Microwave-assisted Alkali Pretreatment Research Articles

Thermostatic microwave-assisted pretreatment of corn stover at atmospheric pressure to enhance saccharification

A large amount of corn stover waste is produced from processing industries. In this study, the thermostatic microwave-assisted alkali pretreatment (TMAAP) of corn stover at atmospheric pressure was investigated to improve the utilization rate. The optimized conditions include pretreated time, NaOH concentration, temperature, initial power, and solid-liquid ratio. The pretreated corn stover samples for the enzymatic hydrolysis were studied on the crystallinity, surface microstructural changes, functional group changes and compositional analysis. The results showed cellulose recovery and lignin removal in the solid residue reached 87.39 % and 87.59 %, respectively when the corn stover was subjected for 45 min at a microwave reactor with an initial 600 W, 100 °C and 5 % NaOH. After TMAAP, the enzyme hydrolysis efficiency of the corn stove reached 85.40 %, which was higher than that of the untreated (59.96 %). The experiment can be carried out at atmospheric pressure without strict conditions. The techno-economic analysis predicts revenue of 22.82 USD by processing 100 kg of waste corn stover combined with enzyme cost analysis. To conclude, glucose (26.37 kg) and xylose (1.19 kg) were produced from corn stover (100 kg, 39.31 % glucan, 17.34 % xylan, 23.60 % lignin). The results can give insights into establishing an efficient alkali pretreatment of corn stove waste to produce glucose.

Application of natural fungi in bioconversion of lignocellulosic waste to second-generation ethanol

The second generation (2G) or cellulosic ethanol can help with diversification of the use of fossil energy sources. However, as bioconversion of plant waste into 2G bioethanol requires expensive additional steps of pre-treatment/hydrolysis of lignocellulosic materials, and this technology has not yet reached the technological readiness level which would allow it to be scaled-up, this process needs more interdisciplinary and comprehensive studies. This work was aimed at experimental study of a full cycle of successive processes of pre-treatment/saccharification using cellulolytic enzymes of filamentous fungi and fermentation of obtained syrups by xylose-fermenting yeast, using selected natural microorganisms for the fungal-based bioconversion of lignocellulosic agricultural waste to 2G ethanol. Using the Plackett-Burman and Box-Behnken methods of mathematical statistics, the optimal conditions for pre-treatment and enzymatic hydrolysis of wheat straw by a hemi- and cellulolytic multi-enzyme complex of the selected fungal strain Talaromyces funiculosus UCM F-16795 were established: microwave-assisted alkali pre-treatment with sodium hydroxide (NaOH) solutions (concentration range 4.6–4.8%), and saccharification conditions of medium pH 4, temperature 40 °С, hydrolysis duration 18 hours, and dilution of culture liquid with a buffer solution 1:1. The total energy of microwave irradiation 1.2 kJ and the ratio of substrate/enzyme solution 100 mg/1 mL were used. Under optimized conditions, wheat straw hydrolysates contained 5.0–7.5 g/L of reducing sugars, which, according to HPLC assessment, contained 0.7–1.0 g/L of glucose, 2.2–2.9 g/L of xylose and 0.7–0.8 g/L cellobiose. We used the selected strain of xylose-fermenting yeast in fermentation of mixtures of the most important monosaccharides in hydrolysates, xylose and glucose, in the concentration range relevant for syrups obtained by us during the optimized saccharification of lignocellulosic substrates with T. funiculosus enzymes. Based on sequencing and phylogenetic analysis, strain UCM Y-2810 was confirmed as Scheffersomyces stipitis; its nucleotide sequences of ITS region and 28S gene rDNA were deposited in GenBank under the accession numbers OP931914 and OP931915, respectively. The ethanologenic process for S. stipitis UCM Y-2810 was studied according to Box-Behnken design, assessing ethanol concentration by gas chromatography-mass spectrometry. Yeast fermentation under static microaerophilic conditions showed a 1.5 times higher rate of bioethanol production and 1.7 times greater efficiency of ethanologenesis per yeast biomass than for submerged cultivation. Optimization of the process of ethanologenesis resulted in the maximum rate of fermentation mixture of sugars, being 11.30 ± 0.36 g/L of ethanol, with optimal values of factors: 30 g/L of xylose, 5.5 g/L of glucose and cultivation for 5.5 days. It was revealed that the tested glucose concentrations did not significantly affect the process of xylose-fermentation by yeast, and non-competitive inhibition of xylose transport by glucose into yeast cells did not occur. This study demonstrated the potential of a full cycle bioconversion of lignocellulosic waste to 2G ethanol based on use of natural fungal strains and optimization of conditions for all steps.

