Optimal Pretreatment Conditions Research Articles

Optimization of chemical solution concentration and exposure time in the alkaline pretreatment applied to sugarcane bagasse for methane production

ABSTRACT Sugarcane is the most traded crop in the world, with Brazil being the world’s largest producer. Sugarcane processing generates up to 28% of sugarcane bagasse (SB) from the entire plant, with only 50% of it used for energy generation. SB is a lignocellulosic biomass that can be converted into biogas. However, the optimization of pretreatment process parameters is essential for its successful scaling up. This study evaluated the effect of mild alkaline pretreatment of SB using NaOH and KOH at concentrations of 1–10% and exposure time of 1–12 hours) on the biochemical methane potential (BMP) under mesophilic temperature. The central composite rotatable design (CCRD) was applied as statistical tool to generate optimal operating pretreatment conditions. The tests were performed in triplicates totalizing 84 batch bottles. The BMP of the untreated SB varied between 297–306 LN CH4 kg VS−1 while the BMP of the pretreated samples with NaOH and KOH were 19% and 20% higher. The optimized conditions were NaOH at 7.7% and KOH at 8.3% KOH for 12 hours. However, the range indicated by the statistical design with CCRD revealed that there was no statistical difference in terms of methane yield when concentrations between 4–10% NaOH and 6–10% KOH during 12 hours were applied, when compared to the specific optimized points. The optimization of the pretreatment parameters demonstrated to be a key-factor to improve the anaerobic digestion of lignocellulosic substrates, leading to a less chemically dependent and more sustainable approach, while allowing a more profitable process.

Organosolv pretreatment of oat husk using oxalic acid as an alternative organic acid and its potential applications in biorefinery

AbstractIn this study, ethanol organosolv treatment of oat husk and the potential effects of phosphoric acid and oxalic acid as alternatives to sulfuric acid were investigated. These acids were determined as effective as sulfuric acid to obtain high quality lignin and glucan and they can be used instead of sulfuric acid in solvent acidification. To determine the purity and recovery of both lignin and glucan, the effects of initial substrate amount, solid-to-liquid ratio, and amount of washing solutions were also examined using a one-factor-at-a-time strategy. Reducing the amount of washing solutions (water, solvent, or both) negatively affected lignin recovery, but it did not affect glucan recovery. The optimum conditions for pretreatment of the oat husk at higher glucan recovery were obtained with 50% aqueous ethanol acidified with oxalic acid at 210 °C for 90 min and solid-to-liquid ratio of 1:2. In the mixture of evaporated glucan-rich and hemicellulose-rich fractions obtained through the optimized condition, 4.62 g/L biomass containing 10.27% protein was produced by the cultivation of Aspergillus oryzae. The fractions obtained from organosolv treatment can be used to obtain value-added products such as biomass production, and thus contributing to a sustainable economy by integrating lignocellulosic substrate residues into the biorefinery.

Enzyme pretreatment of yard waste to improve anaerobic biodegradability: Modeling the interactive effects of enzyme dose, treatment temperature and treatment duration on delignification

Laccase pretreatment of yard waste (YW) was conducted for improving its anaerobic biodegradability. The optimum pretreatment condition based on response surface methodology for maximum delignification was: solid loading 19.7% (w/v) of total solid, treatment duration 9 h, and pretreatment temperature 44.5 °C. The mechanism of biomass delignification was further investigated by the change in physical and chemical properties. Specifically the increase in water retention value (2.05 times), specific porosity (1.72 times), and crystallinity index (1.25 times) in pretreated YW indicates the capability of laccase pretreatment to remove lignin selectively. The methane yield after 30 days of anaerobic digestion for untreated YW was 294 ± 12 mL/g volatile solid (VS) and for laccase pretreated yard waste at the optimum condition was 405 ± 15 mL/gVS. The Modified Gompertz model showed the best fit for untreated yard waste however for pretreated YW logistic function model was the best. The energy balance analysis of the studied method confirmed a positive energy gain of 1.6 kJ/g VS indicates further validation in field scale studies.

