Multi-step approach to add value to corncob: Production of biomass-degrading enzymes, lignin and fermentable sugars

Exploring industrial lignocellulosic waste: Sources, types, and potential as high-value molecules

Lignocellulosic biomass has a promising role in a circular bioeconomy and may be used to produce valuable molecules for green chemistry. Lignocellulosic biomass, such as food waste, agricultural waste, wood, paper or cardboard, corresponded to 15.7% of all waste produced in Europe in 2020, and has a high potential as a secondary raw material for industrial processes. This review first presents industrial lignocellulosic waste sources, in terms of their composition, quantities and types of lignocellulosic residues. Secondly, the possible high added-value chemicals obtained from transformation of lignocellulosic waste are detailed, as well as their potential for applications in the food industry, biomedical, energy or chemistry sectors, including as sources of polyphenols, enzymes, bioplastic precursors or biofuels. In a third part, various available transformation treatments, such as physical treatments with ultrasound or heat, chemical treatments with acids or bases, and biological treatments with enzymes or microorganisms, are presented. The last part discusses the perspectives of the use of lignocellulosic waste and the fact that decreasing the cost of transformation is one of the major issues for improving the use of lignocellulosic biomass in a circular economy and green chemistry approach, since it is currently often more expensive than petroleum-based counterparts.

Integral multi-valorization of agro-industrial wastes: A review

Agriculture and industries related to the agriculture sector generate a large amount of waste each year. These wastes are usually burned or dumped, causing damage to the environment, the economy and society. Due to their composition, they have great potential for obtaining high value-added products in biorefineries. This fact, added to the growing demand for energy and chemicals from fossil resources, is driving the interest of the scientific community in them. Biorefinery processes are hardly profitable when applied individually, so a better alternative is to develop integrated multi-feedstock and multi-product biorefinery schemes using all biomass fractions in a zero-waste approach. However, for industrial scale application, extensive research, scale-up studies, and techno-economic and environmental feasibility analyses are needed. This review compiles information on integrated multi-biorefinery processes from agro-industrial wastes to shed light on the path towards sustainable development and circular bioeconomy.

Inhibition of enzyme hydrolysis of cellulose by phenols from hydrothermally pretreated sugarcane straw

Relatively few studies have addressed the characterization of sugarcane straw (SCS) for production of fermentable sugars through enzyme hydrolysis. Straw is a major co-product of the sugarcane harvest in Brazil that has potential to sustainably increase cellulosic feedstocks in Brazil by 50%. Pretreatment of 10% w/v straw with liquid hot water (LHW) at 180 °C for 50 min (severity, S_o, of 4.05), solubilizes hemicellulose, preserves glucan, and generates 4.49 g/L soluble phenolic compounds in the resulting liquid. Extracts from washing pretreated solids with excess hot water followed by acetone resulted in 1.10 and 0.83 g/L phenolics, respectively. Acetone-derived extracts were more inhibitory and decreased glucose yield for enzyme hydrolysis of Solka Floc (a lignin-free cellulose) by 42%. In comparison, pretreated straw washed with hot water or acetone was readily hydrolyzed to 92% and 97% by cellulase enzyme. Hydrothermally treated SCS has the potential to provide a valuable and added source of fermentable sugars suitable for bioprocessing into biofuels and bioproducts when cellulase enzyme inhibitors are removed after pretreatment.

Thermophilic biohydrogen production strategy using agro industrial wastes: Current update, challenges, and sustainable solutions

Continuously increasing wastes management issues and the high demand of fuels to fulfill the current societal requirements is not satisfactory. In addition, severe environmental pollution caused by generated wastes and the massive consumption of fossil fuels are the main causes of global warming. In this scenario, production of hydrogen from organic wastes is a potential and one of the most feasible alternatives to resolve these issues. However, sensitivity of H₂ production at higher temperature and lack of potential substrates are the main issues which are strongly associated with such kinds of biofuels. Therefore, the present review is targeted towards the evaluation and enhancement of thermophilic biohydrogen production using organic, cellulosic wastes as promising bioresources. This review discusses about the current status, development in the area of thermophilic biohydrogen production wherein organic wastes as key substrate are being employed. The combinations of suitable organic and cellulose rich substrates, thermo-tolerant microbes, high enzymes stability may support to enhance the biohydrogen production, significantly. Further, various factors which may significantly contribute to enhance biohydrogen production have been discussed thoroughly in reference to the thermophilic biohydrogen production technology. Additionally, existing obstacles such as unfavorable thermophilic biohydrogen pathways, inefficiency of thermophilic microbiomes, genetic modifications, enzymes stability have been discussed in context to the possible limitations of thermophilic biohydrogen production strategy. Structural and functional microbiome analysis, fermentation pathway modifications via genetic engineering and the application of nanotechnology to enhance the thermophilic biohydrogen production have been discussed as the future prospective.

