Effect of chemical pretreatments on corn stalk bagasse as immobilizing carrier of Clostridium acetobutylicum in the performance of a fermentation-pervaporation coupled system

Co-pyrolysis of corn stalk and high-density polyethylene with emphasis on the fibrous tissue difference on thermal behavior and kinetics

The thermal properties of various corn stalk tissues (including stem, husk, ear, cob, and leaf), high-density polyethylene (HDPE), and their blends were investigated using thermogravimetric analysis under a nitrogen atmosphere. The results indicate that the thermal decomposition process of corn stalk tissue/HDPE mixtures is delayed with an increasing heating rate, regardless of the tissue type. Besides, the structural differences among various corn stalk tissues significantly influence their thermal behavior, product distribution, and co-pyrolysis kinetics with HDPE. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was conducted to analyze the pyrolytic products of the blends with different corn stalk tissues, revealing that corn cob/HDPE blends produce a higher yield of valuable chemicals, such as the furan derivates and aromatic hydrocarbons. Kinetic analysis was further performed using Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods to determine the activation energy for the reactions occurring during co-pyrolysis. The co-pyrolysis of corn cob/HDPE blend requires the least activation energy (149.3 kJ/mol) among five blends, which was ascribed to the high hemicellulose content in corn cob. Moreover, machine learning algorithms, including random forest (RF) and gradient boost regression tree (GBRT), were applied to predict mass loss in the corn fiber/HDPE blends, which showed RF possessed superior accuracy over GBRT. These findings suggest that isolating plant tissues during the feedstock pre-management could enhance the valorization performance of lignocellulose-waste plastic co-pyrolysis.

Efficient conversion of cane molasses into Tremella fuciformis polysaccharides with enhanced bioactivity through repeated batch culture

Tremella fuciformis polysaccharide (TFPS) is a natural mushroom mucopolysaccharide widely used in health foods, medical care, cosmetic and surgical materials. In this study, we developed an efficient strategy for the repeated batch production of highly bioactive TFPS from the agro-industrial residue cane molasses. Cane molasses contained 39.92 % sucrose (w/w), 6.36 % fructose and 3.53 % glucose, all of which could be utilized by T. fuciformis spores, whereas, the TFPS production efficiency only reached 0.74 g/L/d. Corn cobs proved to be the best immobilized carrier that could tightly absorb spores and significantly shorten the fermentation lag period. The average yield of TFPS in eight repeated batch culture was 5.52 g/L with a production efficiency of 2.04 g/L/d. The average fermentation cycle after optimization was reduced by 61.61 % compared with the initial conditions. Compared to glucose as a carbon source, cane molasses significantly increased the proportion of low-molecular-weight TFPS (TFPS-2) in total polysaccharides from 3.54 % to 17.25 % (w/w). Moreover, TFPS-2 exhibited potent antioxidant capacity against four free radicals (O2-, ABTS+, OH, and DPPH). In conclusion, this study lays the foundation for the efficient conversion of cane molasses and production of TFPS with high bioactivity.

Effect of acidic pretreatment on the microstructural arrangement and anaerobic digestion of Arachis hypogea shells; and process parameters optimization using response surface methodology

Enzymatic hydrolysis of lignocellulose feedstocks has been observed as the rate-limiting stage during anaerobic digestion. This necessitated the need for pretreatment before anaerobic digestion for an effective and efficient process. Therefore, this study investigated the impact of acidic pretreatment on Arachis hypogea shells, and different conditions of H₂SO₄ concentration, exposure time, and autoclave temperature were considered. The substrates were digested for 35 days at a mesophilic temperature to assess the impact of pretreatment on the microstructural organization of the substrate. For the purpose of examining the interactive correlations between the input parameters, response surface methodology (RSM) was used. The result reveals that acidic pretreatment has the strength to disrupt the recalcitrance features of Arachis hypogea shells and make them accessible for microorganisms' activities during anaerobic digestion. In this context, H₂SO₄ with 0.5% v. v^-1 for 15 min at an autoclave temperature of 90 °C increases the cumulative biogas and methane released by 13 and 178%, respectively. The model's coefficient of determination (R²) demonstrated that RSM could model the process. Therefore, acidic pretreatment poses a novel means of total energy recovery from lignocellulose feedstock and can be investigated at the industrial scale.

