Dye removal of activated carbons prepared from NaOH-pretreated rice husks by low-temperature solution-processed carbonization and H3PO4 activation

A coupling of low-temperature sulfuric acid-assisted carbonization and H3PO4 activation was employed to convert NaOH-pretreated rice husks into activated carbons with extremely high surface area (2028 m(2) g(-1)) and integrated characteristics. The influences of the activation temperature and impregnation ratio on the surface area, pore volume of activated carbons were thoroughly investigated. The morphology and surface chemistry of activated carbons were characterized using N2 sorption, FTIR, XPS, SEM, TEM, etc. The adsorption capacity of resulting carbons obtained under optimum preparation conditions was systematically evaluated using methylene blue under various simulated conditions. The adsorption process can be well described by both Langmuir isotherm model and the pseudo-second order kinetics models; and the maximum monolayer capacity of methylene blue was ca. 578 mg g(-1).

Thermo-alkaline pretreatment of waste activated sludge at low-temperatures: effects on sludge disintegration, methane production, and methanogen community structure

Low-temperature thermo-alkaline pretreatment of waste activated sludge (WAS) was studied, within the region of 0-0.2 M NaOH and 60-90°C, for the effects of NaOH concentration and temperature on sludge degradability in anaerobic digestion (AD). Significant disintegration of sludge solids (up to 75.6%) and an increase in methane production (up to 70.6%) were observed in the pretreatment trials. Two quadratic models were successfully generated by response surface analysis (R(2)>0.9, p<0.05) to approximate how the degree of sludge disintegration (SD) and methane production (MP) respond to changes in the pretreatment conditions. The maximum responses of SD (77.8%) and MP (73.9% increase over the control) were shown at [0.16 M NaOH, 90°C] and [0.10 M NaOH, 73.7°C], respectively. NaOH addition showed a significant influence on the evolution of methanogen community structure during AD, whereas temperature did not. Aceticlastic Methanosaeta and Methanosarcina speceies were likely the major methanogens.

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.

Synergistic benefits of ionic liquid and alkaline pretreatments of poplar wood. Part 1: effect of integrated pretreatment on enzymatic hydrolysis

An environmentally friendly pretreatment process was developed to fractionate hemicelluloses and lignin from poplar wood by ionic liquid (IL) pretreatment coupled with mild alkaline extraction. Hemicellulosic and lignin fractions were obtained in high yields, amounting to 59.3% and 74.4%, respectively, which can served as raw materials for production of value-added products. The yield of glucose for the integrated pretreated poplar wood was 99.2%, while it was just 19.2% for the untreated material. The synergistic benefits of the removal of lignin and hemicelluloses, the increase of the cellulose surface area, and the conversion of cellulose fibers from the cellulose I to the cellulose II crystal phase resulted in the high glucose yield for the integrated pretreated substrate. Therefore, the IL based biorefining strategy proposed can integrate biofuels production into a biorefinery scheme in which the major components of poplar wood can be converted into value-added products.

Influence of twin-screw extrusion on soluble arabinoxylans and corn fiber gum from corn fiber

BACKGROUND

The effect of feed moisture content and screw speed in the extrusion process with and without chemical pretreatment of corn fiber was investigated. Different chemical pretreatment methods (NaOH and H2 SO4 solution) were compared. The improvement of reducing sugar, soluble arabinoxylans (SAX) content and the yield of corn fiber gum was measured.

RESULTS

A high reducing sugar content was obtained in the filtrate fraction from the extruded destarched corn fiber (EDCF) with H₂SO₄ pretreatment. Feed moisture content most effectively improved both reducing sugar and SAX content of filtrate. Increasing feed moisture content and screw speed resulted in a higher SAX content in the filtrate of the EDCF with NaOH pretreatment. The SAX content of the residual solid from the EDCF with NaOH pretreatment was higher compared to H₂SO₄ pretreated and unpretreated samples and significantly increased with decreasing feed moisture content. The screw speed did not have a major impact after enzyme hydrolysis. The yield of corn fiber gum was increased by 12% using NaOH pretreatment combined with extrusion process as compared to the destarched corn fiber.