A hybrid pretreatment strategy for delignification of Aloe vera processing waste and its effectiveness towards saccharification

A copious amount of rigid Aloe vera leaf rind (AVLR) has been produced from the aloe gel processing industries are majorly disposed as wastes since it has no commercial value. The cell wall compositional analysis revealed that significant quantity of cellulose (46% ± 0.76, w/w) and hemicellulose (18.5% ± 0.24, w/w) which justifies as potent source for bioethanol production. However, high lignin content (13.95% ± 0.45, w/w) hinders depolymerization of polysaccharides into fermentable sugars and subsequent fermentation for ethanol production. In the present study, microwave-assisted alkali (MAA) pretreatment of AVLR biomass was carried out by varying the power level (160 W, 320 W and 480 W) which showed a maximum delignification (66.38%) at 320 W. Scanning Electron Microscope (SEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD) based characterization were performed to study the extent of delignification in AVLR biomass. The Gas Chromatography-Mass Spectrometry (GC-MS) analysis was performed for the liquid hydrolysate obtained after MAA pretreatment at 320 W indicated that the hydrolysate contained more of oxidized phenolic hydrocarbons that can be potentially utilized for other value-added product synthesis. A comparison of saccharification efficiency was performed using two different cellulase producers namely Aspergillus niger and Aspergillus sp. A maximum saccharification of 68.5% ± 0.34 was achieved by Aspergillus sp., that was 2.8% higher on comparing with untreated AVLR biomass. This indicates the feasibility of MAA pretreatment for AVLR biomass in order to improve the accessibility of fermentable sugars available for ethanol production.

The Effect of Microwave-Assisted Alkali and Xanthomonas t ranslucens ICBB 9762 for Rice Straw Pretreatment on Electricity Generation of Microbial Fuel Cell Inoculated by Staphylococcus saprophyticus ICBB 9554

Rice straw can be utilized as an organic substrate in Microbial Fuel Cell (MFC) to generate electricity by microbes as a biocatalyst. This research was aimed to observe the effect of Xanthomonas translucens ICBB 9762 inoculation pretreatment on microwave-assisted alkali treated rice straw on the lignocellulosic structure change of rice straw and to observe the performance of MFC system fed by treated rice straw. The stages of research included: (1) pretreatment of rice straw through microwave-assisted alkali and Xanthomonas translucens ICBB 9762 inoculation, (2) observation of MFC performance including electrical voltage; electrical current; power density; and Coulombic efficiency, and (3) anolite analysis including COD removal, pH and Eh. The result showed that rice straw was successfully decomposed by inoculation of Xanthomonas translucens ICBB 9762 on microwave-assisted alkali pretreatment which the highest cellulose yield about 29.36 %. Treated rice straw produced better performance than rice straw without pretreatment which the best performance resulted by the combination of Xanthomonas translucens ICBB 9762 inoculation and microwave-assisted alkali pretreatment which produce electrical voltage, electrical current, and power density value of 337.90 mV, 0.39 mA, and 26.20 mW/m2, respectively. The utilization of solid substrate such as rice straw need more attention due to there was COD enhancement while in COD reduction reach COD removal efficiency and coulombic efficiency ranged 5.15 - 54.08 % and 0.25 - 7.83 %, respectively. HIGHLIGHTS Microbial Fuel Cell fueled by lignocellulose substrate, which is rice straw Lignocellulose structure deconstruction through microwave-assisted alkali pretreatment A combination of microwave-assisted alkali and cellulose-degrading bacteria inoculation pretreatment for rice straw generate the highest electricity Electricity generation improvement in microbial fuel cell through mix culture between cellulose-degrading bacteria and exoelectrogen bacteria Cellulose degrading bacteria increase Chemical Oxygen Demand (COD) due to the solubility of low molecular weight organic compounds increasing during microbial fuel cell incubation