Integrated hydrothermal and deep eutectic solvent-mediated fractionation of lignocellulosic biocomponents for enhanced accessibility and efficient conversion in anaerobic digestion

Effective fractionation of lignocellulosic biocomponents of lignocellulosic biomass can increase its utilization in anaerobic digestion for high yield biomethane production. A hydrothermal process was optimized and integrated with a deep eutectic solvent (DES) pretreatment to preferentially fractionate hemicellulose, cellulose, and lignin in rice straw. The optimized hydrothermal process resulted in 96% hemicellulose solubilization at moderately low combined pretreatment severity (log S = 2.26), allowing increased hemicellulosic sugar recovery with minimal formation of inhibitory byproducts. Subsequent DES pretreatment resulted in highly bioaccessible cellulosic pulp, removing 81.3% of lignin that can be recovered and converted into value-added products. Anaerobic digestion of hemicellulosic fraction and cellulosic pulp using a microbial methanogenic consortium seed acclimatized to the lignocellulosic inhibitors resulted in a 33.4% higher yield of methane (467.84 mL g^-1 VS_initial) than with anaerobic digester sludge seed. This integrated approach can facilitate and maximize the targeted utilization of different biocomponents through sustainable biorefining.

Challenges of Biomass Utilization for Bioenergy in a Climate Change Scenario

The climate changes expected for the next decades will expose plants to increasing occurrences of combined abiotic stresses, including drought, higher temperatures, and elevated CO2 atmospheric concentrations. These abiotic stresses have significant consequences on photosynthesis and other plants' physiological processes and can lead to tolerance mechanisms that impact metabolism dynamics and limit plant productivity. Furthermore, due to the high carbohydrate content on the cell wall, plants represent a an essential source of lignocellulosic biomass for biofuels production. Thus, it is necessary to estimate their potential as feedstock for renewable energy production in future climate conditions since the synthesis of cell wall components seems to be affected by abiotic stresses. This review provides a brief overview of plant responses and the tolerance mechanisms applied in climate change scenarios that could impact its use as lignocellulosic biomass for bioenergy purposes. Important steps of biofuel production, which might influence the effects of climate change, besides biomass pretreatments and enzymatic biochemical conversions, are also discussed. We believe that this study may improve our understanding of the plant biological adaptations to combined abiotic stress and assist in the decision-making for selecting key agronomic crops that can be efficiently adapted to climate changes and applied in bioenergy production.

Hydrothermal pretreatment of lignocellulosic biomass for hemicellulose recovery

The hemicellulosic fraction recovery is of interest for integrated processes in biorefineries, considering the possibility of high economic value products produced from their structural compounds of this polysaccharide. However, to perform an efficient recovery, it is necessary to use biomass fractionation techniques, and hydrothermal pretreatment is highlighted as a valuable technique in the hemicellulose recovery by applying high temperatures and pressure, causing dissolution of the structure. Considering the possibility of this pretreatment technique for current approaches to hemicellulose recovery, this article aimed to explore the relevance of hydrothermal pretreatment techniques (sub and supercritical water) as a strategy for recovering the hemicellulosic fraction from lignocellulosic biomass. Discussions about potential products to be generated, current market profile, and perspectives and challenges of applying the technique are also addressed.

