NaOH Treatment Research Articles

Adsorption of Hexavalent Chromium Ions Using Pine Sawdust Cellulose Fibres

In developing countries, agriculture generates not only income but also waste. Therefore, it is essential to recycle this waste for different purposes. This study explored an affordable way to modify pine sawdust to treat chromium-containing wastewater, with successful outcomes. The biosorbent’s surface area was enhanced through pretreatment steps, including NaOH treatment, bleaching, and acid hydrolysis for cellulose fibre extraction. SEM–EDS, TEM, and XRD were used to study the chemical composition and morphology. XRD measurements also revealed a rise in the sizes of crystallites. FTIR results revealed shifts in bands (-OH), (-C-H), and (-COOH), suggesting their involvement in Cr (VI) ion adsorption. TGA/DTA indicated enhanced thermal stability for cellulose extracted from pine sawdust compared to untreated pine sawdust. The adsorption parameters for Cr (VI) ions were investigated through mass, pH, stirring time, and temperature studies. The optimal Cr (VI) adsorption conditions were 2.0 g mass, pH 6, 90 min stirring, 100 mg/L concentration, and 313 K temperature. The adsorption of Cr (VI) ions was best-fit to the Langmuir isotherm model (R2 = 0.9991, kL = 0.09). Pseudo-second-order kinetics (R2 = 0.9999) provided the best description for Cr (VI) biosorption on cellulose fibres (CF). The analysis results confirmed the isotherm and kinetics models. The negative thermodynamic parameters (ΔG° and ΔH°) indicated that the uptake of Cr (VI) ions on the adsorbent was exothermic and spontaneous.

The effectiveness of using cocoa husks in the diet of broiler chickens

From the numerous lists, cocoa waste (husk, cocoa shell) is unconventional for Russian production. The value of the product lies in the content of pectin (10 %), amino acids, protein (27 %), fat (1,5-8,5 %) and dietary fi ber. It is obvious to search for alternative methods in the preparation of this raw material for feeding through the use of chemical and mechanical processing. The purpose of the research was a comparative assessment of the methods of preparation and use of cocoa production waste as part of the diet for the metabolism and productivity of broiler chickens. The experimental part of the work included laboratory experiments and scientifi c and economic experiments, as well as a production check, which was carried out in CJSC “Poultry Farm Orenburg” of the Orenburg region. In the cocoa husk treated with alkali in the amount of 45 g/kg, there was a decrease in the fi ber content from 21,5 to 10,5 % against the background of an increase in the amount of protein from 16,2 to 18,7 % and nitrogen-free extractive substances from 38,6 to 48,5 %, compared with the initial product. The processing did not have a signifi cant eff ect on the content of ash, crude fat and organic matter. Extrusion of cocoa husks treated with alkali had a beneficial effect on the availability of nutrients for digestive enzymes. At the same time, extrusion of processed raw materials with sodium hydroxide in an amount of 45 g/kg on average increased the availability of nutrients by 7–12 abs.%, the content of metabolic energy up to 10 %, compared with chemical processing of cocoa husks. As a result of production tests, the effectiveness of the use of cocoa husks (NaOH treatment 45 g/kg + extrusion) was established when replacing 5,0 % of the grain part in the diet of broiler chickens, which is confirmed by economic calculations and indicators of profitability of production.

Influence of electroless NiP/graphene coating on treated woven ramie fiber and its characterization

Over the years, several researchers have attempted to develop a functional surface through coating technology. However, developing a natural fiber into a functional material continues to be a challenging task. Herein, in the current study, an attempt is made to deposit nickel-phosphorus (NiP)/Graphene (Gr) on the surface of sodium hydroxide (NaOH) treated ramie fiber (RF) to improve its electrical conductivity and wettability. The influence of NaOH treatment, NiP/Gr coating on the fiber surface is studied by microstructural analysis, elemental compositions, x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Atomic force microscopy (AFM), wettability, and electrical conductivity. The obtained results confirm the presence of NiP and Graphene on the treated-coated ramie fiber with intensity peaks at 45° and 28°. The analysis of the microstructures reveal the cauliflower and flakes structure of NiP and graphene. The NaOH-treated and NiP-coated sample (T/NiP/RF) has enhanced electrical conductivity of 56.7% when compared to the untreated NiP-coated sample (NiP/RF), whereas the addition of graphene (T/NiP/Gr/RF) increases the electrical conductivity by 74% (14.85 (Ω cm)−1) compared to T/NiP/RF (8.54 (Ω cm)−1).