CONCLUSION

The results show the great potential of the extrusion process as an effective pretreatment for disruption the lignocelluloses of corn fiber, leading to conversion of cellulose to glucose and hemicelluloses to SAX and isolation of corn fiber gum.

A novel anaerobic co-culture system for bio-hydrogen production from sugarcane bagasse

A novel co-culture of Clostridium thermocellum and Thermoanaerobacterium aotearoense with pretreated sugarcane bagasse (SCB) under mild alkali conditions for bio-hydrogen production was established, exhibiting a cost-effective and synergetic advantage in bio-hydrogen production over monoculture of C. thermocellum or T. aotearoense with untreated SCB. The optimized pretreatment conditions were established to be 3% NaOH, and a liquid to solid ratio of 25:1 at 80°C for 3h. A final hydrogen production of 50.05±1.51 mmol/L was achieved with 40 g/L pretreated SCB at 55°C. The established co-culture system provides a novel consolidated bio-processing strategy for bioconversion of SCB to bio-hydrogen.

Benefit of sodium hydroxide pretreatment of ensiled sorghum forage on the anaerobic reactor stability and methane production

The assessment of the pretreatment effect on the anaerobic digestion process is generally based on the results of batch tests, which may fail in truly predicting full-scale anaerobic reactors performance. Therefore, in this study, the effect of alkaline pretreatment on the anaerobic digestion of ensiled sorghum forage was evaluated by comparing the results of two semi-continuous CSTR (Continuously Stirred Tank Reactor) anaerobic reactors. Results showed that an alkaline pretreatment step, prior to the anaerobic digestion of ensiled sorghum forage, can have a beneficial effect both in enhancing methane production (an increase of 25% on methane production was observed, if compared to that of untreated sorghum) and in giving more stability to the anaerobic digestion process.

NaOH-debittering induces changes in bacterial ecology during table olives fermentation

Limited information is available on the impact of the NaOH treatment on table olive fermentations, and for this reason a polyphasic approach has been adopted here to investigate its effect on the fermentation dynamics and bacterial biodiversity. The microbial counts of the main groups involved in the transformation have not shown any differences, apart from a more prompt start of the fermentation when the olives were subjected to the NaOH treatment. The data produced by culture-independent analyses highlighted that the fermentation of table olives not treated with NaOH is the result of the coexistence of two different ecosystems: the surface of the olives and the brines. A sodium hydroxide treatment not only eliminates this difference, but also affects the bacterial ecology of the olives to a great extent. As proved by high-throughput sequencing, the fermentation of the olives not treated with NaOH was characterized by the presence of halophilic bacteria, which were substituted by Lactobacillus at the later stages of the fermentation, while enterobacteria were dominant when the olives were treated with sodium hydroxide. Higher biodiversity was found for Lactobacillus plantarum isolated during untreated fermentation. Different biotypes were found on the olive surface and in the brines. When the debittering process was carried out, a decrease in the number of L. plantarum biotypes were observed and those originating from the surface of the olive did not differentiate from the ones present in the brines.

Use of artificial neural network (ANN) for the development of bioprocess using Pinus roxburghii fallen foliages for the release of polyphenols and reducing sugars

In present study, different parameters, i.e., percentage of NaOH, loading volume, microwave power (watt) and volume of water during pretreatment were optimized by ANN for release of polyphenols and sugars from pine fallen foliage. ANN used was feed forward back propagation type with 72 input, 72 output and 10 hidden layers coupled with Lvenberg-Marquardt (LM) training algorithms. The predicted optimal values by generated neural network for alkali pretreatment were 6 ml (0.5% NaOH)/g of substrate, soaking time of 10 min followed by 1 min of 100 W microwave. Pretreated sample on enzymatic hydrolysis at 50°C for 20 h with cocktail of cellulase, xylanase and laccase produced by locally isolated consortia released 668.9 mg/g of total sugar and 265.06 mg/g of total polyphenols. Optimization by ANN showed good yield, therefore, indicating its suitability for bioprocess modeling and control for release of reducing sugars and polyphenols from pine foliage.

