Acid Pretreatment Research Articles

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.

High-performance poplar-polyethylene laminates based on microwave-assisted acetic acid pretreatment process with potential application in construction

High-performance poplar-polyethylene laminates based on microwave-assisted acetic acid pretreatment process with potential application in construction

Combined iron (III) chloride/sodium citrate with enzymatic hydrolysis for xylo-oligosaccharides and monosaccharides production from poplar

Currently, the production of xylo-oligosaccharides (XOS) from lignocelluloses by chelating system hydrolysis has not been investigated. Herein, iron (III) chloride/sodium citrate (IC/SC) chelating system hydrolysis and xylanase hydrolysis were used to produce XOS from poplar. Then, the delignification of IC/SC-hydrolyzed poplar was performed by p-toluenesulfonic acid (p-TsOH) pretreatment to increase the accessibility of cellulase. The results demonstrated that 42.3% of XOS with an extremely low by-product (xylose/XOS = 0.11) was produced from poplar by 50 mM IC/SC hydrolysis (molar ratio of 1:1, 170 °C, 60 min) and xylanase hydrolysis. The second step IC/SC hydrolysis and xylanase hydrolysis of poplar increased the yield of XOS to 51.3%. Finally, the glucose yield of p-TsOH-pretreated poplar (60% p-TsOH, 70 °C, 30 min) was greatly increased from 37.5% to 83.8% by cellulase hydrolysis with Tween 80 addition. The novel strategy proposed in this work was feasible for XOS and monosaccharides production from poplar.

Acid and alkali pretreatment of agro by-products: Evaluating torrefaction efficiency and dechlorination

Utilisation of crop residues is limited due to their low energy and high ash content. This study aimed to develop a method for enabling the use of residual agricultural biomass through acid or alkali pretreatment followed by torrefaction. Pepper stems were treated with hydrochloric acid or sodium hydroxide for a brief period of time and rinsed with distilled water. Untreated and acid-pretreated samples had cellulose contents of 43.85% and 36.57%, respectively. The lignin content in the alkali-pretreated samples (22.74%) was lower than that in untreated samples (27.40%). Mass yield decreased with torrefaction temperature, ranging from 86.19% to 49.89%. However, alkali-treated samples showed smaller changes in mass yield (70.31–60.43%) than other samples. Regarding calorific value, untreated samples exhibited the highest increase (26.37%), whereas alkali-treated samples showed a modest increase of 10.62%. Chlorine content was higher in acid-compared with alkali-treated samples but decreased with temperature. Our study demonstrated that agricultural by-products can be used as energy sources through acid or alkali pretreatment prior to torrefaction. Future studies should explore a variety of agricultural by-products and consider pretreatment with different acids or alkalis, such as sulfuric acid and potassium hydroxide.

Pretreatment of free nitrous acid combined with calcium hypochlorite for enhancement of hydrogen production in waste activated sludge

A variety of variables limit the recovery of resources from anaerobic fermentation of waste activated sludge (WAS), hence pretreatment strategies are necessary to be investigated to increase its efficiency. A combination of free nitrous acid (FNA) and calcium hypochlorite [Ca(ClO)2] was employed in this investigation to significantly improve sludge fermentation performance. The yields of cumulative hydrogen for the blank and FNA treatment group were 1.09 ± 0.16 and 7.36 ± 0.21 mL/g VSS, respectively, and 6.59 ± 0.24 [0.03 g Ca(ClO)2/g TSS], 7.75 ± 0.20 (0.06), and 8.58 ± 0.22 (0.09) mL/g VSS for the Ca(ClO)2 groups. The co-treatment greatly boosted hydrogen generation, ranging from 39.97 ± 2.26 to 76.20 ± 4.78 % as compared to the solo treatment. Mechanism analysis demonstrated that the combined treatment disturbed sludge structure and cell membrane permeability even more, which released more organic substrates and enhanced biodegradability of fermentation broth. This paper describes a unique strategy to sludge pretreatment that expands the use of Ca(ClO)2 and FNA in anaerobic fermentation, with implications for sludge disposal and energy recovery.

