Alkali Pretreatment Process Research Articles

Sustainable biofuels from corncobs: optimization of microwave pretreatment for enhanced fermentable sugar yield

Microwave-Assisted Alkali (MAA) pretreatment of corncob biomass was optimized for maximum fermentable sugar yield using dilute sulfuric acid hydrolysis. A Central Composite Design (CCD) investigated the effects of microwave power (450–9000 W), NaOH concentration (1.5 to 4.5% wt./v), and irradiation time (10–20 min) on lignin removal. The optimal MAA pretreatment conditions were found to be 691.73 W, 3.4% NaOH, and 15.5 min, resulting in the selective removal of 73.36% lignin with high retention of cellulose (71.69%) and hemicellulose (22.14%). Characterization techniques (FTIR, SEM, XRD, TGA) confirmed substantial changes in surface morphology, functional groups, crystallinity, and thermal stability of the pretreated corncobs. Dilute sulfuric acid hydrolysis (0.5–2.5%, 110130 °C, 3060 min) of the optimized sample yielded a maximum reducing sugar output of 537.42 mg/g, achieved at 0.534% H2SO4, 122.3 °C, for 58 min. Optimizing Microwave-Assisted Alkali pretreatment process for corncobs could boost biofuel production efficiency, sustainably utilize agricultural waste, and advance a more sustainable energy landscape.

Nutrient Removal Efficiencies in a Bioretention Cell Using Pre-Treated Coconut By-Product as Carbon Source

Abstract In this research, the appropriateness of alkali pre-treatment on coconut by-products was managed by exposing coconut husk and shell to 2M NaOH. The powdered samples were analysed for morphology observation, Fourier Transform Infrared (FTIR), Particle Size Analyzer (PSA), and water quality tests. Weakening the hemicellulose structure resulted from subjecting the coconut shell to alkali pre-treatment shown in the morphology observation. Furthermore, the FTIR analysis exhibited the presence of O-H stretch in all pre-treated samples representing an indication for occurring the lignin breakdown, while an absence of the C=O functional group was shown in both additive samples after their subjection to alkali pre-treatment. In PSA analysis, the particles of all samples were found finer than the particle size distribution standards, in which the smallest D50 was obtained for the treated coconut shell (TCS), followed by untreated coconut shell (UCS), untreated coconut husk (UCH), and treated coconut husk (TCH). Among all the powdered samples (TCS, UCS, UCH, and TCH) analysed in this study, only TCH values met the ranges provided and recommended by the Urban Stormwater Management Manual for Malaysia (MSMA) and the Australian Department of Sustainability, Environment, Water, Population, and Communities (DSEWPC). Meanwhile, a poor removal rate for total suspended solids (TSS) was attained due to the contribution of TSS by the filter media which caused the TSS rates to surpass the inlet values. Additionally, the presence of a high concentration of total phosphorous (TP) in all the tested samples indicated their capabilities to provide PO43 in the bioretention cell, which is a vital nutrient for the plant’s growth. In contrast, Ammoniacal Nitrogen (AN) with a concentration rate as low as 4 mg/L was observed throughout the test periods which showed a significant reduction compared to the rate of AN at the inlet samples ranged between 5.2 and 11.4 mg/L. The findings indicated that coconut by-products, when subjected to an alkali pre-treatment process, are appropriate for incorporation as additives in bioretention filter media.

Life cycle assessment on delignification and nanolignin synthesis pathways

Lignin, a polymeric material which constitutes about 15 – 40% of the lignocellulosic biomass in plants, is not utilized to its fullest potential as it is treated as waste and applied in low-value applications. In recent years, potential lignin applications in nanoscale have been established but the journey towards the commercialization of nanolignin (NL) is still underdeveloped. As the idea of sustainability continues to seep in, the sustainability and environmental performance of NL synthesis is vital and should be focused. Hence, life cycle assessment (LCA) with the impact assessment of global warming potential (GWP), human toxicity potential (HTP) and water depletion (WD), was conducted in this study to analyze various ecological impacts associated with the NL synthesis pathways via birch chips and oil palm empty fruit bunch (EFB). From the eight synthesis pathways analyzed, the LCA results demonstrated that birch-alkali-homogenization (BAH) pathway and EFB-organosolv-homogenization (EOH) pathway has the best overall environmental performance when birch chips and EFB are used as the lignin source, respectively. For every 1 kg of NL produced, 102.76 kg CO2 eq. of GWP, 935.49 m3 air per kg of HTP and 0.28 m3 of WD are contributed by the BAH pathway. Whereas, 1052.13 kg CO2 eq. of GWP, 1158.36 m3 air per kg of HTP and 0.61 m3 of WD are contributed by the EOH pathway. It is found that a novel delignification method like organosolv is not necessary a more ecologically benign alternative as compared to a conventional alkali pretreatment process but dependant on the source of lignocellulosic biomass.