Effect of Ultrasonic Pretreatment of Sewage Sludge on the Performance of Bioelectrochemical Anaerobic Digester

Objectives : This study examined the effect of ultrasonic pretreatment on primary sewage sludge (raw sludge) solubilization and its subsequent microbial electrolysis cells (MECs) operation performance.Methods : To compare the effect of ultrasound on raw sludge solubilization, ultrasonic pretreatment was conducted at 1~4 W/mL energy density for 5~30 min. In MECs operation, raw sludge was used as a control group, and ultrasound pretreated sludge was used as an experimental group. For comparing MECs performance, biogas production, and organic matter removal were analyzed.Results and Discussion : The optimal experimental condition for ultrasonic pretreatment were 30 min of sonication time at 3 W/mL. In methane production, MEC with ultrasound pretreatment (MEC 3W) produced 243 mL/L more methane than that of unpretreated MEC (MEC) by 4,970 mL/L at 1, 3 cycles. In the modified Gompertz model analysis, the lag phase of MEC 3W was 0.46 days, which was 0.12 days longer than MEC. The maximum methane production rate of MEC 3W by 938.5 mL/L/day was also higher than MEC. MEC 3W showed a 1.8% higher TS removal rate, 2.4% VS removal rate than MEC. COD removal rate also improved by 2.0% when ultrasound pretreatment was applied. The methane yield of MEC with ultrasound pretreatment (377.4 mL/g VSin.) was 0.4% higher than that of MEC without pretreatment.Conclusion Ultrasonic pretreatment of sewage sludge improved the methane production and organic removal in microbial electrolysis cells. It is necessary to find the optimal operating conditions to obtain the maximize the performance.

Cation exchange resin pretreatment enhancing methane production from anaerobic digestion of waste activated sludge

The application of anaerobic digestion (AD) to treat waste activated sludge (WAS) still exhibits some limitations, such as low methane production. In this study, cation exchange resin (CER) pretreatment was explored to enhance the efficiency of the AD of WAS. Based on the response surface methodology, the optimal conditions for CER pretreatment were reaction time of 7.4 h, 33.8 g CER (wet weight) /g volatile solids and sludge total solids of 2.4%. Under these optimal CER pretreatment conditions, approximately 30% of metals were removed from the WAS, particularly organic-binding metals. This metal removal disrupted the structures of extracellular polymer substances and led to sludge deflocculation, thereby releasing large amounts of organic substances from the sludge solids. Batch AD experiments showed that CER pretreatment increased the maximal production of volatile fatty acids and methane by 565.7% and 80.5%, respectively. Additionally, CER pretreatment promoted each stage of AD (i.e. solubilisation, hydrolysis, acidification and methanation) and the corresponding activities of key enzymes. Experimental results for semi-continuous AD further confirmed that CER pretreatment enhanced the proportion of methane in the biogas (from 62.75 ± 2.14% to 73.96 ± 0.99%) and the production of methane. An analysis of changes in the microbial communities demonstrated that CER pretreatment enhanced the abundance of microorganisms involved in hydrolysis, acidification and acetification and changed the major methanogenic pathway from acetoclastic methanogens to methylotrophic methanogens. These findings are expected to provide a reference for developing new pretreatment methods for enhancing anaerobic biodegradability of organic matters.

Thermochemical and Enzymatic Saccharification of Water Hyacinth Biomass into Fermentable Sugars

Water hyacinth (WH) is a free-floating perennial aquatic plant that is considered a pest, due to its rapid grown rate and detrimental effects on environment and human health. It is nearly impossible to control WH growth, with mechanical extraction being the most acceptable control method; nevertheless, it is costly and labor-intensive. WH lignocellulosic biomass represents a desirable feedstock for the sustainable production of liquid fuels and chemical products. In this work, optimal conditions of thermochemical pretreatment for the release of reducing sugars (RS) from WH biomass were established: 0.15 mm of particle size, 50 g of dried solid/L of H2SO4 (3% w/v) and 20 min of heating time at 121 °C. Applying this pretreatment, a conversion of 84.12% of the hemicellulose fraction in the raw WH biomass into reducing sugars (277 ± 1.40 mg RS/g DWH) was reached. The resulting pretreated biomass of WH (PBWH) was enzymatically hydrolyzed by using six enzymatic complexes (all from Novozymes). Among them, NS22118 (beta-glucosidase) and Cellic® CTec2 (cellulase and hemicellulose complex) achieved higher saccharifications. By using NS22118 or a mixture of NS22118 and Cellic® CTec2, PBWH conversion into RS was complete. Monosaccharides released after pretreatment and enzymatic hydrolysis were mostly pentoses (arabinose and xylose) and hexoses (glucose), respectively.

