Acid-alkali Pretreatment Research Articles

Comparative Assessment of Fungal Consortium Ligninolytic Enzymes Versus Sequential Acid–Alkali Pretreatments for Bioethanol Production from Rice Straw

Comparative Assessment of Fungal Consortium Ligninolytic Enzymes Versus Sequential Acid–Alkali Pretreatments for Bioethanol Production from Rice Straw

A competitive-adsorption chemical vapor deposition method: Diamond coated on WC-Co substrate without acid-alkali pretreatment by adding graphene oxide particles

Detrimental components existed in substrate surface are regarded as a severe barrier of growing the chemical vapor deposition (CVD) coating. In this work, a novel competitive-adsorption CVD method was proposed to deposit the diamond coating on Co-cemented tungsten carbide (WC–Co) substrate without traditional acid-alkali pretreatment. Graphene oxide (GO) particles were adopted as the adsorbent to introduce the competitive adsorption with Co element during deposition. Four different GO concentrations were conducted to evaluate the effect of GO particles on the coating. The results shown that the WC-Co substrate with GO particles and without pretreatment can be covered by the integrated microcrystalline diamond (MCD) coating (GO-MCD) that presented the similar surface morphology to the MCD coated on WC-Co substrate with acid-alkali pretreatment (P-MCD). Furthermore, Raman spectra, AFM, XPS and XRD patterns only presented a slight difference between the GO-MCD coating and the P-MCD coating. Indentation test suggested that GO particles can enhance the adhesion strength and crack resistance of diamond coating. Meanwhile, GO particles did not deteriorate the tribological property of diamond coating. Hence, our proposed method might provide a promising approach to deposit the desired coating on the given substrate even with some detrimental components.

Simultaneous Saccharification and Fermentation of Empty Fruit Bunches of Palm for Bioethanol Production Using a Microbial Consortium of S. cerevisiae and T. harzianum

A simultaneous saccharification and fermentation (SSF) optimization process was carried out on pretreated empty fruit bunches (EFBs) by employing the Response Surface Methodology (RSM). EFBs were treated using sequential acid-alkali pretreatment and analyzed physically by a scanning electron microscope (SEM). The findings revealed that the pretreatment had changed the morphology and the EFBs’ structure. Then, the optimum combination of enzymes and microbes for bioethanol production was screened. Results showed that the combination of S. cerevisiae and T. harzianum and enzymes (cellulase and β-glucosidase) produced the highest bioethanol concentration with 11.76 g/L and a bioethanol yield of 0.29 g/g EFB using 4% (w/v) treated EFBs at 30 °C for 72 h. Next, the central composite design (CCD) of RSM was employed to optimize the SSF parameters of fermentation time, temperature, pH, and inoculum concentration for higher yield. The analysis of optimization by CCD predicted that 9.72 g/L of bioethanol (0.46 g/g ethanol yield, 90.63% conversion efficiency) could be obtained at 72 h, 30 °C, pH 4.8, and 6.79% (v/v) of inoculum concentration using 2% (w/v) treated EFBs. Results showed that the fermentation process conducted using the optimized conditions produced 9.65 g/L of bioethanol, 0.46 g/g ethanol yield, and 89.56% conversion efficiency, which was in close proximity to the predicted CCD model.

Two-stage acid-alkali pretreatment of vetiver grass to enhance the subsequent sugar release by cellulase digestion

Vetiver grass (VG; Chrysopogon zizanioides) can be used as a potential feedstock for biofuels and biochemical production due to its chemical composition, which is rich in cellulose, hemicellulose, and lignin. However, the complex and recalcitrant nature of a lignocellulosic biomass requires a pretreatment process to disrupt the lignin seal in the cell wall in order to increase the accessibility for enzymatic hydrolysis and to liberate the sugars contained within the cellulose. The sequential acid-base pretreatment of VG using dilute sulphuric acid (H2SO4) followed by sodium hydroxide (NaOH) was found to be optimal when using a 5% (w/v) VG loading in 0.5% (v/v) H2SO4 at 120 °C, 60 min in the first stage followed by 4% (w/v) NaOH at 120 °C, 60 min in the second stage. This gave the highest yield of total reducing sugars (32.6 g/L as 22.0 and 10.6 g/L of hexose and pentose, respectively) in the subsequent cellulase digestion, which was 10.3% and 46.1% higher than that obtained with the single-stage alkali (24.1 g/L) or acid (13.5 g/L) pretreatment, respectively.