Economics of Biofuel Production: A Case of Sorghum and Pearl Millet in India.

Reduction of fossil fuels at an alarming rate has attracted increasing attention to blending biofuels worldwide. India's energy demand is expected to grow at an annual rate of 4-5 times over the next couple of decades. With self-sufficiency levels in crude oil becoming a distant dream, there is growing interest to look out for alternative fuels and the biofuels are an important option for policy makers in India. In this context, this paper reviews the experiences in India in the last two decades with respect to biofuel cultivation and its impact on land use, environment, and the livelihoods of rural communities. The objective of this paper is to assess the economics of biofuel production using Sorghum and Pearl millet feedstocks in India using a Life Cycle Analysis (LCA) approach. Baseline study was conducted during the year 2013 in the Madhya Pradesh state of India covering five districts and 333 sample farmers to understand the farmers perception about the various issues related to the production of biofuels using Indian staple food crops Sorghum and Pearl millet. Empirical data from the multi-locational trials conducted during the years 2014-2015 and 2015-2016 in farmers' fields was used to conduct the LCA analysis. Sorghum and Pearl millet feedstocks which are rain-fed crops are considered for bioethanol production with different pretreatment methods. Net Energy Ratio (NER), Net Energy Balance (NEB), Net Carbon Balance (NCB), and % Carbon reduction were some of the key parameters used for analysis and the results are evaluated based on the environmental impacts through the Life Cycle Assessment at 5% blending. Findings reveal that, dilute alkali pretreatment process is most energy intensive due to consumption of alkali consumption. Whereas dilute acid pretreatment has higher conversion efficiency than the other pretreatment processes which is due to higher glucan and xylan conversion efficiencies.The study concludes that Sorghum feedstock is more energy intensive than Pearl millet feedstock due to higher water requirement and yield. Biofuels, either conventional or advanced, should not been couraged without a comprehensive outlook on the overall impact that will ultimately have on the society, environment, or on the countries' energy security. Efforts should be made toward encouragement of research and development in the field as well as in formulating a comprehensive and effective biofuel policy for India.

Evaluation of the wastewater generated during alkaline pretreatment of biomass for feasibility of recycling and reusing

We evaluated the wastewater generated in the alkali pretreatment process of Miscanthus sacchariflorus with sodium hydroxide for the feasibility of recycling and reusing. After thermal alkali pretreatment of the biomass, the separated alkaline solution and the biomass wash water were filtrated using several different types of membranes to recover sodium hydroxide, as well as to eliminate lignin-hemicellulose fractions from the wastewater. Ion concentration, total organic carbon, and acid-hydrolyzed carbohydrate contents were analyzed to evaluate the quality of the alkaline wastewater. The data indicated that a poly(ether)sulfone-based ultrafiltration (UF) membrane filter with a low molecular weight cut-off was able to recover > 98% sodium ions and to remove > 60% of solubilized organic carbon fractions from the alkaline wastewater. These results indicated that filtration using UF membrane could be an alternative strategy to reuse wastewater and to recover the alkali catalyst in the alkali pretreatment process.

Production of Xylose from Pre-treated Husk of Areca Nut

ABSTRACT Pre-treatment of biomass is a preordained phase for the fragmentation of lignocellulosic biomass to its basic constituents such as lignin and carbohydrate molecules. Existing pre-treatment technologies can extract the desirable chemicals from biomass, however, the choice of biomass is a challenge. The present study worked on husk generated after removing the nut from Areca fruit. The husks are the by-product resulting from the cultivation of Areca nut fruit. The present study focused on the comparison of biochemical characterization of this organic waste biomass before and after the acid and alkali pre-treatment process. Characterization includes thermogravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR), and quantitative analysis of extractives. The present study revealed that the Areca husk fiber contained 29.17% hemicellulose which can be explored as a low-cost source of xylose.