Rapid green microwave assisted extraction of lutein from Chlorella sorokiniana (NIOT-2) – Process optimization

Chloropycean microalgae are looked up as a prospective alternate source for the production of xanthophyll carotenoid lutein. Despite, the market significance and multitude of nutraceutical applications of lutein commercial production from microalgae still remains a challenge due to the prohibitive downstream cost. This necessitates innovative less energy intensive, high lutein yielding green processes. The present work presents a comprehensive study on the rapid green microwave assisted extraction (MAE) of lutein from marine chlorophycean microalgae Chlorella sorokiniana (NIOT-2). The process parameters of microwave assisted alkali pre-treatment like exposure time (ET), alkali concentration (AC) and solid (biomass): liquid (aqueous Potassium hydroxide-KOH) ratio (S: L ratio) were optimized using single factor and response surface method (RSM) experiments. The optimized conditions for microwave assisted alkali pre-treatment (ET:1.47 min; AC: 8.16 M KOH and S:L ratio of 36.8:1 (mg/mL) augmented the lutein yield (20.69 ± 1.2 mg/g) 3.26 fold when compared to conventional extraction (6.35 ± 0.44 mg/g). Lutein extracted using optimized MAE conditions was purified and characterized. Visualization of the MAE extracted algal biomass using Scanning electron microscope confirmed the effective cell disruption. X-ray diffraction (XRD) analysis of microwave assisted alkali treated biomass (83.85%) revealed a significantly higher crystallinity index when compared to untreated control (17.28%). MAE pre-treatment can thus be propounded as a suitable process for lutein extraction from marine microalgae due to its amalgamated rapidity, homogenous heating, less energy intensiveness and high extraction yield.

Corrigendum

Food and Energy SecurityVolume 10, Issue 3 e308 CORRIGENDUMOpen Access Corrigendum First published: 19 August 2021 https://doi.org/10.1002/fes3.308AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL In the article by Sombatpraiwan S et al., entitled “Optimization of microwave-assisted alkali pretreatment of cassava rhizome for enhanced enzymatic hydrolysis glucose yield,” (Sombatpraiwan et al. 2019) Dr. Tawarat’s family name has been corrected and his full name should read “Tawarat Treeamnuk.” REFERENCE Sombatpraiwan, S., Junyusen, T., Treeamnak, T., & Junyusen, P. (2019). Optimization of microwave assisted alkali pretreatment of cassava rhizome for enhanced enzymatic hydrolysis glucose yield. Food Energy Secur., 8, e00174. Volume10, Issue3August 2021e308 ReferencesRelatedInformation

Optimization of Microwave-Assisted Alkali Pretreatment for Enhancement of Delignification Process of Cocoa Pod Husk

In this study, the optimization of microwave-assisted alkaline (MAA) pretreatment is performed to attain the optimal operating parameters for the delignification of cocoa pod husk (CPH). The MAA performance was examined by heating the CPH solid with different particle sizes (60–120 mesh) and NaOH solution with a different sample to a solvent (SS) ratio (0.02–0.05 g/L), for short irradiation time (1–4 min). Box-Behnken Design (BBD) was utilized to optimize the percentage of lignocellulose composition changes. The results show that by enlarging particle size, the content of lignin and cellulose decreased while hemicellulose increased. By prolong irradiation time, the content of lignin and hemicellulose decreased while cellulose elevated. On the other hand, increasing the SS ratio was not significant for hemicellulose content changes. From FTIR and SEM characterization, the MAA drove the removal of lignin and hemicellulose of CPH and increased cellulose slightly. Supported by kinetic study which conducted in this work, it was exhibited that MAA pretreatment technology is an effective delignification method of CPH which can tackle the bottleneck of its commercial biofuel production. 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).

