Liquid Hot Water Pretreatment Research Articles

Effects of different pretreatment methods on chemical composition of sugarcane bagasse and enzymatic hydrolysis

Different pretreatment processes, including liquid hot water (LHW) pretreatment, sodium hydroxide (NaOH) pretreatment, and their combinative pretreatments, were conducted to improve the enzymatic digestibility and sugar recovery from sugarcane bagasse (SCB). LHW pretreatment solubilized over 82% of xylan and 42% of lignin, after which the SCB presented the poorest enzymatic digestibility. NaOH pretreatment could remove 78% of lignin and retain most of glucan. For combinative pretreatments, the sequence of two procedures had a significant effect on the chemical composition, substrate characteristic and the subsequent enzymatic hydrolysis process. LHW-NaOH pretreatment could solubilize over 92% of xylan and remove 76% of lignin, and the highest total sugar recovery of 73% was achieved after 72 h enzymatic hydrolysis. While NaOH-LHW pretreatment, which could remove nearly 84% of lignin, but only solubilize 71% of xylan, showed the highest enzymatic digestibility. The pretreatment efficiency was: NaOH-LHW>NaOH>LHW-NaOH>LHW.

Enhancement of enzymatic saccharification of sugarcane bagasse by liquid hot water pretreatment

Lignocellulosic biomass can be utilized to produce promising biofuels. In this study, liquid hot water pretreatments were performed to break the intricate structure of sugarcane bagasse, which resists the enzyme accessibility to cellulose. The effects of temperatures and times on the hemicellulose degradation (including the yields of pentoses and hexoses, the proportion of monomers and oligosaccharides, as well as limited inhibitors) and cellulose enzymatic digestibility were evaluated. The results indicated that the maximum xylose yields (combined 3.85 g xylose and 13.21 g xylo-oligosaccharides per 100 g raw material) in prehydrolyzate liquid were obtained at 180 °C and 30 min. Due to the effective removal of hemicellulose, the maximum glucose yield in enzyme hydrolyzate reached 37.27 g per 100 g raw material, representing 90.13% of glucose in the sugarcane bagasse. The maximal total sugars yield (combined prehydrolyzate and enzymatic hydrolyzate) were 53.65 g based on 100 g raw material.

Assessing the Feasibility of Biofuel Production from Lignocellulosic Banana Waste in Rural Agricultural Communities in Peru and Colombia

Banana cultivation is widespread in tropical and subtropical regions where many rural agricultural communities exist. The banana plant bears fruit once in its life cycle, leaving behind a significant amount of usable agricultural residue. Current practice leaves this residue to decompose in the field spreading diseases and polluting water supplies. We evaluated the technological feasibility of converting lignocellulosic banana residue to ethanol as a localized biofuel production strategy to improve the livelihoods of rural agricultural communities in Peru and Colombia. Liquid hot water (LHW) and steam explosion pretreatment followed by saccharification and fermentation using commercial cellulolytic enzymes and yeast strain were evaluated for three different lignocellulosic residues independently (pseudostems, leaves, and rachis). Stems and rachis, with higher glucan conversion, appeared more promising for biofuel production than leaves (up to 93 and 77 % glucose yields for rachis and pseudostems, respectively). Steam explosion pretreatment allowed higher glucan conversion for stems and leaves, while LHW was better suited for rachis. Pseudostem is the most abundant residue generated with 306,000 tons/year in Uraba Province (Colombia) and 15,000 tons/year in the Chira Valley (Peru) on a dry weight basis. Potential ethanol production in the Chira Valley was estimated in 4.8 and 76.8 ML year−1 in Colombia, processing stems and rachis combined. This study indicated that there is potential for biofuel production using the lignocellulosic banana residue, which could be expanded to other banana growing communities around the world. Process improvements such as increasing solids loading, water recycling, and optimizing fermentation are still required.