Integrated bioprocess for Se(VI) remediation using duckweed: Coupling selenate removal to biogas production

The use of phytoremediation as a method for wastewater treatment or removal of pollutants is garnering significant interest and duckweed (DW), a free floating macrophyte, depicts significant potential for the removal of nutrients and toxic compounds from contaminated waters. The present work aimed to develop an integrated process for remediating selenate (Se(VI)) using DW biomass and subsequent use of Se(VI) enriched DW for biogas production. The main objective is to extend the application of selenium (Se) enriched DW biomass for biogas production. Se(VI) enriched DW biomass (Se-DW) gave higher methane production (48.38 ± 3.6 mL gCOD−1) than control DW biomass (C-DW) (24.46 ± 3.6 mL gCOD−1). To further enhance methane production, three pre-treatment approaches (acid, alkali and hydrothermal) were assessed and the solid and liquid fractions obtained after pre-treatment were used as a substrate. Pre-treatments increased biogas production in both Se-DW and C-DW than untreated conditions. Liquid fractions gave higher biogas production than solid fractions. In Se-DW, highest biogas production was observed in hydrothermal pre-treated Se-DW, while in C-DW, acid pre-treatment gave higher biogas production. Methane production was shown to be enhanced up to a Se(VI) concentration of 1.7 mg L−1, whereas a concentration beyond this lowered biogas production.

Two-stage sulfite steam pre-treatment achieves extraordinary bioethanol titer from simultaneously saccharification and fermentation of softwood whole slurries

Softwood biomass, which contains rich portion of readily fermentable sugars, is a type of abundant biomass in Canada and Nordic countries. However, its recalcitrant structure has severely limited its utilization in bioconversion. Sulfite treatment during steam pre-treatment to simultaneously enhance ease of hydrolysis and fermentation of softwood biomass has turned to be an attractive strategy to unlock the possibility of converting softwood to bioethanol. Our previous work showed applying one-stage sulfite treatment during the steam pre-treatment under neutral/alkaline conditions could maximize the sulfonation/delignification and hemicellulose sugar retention, while the use of acidic conditions could enhance the homogenous substrates size reduction. To take the advantages of both the neutral/alkaline and acidic conditions, we developed two-stage sulfite steam pre-treatment to maximize the sugar and ethanol production by utilizing Na2SO3 in the first alkaline steam pre-treatment stage and SO2 in a second acidic steam pre-treatment stage. The resulting substrates showed high sulfonation/delignification extent, nearly 100 % sugar recovery, homogeneous substrates size reduction and sufficient detoxification. Without extra hydrolysate detoxification and concentration, 160 g/L fermentable sugars were obtained from the hydrolysis of two-stage sulfite steam pretreated softwood whole slurry at 25% solid loading. And 80 g/L ethanol was generated by directly fermenting these sugars in the whole slurry hydrolysate without additional detoxification or concentration processes. This work significantly contributed to the development of the industrial relevant bioethanol production from softwood biomass.

Coproduction of xylooligosaccharides, glucose, and less-condensed lignin from sugarcane bagasse using syringic acid pretreatment

Current strategies for the production of xylooligosaccharides (XOS) from biomass through non–enzymatic catalysis often led to a certain degree of lignin condensation, which severely restrains subsequent enzyme hydrolysis of cellulose. Herein, syringic acid (SA) pretreatment was investigated to coproduce XOS, glucose, and less-condensed lignin from sugarcane bagasse. SA acted as a catalyst and lignin condensation inhibitor during the pretreatment. The highest XOS yield of 58.7% (27.7% xylobiose and 24.7% xylotriose) was obtained at 180 °C − 20 min − 9% SA, and the corresponding xylose/XOS ratio was only 0.42. Compared with the pretreatment at 180 °C − 20 min − 0% SA, the addition of 9% SA increased the glucose yield from 85.7% to 92.4% and decreased the degree of lignin condensation from 0.55 to 0.42. Moreover, 26.7% of SA could be easily recovered. This work presents a pretreatment strategy in which the efficient production of XOS and the suppression of lignin condensation are achieved simultaneously.