An Alternative Approach to Improve the Butanol Production Efficiency from Sweet Sorghum Stem Juice Using Immobilized Cells Combined with an In Situ Gas Stripping System

The effects of the nitrogen source and buffers used in butanol production with Clostridium beijerinckii TISTR 1461 from sweet sorghum stem juice (SSJ) containing 60 g/L of total sugar were first studied in this paper. Among the various nitrogen sources (dried spent yeast, urea, ammonium acetate, ammonium sulfate), urea was found to be the most suitable for butanol production. SSJ supplemented with urea (0.64 g/L) and cocktail buffers (KH2PO4, 0.5 g/L; K2HPO4, 0.5 g/L; ammonium acetate, 2.2 g/L) gave the highest butanol concentration (PB, 10.13 g/L). Then, the capability of immobilized C. beijerinckii TISTR 1461 cells for butanol fermentation was investigated. Two residual waste materials were examined as immobilized cell carriers. Bamboo chopstick pieces were more appropriate as carriers for cell immobilization than cigarette filter tips. The PB value of the immobilized cells on the bamboo chopstick pieces was ~13% higher than that on the cigarette filter tips. Using the response surface methodology (RSM), 1.9 cm bamboo chopstick pieces with a carrier loading of 1:32 (w/v) were the optimum conditions for cell immobilization for butanol production. Under these conditions, the PB value was 11.62 g/L. To improve the butanol production efficiency, a gas stripping system (GS) was connected to the fermenter. It was found that the PB (14.02 g/L) and butanol productivity (QB, 0.29 g/L·h) values improved by ~21% compared to butanol fermentation using no gas stripping.

Coexpression of VHb and MceG genes in Mycobacterium sp. Strain LZ2 enhances androstenone production via immobilized repeated batch fermentation

Androstenone production is limited by low-efficiency substrate transport and dissolved oxygen levels during fermentation. In this study, the coexpression of the optimized Vitreoscilla hemoglobin (VHb) and sterol transporter ATPase (MceG) genes in Mycobacterium sp. LZ2 (Msp) was investigated to alleviate dissolved oxygen and mass transfer limitations. Results revealed that Msp-vgb/mceG effectively improved the growth, production, and adaptation to dissolved oxygen compared with those of Msp. The increased catalase activity and reduced intracellular ROS levels enhanced cell viability and promoted transcription of genes critical for phytosterol metabolism. Bagasse as an immobilization carrier increased the productivity of Msp-vgb/mceG by 56%. Immobilized repeat batch fermentation reduced the biotransformation period from 60 days to 37 days and improved the productivity from 0.039 g/L/h to 0.069 g/L/h. To the best of our knowledge, this work is the first study on the immobilization of recombinant mycobacteria on bagasse for androstenone production.

Improved glucose recovery from durian peel by alkaline-catalyzed steam pretreatment

Durian (Durio zibethinus Murr.) peel, as agricultural waste, is a potential under-utilized lignocellulosic biomass that is sufficiently available in Thailand. In this study, durian peel from monthong (D. zibethinus Murr. cv. Monthong) and chanee (D.zibethinus Murr. cv. Chanee) were subjected to pretreatment with sodium hydroxide (NaOH) under autoclaving conditions to improve glucose recovery. The effect of NaOH concentration (1%, 2%, 3%, and 4%) and autoclave temperature (110 °C, 120 °C, and 130 °C) was investigated based on the amount of glucose recovered. The optimal NaOH concentration and autoclave temperature were determined to be 2% and 110 °C, respectively, under which maximum glucose (36% and 35% in monthong and chanee peels, respectively) was recovered. Glucose recovery was improved by about 6-fold at the optimal pretreatment condition for both pretreated monthong and chanee when compared to the untreated durian peels. Scanning electron microscopy (SEM) showed great changes to the surface morphology of pretreated durian peel from the two cultivars. X-ray diffraction (XRD) analysis also revealed a rise in cellulose crystallinity index (CrIs) after pretreatment. A combination of mild NaOH concentration and autoclaving is a very effective pretreatment technique for maximum glucose recovery from durian peel.