Inhibition of Acinetobacter baumannii Biofilm Formation Using Different Treatments of Silica Nanoparticles.

There exists a multitude of pathogens that pose a threat to human and public healthcare, collectively referred to as ESKAPE pathogens. These pathogens are capable of producing biofilm, which proves to be quite resistant to elimination. Strains of A. baumannii, identified by the "A" in the acronym ESKAPE, exhibit significant resistance to amoxicillin in vivo due to their ability to form biofilm. This study aims to inhibit bacterial biofilm formation, evaluate novel silica nanoparticles' effectiveness in inhibiting biofilm, and compare their effectiveness. Amoxicillin was utilized as a positive control, with a concentration exceeding twice that when combined with silica NPs. Treatments included pure silica NPs, silica NPs modified with copper oxide (CuO.SiO2), sodium hydroxide (NaOH.SiO2), and phosphoric acid (H3PO4.SiO2). The characterization of NPs was conducted using scanning electron microscopy (SEM), while safety testing against normal fibroblast cells was employed by MTT assay. The microtiter plate biofilm formation assay was utilized to construct biofilm, with evaluations conducted using three broth media types: brain heart infusion (BHI) with 2% glucose and 2% sucrose, Loria broth (LB) with and without glucose and sucrose, and Dulbecco's modified eagle medium/nutrient (DMEN/M). Concentrations ranging from 1.0 mg/mL to 0.06 µg/mL were tested using a microdilution assay. Results from SEM showed that pure silica NPs were mesoporous, but in the amorphous shape of the CuO and NaOH treatments, these pores were disrupted, while H3PO4 was composed of sheets. Silica NPs were able to target Acinetobacter biofilms without harming normal cells, with viability rates ranging from 61-73%. The best biofilm formation was achieved using a BHI medium with sugar supplementation, with an absorbance value of 0.35. Biofilms treated with 5.0 mg/mL of amoxicillin as a positive control alongside 1.0 mg/mL of each of the four silica treatments in isolation, resulting in the inhibition of absorbance values of 0.04, 0.13, 0.07, 0.09, and 0.08, for SiO2, CuO.SiO2, NaOH.SiO2 and H3PO4.SiO2, respectively. When amoxicillin was combined, inhibition increased from 0.3 to 0.04; NaOH with amoxicillin resulted in the lowest minimum biofilm inhibitory concentration (MBIC), 0.25 µg/mL, compared to all treatments and amoxicillin, whereas pure silica and composite had the highest MBIC, even when combined with amoxicillin, compared to all treatments, but performed better than that of the amoxicillin alone which gave the MBIC at 625 µg/mL. The absorbance values of MBIC of each treatment showed no significant differences in relation to amoxicillin absorbance value and relation to each other. Our study showed that smaller amoxicillin doses combined with the novel silica nanoparticles may reduce toxic side effects and inhibit biofilm formation, making them viable alternatives to high-concentration dosages. Further investigation is needed to evaluate in vivo activity.