Investigation of the effects of pretreatment on the elemental composition of ash derived from selected Nigerian lignocellulosic biomass

Lignocellulosic biomass is an important source of renewable energy and a potential replacement for fossil fuels. In this work, the X-ray fluorescence (XRF) method was used to analyze the elemental composition of raw and pretreated lignocellulosic biomass of cassava peels, corn cobs, rice husks, sugarcane bagasse, yam peels, and mixtures of cassava peels and yam peels, corn cobs and rice husks and all five biomass samples combined. The influence of particle size on elemental properties was investigated by screening the selected biomass into two size fractions, of an average of 300 and 435 µm, respectively. The total concentration of Mg, Al, Si, P, S, Cl, Ca, Ti, Cr, Mn, Fe, Co, Cu, Zn, Sn, Ni, Br, Mo, Ba, Hg, and Pb were determined for each of the biomass samples before and after the different pretreatments adopted in this study. From the results of the analysis, there was a significant reduction in the concentration of calcium in all the analyzed biomass after the alkaline pretreatment with rice husks biomass having the lowest concentration of 66 ppm after the alkaline pretreatment. The sulfur content of the acid pretreated biomass increased considerably which is likely due to the sulfuric acid used for the acid pretreatment. The fact that a mixture of biomass feedstock affects the properties of the biomass after pretreatment was validated in the mixed biomass of cassava peels and yam peels biomass as an example. The concentration of Mg in the mixed biomass was 1441 ppm but was 200 ppm and 353 ppm in individual cassava peels and yam peels respectively. The results of this study demonstrated that pretreated mixtures of biomass have varied elemental compositions, which could be an important factor affecting downstream processes, especially if a hybrid feedstock is used in a large-scale application.

Subcritical water pretreatment for agave bagasse fractionation from tequila production and enzymatic susceptibility

This work focuses on the effect of subcritical water pretreatment conditions on agave bagasse chemical composition, biomass fractionation, and enzymatic hydrolysis obtained from the different tequila production processes. The pretreatment was carried out in a batch pressurized reactor within an isothermal regime. The operational conditions for subcritical water pretreatment were (150-190 °C) and (10-50 min). The best operational conditions were selected, based on the increased cellulose content (>50%) in the pretreated solid phase. The conditions for 190 °C for 50 and 30 min of pretreated agave bagasse solids were chosen for enzymatic hydrolysis susceptibility (15 FPU/g of the substrate). The maximum conversion yield (cellulose to glucose) during enzymatic hydrolysis achieved was up to 61.62% (5.86 g/L) in industrial bagasse at 72 h and initial saccharification rate was 0.34 g/(L*h) at 12 h. This study indicates that the agave bagasse is a promising raw material in the development of second-generation biorefineries.

Valorization of Agri-Food Wastes as Sustainable Eco-Materials for Wastewater Treatment: Current State and New Perspectives

The paper addresses environmental protection by valorizing an important agri-food waste category, namely fruit and vegetables with focusing on the main characteristics regarding consumption, waste quantities, and ways for valorizing these materials. Thus, vast research was undertaken in order to emphasize the main commodities and their potential application as adsorbents for organic and inorganic pollutants. The main methods or treatment techniques applied for the valorization of eco-materials as adsorbents were presented and the principal efficiency results were indicated. The advantages and disadvantages of using these eco-materials as adsorbents in wastewater treatment were revealed and future recommendations were established. According to the international statistics, the most purchased and consumed five commodities were studied regarding waste generations as potential conversion into eco-materials with an adsorbent role for water pollutants. Thus, the performances for adsorbents based on fruit wastes (such as citrus, banana, apples, grapes, mango) and vegetable wastes (such as potatoes, tomatoes, cabbage, carrots, cauliflower, and/or broccoli) were studied and highlighted in this research.

Effect of Severity Factor on the Subcritical Water and Enzymatic Hydrolysis of Coconut Husk for Reducing Sugar Production

Preventing the further degradation of monomeric or oligomeric sugar into by-product during biomass conversion is one of the challenges for fermentable sugar production. In this study, the performance of subcritical water (SCW) and enzymatic hydrolysis of coconut husk toward reducing sugar production was investigated using a severity factor (SF) approach. Furthermore, the optimal condition of SCW was optimized using response surface methodology (RSM), where the composition changes of lignocellulose and sugar yield as responses. From the results, at low SF of SCW, sugar yield escalated as increasing SF value. In the enzymatic hydrolysis process, the effect of SCW pressure is a significant factor enhancing sugar yield. A maximum total sugar yield was attained on the mild SF condition of 2.86. From this work, it was known that the SF approach is sufficient parameter to evaluate the SCW and enzymatic hydrolysis of coconut husk. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

