels. However, the natural recalcitrance of such materials to enzymatic hydrolysis is a major obstacle in their efficient utilization. In grasses, much of the recalcitrance is associated with ferulate cross-linking in the cell wall, i.e., with polysaccharide-polysaccharide cross-linking that results from ferulate dehydrodimerization or with lignin-polysaccharide cross-linking that results from the incorporation of (polysaccharide-bound) ferulates or diferulates into lignin, mainly via free-radical coupling reactions. Many pretreatment methods have been developed to address recalcitrance, with ammonia pretreatments in general, and the AFEX (Ammonia Fiber Expansion) process in particular, among the more promising methods. In order to understand the polysaccharide liberating reactions involved in the cleavage of diferulate cell wall cross-links during AFEX pretreatment, reaction products from five esters modeling the major diferulates in grass cell walls treated under AFEX-like conditions were separated and characterized by NMR and HR-MS. Results from this study indicate that, beyond the anticipated amide products, a range of degradation products derive from an array of cleavage and substitution reactions, and reveal various pathways for incorporating ammonia-based nitrogen into biomass.

Microwave-assisted pretreatment of woody biomass with ammonium molybdate activated by H2O2

Pretreatments for enzymatic saccharification are crucial for the establishment of lignocellulosic biorefineries. In this study, we focused on ammonium ions and peroxometal complexes as potential delignifying agents. We first examined the pretreatment of beech wood with nine different ammonium salts in the presence of H(2)O(2). Significant pretreatment effects were found only for ammonium molybdate, which is transformed to a peroxometal complex on reacting with H(2)O(2). Since microwave sensitizer effects are expected for (peroxo)molybdate, beech wood was pretreated using external heating and microwave irradiation. As a result, a maximum sugar yield of 59.5% was obtained by microwave irradiation at 140°C for 30 min, while external heating in an autoclave gave a sugar yield of 41.8%. We also found that an ammonium ion is the key counterion accelerating the pretreatment with molybdate. These results highlight the powerful selective delignifying capability of the H(2)O(2)-activated ammonium molybdate system energized by microwave radiation.

Pretreatment of corn stover and hybrid poplar by sodium hydroxide and hydrogen peroxide

Sodium hydroxide and its derivatives are used as pulping reagents, wherein the spent NaOH is recovered in salt form and reused. In this study, use of low concentration NaOH (1-5%) in pretreatment of corn stover and hybrid poplar was investigated. It was done with the understanding that NaOH can be recovered. One of the main objectives in this study is to explore the potential of H(2)O(2) with NaOH for pretreatment of high lignin substrate such as hybrid poplar. Pretreatment time has not been optimized in this study but held constant at 24 h. Corn stover, after treatment with NaOH under moderate conditions, attains near quantitative glucan digestibility. On the other hand, hybrid poplar requires treatment at higher temperature and NaOH concentration to attain acceptable level of digestibility. Supplementation of hydrogen peroxide in the pretreatment significantly raises delignification and digestibility of hybrid poplar. It was also helpful in retaining the carbohydrates in the treated solids. Retention of hemicellulose after pretreatment provides a significant economic benefit as it eliminates the need for detoxifying hemicellulose sugars. As the residual xylan remaining after pretreatment is an impediment to enzymatic digestion of glucan, supplementation of xylanase has significantly increased the digestibility of glucan as well as xylan of the treated hybrid poplar.

Rapid optimization of enzyme mixtures for deconstruction of diverse pretreatment/biomass feedstock combinations

BACKGROUND

Enzymes for plant cell wall deconstruction are a major cost in the production of ethanol from lignocellulosic biomass. The goal of this research was to develop optimized synthetic mixtures of enzymes for multiple pretreatment/substrate combinations using our high-throughput biomass digestion platform, GENPLAT, which combines robotic liquid handling, statistical experimental design and automated Glc and Xyl assays. Proportions of six core fungal enzymes (CBH1, CBH2, EG1, β-glucosidase, a GH10 endo-β1,4-xylanase, and β-xylosidase) were optimized at a fixed enzyme loading of 15 mg/g glucan for release of Glc and Xyl from all combinations of five biomass feedstocks (corn stover, switchgrass, Miscanthus, dried distillers' grains plus solubles [DDGS] and poplar) subjected to three alkaline pretreatments (AFEX, dilute base [0.25% NaOH] and alkaline peroxide [AP]). A 16-component mixture comprising the core set plus 10 accessory enzymes was optimized for three pretreatment/substrate combinations. Results were compared to the performance of two commercial enzymes (Accellerase 1000 and Spezyme CP) at the same protein loadings.