Structural and emulsion-stabilizing properties of the alkali-extracted arabinoxylans from corn and wheat brans

This study investigated the structural and emulsion-stabilizing capacities of alkali-extracted arabinoxylans from corn and wheat bran (CAXs and WAXs). The results demonstrated that all AXs were mainly composed of arabinose and xylose. WAXs had a higher weight-average molecular weight (Mw, 375–473 KDa) and protein content (3.09–8.68 %) but lower total phenolic acid content (TPC, 1.18–1.91 mg gallic acid equivalents/g) than CAXs; however, CAX stabilized emulsions exhibited smaller and more regular oil droplet size (524–589 nm) and higher absolute value of ζ potential (48–52 mV) compared with WAX stabilized emulsions during storage. Moreover, the increment of NaOH concentration caused a decrease in Mw, protein content, and TPC of CAXs or WAXs and the corresponding CAXs or WAXs emulsions showed bigger and more unstable oil droplets during 14 d storage. The Mw, protein, and TPC were well correlated with their emulsion stability. Furthermore, emulsions stabilized by AXs with low-concentration NaOH could resist better various temperatures, pH, and NaCl. In conclusion, the structural properties of AXs derived from different cereal sources and treated with different concentrations of NaOH varied, leading to differences in their ability to stabilize emulsions. CAXs or WAXs obtained from low-concentration NaOH treatment demonstrated significant potential as highly effective natural emulsifiers.

The Effect of Alkalization on the Mechanical Properties of Sansevieria Fiber Bio-Composit

Alkali treatment of natural fibers has a role in removing hemicellulose and lignin layers. This layer prevents the matrix from bonding with the natural fiber cellulose structure. The use of an inappropriate type of alkali will reduce its effectiveness and can even damage the cellulose layer. This study compared the effectiveness of alkaline NaOH, CaOH and KOH in removing lignin and hemicellulose and their ability to maintain cellulose content. The use of the immersion method in alkaline solutions is well controlled. The FTIR characterization test was used to detect functional group changes, the TGV test to detect heat resistance ability, the XRD test to detect structural changes in crystalline and amorphous properties of sansevieria natural fibers. Furthermore, the tensile test to determine the effect of alkaline treatment on changes in mechanical strength Tensile strength. From the test results it was found that the alkaline NaOH gave the best characteristics by detecting the presence of cellulose, tensile strength and the nature of the crystalline atomic structure.
 Highlights: 
 
 Effectiveness of Alkali Types: Comparison of NaOH, CaOH, and KOH effectiveness in removing lignin and hemicellulose while preserving cellulose content.
 Characterization Techniques: FTIR, TGA, and XRD tests used for functional group changes, heat resistance, and structural properties evaluation.
 NaOH Superiority: Alkaline NaOH treatment demonstrated best results in maintaining cellulose, enhancing tensile strength, and influencing atomic structure.
 
 Keywords: Alkali treatment, Natural fibers, Lignin removal, Cellulose preservation, Tensile strength.

Melt electrospinning writing PCL scaffolds after alkaline modification with outstanding cytocompatibility and osteoinduction

Melt electrospinning writing (MEW) is a promising three-dimensional (3D) printing technology that enables the creation of scaffolds with highly ordered microfibers. Polycaprolactone (PCL) is an ideal material for MEW scaffold fabrication due to its exceptional printability. However, its low cellular affinity can hinder its performance in bone tissue engineering. This study aimed to explore the potential of NaOH treatment as a means of enhancing the cytocompatibility and osteoinductive properties of PCL scaffolds. After modification with a NaOH solution, the physiochemical properties of the MEW PCL scaffold were analyzed. The surface of the scaffold was found to have nanopits and nanogrooves, which differed from the smooth surface of the PCL scaffold. Atomic force microscopy and automatic water contact angle assays revealed an increase in surface roughness and wettability, both of which were found to be beneficial for cell proliferation and adhesion. In vitro experiments demonstrated that the NaOH-treated surface was able to induce osteogenic differentiation of rat bone marrow mesenchymal stem cells (BMSCs) via the integrinα2/β1-PI3K-Akt signaling pathway, which had not been previously observed. The study involved implanting PCL scaffold to repair a cranial defect. After 1 and 3 months of implantation, histological analysis and micro-computed tomography scans showed a higher amount of newly formed bone on the NaOH-treated PCL scaffolds compared to the PCL scaffold. The study concluded that NaOH treatment was a simple and effective way to enhance cellular affinity and osteoinductive property of MEW PCL scaffold. This strategy may provide a cost-efficient method for promoting bone regeneration.