Capability of Immobilized Clostridium beijerinckii TISTR 1461 on Lotus Stalk Pieces to Produce Butanol from Sugarcane Molasses

Immobilized Clostridium beijerinckii TISTR 1461 was used to enhance the butanol production efficiency from sugarcane molasses. Lotus stalk (LS) pieces were used as carriers for cell immobilization. Sugarcane molasses containing 50 g/L of sugar supplemented with 1 g/L of yeast extract was found to be an appropriate medium for bacterial cell immobilization on the LS pieces. Carrier size (4, 12 and 20 mm in length) and carrier loading (1:15, 1:30 and 1:45, w/v) were optimized for high levels of butanol production using response surface methodology (RSM). The batch fermentation was carried out under anaerobic conditions in 1 L screw-capped bottles at 37 °C and an agitation rate of 150 rpm. It was found that the optimum conditions for the butanol production were the carrier size of 4 mm and carrier loading of 1:31 (w/v). Under these conditions, the butanol concentration (PB) was 12.89 g/L, corresponding to the butanol productivity (QB) of 0.36 g/L∙h and butanol yield (YB/S) of 0.36 g/g. These values were higher than those using free cells (PB, 10.20 g/L, QB, 0.28 g/L∙h and YB/S, 0.32 g/g). In addition, it was found that a 24 h incubation time for cell immobilization was appropriate for the immobilization process, which was confirmed by the results of the scanning electron microscope (SEM) and atomic force microscopy (AFM) images and specific surface area measurement. When the fermentation using the immobilized cells was carried out in a stirred-tank reactor (STR), column reactor (CR) and CR coupled with STR, the results showed that all reactors could be used to produce butanol production from the immobilized cells on LS pieces. However, the PB using CR and CR coupled with STR were only 75% and 45% of those using the screw-capped bottle and STR.

Higher nitrogen removal achieved in constructed wetland with polyethylene fillers and NaOH-heating pre-treated corn stalks for advanced treatment of low C/N sewage

Advanced processing of low C/N sewage faces the carbon sources shortage, while quantities of agricultural biomass wastes need to be disposed. This study investigated the potential of quantitative modified biomass addition in constructed wetlands (CWs) filled with polyethylene fillers. Results showed that the lignin in NaOH-heating pretreated corn stalks (NH-CSs) was destroyed, and the wrinkles on the stalks increased and became more soft after pretreatment, which was more conducive to the utilization of carbon sources and attachment of microorganisms. Compared with glucose and sodium acetate, the denitrification with mixed carbon source (glucose and NH-CSs) had the highest effective utilization percentage (61.37%) and NH-CSs were expected to become stable and fast-release carbon sources. After adding 30 g NH-CSs to the rear unit of CW with polyethylene fillers (CW-A), TN removal efficiency was increased by 18.21%, and the average removal efficiency of COD, NH₄⁺-N, TN, and TP reached 54.83%, 89.95%, 64.11%, and 45.04%, respectively. Compared with the traditional CW (CW-B), CW-A had a significant denitrification advantage (P < 0.05), but the removal efficiency and effluent stability of phosphorus were inferior to CW-B. These results indicate that the biomass carbon sources such as corn stalks and polyethylene fillers have a good potential to improve the denitrification in CWs.

The highly-stable immobilization of enzymes on a waste mycelium carrier

Mycelium is an abundant waste from the fermentation industry, and the environmental problems associated with its required disposal seriously limited the development of fermentation industry. In China, millions of tons of various kinds of mycelium residues were produced each year. Research into providing added-value to mycelium, while avoiding its disposal, is hence of paramount importance. Mycelium can be used as carrier for enzymes, while the enzyme immobilization moreover improves their stability and lifetime performance. Carrier recycling, the natural degradation and disposal of artificial polymer carriers are critical issues in immobilization. This research investigated its use to manufacture a highly-stable immobilized enzyme. An acid pretreatment was employed to enhance the adsorption ability of mycelium, and its adsorption ability was compared with other carriers. Under the optimal conditions, a core-shell immobilized enzyme with porous structure was obtained. The stability and the recycle results of the evaluation indicated the excellent performance of the immobilized enzyme. The mycelium recycling was also investigated to verify the practicability. All the results indicated that the use of a mycelium-based carrier was a promising strategy for the reutilization of the fermentation waste, and this technique provides an alternative way to reduce the total amount of the waste mycelium. Meanwhile, the stability and reusability performance of the mycelium-based immobilization could also decrease the influence of the disposal of the solid waste from denatured enzymes to the environment.