Utilization of Seawater in the Pretreatment and Saccharification of Seaweed

The growing need to cater to the energy demand coupled with the urge to mitigate greenhouse gas footprint in the energy sector has led to the exploration of biofuels, such as bioethanol, as a renewable and sustainable source. However, the desire for freshwater in bioethanol production is extremely high and hence it is considered as a high water footprint product. With the scarcity of ever-depleting fresh water resources and its huge consumption in biorefineries, it has become difficult to use fresh water for bioconversions. The use of abundantly available seawater as a substitute for freshwater was suggested to reduce the water footprint of bioethanol production. Furthermore, bioethanol production using seaweeds or macroalgal resources has shown great promise and significance in global sustainable development. Therefore, in the present study, pretreatment and saccharification of Chaetomorpha sp., a green seaweed, was carried out using seawater based reaction medium. The optimal pretreatment conditions were obtained using the microwave at 6.681% substrate loading, 1.487% NaOH and 7.724 min duration, which resulted in a maximum reducing sugar yield of 0.196 g/g. These findings reveal that seawater can produce comparably digestible solids to those of fresh water and can be used as an alternative to fresh water usage in biofuel production.

Deep eutectic solvent with bifunctional Brønsted-Lewis acids for highly efficient lignocellulose fractionation

Green and low cost deep eutectic solvents (DESs) are promising to replace the solid acids and ionic liquids in biomass fractionation process. To enhance the lignocellulose pretreatment efficiency, an acidic DES that composed of Brønsted acid (ZnCl2) as hydrogen bond acceptor and Lewis acid (lactic acid) as hydrogen bond donator was designed. This bifunctional DES was used for the extraction of lignin from poplar sawdust. Under the optimal pretreatment condition, the ZnCl2-lactic acid DES could recover 95.2 wt% of lignin with a purity of 92.1%. The recovered lignin demonstrated a low polydispersity of 1.67 and small amount of β-aryl-ethers. Moreover, the acidic DES had a good recyclability and reusability. Such performance was attributed to the presence of bifunctional acid sites, which help selectively cleave lignin-carbohydrate complex linkages. The acidity and polarity of Brønsted acid can be modulated by the Lewis acid, thus synergistically promote the lignin extraction and production.

Degradation of rifamycin from mycelial dreg by activated persulfate: Degradation efficiency and reaction kinetics

Rifamycin mycelial dreg (RMD) is a biological waste, and its residual rifamycin (RIF) is potentially harmful to both the environment and human health. In this work, thermally activated persulfate (PDS) oxidative degradation of RIF in RMD was developed for the first time. The effects of reaction temperature, initial PDS concentration, and pH on RIF degradation in RMD were investigated, and the treatment conditions were optimized using response surface methodology (RSM). The results showed that 90 °C, 50 mg/g PDS, and pH = 5.3 were the optimal pretreatment conditions, and 100% degradation efficiency of RIF (734 mg/kg) was achieved. SEM and FTIR analyses confirmed that the RIF was destroyed and decomposed after the oxidation reaction. The possible degradation pathways of RIF in the thermally activated PDS system were discussed through HPLC/MS and ESR analyses. The intermediate product was identified, and the toxicity of the final product was predicted to be low or nontoxic. In this work, a degradation pathway of RMD was proposed by activating persulfate, which facilitates subsequent resource utilization and provides meaningful guidance for the practical treatment of antibiotic mycelium residue (AMR).

Unrevealing the role of in-situ Fe(II)/S2O82- oxidation in sludge solid–liquid separation and membrane fouling behaviors of membrane bioreactor (MBR)

Membrane bioreactor (MBR) has received continuous attention in waste activated sludge treatment, however, membrane fouling still remains a big and inevitable challenge to its wide applications. Ferrous-persulfate (Fe(II)/S2O82–) oxidation possesses the outstanding oxidizing capability and high-efficiency in degrading refractory organics and enhancing sludge solubilization. In this study, in-situ Fe(II)/S2O82- oxidation was coupled for pretreating sludge, and the effect on the subsequent filtration performance and membrane fouling behaviors in MBR was investigated. Fe(II)/S2O82- oxidation had an outstanding effect on enhancing filterability of mixed sludge liquor and alleviating membrane fouling. Under the optimal pretreatment condition of 1.5/1.2 mmol-Fe(II)-S2O82-/g-VS, the membrane flux of reactor reached 20.6 mL/s/m2, and a 46.6% decrease in trans-membrane pressure (TMP) was obtained compared to the raw sludge without pretreatment. Correlation analysis reveal that polysaccharides in extracellular polymeric substances was the decisive factor affecting the membrane fouling behavior. The strong oxidizing ability of in-situ Fe(II)/S2O82- pretreatment could effectively break the glutinous and pilotaxitic biopolymer matrix deposited on the membrane surface, and rupture the hydrophilic bonds of proteins and polysaccharides. The high molecular weight biopolymers were brought down, with the water bounded inside the flocs released into liquid phase. Iron-mediated coagulation was also conductive to the re-aggregation of the fine particles and subsequent membrane fouling control. For raw sludge, the predominated fouling mechanisms were intermediate pore blocking and cake layer formation, while complete pore blocking and standard pore blocking occurred more frequently for pretreated sludge. This work provides a promising approach based on Fe(II)/S2O82- oxidation processes for efficient abatement of membrane fouling and sludge treatment.