The Influence of Hemicellulose and Lignin Removal on the Enzymatic Digestibility from Sugarcane Bagasse

Sugarcane bagasse (SCB) was pretreated with liquid hot water (LHW) and aqueous ammonia (AA), with the objective of investigating the influence of hemicellulose and lignin removal on the enzymatic digestibility and sugar recovery. The experimental results show that LHW and aqueous ammonia have a good performance in terms of hemicellulose dissolution and lignin removal respectively. The biggest xylan recovery of 74.3 % was obtained for LHW pretreatment at 160 °C, 5 % w/v for 20 min with the xylan dissolution of 83.1 %. And the biggest lignin removal of 84.0 % was obtained for aqueous ammonia pretreatment at 160 °C, 10 % w/v for 60 min. Moreover, the aperture and surface area of the sample were enlarged by the liquid hot water, which improves the accessibility of the substrate to the enzyme. The lignin removal caused by aqueous ammonia pretreatment can reduce the absorption of enzyme. In addition, the correlation between the compositional change and the enzymatic digestibility indicates that the removal of hemicellulose was more effective than lignin for destruction of the hemicellulose–lignin–cellulose structure.

Liquid hot water pretreatment of sugarcane bagasse and its comparison with chemical pretreatment methods for the sugar recovery and structural changes

Liquid hot water (LHW), dilute hydrochloric acid (HCl) and dilute sodium hydroxide (NaOH) were applied to sugarcane bagasse (SB). Application of the same analytical methods and material balance approaches facilitated meaningful comparisons of glucose and xylose yields from combined pretreatment and enzymatic hydrolysis. All pretreatments enhanced sugar recovery from pretreatment and subsequent enzymatic hydrolysis substantially compared to untreated sugarcane bagasse. Adding Tween80 in the enzymatic hydrolysis process increased the conversion level of glucan/xylan by 0.3-fold, especially for the low pH pretreatment where more lignin was left in the solids. The total sugar recovery from sugarcane bagasse with the coupled operations of pretreatment and 72h enzymatic digestion reached 71.6% for LHW process, 76.6% for HCl pretreatment and 77.3% for NaOH pretreatment. Different structural changes at the plant tissue, cellular, and cell wall levels might be responsible for the different enzymatic digestibility. Furthermore, a combined LHW and aqueous ammonia pretreatment was proposed to reduce energy input and enhance the sugar recovery.

Fractionation of cellulase and fermentation inhibitors from steam pretreated mixed hardwood

The purpose of liquid hot water and steam pretreatment of wood is to fractionate hemicelluloses, partially solubilize lignin, and enhance enzyme hydrolysis of cellulose. The pretreatment also solubilizes sugar oligomers, lignin-derived phenolic compounds, acetic acid, and furan derivatives that inhibit cellulase enzymes and/or impede fermentation of hydrolysates by yeasts. This work extends knowledge of the relative contribution of identified inhibitors, and the effect of temperature on their release when pretreated materials are washed and filtered with hot water. Dramatic yield improvements occur when polymeric or activated carbon adsorbs and removes inhibitors. By desorbing, recovering, and characterizing adsorbed molecules we found phenolic compounds were strong inhibitors of enzyme hydrolysis and fermentation of concentrated filtrates by Saccharomyces cerevisiae wine yeast NRRL Y-1536 or xylose fermenting yeast 424A (LNH-ST). These data show that separation of inhibitors from pretreatment liquid will be important in achieving maximal enzyme activity and efficient fermentations.

Production of Binderless Particleboard Using Rice Straw Pretreated with Liquid Hot Water

Bonding of agricultural lignocellulosic fibers can be improved by liquid hot water pretreatment. This work applied liquid hot water pretreatment to rice straw. The pretreated rice straw was used to make binderless particleboard. The effect of reaction temperature and residence time on the yield of cellulose pulps, chemical composition of rice straw, and modulus of rupture, internal bond and water absorption of the resulted binderless particleboard were investigated. The results indicated that the yield of cellulose pulps decreased with increasing reaction temperature and residence time, whereas the degradation of hemicellulose increased. The modulus of rupture and internal bond increased while water absorption of panels decreased as pretreatment severity increased. The optimum pretreatment condition, with 18.1 MPa of modulus of rupture, 0.240 MPa internal bond and 63.7% of water absorption of panels, occurred under 170°C temperature and 15 minute residence time.