Changes in the Specific Charge Amount on the Surface of Cotton Fibres during the Alkali Pre-treatment Process

The aim of the pre-treatment process is to prepare cotton fabrics for subsequent technological operations, which are, in the majority, carried out in aqueous solutions. The pre-treatment processes modify, to some extent, the properties of cotton, resulting in a significant change in their zeta potential, the amount of specific surface charge or free energy surface. This study makes an assessment of the effect of the alkali pre-treatment process on changes in the amount of negative specific charges on cotton knitted surfaces, known as cationic demand. A “back-titration” method with the use of a Muetek PCD device was adopted for these experiments. It was found that the conventional process of alkali treatment of raw cotton knitted fabrics using sodium hydroxide in the presence of non-ionic surfactant reduced by nearly 50% the amount of negative specific surface charge. Also, changes in weight loss and improvements in the whiteness index, as well as the wettability of alkali pre-treated cotton knitwear, were observed.

Xylitol Production From Byproducts Generated During Sequential Acid-/Alkali-Pretreatment of Empty Palm Fruit Bunch Fiber by an Adapted Candida tropicalis

Xylose is a pentose sugar with the potential to convert a variety of valuable chemical products. In this study, acidic pretreatment wastewater generated during a sequential acid-/alkali-pretreatment process was recycled to increase the hydrolyzed hemicellulose fraction from empty palm fruit bunch fiber (EPFBF), a lignocellulosic biomass. The xylose in the reused wastewater was subjected to overliming and an activated charcoal column was used to remove inhibitory compounds, for xylitol fermentation using the adapted C. tropicalis strain. The cell growth and xylose uptake rates in the adapted strain were 1.7- and 5-fold higher, respectively, compared to the wild-type strain. During batch fermentation using the adapted yeast strain and the post-pretreated xylose solution, 35.2 ± 0.8 g/L xylitol was obtained within 61 h for a production yield of 0.44 g xylitol/g xylose. These results indicate that xylose in the byproducts produced in the bioethanol process could be recovered for production of xylitol.

High xylan recovery using two stage alkali pre-treatment process from high lignin biomass and its valorisation to xylooligosaccharides of low degree of polymerisation

In the present work, xylan from arecanut husk was extracted using 2 stage alkaline pretreatment process. In first step, biomass was incubated in alkali at different temperatures (25 °C, 50 °C and 65 °C), alkali concentrations (5%, 10%, 15% and 20% w/v), and incubation periods (8 h, 16 h and 24 h) and evaluated for xylan recovery. It was observed that 40–52% of available xylan could be recovered using 10% alkali when incubated for 8–24 h at 65 °C. Subsequently, the alkali pretreatment operating conditions which provided good xylan recovery were processed further using hydrothermal treatment to extract more xylan. For maximum xylan recovery (>90%), best operating conditions were identified when biomass was treated under hydrothermal treatment (1, 1.5 and 2 h) with varying incubation periods (8, 16, 24 h) and alkali concentrations (5%, 10%) using full factorial design. Incubating arecanut husk with 10% w/v NaOH, at 65 °C for a period of 8 h, followed by hydrothermal treatment at 121 °C for 1 h helped recover >94% xylan. In the next step, enzymatic hydrolysis process was optimized to recover maximum XOS (Optimized condition: 50 °C, pH 4 and 10 U enzyme dose). The hydrolysate comprised of xylobiose: 25.0 ± 1.2 g/100 g xylan (∼71% of XOS), xylotriose: 9.2 ± 0.65 g/100 g xylan (26.2% of XOS) and xylotetrose: 0.9 ± 0.04 g/100 g xylan (2% of XOS). The developed process enables to reduce alkali consumption for high recovery of xylan from biomass with relatively higher lignin content for its valorisation into a potential prebiotic oligosaccharide.