Co-digestion of Theobroma cacao (Cocoa) pod husk and poultry manure for energy generation: Effects of pretreatment methods

In this study, biogas was produced from the anaerobic co-digestion of Cocoa pod husk (CPH) and poultry manure. Pretreatment of the CPH was carried out using sulfuric acid and hydrogen peroxide. The physicochemical, elemental and structural analyses were carried out on the CPH before and after pretreatment. The microbial composition of the fermenting materials were also determined using standard method while the Fourier Transform Infra-red (FTIR) spectroscopy was used to identify the structural changes that took place after pretreatments. Use of alkaline hydrogen peroxide caused high solubilization of the lignin component of the CPH and reduced up to 81% of lignin i.e. initial value of 21.7% m.m^-1 to final value of 4.2% m.m^-1. Similarly, the alkali reduced the hemicellulose content of the CPH from 27.0% m.m^-1 to 8.5% m.m^-1. Overall, there was 68% increase in biogas volume from the alkaline pretreated CPH.

Mechanical pretreatment of lignocelluloses for enhanced biogas production: Methane yield prediction from biomass structural components

In this study, mechanical pretreatment was applied to six different lignocelluloses in two different treatment phases and the prediction of their methane yield was done from biomass chemical composition. Physicochemical, proximate and microbial analyses were carried out on both pretreated and untreated biomass using standard methods. Mechanical pretreatments caused the breakdown of structural materials in all the used biomass which was characterized by reduction of the lagging time during anaerobic digestion and the subsequent increase in methane yield up to 22%. The different loading rate of biomass had no effect on the overall methane yield increase. Both single and multiple linear regressions models were used in order to correlate the chemical composition of the biomass with their methane potentials and a fairly high correlation (R² = 0.63) was obtained. The study also showed that the pretreatments are economically feasible. Therefore, its further application to other biomass is encouraged.

Combining Autoclaving with Mild Alkaline Solution as a Pretreatment Technique to Enhance Glucose Recovery from the Invasive Weed Chloris barbata

Developing an optimum pretreatment condition to enhance glucose recovery assessed the potential of Chloris barbata, which is a common invasive weed in Thailand, as a feedstock for bioethanol production. Chloris barbata was exposed to autoclave-assisted alkaline pretreatment by using different sodium hydroxide (NaOH) concentrations (1% to 4%) and heat intensities (110 °C to 130 °C) that were dissipated from autoclaving. The optimum condition for pretreatment was determined to be 2% NaOH at 110 °C for 60 min. At this condition, maximum hydrolysis efficiency (90.0%) and glucose recovery (30.7%), as compared to those of raw C. barbata (15.15% and 6.20%, respectively), were observed. Evaluation of glucose production from 1000 g of C. barbata based on material balance analysis revealed an estimated yield of 304 g after pretreatment at the optimum condition when compared to that of raw C. barbata (61 g), an increase of five-fold. Structural analysis by the scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed the disruption of the intact structure of C. barbata and an increase in the cellulose crystallinity index (CrI), respectively. The results from this study demonstrate the efficiency of using C. barbata as a potential feedstock for bioethanol production.

Biochemical engineering in China

Chinese biochemical engineering is committed to supporting the chemical and food industries, to advance science and technology frontiers, and to meet major demands of Chinese society and national economic development. This paper reviews the development of biochemical engineering, strategic deployment of these technologies by the government, industrial demand, research progress, and breakthroughs in key technologies in China. Furthermore, the outlook for future developments in biochemical engineering in China is also discussed.

Optimization of process parameters for anaerobic fermentation of corn stalk based on least squares support vector machine

In order to improve the yield and efficiency of biogas produced from anaerobic fermentation of corn stalk, least squares support vector machine (LS-SVM) was used to optimize the pretreatment process parameters. Weight of corn stalk, ultrasonic duration time, alkali pretreatment (2% NaOH) time, and single/dual-frequency ultrasound were selected as the experimental factors of orthogonal experimental design (OED). A new modeling method combining LS-SVM and OED was proposed to establish the predictive model between cumulative biogas production (CBP) and pretreatment process parameters. The effect of experimental factors on CBP was analyzed by two-dimensional (2D) and three-dimensional (3D) contour maps of the predictive model. The optimum parameters for process pretreatment were as follows: weight of corn stalk 53 g, dual-frequency ultrasound, ultrasonic duration time 33 min, alkali pretreatment time 56 h. The CBP of the optimal conditions obtained was 22.69 L and was 14.13% higher than that of optimal conditions for OED.