Integrated glycolysis and pyrolysis process for multiple utilization and cadmium collection of hyperaccumulator Sedum alfredii

Phytoremediation is a cost-effective and environmentally-friendly method to treat cadmium (Cd) contaminated soils, however, there is still a lack of safe disposal methods of harvested hyperaccumulators. In this study, by integrating glycolysis and pyrolysis, we investigated the possibility of bioproduct production and Cd collection from the hyperaccumulator Sedum alfredii. By means of acid-alkali pretreatment, the degree of cellulose polymerization was reduced by 36.24% while the surface accessibility was increased by 115.80%, resulting in a bioethanol yield of 9.29%. Meanwhile, 99.22% of total Cd of biomass could be reclaimed by collecting H2SO4-pretreatment waste. The saccharification residue was subsequently modified by NaOH-pretreatment-filtrate and converted into biochar at 500 °C which possessed a maximum Cd2+ sorption capacity of 60.52 mg g−1 based on the Langmuir model. Furthermore, sustainability analysis indicated that the economic input of this process is acceptable when considering its good environmental benefits. Taken together, our study provides a strategy for simultaneous bioethanol and biochar production during Cd collection from the hyperaccumulator S. alfredii, which could be a promising alternative for the suitable treatment of metal-enriched plants.

Enhancing biogas production of anaerobic co-digestion of industrial waste and municipal sewage sludge with mechanical, chemical, thermal, and hybrid pretreatment

This study presents the effect of mechanical, chemical, thermal, and hybrid pretreatment on anaerobic digestion of fruit-juice industrial waste (FW) co-digested with municipal sewage sludge (MSS). The pretreatment of the substrates with ultrasonication, microwave, weak alkali-acid caused an increase in cumulative biogas production of approximately 20.9, 14.9, 8.1, and 5.2%, respectively. Beside this, thermal and strong acid-alkali pretreatment reduced biogas production. The highest cumulative biogas and methane yield was increased with hybrid pretreatment which contains ultrasonication (US) and alkali (AL) pretreatment by 36% and 49%, respectively. Also, compared to untreated mixture, the soluble COD, carbohydrate, and protein removal efficiencies were increased from 42.6% to 65.6%, 65.1% to 86.6%, and 17.3% to 62.4%, respectively for US-AL pretreatment. The kinetic parameters of cumulative biogas production for the selected reactors were further estimated with Monod, Cone, and Transference Function models.

Carbocation scavenger assisted acid pretreatment followed by mild alkaline hydrogen peroxide (AHP) treatment for efficient production of fermentable sugars and lignin adsorbents from hardwood biomass

Pretreatment is one of the key steps in lignocellulosic biorefinery. Single stage acid pretreatment is often insufficiently satisfactory to overcome biomass recalcitrance, as the presence of insoluble lignin with repolymerized structure always hinders biomass fractionation and saccharification. In this work, a sequential acid-alkali pretreatment was developed to promote biomass fractionation, saccharification and holistic utilization. Results indicated that the addition of 2-naphthol in acid pretreatment enhanced lignin reactivity towards alkali post-treatment. A synergistic effect was observed between 2-naphthol additive and alkali post-treatment in improving biomass saccharification. As a result, up to 90 % of carbohydrates in raw biomass was released and recovered as fermentable sugars after pretreatment and enzymatic hydrolysis. Besides, enzymatic hydrolysis at cellulose loading of 8 % led to a high glucose concentration of 75.51 g/L in enzymatic hydrolysate. Moreover, lignin recovered after alkaline hydrogen peroxide (AHP) treatment and enzymatic hydrolysis both showed great adsorption performance for lead ions, presenting value-added lignin materials. Finally, the mass balance and energy analysis revealed an optimal fractionation of poplar biomass that could achieve an energy recovery of 86 %.

Improved hydrolysis yields and silica recovery by design of experiments applied to acid-alkali pretreatment in rice husks

In this work, a two-step pretreatment using acid and alkali was optimized for rice rusks (Oryza sativa) using a 25−1 fractional factorial design (FFD), followed by a central composite design (CCD) to further optimization of enzymatic saccharification. The effect of five variables was simultaneously evaluated: H2SO4 concentration (from 0–5.4 % w/w); NaOH concentration (0–6 % w/w); temperature (85–125 °C); time (20–100 min) and solid to liquid ratio (S/L = 5–12.5 % w/w). The best pretreatment conditions were: 1.8 % w/w of H2SO4 in the first step and 6 % w/w of NaOH at 85 °C for 100 min at a S/L = 12.5 % (w/w) in the alkaline step, which resulted in 58.7 mg of glucose/g substrate, an 8-fold increase compared to the sample in natura (7 mg/g). In rice husks, in contrast to the results commonly found in literature, NaOH extracts mainly silica instead of lignin, while H2SO4 has an important role in lignin removal. High purity silica (97 %) was isolated at high yields (70 %) from the alkaline liquor by a simple and scalable process, which could contribute to making ethanol production from this biomass economically viable.