Combination of liquid hot water pretreatment and wet disk milling to improve the efficiency of the enzymatic hydrolysis of eucalyptus

Combination of liquid hot water pretreatment (LHWP) and wet disk milling (WDM) was investigated in this study to enhance the sugar recovery yield both in prehydrolyzate and enzymatic hydrolyzate. The results show that WDM with LHWP at 180°C for 20min produced maximum xylose and glucose yields of 91.62% and 88.12%, respectively, which are higher than that of dilute acid pretreatment or individual LHWP. Corresponding concentration of fermentation inhibitors such as acetic acid, HMF, and furfural in the prehydrolyzate are about 0.98, 0.07 and 0.78g/L, respectively, which indicated that the detoxification may be not required in the next fermentation step. The acid-insoluble lignin recovery in the insoluble solid resulting from enzymatic hydrolysis, was 25.67/100g raw material, representing 90.7% of acid-insoluble lignin in the eucalyptus biomass. It can be concluded that liquid hot water pretreatment combined with wet disk milling can be successfully applied to eucalyptus.

EFFECT OF STRUCTURAL CHANGES ON ENZYMATIC HYDROLYSIS OF EUCALYPTUS, SWEET SORGHUM BAGASSE, AND SUGARCANE BAGASSE AFTER LIQUID HOT WATER PRETREATMENT

A woody (eucalyptus (Eu)) and two herbaceous materials (sweet sorghum bagasse (SSB) and sugarcane bagasse (SCB)) were used to evaluate the effect of liquid hot water (LHW) pretreatment on enzymatic hydrolysis of various lignocelluloses. The results showed that enzymatic hydrolysis efficiency of pretreated materials was SCB>SSB>Eu at 5% solids loading, while SSB>SCB>Eu was at 10% and 20% solids loadings. This indicated the enzymatic hydrolysis efficiency of SCB could be influenced by solids concentration. The differences in surface morphology, crystalline structure, and functional groups of pretreated samples were also examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. SEM photographs and crystallinity indexes (CrI) showed that the structural compactness was Eu>SSB>SCB for both of untreated and treated materials. FTIR spectra showed that the conspicuousness of physicochemical changes was SCB>SSB>Eu. The differences in enzymatic hydrolysis efficiency of pretreated materials can be ascribed mainly to the structural differences.

Hydrolysis of sweet sorghum bagasse and eucalyptus wood chips with liquid hot water

The chemical composition, hydrolysis products, and kinetics during liquid hot water pretreatment of sweet sorghum bagasse (SSB) and eucalyptus wood chips (EWC) were investigated. Under optimal conditions, a total xylose recovery of 79.6% and 55.6% for SSB and of 74.9% and 84.4% for EWC was achieved after pretreatments in a step-change flow rate reactor (184°C, 20ml/min, 8min, and 10ml/min, 10min) and batch stirred reactor (184°C, 5%w/v, 18min), respectively. More than 90% of the xylose was recovered as oligomers from SSB, independent of the type of reactor employed. The activation energies of xylan decomposition of SSB in the step-change flow rate reactor was 6.5-fold greater than that of EWC in the batch stirred reactor due to accumulation of acidic products. These findings show that sugar recovery is dependent on the reactor configuration for specific substrates.

Deletion of the PHO13 gene in Saccharomyces cerevisiae improves ethanol production from lignocellulosic hydrolysate in the presence of acetic and formic acids, and furfural

For efficient bioethanol production from lignocellulosic biomass by Saccharomyces cerevisiae, it is necessary to improve cellular tolerance to toxic compounds released during the pretreatment of biomass. The gene encoding p-nitrophenylphosphatase, PHO13, was disrupted in a recombinant xylose-fermenting S. cerevisiae strain, which improved ethanol production from xylose in the presence of three major inhibitors, acetic and formic acids, and furfural. In medium supplemented with 30mM acetic acid, the ethanol yield obtained by the ΔPHO13 mutant was 0.45 g-ethanol/g-xylose. Notably, the specific ethanol productivity of the mutant in the presence of 90mM furfural was fourfold higher than that of the control strain. The PHO13-disrupted strain produced ethanol from rice straw hydrolysate obtained by liquid hot-water pretreatment with a greater than fourfold higher xylose consumption rate than the control. Together, our findings demonstrate that PHO13 deletion is a simple, but effective, approach for improving cellulosic bioethanol production by S. cerevisiae.