An Effective Modification with Mild Alkali Pretreatment for Enhancing the Biodegradation of Wheat Straw by Pycnoporus sanguineus NFZH-1

A delignification pretreatment is important for enhancing lignocellulose biodegradation. Alkali pretreatment is a promising approach. Fiber morphology, alkaline nitrobenzene oxidation, and ozonation were used to characterize the wheat straw modified by mild alkali pretreatment (2% sodium hydroxide (NaOH) at 121 °C for 30 min), and for studying the advantageous performance by Pycnoporus sanguineus NFZH-1 in the aspects of lignin and carbohydrate biodegradation. The results indicated a powerful and selective delignification in the mild alkali pretreatment process. The relative contents of the G unit and the T form both decreased with mild alkali pretreatment. Meanwhile, epicuticular wax removal and increased porosity was observed in the fibrous tissue of alkali-treated wheat straw. Thus, the biodegradation of the Klason lignin in alkali-treated wheat straw was clearly enhanced and reached 41.4% during the following 10 days of fermentation with P. sanguineus NFZH-1. In addition, the modification of fiber tissue with a mild alkali pretreatment enhanced the biodegradation of xylan. The biodegradation of the chemical constituents of the wheat straw was enhanced by the effective modification with a mild alkali pretreatment. The enhanced biodegradation will be helpful for improving the efficiency of straw return.

Comparison of Dilute Acid, Alkali, and Biological Pretreatments for Reducing Sugar Production from Eucalyptus

The effects of chemical pretreatments (dilute H2SO4, dilute NaOH, and NH4OH) and biological pretreatments (Coriolus versicolor and Daedalea quercina) on the enzymatic hydrolysis of Eucalyptus were investigated. The results showed that Eucalyptus obtained from different regions possess similar chemical compositions and that the optimum particle sizes for reducing sugar production were 60- to 80-mesh. Contrary to the negative influences of a dilute H2SO4 pretreatment, an alkali pretreatment showed positive effects on Eucalyptus saccharification. This phenomenon may had been attributed to the efficient removal of lignin and the stronger structural damage during the alkali pretreatment process. In comparison with the chemical pretreatments, a higher reducing sugar yield could be achieved from the biological pretreated Eucalyptus. The highest reducing sugar yield of 97.14 mg/g was obtained from the Guangxi (GX) Eucalyptus that was pretreated with Daedalea quercina.

Lignocellulosic butanol production from Napier grass using semi-simultaneous saccharification fermentation

Napier grass is a potential feedstock for biofuel production because of its strong adaptability and wide availability. Compositional analysis has been done on Napier grass which was collected from a local area of Taiwan. By comparing acid- and alkali-pretreatment, it was found that the alkali-pretreatment process is favorable for Napier grass. An overall glucose yield of 0.82g/g-glucosetotal can be obtained with the combination of alkali-pretreatment (2.5wt% NaOH, 8wt% sample loading, 121°C, and a reaction time of 40min) and enzymatic hydrolysis (40FPU/g-substrate). Semi-simultaneous saccharification fermentation (sSSF) was carried out, where enzymatic hydrolysis and ABE fermentation were operated in the same batch. It was found that after 24-h hydrolysis, followed by 96-h fermentation, the butanol and acetone concentrations reached 9.45 and 4.85g/L, respectively. The butanol yield reached 0.22g/g-sugarglucose+xylose. Finally, the efficiency of butanol production from Napier grass was calculated at 31%.

Reinforced alkali-pretreatment for enhancing enzymatic hydrolysis of sugarcane bagasse

Microwave irradiation (MWI) and ionic liquid (IL) assisted methods were chosen to strengthen the alkali pretreatment process to improve saccharification efficiency of sugarcane bagasse (SCB). Four different pretreatment approaches namely alkali, IL, MWI-alkali and IL-alkali pretreatments were compared. The chemical composition, morphology and crystal performance of the substrates were analyzed by the standardized methods of the National Renewable Energy Laboratory, field emission scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. IL assisted treatment brought the highest lignin removal (78.51%), and the glucan and xylan conversion achieved 99.51% and 92.76%, respectively, after 72h of enzymatic hydrolysis. The similar effect occurred for MWI assisted alkali-pretreatment approach. SEM and XRD analyses showed that the strengthened process obviously changed the structure and crystallinity of the substrates. Moreover, as a persuasive tool, the fractal-like theory was used to study the enzymatic hydrolysis kinetics.