Production of Fermentable Sugars from Cassava Stem using Hybrid Pretreatment Technology

One of the crucial steps in the enzymatic hydrolysis of biomass is pretreatment. We investigated the applicability of a hybrid pretreatment method, This involved acid treatment followed by alkali before the production of fermentable sugars from cassava stem. The substrate was initially treated with acid (1% oxalic acid at 100 °C for 2 h), followed by treatment with a 10% NaOH–urea mixture (by mixing 5 g each of NaOH and urea in 100 mL of water) at 100 °C for 1 h. A cellulose recovery of 98.55% was obtained with the acid-alkali pretreatment method.

Two-Stage Acid-Alkali Pretreatment of Vetiver Grass to Enhance the Subsequent Sugar Release by Cellulase Digestion

Two-Stage Acid-Alkali Pretreatment of Vetiver Grass to Enhance the Subsequent Sugar Release by Cellulase Digestion

Macromolecules Evolution in Sequential Acid-Alkali Pretreatment of Corn Stalk

Macromolecules Evolution in Sequential Acid-Alkali Pretreatment of Corn Stalk

Extraction and characterization of lignins from cashew apple bagasse obtained by different treatments

Lignins were extracted from different hydrolysates from the cashew apple bagasse (CAB). The hydrolysates, in turn, were obtained by pretreating the CAB with diluted acid (DA), acid/alkali (AA) and alkaline hydrogen peroxide (AHP). Lignin removal levels with AA and AHP were of 98.0% and 96.9%, resulting in high extraction yields and highly thermostable lignins. The lowest lignin yield was observed with the acid-only pretreatment. The FT-IR results showed that there was no significant difference between the main structures of the lignin isolated from the DA and AHP pretreatments, when compared to sugarcane lignin (SCL), the only exception being the lignin from AA. An 1H–13C HSQC NMR analysis demonstrated that AA pretreatment reduced the syringyl (S) and hydroxyphenyl (H) units, but increased the condensed guaiacyl (G) units, which may contribute to the higher thermal stability of the isolated lignins and to the absence of attached residues of carbohydrates. The detailed structural properties of the lignins extracted from CAB will enable the efficient utilization of these macromolecules within the biorefinery concept, with a positive impact on the economy.

Bioethanol production from oil palm empty fruit bunch with SSF and SHF processes using Kluyveromyces marxianus yeast

This research aimed to study bioethanol production from Oil Palm Empty Fruit Bunches (OPEFB) with Simultaneous Saccharification and Fermentation (SSF) and Separate Hydrolysis and Fermentation (SHF) by Klyveromyces marxinus. The basic steps for bioethanol production from lignocellulosic biomass are (1) pretreatment for delignification, which is necessary to liberate cellulose and hemicellulose; (2) hydrolysis of cellulose and hemicellulose to generate fermentable sugars; and (3) fermentation of bioethanol from sugars. In step (1) OPEFB was subjected to acid–alkali pretreatment with a dilute acid solution (at substrate loading 12.50%w/v, sulfuric acid concentration 0.2 M, at 121 °C for 53 min) followed by an alkali solution (NaOH 5%w/v, at 121 °C for 20 min), which resulted in 72.10%wt cellulose yield with hemicellulose and lignin yields of 3.24%wt and 17.60%wt, respectively. Then the optimal conditions for ethanol production by SSF process were investigated by Response Surface Methodology. The four manipulated factors were temperature (30–45 °C), substrate loading (5–15% w/v), pH (4–6), and yeast concentration (1–5%v/v), and the maximal 0.281 g/g bioethanol yield was found at 12.24%w/v, pH 4.5, yeast concentration 2.04%v/v, and 36.94 °C. In SHF, hydrolysis and fermentation steps were conducted at the optimal conditions for SSF, giving 0.584 g/g reducing sugar and 0.258 g/g bioethanol yield. The results demonstrate that an acid–alkali pretreatment could remove hemicellulose and lignin from lignocellulosic biomass, increasing cellulose yield, while SSF performed better than SHF with both quicker processing and higher bioethanol concentration.