Alkaline post-treatment for improved sludge anaerobic digestion

Alkaline post-treatment was tested in order to improve sludge anaerobic digestion. Between the 8th and the 12th hour of a 24-h digestion cycle, 5% of sludge was extracted from a semi-continuous digester with a sludge retention time of 20 days. The sludge was then disintegrated with 0.1 mol/L NaOH and returned to the digester after neutralization. The results showed that alkaline post-treatment increased the level of soluble organic substances in the extracted sludge, particularly of volatile fatty acids and polysaccharides. This process resulted in a 33% enhancement of biogas production in comparison with the control. When the ratio of the recycled sludge was further increased to 10% or 15%, the increment of biogas yield was reduced, due to excessive inactivation of anaerobic bacteria in the digester. Alkaline post-treatment had a minimal impact on the dewaterability of digested sludge.

Production of polyols via direct hydrolysis of kraft lignin: effect of process parameters

Kraft lignin (KL) was successfully depolymerized into polyols of moderately high hydroxyl number and yield with moderately low weight-average molecular weight (Mw) via direct hydrolysis using NaOH as a catalyst, without any organic solvent/capping agent. The effects of process parameters including reaction temperature, reaction time, NaOH/lignin ratio (w/w) and substrate concentration were investigated and the polyols/depolymerized lignins (DLs) obtained were characterized with GPC-UV, FTIR-ATR, (1)H NMR, Elemental & TOC analyzer. The best operating conditions appeared to be at 250°C, 1h, and NaOH/lignin ratio ≈0.28 with 20 wt.% substrate concentration, leading to <0.5% solid residues and ∼92% yield of DL (aliphatic-hydroxyl number ≈352 mg KOH/mg and Mw≈3310 g/mole), suitable for replacement of polyols in polyurethane foam synthesis. The overall % carbon recovery under the above best conditions was ∼90%. A higher temperature favored reduced Mw of the polyols while a longer reaction time promoted dehydration/condensation reactions.

Separation and characterization of effective demulsifying substances from surface of Alcaligenes sp. S-XJ-1 and its application in water-in-kerosene emulsion

The main goal of this work was to analyze the effect of surface substances on demulsifying capability of the demulsifying strain Alcaligenes sp. S-XJ-1. The demulsifying substances were successfully separated from the cell surface with dichloromethane-alkali treatment, and exhibited 67.5% of the demulsification ratio for water-in-kerosene emulsions at a dosage of 356mg/L. FT-IR, TLC and ESI-MS analysis confirmed the presence of a carbohydrate-protein-lipid complex in the demulsifying substances with the major molecular ions from mass-to-charge ratio (m/z) 165 to 814. After the substances separated, the cell morphology changed from aggregated to dispersed, and the concentration of cell surface functional groups decreased. Cell surface hydrophobicity and the ability of cell adhesion to hydrophobic surface of the treated cells was also reduced compared with original cell. It was proved that the demulsifying substances had a significant effect on cell surface properties and accordingly with demulsifying capability of Alcaligenes sp. S-XJ-1.

Synergistic benefits of ionic liquid and alkaline pretreatments of poplar wood. Part 2: characterization of lignin and hemicelluloses

The effect of proposed integrated pretreatment on enzymatic hydrolysis of poplar wood has been reported in Part 1. Part 2 of this work investigated the detailed structural features of the isolated lignin and hemicellulosic fractions, which were obtained in high yields. The chemical structures of these polymer fractions obtained were compared with the corresponding alkaline lignin and hemicelluloses extracted from the raw material without ionic liquid (IL) pretreatment. The yields of alkaline lignin and hemicelluloses obviously increased after the IL pretreatment. No apparent degradation occurred for both lignin and hemicellulosic fractions during this integrated pretreatment process. The lignin fraction (RCEL), which obtained after the enzymatic hydrolysis, exhibited high percentages of β-O-4' aryl ether linkages and S/G ratio. It is believed that the high molecular weight and high purity hemicellulosic and lignin fractions obtained can serve as raw materials for the production of value-added products.