Lab-scale Technology for Biogas Production from Lignocellulose Wastes

Currently-operating biogas plants are based on the treatment of lignocellulose biomass, which is included in materials such as agriculture and forestry wastes, municipal solid wastes, waste paper, wood and herbaceous energy crops. Lab-scale biogas technology was specially developed for evaluating the anaerobic biodegrability and the specific methane yields of solid organic substrates. This technology falls into two main categories – pretreatment equipments, and fermentation equipments. Pretreatment units use physical principles based on mechanical comminution (ball mills, macerator) orhydrothermal treatment (liquid hot water pretreatment technology). The biochemical methane potential test is used to evaluate the specific methane yields of treated or non-treated organic substrates. This test can be performed both by lab testing units and by lab fermenter.

Enzymatic Saccharification and Ethanol Fermentation of Reed Pretreated with Liquid Hot Water

Reed is a widespread-growing, inexpensive, and readily available lignocellulosic material source in northeast China. The objective of this study is to evaluate the liquid hot water (LHW) pretreatment efficiency of reed based on the enzymatic digestibility and ethanol fermentability of water-insoluble solids (WISs) from reed after the LHW pretreatment. Several variables in the LHW pretreatment and enzymatic hydrolysis process were optimized. The conversion of glucan to glucose and glucose concentrations are considered as response variables in different conditions. The optimum conditions for the LHW pretreatment of reed area temperature of 180°C for 20min and a solid-to-liquid ratio of 1 : 10. These optimum conditions for the LHW pretreatment of reed resulted in a cellulose conversion rate of 82.59% in the subsequent enzymatic hydrolysis at 50°C for 72 h with a cellulase loading of 30 filter paper unit per gram of oven-dried WIS. Increasing the pretreatment temperature resulted in a higher enzymatic digestibility of the WIS from reed. Separate hydrolysis and fermentation of WIS showed that the conversion of glucan to ethanol reached 99.5% of the theoretical yield. The LHW pretreatment of reed is a suitable method to acquire a high recovery of fermentable sugars and high ethanol conversion yield.