Prospects of utilizing seawater as a reaction medium for pretreatment and saccharification of rice straw

The transition towards a bio-based economy has led to an unprecedented surge in fresh water consumption that renders biofuel a high water footprint product. The depleting fresh water resources have exacerbated the situation which necessitates the exploration of non-potable water for biorefinery purposes. In the current study, seawater is used as a plausible alternative reaction medium for pretreatment and saccharification of rice straw. Response Surface Methodology (RSM) based on Box-Behnken Design (BBD) was employed to model, predict and validate cellulose release and reducing sugar yield from rice straw subjected to microwave-NaOH pretreatment. The optimized pretreatment conditions were determined to be 8.54% substrate loading, 1.94% NaOH and 4.09 min which resulted in the maximum cellulose release of 65.43% and reducing sugar yield of 0.554 g/g. Several physico-chemical studies of the raw and pretreated biomass were carried out using bomb calorimetry, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) analysis and thermal gravimetric analysis (TGA) to examine the efficacy of pretreatment. Evidences of an apparent delignification was substantiated by the increase in surface area from 7.719 to 44.188 m2 g−1and pore volume from 0.039 to 0.071 mlg−1 which was consistent with the decrease in energy density and distorted surface morphology of the pretreated biomass. Further, the FTIR revealed a reduced peak in the absorption spectral bands at 1636 cm−1 which confirmed the pretreatment mediated degradation of lignin and hemicellulose. This finding provides evidence on the prospects of utilizing abundantly available seawater resource as a reaction medium for sustainable biofuel production.

One-pot ethanol production under optimized pretreatment conditions using agave bagasse at high solids loading with low-cost biocompatible protic ionic liquid

Wash-free one-pot ethanol conversion using Agave bagasse with a low-cost ionic liquid under optimized pretreatment conditions and high solids loading is demonstrated.

Ex vivo tolerization and M2 polarization of macrophages dampens both pro- and anti-inflammatory cytokine production in response to diabetic wound fluid stimulation

Monocytes/macrophages play a prominent role in cutaneous wound healing. Persistent inflammation in diabetic wounds is associated with the inability of monocytic cells to switch from a phagocytic M1 (classically activated) to an anti-inflammatory, pro-regenerative M2 (alternatively activated) phenotype and as consequence, the proliferative phase of healing does not commence. A targeted cell therapy approach could potentially restore the pathological wound microenvironment through paracrine signalling to enable healing. This study investigated whether in vitro pre-treatment of monocytic (J774.1 A) cells - using a combination of endotoxin-induced immune tolerance (Pam3CSK4) and M2 polarization (IL-4) - could make these cells impervious to the pathological wound microenvironment and enhance the release of anti-inflammatory cytokines/growth factors. The effect of Pam3CSK4-induced tolerance and IL-4-associated polarization was assessed independently and in combination, on the expression of intracellular (flow cytometry) and secreted (ELISA) cytokines (TNF-ɑ, IL-6, IL-10, TGF-β) with and without re-stimulation to define the optimal pre-treatment conditions. Successive pre-treatment approach consisting of endotoxin tolerance followed by IL-4 priming, dampened TNF-ɑ release and induced intracellular TGF-β production upon re-stimulation. To mimic a chronic wound microenvironment, the J774A.1 monocytes were differentiated into macrophages using GM-CSF prior to pre-treatment (optimal condition) and subsequently exposed to diabetic wound fluid. The data demonstrated that in the presence of wound fluid, the successive pre-treatment, promoted M2 polarization (CD206) of monocytic cells and significantly dampened the intracellular production of both pro-inflammatory (TNF-ɑ, IL-6) and anti-inflammatory (IL-10, TGF-β) cytokines.