Sequential dilute acid and alkali deconstruction of sugarcane bagasse for improved hydrolysis: Insight from small angle neutron scattering (SANS)

Cellulosic bioethanol is a promising renewable and substitute source of energy. To make the bioconversion of LCB to fuels cost effective and energy efficient, it is essential to reduce the recalcitrance of LCB and unravel the process of biomass deconstruction. Present study employed sequential dilute acid-alkali pretreatment of sugarcane bagasse (SCB) for enhancing its bioconversion to ethanol. Box-Behnken and D-optimal designs were used to optimise the process of dilute acid and alkali pretreatments sequentially, resulting in an optimum concentration of 3% (v/v) and 5% (w/v) for H2SO4 and NaOH with solid SCB loadings of 18 and 15% (w/w), respectively, for 30 min at 121 °C. The effectiveness of sequential pretreatment was supported by increased cellulose content (83%), drop in hemicellulose, enhanced delignification and 60% enzymatic hydrolysis of SCB by in-house Trichoderma reesei cellulases at enzyme dose of 20 FPU/g. The favourable multi-length scale ultrastructural changes in SCB induced by pretreatment were confirmed by FT-IR, SEM, EDX, TGA, XRD and small angle neutron scattering (SANS). SANS revealed increase in small pore radii from 11.1 to 18.5 Å, indicating improved biomass porosity after sequential pretreatment. Thus, sequential pretreatment of LCB effectively reduced the recalcitrance and could be more useful in lignocellulosic biorefinery applications.

Experimentally designed corn biomass fractionation to obtain lignin nanoparticles and fermentable sugars

Pretreatment steps carefully designed are essential to achieve a more integral and profitable use of plant biomasses in their conversion into building blocks to produce bioethanol and biomaterials. In this work, lignin extraction from corn biomass was optimized using a design of experiments (DOE) applied to a sequential acid-alkali pretreatment, varying temperature, time, and NaOH concentration in the alkali step. Selective extraction of lignin allowed the preparation of lignin nanoparticles, at the same time that it favored glucose release by hydrolysis of the cellulosic matrix. According to DOE results, alkali concentration was the most relevant factor for lignin removal and 2% NaOH, at 90 to 95 °C for 20 to 35 min would be enough to achieve less than 10% of residual lignin in the solid. These conditions were experimentally validated and resulted in a hydrolysis yield of 87.4 ± 7.3% and in a liquor containing approximately 50% of the initial lignin content. A great quantity of this neat lignin (92.9 ± 6.3%) was recovered by non-solvent addition as spherical nanoparticles, with a diameter smaller than 100 nm, and stable in a large pH range (5 to 11). Therefore, the optimization presented herewith resulted in lignin valorization by the suitable fabrication of value-added lignin nanoparticles, concomitantly to improved hydrolysis yields of cellulose aiming at bioethanol production.

Valorization of Rice Straw for Ethanol Production and Lignin Recovery Using Combined Acid-Alkali Pre-treatment

Rice straw was sequentially pre-treated with sulphuric acid (3% v/v) and sodium hydroxide (4% w/v) which resulted in the removal of ~ 90% hemicelluloses and ~ 55% lignin, respectively. The pre-treated rice straw was saccharified with cellulases to produce 787 mg/g reducing sugars, which were further fermented with Saccharomyces cerevisae HAU. The acid hydrolysate produced after acid treatment was also subjected to fermentation by Pichia stipitis NCIM 3499. The hexose and pentose fermentation leads to production of 26.9 g/L and 9.4 g/L of ethanol (79% and 93% fermentation efficiency, respectively). High purity (98%) lignin (146 mg/g dry substrate) was precipitated by direct acidification with HCl from the spent liquor obtained after alkali treatment. Extracted lignin was characterized by FTIR and TGA. Overall, the study aimed at effective utilization of all major polymers of rice straw into valuable products making the bioethanol production process more sustainable.