Dye adsorption of mesoporous activated carbons produced from NaOH-pretreated rice husks

In continuation of previous work on utilizing rice husks, this study aimed to prepare mesoporous activated carbons using residues of sodium hydroxide-pretreated RHs, and then examine their dye adsorption performance. The influences of the activation temperature and activation time on the surface area, pore volume, and pore radius of the activated carbon were investigated based on nitrogen adsorption/desorption isotherms and transmission electron microscopy. The adsorptive behavior of the mesoporous activated carbons obtained under optimum preparation conditions was evaluated using methyleneblue as the model adsorbate. The adsorption kinetics was studied by pseudo-first-and pseudo-second-order models, and the adsorption isotherms were studied by Langmuir and Freundlich models. The pseudo-second-order model and Langmuir isotherm were found to fit well the adsorption characteristics of the as-prepared mesoporous activated carbons. Thermodynamic data of the adsorption process were also obtained to elucidate the adsorption thermo-chemistry between the activated carbons produced from NaOH-pretreated RHs and MB molecules.

Selection of the best chemical pretreatment for lignocellulosic substrate Prosopis juliflora

Pretreatment is a pre-requisite step in bioethanol production from lignocellulosic biomass required to remove lignin and increase the porosity of the substrate for saccharification. In the present study, chemical pretreatment of Prosopis juliflora was performed using alkali (NaOH, KOH, and NH3), reducing agents (Na2S2O4, Na2SO3) and NaClO2 in different concentration ranges at room temperature (30±2 °C) to remove maximum lignin with minimum sugar loss. Further, biphasic acid hydrolysis of the various pretreated substrates was performed at mild temperatures. Considering the amount of holocellulose hydrolyzed and inhibitors released during hydrolysis, best chemical pretreatment was selected. Among all the chemicals investigated, pretreatment with sodium dithionite at concentration of 2% (w/v) removed maximum lignin (80.46±1.35%) with a minimum sugar loss (2.56±0.021%). Subsequent biphasic acid hydrolysis of the sodium dithionite pretreated substrate hydrolyzed 40.09±1.22% of holocellulose and released minimum amount of phenolics (1.04±0.022 g/L) and furans (0.41±0.012 g/L) in the hydrolysate.

Anaerobic digestion of poplar processing residues for methane production after alkaline treatment

Poplar processing residues were used for methane production by anaerobic digestion after alkaline treatment and methane production was measured. The highest methane production of 271.9 L/kg volatile solid (VS) was obtained at conditions of 35 g/L and 5.0% NaOH, which was 113.8% higher than non-alkaline treated samples, and 28.9% higher than that of corn straw, which is the conventional anaerobic digestion material in China. The maximal enhancement of 275.5% obtained at conditions of 50 g/L and 7.0% NaOH. Degradation of cellulose, hemicellulose and lignin after treatment increased by 4.0-9.0%, 3.3-6.2%, and 11.1-20.5%, respectively, with NaOH dose ranged from 3.0% to 7.0%. Scanning electron microscopy (SEM), FTIR spectra and Crystallinity measurements showed that the lignocellulosic structures were disrupted by NaOH. The results indicate poplar processing residues might be an efficient substrate for methane production after alkaline treatment.

Impact of cationic polyelectrolyte on the nanoshear hybrid alkaline pretreatment of corn stover: morphology and saccharification study

Cationic polyelectrolyte was first used as the additive in the nanoshear hybrid alkaline pretreatment of corn stover. The novel nanoshear hybrid pretreatment process was recently developed at MSU. The chemical compositions and morphologies were investigated by SEM, TEM, confocal CLSM, and XPS to elucidate the degradation mechanism of cellular structures. At room temperature and fast processing conditions (~2 min), lignin was found to redistribute on the inner and outer surfaces of the cell wall as lignin aggregate droplets instead of being extracted. Free microfibrils in the residues were also observed. The yields of enzymatic hydrolysis were enhanced for the pretreated corn stover with the aid of polyelectrolyte as an additive. We speculate that lignin was effectively modified which opened up the cell wall structure during the short pretreatment process and prevented non-productive binding of enzymes in the enzyme hydrolysis reaction.