Effect of microwave‐assisted alkali pre‐treatment on fractionation of pistachio shell and enzymatic hydrolysis of cellulose‐rich residues

AbstractBACKGROUNDPistachio shell is a lignocellulosic biomass with a high potential to be converted into chemicals, biopolymers, and biofuels. Alkaline pre‐treatment is an effective way to extract hemicellulose and increase the cellulose hydrolysis. However, there are some disadvantages to this process, such as a long processing time and the formation of high amounts of degradation products. Microwave irradiation can be used to enhance the effectiveness of alkaline treatment. In this study, microwave‐assisted alkali pre‐treatment (MAAP) was carried to fractionate pistachio shell into its valuable components (i.e., hemicellulose and cellulose), and the enzymatic hydrolysis of cellulose‐rich residues was performed to produce fermentable sugars.RESULTSThe MAAP conditions (microwave power, NaOH concentration, and pre‐treatment time) were studied and optimized by Box–Behnken design to obtain the highest hemicellulose and cellulose yields. Optimal pre‐treatment conditions were microwave power of 224 W, NaOH concentration of 1.96 N, and pre‐treatment time of 2.63 min. Under these conditions, the recoveries were 58.35% and 92.46% for hemicellulose and cellulose, respectively. Additionally, compositional analysis carried out on the solid and liquid fractions obtained from the pre‐treatments indicated that the main components in the liquid phases were xylooligosaccharides (XOS) and the solid phases were enriched in cellulose. MAAP enhanced the enzymatic hydrolysis yield, and a maximum glucan to glucose conversion yield of 82.67 mol% was obtained for the solid pre‐treated under optimum conditions.CONCLUSIONThe studied MAAP process could be an effective and viable option to extract hemicellulose from pistachio shell and increase the enzymatic digestibility of cellulose‐rich solid residues. © 2020 Society of Chemical Industry (SCI)

Optimization of microwave-assisted alkali pretreatment followed by acid hydrolysis of sugarcane straw for production of acetone-butanol-ethanol

ABSTRACT The production of acetone-butanol-ethanol (ABE) calls for effective pretreatment and hydrolysis techniques to maximize reducing sugar yields. In this study, optimized microwave-assisted alkali (MAA) pretreatment followed by acid hydrolysis was assessed for the production of reducing sugars from sugarcane straw (SCS). To evaluate effects of MAA pretreatment on SCS composition, response surface methodology (RSM) was employed upon subjecting SCS to 320, 640, and 960 W microwave power, using 1–3% (w/v) NaOH, and residence time of 5, 15, and 25 min. The pretreated SCS was made to undergo acid hydrolysis at 121 °C temperature and reaction time of 10–60 min to release reducing sugars. ABE was produced by anaerobic fermentation of reducing sugars using Clostridium beijerinkii. After pretreatment, maximum responses of 76.3% lignin removal, 21.1% hemicellulose, and 71.9% cellulose were achieved at 640 W microwave power, 2.8% NaOH concentration, and 19 min. The maximum reducing sugar concentration was 46.2 g/L while 18.7 g/L of ABE was produced. The results revealed that optimized MAA pretreatment followed by acid hydrolysis can enhance the yield of reducing sugars for ABE production with no need for costly enzymes.

Effect of microwave assisted alkali pretreatment and other pretreatment methods on some properties of bamboo fibre reinforced cement composites

This study investigated the effectiveness of microwave irradiation pre- treatment in combination with sodium hydroxide and other pretreatment methods on bamboo fiber cement composite characteristics. The materials used for this study include bamboo fibers, Portland cement, fine sand and calcium chloride. Microwave assisted sodium hydroxide (MT), sodium hydroxide alone (AA) and hot water (HT) treatments were used to pre-treat the bamboo fiber before its use in the cementitious composite. Mechanical tests were conducted after 7, 14 and 28 days while Fourier transformed Infrared spectroscopy (FTIR) with Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to characterise the composites. The use of microwave assisted alkali treatment is observed to have the best performance due to its more efficient role in improving fiber roughness, ductility and toughness in the cementitious composites.