Functional and Tableting Properties of Alkali-Isolated and Phosphorylated Barnyard Millet (Echinochloa esculenta) Starch.

The functional and tableting properties of barnyard millet starch (Echinochloa esculenta) were investigated in its native (alkali-treated) and chemically modified (phosphorylated) states. The grains were pulverized, soaked, and ground before filtration to separate starch and protein. Multiple NaOH treatments were performed. The starch was washed, neutralized, and dried. Sodium tripolyphosphate (STPP) and sodium sulfate were used to modify the starch, followed by maceration, washing, and drying to remove unreacted chemicals. The amylose content of alkali-treated barnyard millet starch increased by 19.96 ± 3.56% w/w. The amount of protein, the kind of starch used, and the size of the starch granules, all affected the ability of the starch granules to swell up. It was observed that alkali-extracted barnyard millet starch (AZS) has a swelling power of 194.3 ± 0.0064% w/w. The swelling capacity of treated starch was lesser as compared to the native alkali barnyard millet starch. Decrement in swelling power of phosphorylated starch was observed due to tightening of bonds in the molecular structure. The moisture content of the excipients may affect the overall stability of the formulation. The moisture content of the AZS was found to be 15.336 ± 1.012% w/w. Compared to AZS, cross-linked barnyard millet starch had a moisture content that was up to 20% lower than AZS. The Hausner ratio for phosphorylated starch was found to be 1.25, which indicates marked flow property. Similar morphologies could be seen in the alkali-isolated barnyard millet starch and the cross-linked/phosphorylated barnyard millet that was cross-linked using a mixture of sodium sulfate and sodium tripolyphosphate. The modest degree of substitution would have no effect on the surface morphology as shown by the scanning electron microscopic study. The crushing and compacting abilities of modified barnyard millet starch were also improved, but its friability and rate of disintegration were decreased. The whole study revealed that after cross-linking, barnyard millet had good tableting properties and it can be used as an excipient in drug delivery.

Investigating the influence of different pretreatment methods on the morphological structure of Arachis hypogea shells

This study investigates the effect of acid, alkali, and thermal pretreatment methods on the morphological structure of Arachis hypogea shells. Arachis hypogea shells were pretreated with H2SO4, NaOH, and conventional thermal treatment. The effect of the pretreatment on the microstructure, crystallinity and functional groups was examined using Structural Electron Microscopy, X-ray Diffraction, and Fourier Infra-red Transform (FTIR). The results showed that the different pretreatment techniques have varying effects on the microstructure of the feedstock. The crystallinity index of Arachis hypogea shells differs with treatment, and the FTIR results indicated that the functional groups were detected at different wavenumbers.

Enhancement of methane yield of Arachis hypogea shells using chemical pretreatment techniques

Anaerobic digestion of lignocellulose feedstocks requires a lengthy period, and the process's efficiency is always low without catalysis. Therefore, this study investigated the influence of chemical pretreatment methods on the methane yield of Arachis hypogea shells using H2SO4 and NaOH. The pretreated substrates were digested in a lab-batch digester for 30 days at mesophilic temperature (37 °C). The optimum methane yield of 205.22 ml/gVSadded was recorded at 0.5% (v.v-1) H2SO4 for 15 min, while 3% (w/w) NaOH treatment for 15 min released the optimum methane yield of 256.78 ml/gVSadded.