Side-chain motion of components in wood samples partially non-crystallized using NaOH-water solution

Wood samples (Picea jezoensis Carr.) were treated with solutions of aqueous NaOH (0-0.20 concentration fraction) and each treated samples evaluated by dynamic mechanical analyses (DMA). NaOH treatment was shown to affect the interactions between microfibrils and the surrounding matrix and, in particular, the dynamics of methylol groups in the microfibrils. The former is not dependent on the degree of crystallization but rather on the eluviation of the matrix. The latter depends on the degree of crystallization. Alkali treatment induces changes in the polymer domains as a result of matrix eluviation. This decreases the dynamics of methylol groups at NaOH concentrations less than 0.11. On the other hand, alkali treatment causes non-crystallization at concentrations greater than 0.11, which quantitatively increases the flexibility of methylol groups. Crystallinity decreased, and main-chain dynamics increased, following treatment with highly concentrated NaOH solutions. The dynamics of lignin also increased due to weakened interactions with microfibrils due to non-crystallization.

Pretreatment of Agave americana stalk for enzymatic saccharification

Agave americana is one of commonly grown agave species but currently less valuable because its large flower stalk cannot be used for producing alcoholic beverage. In the present study, the stalk was pretreated with dilute acid (DA), sulfite (SPORL), and sodium hydroxide (NaOH) to preliminarily assess its potential as feedstock for bioethanol production. The changes of cell wall components during the pretreatments, enzymatic digestibility of the pretreated stalks, and the adsorption of cellulases on the substrates were investigated. Results indicated that the pretreatments significantly improved the enzymatic digestibility of the agave stalk. SPORL pretreatment gave higher substrate and sugar yields, while NaOH pretreated stalk had better digestibility under the investigated conditions. The better hydrolysability of NaOH-pretreated stalk was attributed to low lignin and hemicellulose content and high affinity to cellulases.

Enhancement of enzymatic digestibility of Eucalyptus grandis pretreated by NaOH catalyzed steam explosion

NaOH catalyzed steam explosion was applied to improve the enzymatic digestibility of Eucalyptus grandis. The impregnation of wood chip with NaOH solutions before steam explosion was carried out to investigate the effects of alkaline catalysis on solid recovery, enzymatic digestibility, and glucose recovery. The lignin removal was significantly affected by NaOH as a catalyst and the glucose recovery increased with increased severity index. The use of NaOH showed higher enzymatic digestibility than the use of water at most severity indexes due to the delignification of biomass and the increase of accessibility to cellulose of enzyme. The maximum glucose recovery was 65.55% having 4.4361 of severity index with 7wt.% of NaOH catalyzed steam explosion at 210°C during 9min. NaOH catalyzed steam explosion was effective to enhance the enzymatic digestibility due to the removal of lignin.

Inhibitory effect on in vitro Streptococcus oralis biofilm of a soda-lime glass containing silver nanoparticles coating on titanium alloy

This paper reports the effect of soda-lime-glass-nAg coating on the viability of an in vitro biofilm of Streptococcus oralis. Three strains (ATCC 35037 and two clinical isolates from periodontitis patients) were grown on coated with glass, glass containing silver nanoparticles, and uncoated titanium alloy disks. Two different methods were used to quantify biofilm formation abilities: crystal violet staining and determination of viable counts. The influence of the surface morphology on the cell attachment was studied. The surface morphology was characterized by scanning electron microscopy (SEM) and using a profilometer. SEM was also used to study the formation and the development of biofilm on the coated and uncoated disks. At least a >99.7% inocula reduction of biofilm respect to titanium disks and also to glass coated disks was observed in the glass-nAg coated disks for all the studied strains. A quantitative evaluation of the release of silver was conducted in vitro to test whether and to what extend the biocidal agent (silver) could leach from the coating. These findings suggest that the biofilm formation of S. oralis strains is highly inhibited by the glass-nAg and may be useful for materials which require durable antibacterial effect on their surfaces, as it is the case of dental implants.

Alkali and heat treatment of titanium implant material for bioactivity

PURPOSE

This study was conducted to evaluate alkali- and heat-treated titanium implant material.