Extraction of Cellulose Nano-Whiskers Using Ionic Liquid-Assisted Ultra-Sonication: Optimization and Mathematical Modelling Using Box–Behnken Design

This study focuses on the extraction of cellulose nano-whiskers (CNWs) from the leaves of Adansonia kilima (AK), usually known as African baobab, using a combination of a microwave-assisted alkali (KOH) pre-treatment with subsequent bleaching process prior to ultra-sonication. Ultra-sonication was carried out using the ionic liquid (IL) 1-butyl-3-methylimidazolium hydrogen sulfate (Bmim-HSO4). Process parameters for ultra-sonication were optimized using a two-level factorial Box–Behnken design (BBD). Process variables such as ultra-sonication power (x1), hydrolysing time (x2) and temperature (x3) were varied. Responses selected were percentage crystallinity index, CrI% (y1) and yield% (y1) for the finally procured CNWs sample. Regression analysis was carried out to develop quadratic model to analyze the effect of process variables on IL-assisted ultra-sonication process. Analysis of variance (ANOVA) showed that ultra-sonication power was the most influential aspect for hydrolyzing the amorphous segments of crude cellulose extracted from baobab leaves. A relative study of the physio-chemical properties of the starting lignocellulosic substrate (AK), KOH pre-treated, bleached and IL-assisted ultra-sonicated CNWs was conducted. The synthesized samples were characterized using Fourier transform infrared spectroscopy, Scanning electron microscopy, atomic force microscopy, high resolution transmission electron microscopy, X-ray diffraction and thermo-gravimetric and zeta potential analysis. Under optimum condition, the extracted CNWs showed an average width of 15–20 nm; with high crystallinity index of 86.46%. This research provides an insight about the delignification of Adansonia kilima (AK) leaves and its effective conversion to CNWs having high crystallinity.

Optimization of microwave‐assisted alkali pretreatment of cassava rhizome for enhanced enzymatic hydrolysis glucose yield

AbstractThis research establishes the optimal microwave‐assisted alkali pretreatment (MAP) condition of cassava rhizome (CR) using response surface methodology with Box–Behnken design for enhanced enzymatic hydrolysis glucose yield. The pretreatment parameters included microwave power (300–900 W), irradiation time (5–15 min), and NaOH concentration (3%–7% w/v); and the enzymatic hydrolysis was 24 and 48 hr. Quadratic models were generated and statistical analysis performed to validate the adequacy of the models. The results indicated that the optimal MAP condition was 840 W microwave power, 9 min irradiation time, and 3% w/v NaOH concentration. Under the optimal condition, the predicted and experimental glucose yields were 15.39 and 15.82 g/100 g native cassava rhizome (NCR) for 24 hr hydrolysis, and 16.40 and 16.95 g/100 g NCR for 48 hr hydrolysis, indicating good agreement. In addition, this study examined the effect of MAP on the physical characteristics and morphology of NCR and pretreated CR. The results showed significant structural changes in pretreated CR, indicating that MAP enhanced enzymatic accessibility and glucose yield.

Assessment of microwave-assisted alkali pretreatment for the production of sugars from banana fruit peel waste

ABSTRACTThe current investigation deals with the application of microwave energy to facilitate alkali (NaOH) pretreatment on banana peel waste (BPW) to achieve optimal reducing sugar. We studied the effect of microwave power (100 to 600 W) and irradiating time (1 to 6 min) on composition and reducing sugar content of BPW. The enzymatic hydrolysis of microwave-assisted alkali-pretreated BPW at 600 W for 2 min gave the maximum reducing sugar (0.561 g/g) of dry biomass waste. Atomic force microscopy revealed that the surface of all BPW was changed noticeably when microwave-assisted alkali pretreatment was employed. X-ray diffraction study revealed a 5-fold increment in the degree of crystallinity in optimal microwave alkali-treated samples (54.45%) as compared to the untreated sample (10.55%). Overall, the microwave-assisted alkali pretreatment removed a significant amount of hemicelluloses and lignin and led to a high amount of sugar production, suggesting microwave heating pretreatment as a potential alternative to conventional methods to achieve maximal reducing sugars.