Determination of multiple organic flame retardants in maricultural water using High-volume/High-throughput Solid-phase extraction followed by liquid/gas chromatography tandem mass spectrometry

A rapid and efficient analytical method is proposed and optimized for the enrichment, extraction and instrument analysis of four typical organic flame retardants (OFRs), including organophosphate esters (OPEs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDs) and dechlorane compounds (Dechloranes) in maricultural waters using High-volume/High-throughput Solid-phase extraction with in-situ ultrasonic technique followed by high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) and gas chromatography tandem mass spectrometry (GC–MS) instrumental detection. The optimized pretreatment conditions were that the analytes were enriched by XAD-2 resins and eluted repeatedly with 50 mL hexane/acetone (1:1, v:v) for 5 min. The results of method validation exhibited that the developed method can be used for quantitative detection of 11 OPEs, 13 PBDEs, 3 HBCDs and 5 Dechloranes in water samples. The method detection limits (MDLs) and limits of quantification (LOQs) are 0.4–26.2 pg/L and 1.5–87.4 pg/L for OPEs, 23.3–35.4 pg/L and 77.5–117.9 pg/L for HBCDs, 0.8–97.4 pg/L and 2.6–324.7 pg/L for PBDEs and 9.3–78.5 pg/L and 31.0–261.8 pg/L for Dechloranes, respectively. The method was successfully applied in lagoon maricultural areas in Hainan province, and the results showed that 4 OFRs were detected in almost all water samples. Total concentrations of 18 water samples were 1.89–39.97 ng/L for OPEs, 0.18–5.40 ng/L for PBDEs, ND-0.24 ng/L for HBCDs and 0.01–1.77 ng/L for Dechloranes, respectively. The optimized analytical method is highly sensitive and efficient with expectation to play an essential role in monitoring the ultra-trace organic pollutants and providing an effective risk assessment in ecological environment.

Production of lignin-containing nanocellulose from poplar using ternary deep eutectic solvents pretreatment

Developing green and sustainable reagents and materials is of great significance for the lignin-containing nanocellulose (LNC) production. In this study, new green ternary deep eutectic solvents (DESs) pretreatment followed by microfluidization were used to prepare LNC from poplar. Under optimal pretreatment conditions (choline chloride: lactic acid: p-toluenesulfonic acid molar ratio of 2:10:1, 100 °C), ultrafine ribbon-like LNCs about 23.29 nm wide and 1.16 nm thick with uniformly distributed spherical lignin particles were obtained. The yield of the LNC reached 64.65%. The LNC exhibited cellulose I crystal structure, good dispersion stability in water and high lignin content of 27.65%. The LNC also possessed high thermal stability (Tmax = 370 °C). Additionally, the LNC suspensions showed high viscosity and strong gel-like behavior. The novel ternary DESs pretreatment combined with microfluidization process offers a promising route in converting hardwood biomass into value-added LNC.

Optimisation of enzymatic saccharification of wheat straw pre-treated with sodium hydroxide

To enhance the reducing sugar yield in enzymatic hydrolysis, various factors (NaOH concentration, solid content and pre-treatment time) that affect the pre-treatment process were investigated and evaluated based on the reducing sugar yield of the subsequent enzymatic hydrolysis. The enzymatic hydrolysis was based on the cellulase from Trichoderma reesi ATCC 26921, the optimum NaOH pre-treatment conditions were an NaOH concentration of 1.0% (w/w), a solid content of 5.0% (w/v) and a pre-treatment time of 60 min. Various parameters that affect the enzymatic hydrolysis of wheat straw, including the solid content, enzyme loading, pH and hydrolysis time, were investigated and optimized through a Box–Behnken design and response surface methodology. The predicted optimum conditions for enzymatic hydrolysis were a solid content of 8.0% (w/v), an enzyme loading of 35 FPU/g substrate, a temperature of 50 °C, a pH of 5.3 and a hydrolysis time of 96 h. The experimental result showed that the maximum reducing sugar yield was 60.73% (53.35% higher than the wheat straw without NaOH pre-treatment), which is in accordance with the predicted conditions.