Effect of pretreatment processes on physicochemical properties of hydroxyapatite synthesized from Puntius conchonius fish scales

The current study emphasizes on the novel idea of synthesizing hydroxyapatite (HAp) from Puntius conchonius fish scales’ bio-waste and study the effect of acid, alkali and acid–alkali pretreatments on its physicochemical properties. Material characterization is carried out to study the physicochemical properties of the synthesized HAp using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX) and transmission electron microscopy (TEM) analysis. FTIR and XRD plots show peaks corresponding to natural bone apatite which confirms the formation of HAp. TG analysis shows a maximum weight loss of 2.28% indicating high thermal stability of HAp beyond 800 $$^{\circ }$$ C. SEM micrographs illustrate highly porous morphology with interconnected pores. EDX analysis of the HAp exhibits close proximity of the calcium/phosphorous (Ca/P) ratio to natural bone apatite. TEM micrographs show the formation of polycrystalline HAp particles with size ranging from $$38\pm 1.54$$ to $$219\pm 5.88~\hbox {nm}$$ . A comparative study on the physicochemical properties of HAp synthesized using three different pretreatment processes is performed. Results reveal that HAp synthesized from acid-treated fish scales show highest yield percentage, better thermal stability and highly porous morphology with a particle size of $$38 \pm 1.54~\hbox {nm}$$ . Thus, HAp synthesized from acid-treated fish scales can be a promising candidate for the development of porous bone scaffolds.

Synthesis of silver nanoparticles by using rice husk extracts prepared with acid–alkali pretreatment extraction process

Phenolic acids are the major bioactive compounds responsible for the reducing properties of rice husk. This study quantified the phenolic acid profile, total phenolic content (TPC), reducing power, and ferric-reducing antioxidant power (FRAP) of rice husk extracts ameliorated with acid–alkali pretreatment extraction (AAPE) process. The AAPE rice husk extract exhibited higher phenolic content (TPC: 3428 mg gallic acid equivalent (GAE)/100 g husk) and possessed stronger reducing properties (FRAP of 1433 mM FeSO4/g husk) than the rice husk extract with hot water extraction (TPC: 33 mg GAE/100 g husk, FRAP: 12 mM FeSO4/g husk). A green synthesis process for preparing silver nanoparticles (AgNPs diameter approximately 19 nm) with stable dispersion was obtained, and a conceptual model using caffeic acids as protective agents in synthesized AgNPs was conducted. The recycling of rice husk not only reduces the pollution from the use of chemical reducing agents and dispersants but also enhances the value-addition of the husk.

Nanostructured MnO2 catalyst in E. crassipes (water hyacinth) for indigo carmine degradation

Se estudió el uso de la materia seca del jacinto de agua (Eichhornia crassipes) como matriz-soporte para nano-MnO2 y su eficiencia en la eliminación de índigo carmín (IC). Se ensayaron diferentes procesos de pretratamiento y los resultados indicaron que un tratamiento previo ácido-alcalino es un método eficiente para unir las nanopartículas (NPs) a la matriz celulósica. Así mismo, las NPs de MnO2 se sintetizaron por reducción sonoquímica de MnO4- utilizando diferentes métodos (un sistema emisor de ultrasonido, baño de ultrasonido y reacción convencional con etanol como medio). El material sintetizado se caracterizó por ATR-IR, AAS, DRX, SEM, isotermas de adsorción de nitrógeno, EDS y pHpzc. Se exploró la capacidad de eliminación de IC por parte del material nanoestructurado y la naturaleza química de los productos de degradación en muestras acuosas. Se analizó el efecto de diversos parámetros tales como temperatura, pH, concentración inicial de IC, entre otros. Finalmente, el material nanoestructurado, obtenido con un baño de ultrasonido, mostró una eficiencia de 97,6% en la eliminación del color característico de IC en 5 min, sin perder la eficiencia en la degradación del colorante por varios ciclos consecutivos. A través de este enfoque, se pueden eliminar efluentes ambientalmente peligrosos provenientes de actividades comerciales como la industria textil, de manera eficiente y a un bajo costo, mediante el uso de materiales nanocompuestos biodegradables cuya síntesis es de fácil aplicación.

Comparison of two-stage acid-alkali and alkali-acid pretreatments on enzymatic saccharification ability of the sweet sorghum fiber and their physicochemical characterizations

Two-stage acid/alkali pretreatment was used to enhance the saccharification efficiency of sweet sorghum fiber. The physicochemical characterizations of the pretreated fibers were evaluated by SEM, FTIR and XRD. The acid and alkali sequence in the two-stage pretreatment process was compared, and their dosage was optimized. The results indicated that the two-stage pretreatment showed better saccharification performance when compared with conventional single stage pretreatment. And compared with the acid-alkali sequence, the alkali-acid sequence achieved higher glucose yield (0.23g·g−1) under the optimized conditions, which was 1.64 and 1.21 times higher than that of the single stage and the acid-alkali pretreatments, respectively. Overall, the two-stage pretreatment process is a promising approach to achieve high fermentable glucose conversion rate of cellulosic material.