Fermentative Production of Value-Added Products from Lignocellulosic Biomass

Bioconversion of lignocellulosic biomass (agro residues, grasses, wood, weed, dedicated energy crops and others) into biofuels and other value-added products offers numerous geopolitical, environmental, and strategic benefits. Lignocellulosic biomass (LB) is the most abundant renewable organic resources (~200 billion tons annually) on earth that are readily available for conversion to biofuels and other value-added products (industrial enzymes, organic acids, pharmaceuticals, commodity chemicals, and food/feed). However, they have not yet been tapped for the commercial production of these products. The last three decades witnessed the success made in research and development for the conversion of LB into biofuels and other commercially viable products. Despite the success achieved in the laboratory, there are several challenges for the successful bioconversion of lignocellulosic substrates into value-added products at commercial scale. The future of lignocellulosics conversion is expected to lie in improvement in pretreatment technologies, cellulolytic enzymes producing microorganisms, fullest exploitation of biomass components, and process integration. Further, advancement in system-biology-based “OMICS” approaches may provide new breakthroughs for the development of biocatalysts/enzyme titers for the cost effective production of commodity chemicals and fuels from biomass. This special issue presents a diverse range of experimental advancements on biomass pretreatment, enzymatic saccharification, production of cellulosic biofuels, polyhydroxyalkanoates (PHA), polyhydroxybutyrate (PHB), and lovastatin and blends of polyacrylonitrile (PAN) and lignin. Authors here report on process variables including feedstock types (grasses and sugarcane-based agro residues), bioprocess engineering simulations, multivisual structural analysis of lignocellulosics after pretreatment, improvements in cellulase-mediated hydrolysis, and modification in fermentation strategies for the production of a range of value-added products. Selection of suitable lignocellulosic substrates plays a key role for the economic cellulosic ethanol production. Factors such as availability of feedstock and presence of high amount of carbohydrates and lignin amounts are critical for biofuels production at large scale under the biorefinery concept. Of particular interest in this regard is the use of sugarcane residues, corn stover, and grasses as a second-generation feedstock. L. Canilha et al. comprehensively reviewed the technologies (pretreatment methods, detoxification, hydrolysis, fermentation, and end-product distillation) for second-generation (2G) ethanol production from sugarcane residues (sugarcane bagasse and straw). Grasses are another excellent feedstock for 2G ethanol production in countries like Thailand. J. Wongwatanapaiboon et al. collected data on composition of cellulose, hemicellulose, and lignin in 18 types of grasses followed by the alkaline peroxide mediated pretreatment. The pretreated materials were evaluated for ethanol production under simultaneous saccharification and fermentation approach employing yeasts cocultures. J. Lu et al. explored the Reed as a primary source for 2G ethanol production. They presented the data on sugar recovery after liquid hot water pretreatment followed by enzymatic hydrolysis and conversion of sugars into ethanol under separate hydrolysis and fermentation. J. E. Jessen and J. Orlygsson examined the 2G ethanol production from various feedstocks (hemp stem, grass, wheat straw, newspaper, and cellulose) employing a new thermophilic isolate, Thermoanaerobacter J1, from a hot spring in Iceland in addition to the exploration of a mechanism of electron-scavenging systems on end-product formation. For the economization of biofuel or any value-added product formation from lignocellulosic materials, the efficient bioconversion of cellulose and hemicellulose into monomeric sugars is inevitable. In this line, A. D. Eckard et al. demonstrated the mechanism of casein (skimmed milk protein) action to improve the enzymatic saccharification of corn stover. Pretreatment is the key technology for the direct methanation of agroresidues. Y. Feng et al. investigated the changes in the maize straw characteristics during the methanation process. M. A. K. M. Zahari et al. optimized major influential parameters for poly(3-hydroxybutyrate) production from oil palm frond (OPF) juice by Cupriavidus necator CCUG52238T and concluded that OPF juice could be a competitive carbon source for the economic production of PHB. P. Chakraborty et al. presented the data on modified feeding strategies using a mixture of volatile fatty acids and artificial rumen fluid to maximize the PHA production by Ralstonia eutropha. Towards the pharmaceuticals intermediate production, M. F. Jahromi et al. investigated the lovastatin production by Aspergillus terreus under solid-state fermentation using rice straw and oil palm frond. M. O. Seydibeyoglu examined the properties of blends of polyacrylonitrile (PAN) and lignin followed by the structural analysis employing modern structural tools. We sincerely hope readers will find these papers helpful to their research pursuits. It has been our pleasure to put together this special issue in Journal of Biomedicine and Biotechnology.

Combination of biological pretreatment with liquid hot water pretreatment to enhance enzymatic hydrolysis of Populus tomentosa

A novel stepwise pretreatment of combination of fungal treatment with liquid hot water (LHW) treatment was conducted to enhance the enzymatic hydrolysis of Populus tomentosa. The results showed that lignin and cellulose increased with the elevating temperature, while significant amount of hemicellulose was degraded during the LHW pretreatment. A highest hemicellulose removal of 92.33% was observed by combination of Lenzites betulina C5617 with LHW treatment at 200°C, which was almost 2 times higher than that of sole LHW treatment at the same level. Saccharification of poplar co-treated with L. betulina C5617 and LHW at 200°C resulted in a 2.66-fold increase of glucose yield than that of sole LHW treatment, and an increase (2.25-fold) of glucose yield was obtained by the combination of Trametes ochracea C6888 with LHW. The combination pretreatment performed well at accelerating the enzymatic hydrolysis of poplar wood.

Biochemical processing of reed canarygrass into fuel ethanol

Reed canarygrass is a temperate perennial grass of interest as a bioenergy crop. The canarygrass was evaluated for conversion to bioethanol using liquid hot water and dilute ammonia pretreatments prior to fermentation. The resulting hydrolysates were evaluated for production of ethanol, xylose and soluble xylans. Dilute ammonia gave higher yield efficiencies than liquid hot water. The optimal condition for dilute ammonia (4% w/v) pretreatment was 170°C for 20 min. Hydrolysates were converted to ethanol using Saccharomyces in the presence of a blend of commercial cellulases and additional carbohydrases. The final ethanol conversion efficiency was 84% based upon total hexosans, with 72% of the xylan converted to soluble xylan oligomers. Copyright , Oxford University Press.