An integrated biorefinery process for adding values to corncob in co-production of xylooligosaccharides and glucose starting from pretreatment with gluconic acid

Increasing attention has been paid to the production of high value-added products from lignocellulosic biomass. This study aims to valorize corncob, utilizing it as feedstock for a multi-biorefinery framework, using gluconic acid in the pretreatment. In attempts to maximize yield of xylooligosaccharides, corncob was first subjected to hydrolysis by gluconic acid using response surface methodology, from which the maximum xylooligosaccharides yield of 56.2% was achieved using 0.6 mol/L gluconic acid at 154 °C for 47 min. Results indicated that gluconic acid was an effective solvent for xylooligosaccharides production: a total of 180 g of xylooligosaccharides was obtained from 1 kg corncob as a result of hydrolysis. Moreover, 86.3% conversion of cellulose was achieved from enzymatic hydrolysis of gluconic acid-treated corncob at 10% solids loading. This study presents a strategy for valorizing corncob using it to produce xylooligosaccharides and glucose, which should pave the way for valorizing other agriculture wastes.

Green sustainable process to revalorize purple corn cobs within a biorefinery frame: Co-production of bioactive extracts

Purple corn (Zea mays L.) is used for the preparation of traditional drinks and desserts, generating great quantities of residues. The scarce information about purple corn cob (PCC) is encouraging an interest in exploring its potential as a valuable source of bioactive compounds with benefits for human health. In this study, a green method based on hydrothermal processing was used for the simultaneous extraction of oligosaccharides and phenolic compounds from PCC. For this purpose, the effects of three factors (time, temperature and pH) on the oligosaccharide content (OSC), total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), as well as on the antioxidant activity measured with three different methods (DPPH, ABTS and FRAP) were evaluated. The bioactive extract obtained under optimal conditions presented a high content of bioactive compounds exhibiting a notable antioxidant capacity and moderate inhibitory activities towards xanthine oxidase. This extract was also structurally characterized by FTIR, HPAEC-DAD, MALDI-TOF-MS and TGA, and the HPLC-ESI-MS analysis led to the tentative identification of 15 antioxidant phenolic compounds. Thus, this research demonstrated that this residue from the food industry has a high potential for obtaining several bioactive compounds that can be utilized as multi-functional ingredients in the food and pharmaceutical industries.

Engineering aspects of hydrothermal pretreatment: From batch to continuous operation, scale-up and pilot reactor under biorefinery concept

Different pretreatments strategies have been developed over the years mainly to enhance enzymatic cellulose degradation. In the new biorefinery era, a more holistic view on pretreatment is required to secure optimal use of the whole biomass. Hydrothermal pretreatment technology is regarded as very promising for lignocellulose biomass fractionation biorefinery and to be implemented at the industrial scale for biorefineries of second generation and circular bioeconomy, since it does not require no chemical inputs other than liquid water or steam and heat. This review focuses on the fundamentals of hydrothermal pretreatment, structure changes of biomass during this pretreatment, multiproduct strategies in terms of biorefinery, reactor technology and engineering aspects from batch to continuous operation. The treatise includes a case study of hydrothermal biomass pretreatment at pilot plant scale and integrated process design.

Comparative study on different pretreatment on enzymatic hydrolysis of corncob residues

Under the situation of increasingly severe challenge of energy consumption, it is of great importance to make full use of bioresources such as forestry and agricultural residues. Herein, the corncob residues generated after processing corncob were enzymatically hydrolyzed to yield fermentable sugars. To overcome the recalcitrance of corncob residues, three kinds of pretreatment methods, i.e., sulfonation, PFI refining, and wet grinding, were applied; their effects on enzymatic hydrolysis and main characteristics of corncob residues substrate were investigated. The results showed that the enzymatic digestibility of the substrate was greatly enhanced by employing each method. The wet grinding exhibited obvious advantages, e.g., the conversion yield of cellulose to glucose and glucose concentration reached 96.7% and 32.2 g/L after 59 h of enzymatic hydrolysis, respectively. The improvement in enzymatic hydrolysis was mainly attributed to the altered characteristics of the substrate such as swelling ability, specific surface area, and particle size and distribution.