Biocatalytic Synthesis and Characterization of Starch Ferulate Based on Ultrasonic Pretreatment of Substrate

To improve the hydrophobicity and biological activity of corn starch, starch ferulate was prepared by Novozym 435 lipase catalyzed transesterification of ultrasonic pretreated corn starch and ethyl ferulate. The ferulic acylation of starch was confirmed by UV and Fourier transform infrared spectroscopy (FT-IR). Starch ferulate was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimeter (DSC). In addition, the hygroscopicity and free radical scavenging ability of esterified starch (ES) were evaluated. In the results, the maximum degree of substitution (DS) of ES was 0.0728 under the optimal ultrasonic pretreatment conditions, which was much higher than that of 0.0142 without ultrasonic pretreatment. The XRD and DSC analysis showed that ferulic acylation destroyed the crystalline structure of corn starch to a certain extent. Moreover, ferulic acylation can improve the hydrophobicity and free radical scavenging ability of starch. In conclusion, ES obtained with ultrasonic pretreatment followed by enzyme catalysis can improve physical and chemical properties of starch. Ultrasonic provides an effective method for synthesizing high-quality modified starch and lays a theoretical foundation for expanding the application of corn starch.

Enhanced Leaching of Zinc from Zinc-Containing Metallurgical Residues via Microwave Calcium Activation Pretreatment

Given the shortage of zinc resource, the low utilisation efficiency of secondary zinc resource, and the crucial problem that the synchronous dissolution of zinc from different mineral phases, an activation pretreatment method merged with calcium activation and microwave heating approach was proposed to enhance the zinc leaching from complex encapsulated zinc-containing metallurgical residues (ZMR). Results indicated that under the optimal pretreatment conditions, including microwave activation temperature of 400 °C, CaO addition of 25% and activation time of 20 min, the zinc leaching rate reached 91.67%, which was 3.9% higher than that by conventional roasting pretreatment. Meanwhile, microwave heating presents excellent treatment effects, manifested by the zinc leaching rates, all exceeding that of conventional roasting under the same conditions, while the process temperature is decreased by 200 °C. In addition, XRD and SEM-EDS analysis denoted that microwave calcification pretreatment can effectively promote the transformation of the refractory zinc minerals like Zn2SiO4 and ZnFe2O4 into the easily leachable zinc oxides. The distinctive selective heating characteristics of microwave heating strengthened the dissociation of mineral inclusion, and the generated cracks increased the interfacial reaction area and further enhancing the leaching reaction of zinc from ZMR.

Optimization of oxalic and sulphuric acid pretreatment conditions to produce bio-hydrogen from olive tree biomass

This study investigated the best pretreatment conditions for olive tree biomass (OTB) to produce bio-hydrogen. The pretreatment conditions were optimized with response surface methodology for the dark fermentative hydrogen production to achieve maximum reducing sugar recovery and the independent variables were residence time (30–90min), temperature (100–140 °C), and acid concentration (0.5–3 %w/w for sulfuric and 5–10 %w/w for oxalic acid). Maximum reducing sugar obtained after sulfuric acid pretreatment and oxalic acid pretreatment at optimal pretreatment conditions were 37 g/L and 28 g/L, respectively. An approximately 20-fold increase in sugar concentration was achieved in pretreatment with sulfuric acid compared to the untreated control. The highest hydrogen yield was 0.83 and 0.91 mol H2/mol reducing sugar for oxalic acid pretreatment and sulfuric acid pretreatment, respectively. The results show that OTB has the potential to be used in bioenergy production.

Highly efficient enzymolysis and fermentation of corn stalk into L-lactic acid by enzyme-bacteria friendly ionic liquid pretreatment

Ionic liquids (ILs) have been widely used in the pretreatment of biomass. However, the effects of residual ILs on the enzymolysis and fermentation of biomass are still unknown. Therefore, a large quantity of water-washing is usually followed after biomass pretreatment to eliminate the inhibition of residual ILs on subsequent hydrolysis and fermentation steps. In this work, the effect of choline glycine ([Ch][Gly]) concentration on the activity of cellulase and Bacillus sp. strain P38 was systematically investigated to explore the impacts of residual ILs on enzymolysis and fermentation. The results confirmed that the activities of them were almost not inhibited in low concentrations (less than 0.5 wt%) of [Ch][Gly]. Under optimal pretreatment conditions, the maximum cellulose digestibility was 99.23%. Enzymatic hydrolysate was suitable for L-lactic acid fermentation without appreciable inhibition, and the highest sugar-acid conversion rate of 96.33% was obtained by simplified detoxification. This work provides an economic route to produce fermentable sugar and L-lactic acid, which shows an industrial application prospect in lignocellulosic biorefinery.