Alkali pretreatment enhances biogas production in the anaerobic digestion of pulp and paper sludge

The objective of this research was to develop an alkali pretreatment process prior to anaerobic digestion (AD) of pulp and paper sludge (PPS) to improve the methane productivity. Different concentrations of sodium hydroxide solution were used to pretreat PPS, and then followed by AD of PPS and monosodium glutamate waste liquor (MGWL). Laboratory-scale experiments were carried out in completely mixed bioreactors, 1 L capacity with 700 mL worked. Optimal amount of sodium hydroxide for organics solubilization in the step of pretreatment was 8 g NaOH/100 g TS sludge. Under this condition, the PPS flocs structure was well disrupted resulting in the void rate and fiber size decreased after pretreatment, and SCOD increased up to 83% as well as the peak value of VFA concentration attained 1040 mg acetic acid/L during AD. The AD efficiency of PPS with and without pretreatment was evaluated. The highest methane yield under optimal pretreatment condition was 0.32 m 3 CH 4/kg VS removal, 183.5% of the control. The results indicated that alkali/NaOH pretreatment could be an effective method for improving methane yield with PPS.

Microwave-assisted Alkali Pre-treatment of Wheat Straw and its Enzymatic Hydrolysis

Microwave-assisted alkali pre-treatment of wheat straw and its enzymatic hydrolysis were investigated and compared with the conventional alkali pre-treatment process. First, the effect of microwave power and pre-treatment time on the weight loss and composition of wheat straw was examined. The results show that the higher microwave power with shorter pre-treatment time and the lower microwave power with longer pre-treatment time had the same effect on the weight loss and composition at the same energy consumption. The comparison was then made between the effect of the microwave-assisted alkali pre-treatment and the conventional alkali one on the weight loss and composition of wheat straw. The wheat straw had a weight loss of 48·4% and a composition of cellulose 79·6%, lignin 5·7% and hemicellulose 7·8% after 25 min microwave-assisted alkali pre-treatment at 700 W, compared with a weight loss of 44·7% and a composition of cellulose 73·5%, lignin 7·2% and hemicellulose 11·2% after 60 min conventional alkali pre-treatment. The microwave-assisted alkali pre-treatment removed more lignin and hemicellulose from wheat straw with shorter pre-treatment time compared with the conventional alkali one. Finally, the enzymatic hydrolysis of pre-treated wheat straw (substrate concentration 50 g l−1, enzyme loading 20 mg g−1 substrate) was also investigated and the results indicate that the microwave-assisted alkali pre-treated wheat straw had higher hydrolysis rate, reducing sugar concentration and glucose content in the hydrolysate than the conventional alkali pre-treated one. Microwave-assisted alkali pre-treatment is a potential alternative of wheat straw pre-treatment for its enzymatic hydrolysis.

Agar yield, quality and standing crop biomass of Gelidium serrulatum, Gelidium floridanum and Pterocladia capillacea in Venezuela

Venezuela and the nearby islands have natural resources of three agarophyte species in the Gelidiales: Gelidium serrulatum, Gelidium floridanum and Pterocladia capillacea. Standing crop biomass for two of these species, G.serrulatum and P.capillacea, varies between 1.4–0.5 and kg dry wt/m 2. The agar yield from G.serrulatum and G.floridanum ranges from 12 to 34%, depending on the method of extraction. Agar extraction of both species directly into 0.25 N NaOH provided significantly higher gel strengths (>1100 g/cm 2) than either extraction in water or using an alkali pretreatment process of 1.0 N NaOH. Direct extraction of agar in 0.25 N NaOH led to an improvement of gel strength by almost three times that of extraction in water for G.serrulatum. Agar extractions from P. capillacea showed yields ranging from 12 to 32% (depending on extraction process) and gel strengths were highest in the samples extracted after pretreatment in 1.0 N NaOH. In all cases treatment with alkali led to a reduction in percent sulfate of agar and an increase in 3, 6-anhydrogalactose. Both chemical analyses and 13C NMR indicate that the agars from G.serrulatum and G.floridanum are pyruvated. This pyruvated agar did not partition out into different hydrophilic and hydrophobic fractions based on sequential ethanol extraction of G.serrulatum. The agar quality, yields and biomass data suggest that Venezuela could provide commercial quantities of these important agarophytes.