MATERIALS AND METHODS

Ninety-eight square plates of commercially pure titanium were divided into three groups. Group 1 plates were left untreated, and groups 2 and 3 were subjected to anodization and alkali treatment for 24 and 48 hours, respectively. Treated specimens were then subdivided into three equal subgroups (a, b, and c), which were heat treated for 1 hour at temperatures of 500°C, 700°C, and 800°C, respectively. Changes in the crystalline structure were analyzed using x-ray diffractometry. Surface roughness was measured using a surface roughness tester. Selected specimens were immersed in a specially prepared simulated body fluid for 10 days. Calcium and phosphorous deposition on the specimens was detected using energy dispersive x-ray analysis.

RESULTS

Increasing the alkali treatment period and heat treatment temperature positively affected surface roughness and formation of a bioactive sodium titanium oxide (sodium titanate) layer on the titanium surface, especially after heat treatment at 800°C. There was a significantly higher calcium deposition on specimens of group 3 in comparison with those of groups 1 and 2. The results of pH and ion concentration changes of the used simulated body fluid confirmed the results of energy dispersive x-ray analysis.

CONCLUSION

Alkali and heat treatment of titanium implant materials created better treatment conditions for obtaining a bioactive implant material.

Preparation of activated carbon by microwave heating of langsat (Lansium domesticum) empty fruit bunch waste

The feasibility of langsat empty fruit bunch waste for preparation of activated carbon (EFBLAC) by microwave-induced activation was explored. Activation with NaOH at the IR ratio of 1.25, microwave power of 600 W for 6 min produced EFBLAC with a carbon yield of 81.31% and adsorption uptake for MB of 302.48 mg/g. Pore structural analysis, scanning electron microscopy and Fourier transform infrared spectroscopy demonstrated the physical and chemical characteristics of EFBLAC. Equilibrium data were best described by the Langmuir isotherm, with a monolayer adsorption capacity of 402.06 mg/g, and the adsorption kinetics was well fitted to the pseudo-second-order equation. The findings revealed the potential to prepare high quality activated carbon from langsat empty fruit bunch waste by microwave irradiation.

Pilot-scale ethanol production from rice straw hydrolysates using xylose-fermenting Pichia stipitis

Ethanol was produced at pilot scale from rice straw hydrolysates using a Pichia stipitis strain previously adapted to NaOH-neutralized hydrolysates. The highest ethanol yield was 0.44 ± 0.02 g(p)/g(s) at an aeration rate of 0.05 vvm using overliming-detoxified hydrolysates. The yield with hydrolysates conditioned by ammonia and NaOH was 0.39 ± 0.01 and 0.34 ± 0.01 g(p)/g(s), respectively, were achieved at the same aeration rate. The actual ethanol yield from hydrolysate fermentation with ammonia neutralization was similar to that with overliming hydrolysate after taking into account the xylose loss resulting from these conditioning processes. Moreover, the ethanol yield from ammonia-neutralized hydrolysates could be further enhanced by increasing the initial cell density by two-fold or reducing the combined concentration of furfural and 5-hydroxymethyl furfural to 0.6g/L by reducing the severity of operational conditions in pretreatment. This study demonstrated the potential for commercial ethanol production from rice straw via xylose fermentation.

Effect of additives on subcritical water hydrolysis of whey protein isolate

The objective was to examine the effect of the additives acetic acid, lactic acid, sodium bicarbonate, sodium chloride, and sodium hydroxide on the hydrolysis of whey protein isolate with subcritical water. A screening experimental design was used to study the effect of temperature, time, and additives. The most influential additive, sodium bicarbonate, along with temperature and time was used in a second experimental design to predict the treatment conditions to maximize the degree of hydrolysis and production of free amino acids. The maximum degree of hydrolysis achieved was 50% at a concentration of 1.24 M sodium bicarbonate, 291 °C, and 28 min. The highest concentration of total amino acids was 83.0 mg/g of whey protein isolate with 0.83 M sodium bicarbonate at 264 °C for 29 min. Compared to water alone, sodium bicarbonate increased the degree of hydrolysis 4-fold and the production of amino acids by 44% and decreased peptides' molecular weight.