Enhancing the pyrolytic conversion of biosolids to value-added products via mild acid pre-treatment

High concentrations of inorganic matter such as silicates, alkali and alkaline earth metals (AAEMs), and heavy metals (HMs) in biosolids limit their pyrolysis conversion to high-value products. Therefore, the reduction or passivation of the deleterious pyrolytic activities of these native inorganics in biosolids can enhance the yield and quality of products obtained during pyrolysis. The pyrolysis of raw and 3% sulfuric acid pre-treated biosolids was carried out in a fluidised bed reactor at 300–700 ℃, and the influence of pre-treatment was examined on biochar properties, gas production, and bio-oil composition. At all temperatures, the selective removal of ash-forming elements (demineralisation) in biosolids by pre-treatment improved organic matter devolatilisation yielding higher bio-oil and lower biochar than untreated biosolids. Demineralisation weakened gas production, particularly at higher pyrolysis temperatures. At 700 ℃, the in-situ formation of acidic metal sulfate salts in sulfuric acid-infused biosolids facilitated H+ release, thereby increasing H2 yield to a maximum of 15 mol% compared to 8 mol% from untreated biosolids and 4 mol% from demineralised biosolids. Biochar produced from treated biosolids had considerably lower HMs concentration and higher organic matter retention compared to raw biosolids biochar. The effect of pre-treatment on biochar properties was profound at 700 ℃ pyrolysis temperature. Pre-treatment increased biochar fixed carbon by 57%, calorific value by 37%, fuel ratio by 44%, doubled the specific surface area from 55 to 107 m2/g, and enhanced porous structure formation. At 300 ℃, the major chemical compounds in the bio-oil were amides (20%), N-heterocyclics (25%), and ketones (30%), and higher temperatures favoured phenols and aromatic hydrocarbon production. Pre-treatment enhanced the selectivity of furans by 10-fold, anhydrosugars by 2-fold, and aromatic hydrocarbons by 1.5-fold relative to the raw biosolids bio-oil. Acid pre-treatment is a promising strategy for improving biosolids quality as feedstock for pyrolysis to generate high-value products.

Impact of xylan on field productivity and wood saccharification properties in aspen.

Xylan that comprises roughly 25% of hardwood biomass is undesirable in biorefinery applications involving saccharification and fermentation. Efforts to reduce xylan levels have therefore been made in many species, usually resulting in improved saccharification. However, such modified plants have not yet been tested under field conditions. Here we evaluate the field performance of transgenic hybrid aspen lines with reduced xylan levels and assess their usefulness as short-rotation feedstocks for biorefineries. Three types of transgenic lines were tested in four-year field tests with RNAi constructs targeting either Populus GT43 clades B and C (GT43BC) corresponding to Arabidopsis clades IRX9 and IRX14, respectively, involved in xylan backbone biosynthesis, GATL1.1 corresponding to AtGALT1 involved in xylan reducing end sequence biosynthesis, or ASPR1 encoding an atypical aspartate protease. Their productivity, wood quality traits, and saccharification efficiency were analyzed. The only lines differing significantly from the wild type with respect to growth and biotic stress resistance were the ASPR1 lines, whose stems were roughly 10% shorter and narrower and leaves showed increased arthropod damage. GT43BC lines exhibited no growth advantage in the field despite their superior growth in greenhouse experiments. Wood from the ASPR1 and GT43BC lines had slightly reduced density due to thinner cell walls and, in the case of ASPR1, larger cell diameters. The xylan was less extractable by alkali but more hydrolysable by acid, had increased glucuronosylation, and its content was reduced in all three types of transgenic lines. The hemicellulose size distribution in the GALT1.1 and ASPR1 lines was skewed towards higher molecular mass compared to the wild type. These results provide experimental evidence that GATL1.1 functions in xylan biosynthesis and suggest that ASPR1 may regulate this process. In saccharification without pretreatment, lines of all three constructs provided 8-11% higher average glucose yields than wild-type plants. In saccharification with acid pretreatment, the GT43BC construct provided a 10% yield increase on average. The best transgenic lines of each construct are thus predicted to modestly outperform the wild type in terms of glucose yields per hectare. The field evaluation of transgenic xylan-reduced aspen represents an important step towards more productive feedstocks for biorefineries.

Effects of Acid Pretreatment on Purity of Copper Foil Recovered by Electrolytic Refining from Waste Printed Circuit Board

Effects of Acid Pretreatment on Purity of Copper Foil Recovered by Electrolytic Refining from Waste Printed Circuit Board

Production of optical pure L-lactic acid from Cabernet Sauvignon grape pomace by engineered Lactiplantibacillus plantarum

Cabernet Sauvignon grape pomace contains carbohydrates and various amino acids that could be used as substrates for lactic acid (LA) production. In this study, a mutant strain of L. plantarum with deletion of the D-lactate synthesis gene was developed and used to produce optical pure L-LA from grape pomace. The highest optical purity of the L-LA produced by this mutant strain was 99.61%. The direct bioconversion of the raw substrate showed a low LA yield. Several pretreatment methods were applied to improve the LA yield, including ball milling, hydrothermal, dilute acid pretreatment, alkaline pretreatment, and combined wet alkaline mechanical pretreatment. Due to the efficient delignification, alkaline pretreatment achieved the highest lactic acid yield of 96.26% at 15% solid loading, with corresponding LA concentration and volumetric productivity of 18.45 g/L and 2.30 g/L·h, respectively.