Effect of pre-treated waste tire rubber on properties of concrete

In present day scenario the human activities have led to environmental degradation with increased urbanization contributing to many fold increase in constructing activities, which uses limited natural resources. Therefore, prevention of resource over-utilization and recycling of the waste is of utmost priority in construction sector. Waste tires rubber is one such potential material which can be used in concrete as replacement for fine aggregates replacement. This study represents the effect of addition of crumb rubber in concrete as sand replacement ranging from 5-20% on volume basis. The study evaluated the workability, compressive strength, ultrasonic pulse velocity (UPV), electrical resistivity and water permeability at 28 days. Tire rubber was also pre-treated with NaOH and KMnO4 as an effort to enhance its bonding characteristics. The contact angle was measure to test the efficacy of the treatment in reducing water hydrophobicity of crumb rubber. The treatment of tire rubber with NaOH and KMnO4 proved to be promising in regaining some of lost compressive strength and improved water permeability. However, both treatment processes didn’t have any significant effect on the workability. The NaOH treatment proved to be an overall better treatment than KMnO4 which was due to the reduced hydrophobicity as depicted by lower contact angle.

Performance evaluation of treated coconut fibre in cementitious system

In this study, concentrated cement pore solution (CPS) was prepared and coconut fibre was soaked in it, to mimic worst condition of cementitious medium. Four coconut fibre samples were studied; the first was untreated fibre (NT), the second sample was NaOH treated fibre, while the third and fourth samples were NT and NaOH fibres soaked in CPS for 28 days, respectively. Each fibre was characterized by determining their physical and mechanical properties. Hydrophilic/hydrophobic characters were determined by measuring contact angles in water, while surface morphology of the fibre samples were studied with the aid of scanning electron microscopy. EDS was used to determine the elemental composition of the fibres, while Thermogravimetric analysis was performed to assess thermal stability of the fibre samples. Crystallinity of the fibres as well as the functional group composition present in each fibre samples, was determined using XRD and FTIR respectively. The results showed that fibres treated with NaOH and those exposed to CPS had higher densities (1.94 g/cm3) than untreated fibre (1.64 g/cm3), while the tensile strength was greatly increased by about 120%. SEM images of the fibres indicated that NaOH and CPS caused removal of lignin and hemicellulose, making the lumens to be smaller compared to untreated fibre. Similarly, crystallinity of the fibre was increased due to NaOH and CPS treatment, compared to the untreated fibres. CPS was found to improve thermal stability of the fibres. It was concluded that CPS did not pose any threat to performance of fibre.

Insight into the construction of multi-cavity micro-mesoporous SSZ-13: Dissolution, Al backfilling and framework reconstruction

The alkali leaching post-treatment method is a simple, economical and general route for introducing mesopores into SSZ-13, while the existing studies have rarely addressed the Al behavior between solution and zeolites framework during the alkali treatment. In this paper, a series of multi-cavity micro-mesoporous SSZ-13 were successfully prepared by using the alkali leaching post-treatment method at various treatment time. Extensive characterization illustrated that Al backfilling and zeolite framework reconstruction also existed during the NaOH treatment, besides the destruction of the zeolite framework due to the dissolution of Si and Al at the beginning of the reaction, and Al was preferentially backfilled into eight-membered ring (8 MR) to repair the zeolite framework and then filled into six-membered ring (6 MR) to reconstruct the zeolite framework. Concurrently, the amount of Brønsted acid (B acid) showed a decreasing-increasing-stabilizing trend during the progress. The catalytic activity and hydrothermal stability tests confirmed that multi-cavity micro-mesoporous SSZ-13 showed excellent catalytic activity for NH3 selective catalytic reduction (NH3-SCR) and good hydrothermal stability. This study provided basic guidance for the optimal design of the post-treatment alkali leaching route, which was highly significant for the development of hierarchically porous zeolites.