Overall evaluation of microwave-assisted alkali pretreatment for enhancement of biomethane production from brewers’ spent grain

In this study, microwave-assisted alkali pretreatment for brewers’ spent grain (BSG) waste was comprehensively investigated using Box-Behnken design under varying operating parameters, i.e. microwave power, pretreatment time and alkali/biomass (A/B) ratio. Both quantitative and qualitative characterization analysis such as crystallinity index (CrI), specific surface area (SSA), morphology and compositional analyses were conducted on pretreated samples. Standard biomethane potential (BMP) tests were performed for each pretreated sample to observe the biomethane enhancement after pretreatment. Under optimized conditions, it was observed that the pretreatment technique has facilitated removal of 46% of lignin and 38% of hemicellulose and improved the SSA of samples from 9.55 to 161.98 m2/g, contributing to 52% increase in BMP value. Meanwhile, mathematical models with correlation coefficients of 97.9% and 98.2% respectively were built to predict both the soluble chemical oxygen demand (COD) yield and BMP after pretreatment. Furthermore, a simplified concept of overall evaluation mechanism for pretreatment has been introduced, taking into account waste-removal, energetic and economic indices. Under the proposed evaluation mechanism, the caustic soda price was found to play a more important role than the prices of industry electricity and wholesale natural gas.

Physicochemical treatment for improving bioconversion of cassava industrial residues

In the present study, a comparison of two types of microwave pretreatment such as microwave assisted alkali and microwave assisted acid were studied using cassava pulp as the substrate. The effect of pretreatment agent concentration, microwave power and pretreatment time on enzymatic saccharification was studied using a response surface method according to Central Composite design. Under optimized conditions, microwave assisted alkali pretreatment of cassava pulp with 2.27% NaOH at 125 W for 18 min followed by enzymatic hydrolysis gave reducing sugar yield of 0.472 g g−1 dry biomass, while microwave assisted acid treatment with 1.95% H2SO4 at 135 W for 25 min showed reducing sugar yield of 0.306 g g−1 dry biomass. The yield from microwave assisted alkali was higher and was 2.7 times higher than that obtained with raw cassava pulp. Microwave assisted liquefaction of pretreated cassava pulp at 100 W for 30 min using amylase lowered the process time. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 577–583, 2018

Microwave assisted alkali pretreatment of fruit peel wastes for enzymatic hydrolysis

The present study proved the potential of generating reducing sugars from various fruit peel wastes (pineapple, mango, orange) using microwave assisted alkali pretreatment. The results showed that enzymatic hydrolysis of pretreated pineapple peel waste produced maximum reducing sugar, i.e. 0.774 g/g dry biomass. X-ray diffractionstudy revealed the prominent role of microwave heating in the disruption of recalcitrant lignocellulosic structures and improving the enzymatic digestibility of FPWs. We believe that microwave assisted alkali pretreatment of FPWs could be an energy-saving technology aimed to valorize the agro-industrial wastes in a cost effective way.

Microwave-Assisted Alkali Pre-Treatment, Densification and Enzymatic Saccharification of Canola Straw and Oat Hull.

The effects of microwave-assisted alkali pre-treatment on pellets’ characteristics and enzymatic saccharification for bioethanol production using lignocellulosic biomass of canola straw and oat hull were investigated. The ground canola straw and oat hull were immersed in distilled water, sodium hydroxide and potassium hydroxide solutions at two concentrations (0.75% and 1.5% w/v) and exposed to microwave radiation at power level 713 W and three residence times (6, 12 and 18 min). Bulk and particle densities of ground biomass samples were determined. Alkaline-microwave pre-treated and untreated samples were subjected to single pelleting test in an Instron universal machine, pre-set to a load of 4000 N. The measured parameters, pellet density, tensile strength and dimensional stability were evaluated and the results showed that the microwave-assisted alkali pre-treated pellets had a significantly higher density and tensile strength compared to samples that were untreated or pre-treated by microwave alone. The chemical composition analysis showed that microwave-assisted alkali pre-treatment was able to disrupt and break down the lignocellulosic structure of the samples, creating an area of cellulose accessible to cellulase reactivity. The best enzymatic saccharification results gave a high glucose yield of 110.05 mg/g dry sample for canola straw ground in a 1.6 mm screen hammer mill and pre-treated with 1.5% NaOH for 18 min, and a 99.10 mg/g dry sample for oat hull ground in a 1.6 mm screen hammer mill and pre-treated with 0.75% NaOH for 18 min microwave-assisted alkali pre-treatments. The effects of pre-treatment results were supported by SEM analysis. Overall, it was found that microwave-assisted alkali pre-treatment of canola straw and oat hull at a short residence time enhanced glucose yield.