Tissue‐specific biomass recalcitrance in corn stover pretreated with liquid hot‐water: SEM imaging (part 2)

In the first part of our work, we combined compositional analysis, pretreatment and enzyme hydrolysis for fractionated pith, rind, and leaf tissues from a hybrid stay-green corn, in order to identify the role of structural characteristics on enzyme hydrolysis of cell walls. Hydrolysis experiments coupled with chemical analysis of the different fractions of corn stover showed significant differences in cell wall structure before and after liquid hot water pretreatment. The extent of enzyme hydrolysis followed the sequence rind < leaves < pith with 90% conversion of cellulose to glucose in 24 h in the best cases. Since similar lignin contents remained after liquid hot water pretreatment of leaves, rind, and pith, our results indicated that the amount of lignin alone is not sufficient to explain the different enzymatic hydrolysis characteristics of the fractions. While the role of structural characteristics on enzyme hydrolysis of cell walls is measured as described in part I, the SEM images presented in this part II of our work show that sugar yields from enzymatic hydrolysis of corn fractions correlate with changes in plant cell wall structure both before and after liquid hot water pretreatment.

Effect of hot water extraction and liquid hot water pretreatment on the fungal degradation of biomass feedstocks

Exhaustive hot water extraction (HWE) and liquid hot water (LHW) pretreatment were evaluated for their effects on degradation of biomass feedstocks (i.e., corn stover, wheat straw, and soybean straw) by Ceriporiopsis subvermispora. HWE (85°C for 10min) partially removed water soluble extractives and subsequently improved fungal degradation on wheat straw while it had little or no effect on the fungal degradation of corn stover and soybean straw. In contrast, LHW pretreatment at 170°C for 3min improved the fungal degradation of soybean straw; thus, lignin removal of 36.70% and glucose yield of 64.25% were obtained from the combined LHW and fungal pretreatment. However, corn stover, which was effectively degraded by fungal pretreatment alone, was less affected by this combined pretreatment. Our results indicated that a HWE or LHW pretreatment conducted under mild conditions worked synergistically with fungal degradation for some recalcitrant feedstocks.

Hydrothermal pre-treatment and enzymatic hydrolysis of sunflower stalks

The production of fermentable sugars by biochemical conversion of pretreated sunflower stalks is studied in this work. Liquid hot water pre-treatment, in a temperature range from 180 to 230°C was used. After pre-treatment, solid residue and liquid fractions are separated by filtration. Pretreated solids are further submitted to enzymatic hydrolysis for glucose release using a commercial enzyme preparation. Enzymatic hydrolysis yields show that 90% glucose conversion can be obtained after 72h enzyme action on pretreated sunflower stalks at 220°C. Nevertheless, under such pre-treatment conditions most of the hemicellulosic sugars are lost due to solubilisation and degradation reactions. Taking into account all sugars that can be obtained from this agricultural residue, the best results in terms of potential ethanol production is found when pretreating sunflower stalks at 190°C. The characterization of hydrolysate composition is also discussed as inhibitor compounds are also found in liquid fractions issued from pre-treatment.

Analysis of coffee cut-stems (CCS) as raw material for fuel ethanol production

Coffee cut-stems (CCS) represent a promising candidate for fuel ethanol production in tropical countries because of their high availability and high biomass yield per hectare. In this work, pretreatment of this agricultural residue with dilute sulfuric acid and liquid hot water (LHW) was integrated in the simulation and economic assessment of the process for fuel ethanol production. High reducing sugars concentration and ethanol yields were obtained with the LHW pretreatment at a high energy cost. Acid pretreatment is still one of the most applied technologies for lignocellulosic materials due to its efficiency and lower energy consumption. For the determination of the pollution environmental impact index of the process with and without cogeneration system, the Waste Reduction Algorithm (WAR) was used. Thus, the high lignin and low water contents of the coffee cut-stems signified a high potential for energy cogeneration.