Effects of dissolution by alkali treatment on anisotropic surface properties and flotation behavior of spodumene

The effect of dissolution pretreatment of spodumene using NaOH and Na2CO3 was investigated by micro-flotation test, contact angle measurement, XPS, ICP and AFM imaging. The results showed that NaOH treatment activated the spodumene flotation whilst Na2CO3 showed little depression effect. NaOH had more significant activating effect on the spodumene (001) surface than (110) surface. The surface dissolution was confirmed by AFM, showing that weak surface dissolution was observed in ultrapure water and Na2CO3 solution, while there was strong surface dissolution in NaOH solution. Some precipitates coated the surface at the very start in NaOH and Na2CO3 solution, and the precipitates redissolved rapidly in NaOH solution while redissolved very slowly in Na2CO3 solution. The ICP results verified the release of Si, Al and Li from spodumene surface. NaOH treatment gave larger relative contents of Al on spodumene surface than Na2CO3, and the relative contents of Al on the (001) surface increased to a greater extent than on the (110) surface, as revealed by XPS analysis. From the point of crystal structure, the dissolution made more dangling Al exposed on the (001) surface, making it more favor of NaOL adsorption.

A technique for high-density wood softening in the micro-sectioning process for wood anatomy studies

Summary Wood identification for commercial applications is important and has a significant demand worldwide. Microscopic wood identification involves many processes such as softening, sectioning, and data analysis. Softening of wood is a crucial method for obtaining good sections for microscopic analysis but softening high-density wood is difficult. An alternate method of softening high-density wood for wood identification is presented. Different concentrations of alkali, NaOH, were tried, and optimized for different treatment times to obtain adequate softening of high-density wood. 20% NaOH treatment for 5 days at 30°C was used to soften high-density wood of variable density between 1 and 1.118 g/cm3. The species studied were Calophyllum spp., Shorea robusta, and Handroanthus spp., in which softening was satisfactory.

Investigation of CO2 Adsorption on Avocado Stone-Derived Activated Carbon Obtained through NaOH Treatment.

Activated carbons were prepared from avocado stone through NaOH activation and subsequent carbonization. The following textural parameters were achieved: specific surface area: 817-1172 m2/g, total pore volume: 0.538-0.691 cm3/g, micropore volume 0.259-0.375 cm3/g. The well-developed microporosity resulted in a good CO2 adsorption value of 5.9 mmol/g at a temperature of 0 °C and 1 bar and selectivity over nitrogen for flue gas simulation. The activated carbons were investigated using nitrogen sorption at -196 °C, CO2 sorption, X-ray diffraction, and SEM. It was found that the adsorption data were more in line with the Sips model. The isosteric heat of adsorption for the best sorbent was calculated. It was found that the isosteric heat of adsorption changed in the range of 25 to 40 kJ/mol depending on the surface coverage. The novelty of the work is the production of highly microporous activated carbons from avocado stones with high CO2 adsorption. Before now, the activation of avocado stones using NaOH had never been described.

Area-Selective Depolymerization of Hydroxycinnamates Visualized by Raman Imaging in Miscanthus sinensis cv. Cell Wall.

Lignin-carbohydrate complexes (LCCs) are regarded as a barrier for lignocellulosic biomass refinery. Here, confocal Raman microspectroscopy has been used to visualize the dissolution of hydroxycinnamates (HCMs) incorporated into LCCs by ether and ester bonds for energy crops Miscanthus sinensis cv. during successive NaOH (2.5% w/w) treatment. Raman spectral analysis indicated that mild NaOH treatment resulted in a higher proportion of HCM depolymerization in highly lignified middle lamella areas (>66.0%) than carbohydrate-abundant secondary walls. Furthermore, Raman imaging revealed preferential depolymerization of lignin from the sclerenchyma fiber (Sf) and parenchyma (Par) secondary wall with an increment of treatment time from 0 to 25 min, while middle lamella areas of Sf and Par were less affected where the depolymerization of HCMs was closely related with that of lignin (coefficient factors > 0.96). A better understanding of the depolymerization behavior for HCMs accompanied by lignin depolymerization was important to break LCC bonds in herbaceous biomass efficiently.