The Recycle of Red Mud as NH3-SCR Catalyst by Acid Pretreatment: Insight into the Interaction Between Iron and Titanium Species

The Recycle of Red Mud as NH3-SCR Catalyst by Acid Pretreatment: Insight into the Interaction Between Iron and Titanium Species

Integrated biohydrogen production and dairy manure wastewater treatment via a microalgae platform

The present study aimed to investigate the feasibility of sustainable biohydrogen production from dairy manure wastewater using a microalgae platform to achieve simultaneous wastewater treatment and clean energy production. Compared to single-stage microalgae cultivation, two-stage cultivation of indigenous wastewater bacteria and carbohydrate-rich microalgae Chlorella vulgaris ESP-6 achieved satisfactory removal of nutrients and chemical oxygen demand. The resulting biomass, with high carbohydrate content (48.8 ± 2.3%), was used as alternative feedstock for biohydrogen production by Clostridium butyricum CGS5 via dark fermentation after thermal acid pretreatment. The implementation of an automatic pH control strategy significantly promoted H2 generation, resulting in a hydrogen yield of 211 mL/g VS and a maximum productivity of 391.1 mL/L/h. To the best of our knowledge, this is the first integrated study of dairy manure wastewater treatment and biohydrogen production with high H2 yield and productivity comparable to those reported in the literature.

Mechanism of enhanced enzymatic hydrolysis performance by ethanol assisted deep eutectic solvent pretreatment- from the perspective of lignin

Valorization of lignocellulose has received a lot of attention due to the abundance of lignocellulosics. It was showed that synergistic carbohydrate conversion and delignification could be achieved via ethanol assisted DES (choline chloride/lactic acid) pretreatment. To explore the reaction mechanism of lignin in the DES, milled wood lignin obtained from Broussonetia papyrifera was subjected to pretreatment at critical temperatures. The results suggested that ethanol assistance could contribute the incorporation of ethyl groups and reduce condensation structures of Hibbert’s ketone. Adding ethanol at 150 °C not only decreased formation of condensed G unit (from 7.23% to 0.87%), but also removed J and S’ substructures, thus effectively reducing the adsorption of lignin on cellulase, and promoting the glucose yield after enzymatic hydrolysis.

Comparison of acid and alkaline pre-treatment on methane production from empty palm oil fruit bunches (OPEFB): Effect on characteristics, digester performance, and correlation of kinetic parameters

This paper focused on comparing the impact of two different chemical pretreatments on various characteristics of OPEFBs (i.e., physical, structural, and morphological properties), methane production, digestate characteristics, and kinetic modelling. The biochemical methane potential (BMP) test showed that alkaline-treated OPEFBs produced higher methane yields than acid-treated OPEFBs. Accordingly, the methane yields became far higher after NaOH pretreatment, showing 0.186–0.224 m3CH4/kg VSadded compared with 0.102 m3CH4/kg VSadded and 0.093–0.115 m3CH4/kg VSadded from untreated and acid-treated OPEFBs. The best treatment was alkaline pretreatment of P2N3, which gave the highest methane yield increase (by 1.2-fold). The Scanning Electron Microscopy and Energy Dispersive X-ray (SEM-EDX) results of acid-treated OPEFBs indicated disruption of cell wall and loss of some minerals. However, alkaline-treated OPEFBs have more pores due to silica and other chemicals releases (i.e., lignin, hemicellulose, etc.). The kinetic study showed that all models (i.e., modified Gompertz, logistic, and transference) were in good agreement with the experimental data. Both experimental data and models confirmed P2N3 (i.e., NaOH concentrations of 3.8%) as the best results, indicated by the highest lignin reduction and methane production. This study showed an excellent opportunity to digest alkaline-treated OPEFBS, yet more in-depth investigations with sustainability and circular economy perspectives are needed.