Hydrothermal and microwave assisted alkali pretreatment for fractionation of arecanut husk

Alkaline pretreatment assisted with hydrothermal and microwave irradiation as heating mechanisms were evaluated for their efficiency to develop a lignocellulosic biorefinery from arecanut husk. Hydrothermal treatment was carried out at 121°C for 1, 1.5 and 2h and microwave irradiation was performed at three power levels of 900, 540 and 180W at two time periods (1 and 3min). Hydrothermal treatment (1h) of biomass soaked in 20% w/v NaOH solution resulted in average recovery of 82% hemicellulose with 69.7% lignin removal. Whereas, for hydrothermal treatment (1h) of alkali-biomass mixture (no soaking), 74.9% of hemicellulose were recovered with 64.6% lignin removal. Increasing the reaction time from 1 to 1.5h resulted in significant increase in average hemicellulose yield (83.5%). However, prolonging hydrothermal treatment time to 2h did not result in further increase in average hemicellulose yield (82.3%). The residue obtained after hydrothermal pretreatment (1.5h) was concentrated in cellulose (average 69.2%). Compared to hydrothermal treatment, microwave treated biomass yielded low hemicellulose recovery and maximum yield (52%) was obtained at 900W and 3min exposure. FTIR analysis confirmed the presence of functional groups associated with xylan of hemicellulose precipitate. Enzymatic hydrolysis of pretreated residue (unbleached and bleached) using cellulase and β- glucosidase released 75–79% reducing sugars from cellulose. The amount of glucose released from pretreated biomass was 71.5±1.9% in comparison to 2.2±0.1% as obtained from enzymatic hydrolysis of untreated biomass. Thus, the developed process generated cellulose rich residue, hemicellulose as precipitate and liquor rich in lignin.

Improving enzymatic saccharification of cassava stem using peroxide and microwave assisted pre-treatment techniques

The effectiveness of microwave assisted alkali (MAA) and alkaline hydrogen peroxide (AHP) pre-treatment methods in improving the enzymatic saccharification of cassava stem was investigated. Ground cassava stems were by MAA method by varying microwave power, NaOH concentration and pre-treatment time. AHP method was performed at various H2O2 concentrations, pre-treatment temperatures and times. The results showed that reducing sugar yield was higher from MAA pretreated stem when compared with AHP pre-treatment, which demonstrated that MAA pre-treatment was effective in releasing sugars. SEM studies on the pre-treated samples revealed extensive distortion of fibres in MAA pre-treated than AHP pre-treated samples, which showed pores and cracks in the fibrous structure. Spectral studies showed the change in the chemical structure of pre-treated samples. The work revealed that the studied pre-treatment methods were effective in improving the enzymatic saccharification of cassava stem.

Microwave-Assisted Alkali Pretreatment for Enhancing Pineapple Waste Saccharification

The effectiveness of microwave-assisted sodium hydroxide pretreatments to enhance the saccharification performance of pineapple waste was evaluated. Microwave alkali pretreatments for short exposure times (up to 60 s) significantly improved the yield of the enzymatic hydrolysis compared with non-pretreated waste. The greatest increase of fermentable (35.7%) and total sugars (33.5%) was obtained at 6.375 W/g for 5 s. However, longer exposure times resulted in sugar degradation and released fermentation inhibitors, such as phenols or hydroxymethylfurfural (HMF), as a consequence of thermal degradation. Nevertheless, the obtained phenols values were not sufficient to inhibit subsequent fermentation. Scanning electron microscope (SEM) images confirmed that applying microwaves for short exposure times promoted structural changes that improved enzymatic hydrolysis. By contrast, an increase in the severity of the treatment led to a compacted structure, which hindered access to enzymes and consequently reduced the release of sugars into the medium.