Characterization of friction and wear of phenolic resin matrix composites reinforced by bamboo fibers of alkaline and LaCl3 treatment

Mechanical and tribological properties of phenolic resin matrix composites reinforced by bamboo fibers, which were pre-treated with sodium hydroxide (NaOH) and post-treated with lanthanum chloride (LaCl3), were characterized by hardness, impact, microscratch tests, friction and wear testers, and thermogravimetric analysis. Bamboo fibers before and after modification were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Hemicellulose and lignin of bamboo fibers can be dissolved by alkaline or NaOH treatment, resulting in a rough surface. The high coordination number of rare earth atoms in LaCl3 solution enhanced the formation of chemical bonds between the hydroxyl groups of bamboo fibers and the oxygen-containing groups on the molecular chain of phenolic resin. The hardness and impact strength of the composites both firstly increased and then decreased with an increase in LaCl3 concentration or soaking duration in LaCl3 solution. Tribological performance (e.g. high-temperature friction coefficient, wear rate, thermogravimetric loss, crack propagation) of phenolic resin matrix composites was significantly improved by the treated bamboo fibers. The optimum mechanical and tribological properties of bamboo fiber-reinforced phenolic resin matrix composites were achieved under the conditions of LaCl3 concentration of 10% and soaking duration of 30 min.

Experimental investigation on mechanical properties of Kenaf fibre reinforced epoxy composites with annona squamosa powder

The adoption of biodegradable and environmentally-friendly composite materials is gaining momentum in diverse engineering sectors due to their growing popularity. The present investigation focuses on analysing the influence of fibre treatment on the mechanical properties of hybrid composites made of Kenaf fibres and epoxy matrix. The fibre is subjected to NaOH treatment initially, which is subsequently followed by a comprehensive drying process. The second scenario involves the utilisation of custard apple seed powder, a biodegradable filler material, to modify the matrix. The utilisation of microscopy is employed as a means to analyse the modified fibres and to identify any potential surface alterations that may have taken place. Following this, epoxy composites are fabricated by utilising modified and unmodified Kenaf fibres through a basic hand layup method with vacuum bagging. The composites that have been prepared are subsequently evaluated for their characteristics through tensile and flexural measurements, in compliance with the applicable ASTM standards.

Sodium Hydroxide Hydrothermal Extraction of Lignin from Rice Straw Residue and Fermentation to Biomethane

The purpose of the NaOH pretreatment of rice straw with a recycling strategy was to enhance the economic efficiency of producing biomethane. Anaerobic digestion is used for converting rice straw into biogas. In this work, 5% NaOH and rice straw mixed samples were autoclaved at 121 °C for 20 min for lignin removal. The NaOH black liquor was separated using filtration for the subsequent treatment cycle. The NaOH liquor was utilized in one more subsequent recycling procedure to test its ability to remove lignin from the rice straw. The 5% NaOH treatment results in a reduction in rice straw (RC) lignin of 73.6%. The lignin content of the recycled NaOH-filtrated rice straw samples (RCF1) was reduced by 55.5%. The 5% NaOH-treated rice straw sample yields a total cumulative biogas of 1452.4 mL/gVS, whereas the recycled NaOH-filtered (RCF1) samples generate 1125.2 mL/gVS after 30 days of incubation. However, after 30 days of incubation, the untreated rice straw (RCC) bottle produced a total of 285.5 mL/gVS of biogas. The total increase in methane output after NaOH treatment is 6–8 times greater, and the biogas yield improves by 80–124%. We show here that the recycled NaOH black solution has still the effectiveness to be used for successive pretreatment cycles to remove lignin and generate methane. In the meantime, the NaOH black solution contains useful materials (lignin, sugars, potassium, and nitrogen) that could be purified for commercial purposes, and more importantly recycling the NaOH solution decrease the chances of environmental pollution. Thus, recycling NaOH decreased chemical consumption, which would provide net benefits instead of using fresh NaOH solution, had a lower water consumption, and provided the prospect of producing an optimum yield of methane in anaerobic digestion. This method will decrease the chemical treatment costs for biomass pretreatment prior to anaerobic digestion. Recycling of NaOH solution and the integration of pretreatment reactors could be a novel bioprocessing addition to the current technology.