Effects of Acid and Alkali Pretreatments on Carbohydrate Release from Sweet Sorghum and Sweet Pearl Millet Bagasse for Bioethanol Production

Effects of Acid and Alkali Pretreatments on Carbohydrate Release from Sweet Sorghum and Sweet Pearl Millet Bagasse for Bioethanol Production

Comparison of methods for determining organic carbon content of urban soils in Central Ohio

Reliable methods are key to quantify organic carbon in urban soils. Samples from across the Ohio State University campus were divided into two datasets (a) pH ≤ 7.5 and (b) pH ≥ 7.8. Organic carbon was assessed using multiple methods, including heated acid dichromate digestion (OCDichromate), loss-on-ignition (LOI) at 400 °C and 550 °C, a dry combustion method (OCTC), and an acid pre-treatment (OCacid). Mean organic C, in g kg−1, were OCTC (39.8), LOI550 (39.8), LOI400 (33.2), OCDichromate (31.8) for soils with pH ≤ 7.5. LOI400 and OCDichromate were more accurate than OCTC and LOI550. Mean organic C, in g kg−1, were LOI550 (23.6) > OCacid (20.2) ≥ LOI400 (17.9), OCDichromate (16.0) for soils with pH ≥ 7.8. Similar to pH ≤ 7.5 soils, LOI400 and OCDichromate methods were more accurate measures of OC. The two loss-on-ignition methods and the dichromate method were strongly correlated with each other (r = 0.91) however the two dry combustion methods were weakly correlated with the others (0.45 ≥ r ≤ 0.67). The dichromate oxidation proved to have the lowest variance of the methods tested (29.7 g2 kg−2). Paired t-tests found no significant differences between the loss-on-ignition 400° and the acid-pretreatment methods, and no significant differences between the dichromate and inorganic subtraction method (p < 0.05). Dichromate oxidation method should be implemented to measure soil organic carbon in urban soils that have carbonates present, especially dolomite. The dichromate oxidation method was found to be simple, rapid, and reliably determines SOC without the need to remove SIC.

Enhanced methane yield in anaerobic digestion of waste activated sludge by combined pretreatment with fungal mash and free nitrous acid

This study explores a novel approach for enhancing anaerobic digestion of waste activated sludge (WAS) through the combined pretreatment of fungal mash and free nitrous acid (FNA). Aspergillus PAD-2, a fungal strain with superior hydrolase secretion, was isolated from WAS and cultivated in-situ on food waste to produce fungal mash. The solubilization of WAS by fungal mash achieved a high soluble chemical oxygen demand release rate of 548 mg L−1 h−1 within first 3 h. The combined pretreatment of fungal mash and FNA further improved the sludge solubilization by 2-fold and resulted in a doubled methane production rate of 416±11 mL CH4 g−1 volatile solids. The Gompertz model analysis revealed a higher maximum specific methane production rate and shortened lag time by the combined pretreatment. These results demonstrate that the combined fungal mash and FNA pretreatment offers a promising alternative for fast anaerobic digestion of WAS.

Bioprocess development for the production of xylooligosaccharide prebiotics from agro-industrial lignocellulosic waste

The development of sustainable biorefineries and bioeconomy has been the mandate of most of the governments with major focus on restricting the climate change concerns and finding new strategies to maintain the global food supply chain. Xylooligosaccharides (XOS) are short-chain oligomers which due to their excellent prebiotic potential in the nutraceutical sector has attracted intense research focus in the recent years. The agro-industrial crop and food waste can be utilized for the production of XOS which are derived from hemicellulose fraction (xylan) of the lignocellulosic materials. The extraction of xylan, is traditionally achieved by acidic and alkaline pretreatments which, however, have limited industrial applications. The inclusion of cutting-edge and environmentally beneficial pretreatment methods and technologies such as deep eutectic solvents and green catalysts are preferred. Moreover, the extraction of xylans from biomass using combinatorial pretreatment approaches may help in economizing the whole bioprocess. The current review outlines the factors involved in the xylan extraction and depolymerization processes from different lignocellulosic biomass and the subsequent enzymatic hydrolysis for XOS production. The different types of oligosaccharides and their prebiotic potential for the growth of healthy gut bacteria have also been explained. The introduction of modern molecular technologies has also made it possible to identify enzymes and microorganisms with the desired characteristics for usage in XOS industrial production processes.