RESULTS

When analyzed with GENPLAT, corn stover gave the highest yields of Glc with commercial enzymes and with the core set with all pretreatments, whereas corn stover, switchgrass and Miscanthus gave comparable Xyl yields. With commercial enzymes and with the core set, yields of Glc and Xyl were highest for grass stovers pretreated by AP compared to AFEX or dilute base. Corn stover, switchgrass and DDGS pretreated with AFEX and digested with the core set required a higher proportion of endo-β1,4-xylanase (EX3) and a lower proportion of endo-β1,4-glucanase (EG1) compared to the same materials pretreated with dilute base or AP. An optimized enzyme mixture containing 16 components (by addition of α-glucuronidase, a GH11 endoxylanase [EX2], Cel5A, Cel61A, Cip1, Cip2, β-mannanase, amyloglucosidase, α-arabinosidase, and Cel12A to the core set) was determined for AFEX-pretreated corn stover, DDGS, and AP-pretreated corn stover. The optimized mixture for AP-corn stover contained more exo-β1,4-glucanase (i.e., the sum of CBH1 + CBH2) and less endo-β1,4-glucanase (EG1 + Cel5A) than the optimal mixture for AFEX-corn stover. Amyloglucosidase and β-mannanase were the two most important enzymes for release of Glc from DDGS but were not required (i.e., 0% optimum) for corn stover subjected to AP or AFEX. As a function of enzyme loading over the range 0 to 30 mg/g glucan, Glc release from AP-corn stover reached a plateau of 60-70% Glc yield at a lower enzyme loading (5-10 mg/g glucan) than AFEX-corn stover. Accellerase 1000 was superior to Spezyme CP, the core set or the 16-component mixture for Glc yield at 12 h, but the 16-component set was as effective as the commercial enzyme mixtures at 48 h.

CONCLUSION

The results in this paper demonstrate that GENPLAT can be used to rapidly produce enzyme cocktails for specific pretreatment/biomass combinations. Pretreatment conditions and feedstock source both influence the Glc and Xyl yields as well as optimal enzyme proportions. It is predicted that it will be possible to improve synthetic enzyme mixtures further by the addition of additional accessory enzymes.

Automated assay for screening the enzymatic release of reducing sugars from micronized biomass

Background

To reduce the production cost of bioethanol obtained from fermentation of the sugars provided by degradation of lignocellulosic biomass (i.e., second generation bioethanol), it is necessary to screen for new enzymes endowed with more efficient biomass degrading properties. This demands the set-up of high-throughput screening methods. Several methods have been devised all using microplates in the industrial SBS format. Although this size reduction and standardization has greatly improved the screening process, the published methods comprise one or more manual steps that seriously decrease throughput. Therefore, we worked to devise a screening method devoid of any manual steps.

Results

We describe a fully automated assay for measuring the amount of reducing sugars released by biomass-degrading enzymes from wheat-straw and spruce. The method comprises two independent and automated steps. The first step is the making of "substrate plates". It consists of filling 96-well microplates with slurry suspensions of micronized substrate which are then stored frozen until use. The second step is an enzymatic activity assay. After thawing, the substrate plates are supplemented by the robot with cell-wall degrading enzymes where necessary, and the whole process from addition of enzymes to quantification of released sugars is autonomously performed by the robot. We describe how critical parameters (amount of substrate, amount of enzyme, incubation duration and temperature) were selected to fit with our specific use. The ability of this automated small-scale assay to discriminate among different enzymatic activities was validated using a set of commercial enzymes.

Conclusions

Using an automatic microplate sealer solved three main problems generally encountered during the set-up of methods for measuring the sugar-releasing activity of plant cell wall-degrading enzymes: throughput, automation, and evaporation losses. In its present set-up, the robot can autonomously process 120 triplicate wheat-straw samples per day. This throughput can be doubled if the incubation time is reduced from 24 h to 4 h (for initial rates measurements, for instance). This method can potentially be used with any insoluble substrate that is micronizable. A video illustrating the method can be seen at the following URL: http://www.youtube.com/watch?v=NFg6TxjuMWU