Novel distillation process for effective and stable separation of high-concentration acetone-butanol-ethanol mixture from fermentation-pervaporation integration process

BACKGROUND

One of the major obstacles of acetone-butanol-ethanol (ABE) fermentation from renewable biomass resources is the energy-intensive separation process. To decrease the energy demand of the ABE downstream separation processes, hybrid in situ separation system with conventional distillation is recognized as an effective method. However, in the distillation processes, the high reflux ratio of the ethanol column and the accumulation of ethanol on top of the water and butanol columns led to poor controllability and high operation cost of the distillations. In this study, vacuum distillation process which is based on a decanter-assisted ethanol-butanol-water recycle loop named E-TCD sequence was developed to improve the conventional separation sequence for ABE separation. The permeate of in situ pervaporation system was used as the feed.

RESULTS

The distillation processes were simulated and optimized by iterative strategies. ABE mixture with acetone, butanol and ethanol concentrations of 115.8 g/L, 191.4 g/L and 17.8 g/L (the other composition was water) that obtained from fermentation-pervaporation integration process was used as the feed. A plant scaled to 1025 kg/h of ABE mixture was performed, and the product purities were 100 wt% of butanol, 99.7 wt% of acetone and 95 wt% of ethanol, respectively. Results showed that only 5.3 MJ/kg (of butanol) was required for ABE separation, which was only 37.54% of the energy cost in conventional distillation processes.

CONCLUSIONS

Compared with the drawbacks of ethanol accumulation in butanol-water recycle loop and the extremely high recovery rate of ethanol in conventional distillation processes, simulation results obtained in the current work avoided the accumulation of ethanol based on the novel E-TCD sequence.

Effect of pretreatments on corn stalk chemical properties for biogas production purposes

Different pretreatments were evaluated on corn stalk (Zea mays) applied as a lignocellulosic source in anaerobic co-digestion with swine manure, using sulfuric acid (H₂SO₄) and hydrogen peroxide (H₂O₂) for biogas production purposes. Using H₂SO₄ we achieved a 75.1% removal of the hemicellulose fraction, in low acid concentrations (0.75% v.v^-1). However, this technique inhibited the co-digestion process. Pretreatment with 12% of H₂O₂ (pH 11.5) increased the cellulose fraction by 73.4% and reduced the lignin content by 71.6%. This pretreatment is recommended for biogas production, as it increased the final volume of biogas by 22% and reduced the digestion time by one third. So, a promising alternative was obtained in order to facilitate the anaerobic digestion of the carbohydrates present in this biomass.

Lipase immobilization on high water adsorbing capacity bagasse: applications in bio-based plasticizer synthesis

This study investigates the structure and water adsorbing capacity of bagasse and of sodium hydroxide pretreated bagasse. The structures of bagasse and bagasse-NaOH were compared by SEM and XRD. Candida antarctica lipase B was then immobilized on bagasse, bagasse-NaOH and DPA@bagasse-NaOH. The expressed activity and immobilization yield of lipase immobilized on bagasse-NaOH (1.0%) was 36% and 45% higher than that on bagasse. When dopamine (DPA) was used as cationic polymer monomer via self-polymerization for mediating immobilization, the protein loading amounts and activity of lipase immobilized on DPA@bagasse-NaOH were higher than that of bagasse-NaOH. When the DPA concentration was 100 mg/ml, the immobilized lipase expressed activity reached its highest value (800 U/g), where the immobilization yield achieved 96.8%, which was 3.93-fold of lipase immobilized on native bagasse (24.6%). Then the immobilized lipases were used to synthesize a bio-based plasticizer. Lipase immobilized on DPA@bagasse-NaOH exhibited a significantly improved operational stability. Even after 12 batches, a high ester yield (84.2%) was maintained. Additionally, poly (vinyl chloride) PVC blends plasticized with methyl oleate as a secondary plasticizer were investigated. It was discovered that methyl oleate can be used as an effective bio-based plasticizer for PVC. These results indicate that bagasse with high water adsorbing capacity and self-polymerized DPA layer could create a favorable microenvironment for bio-based plasticizer synthesis in esterification reactions.

Bio-plasticizer production by hybrid acetone-butanol-ethanol fermentation with full cell catalysis of Candida sp. 99-125

Hybrid process that integrated fermentation, pervaporation and esterification was established aiming to improve the economic feasibility of the conventional acetone-butanol-ethanol (ABE) fermentation process. Candida sp 99-125 cells were used as full-cell catalyst. The feasibility of batch and fed-batch esterification using the ABE permeate of pervaporation (ranging from 286.9 g/L to 402.9 g/L) as substrate were compared. Valuable butyl oleate was produced along with ethyl oleate. For the batch esterification, due to severe inhibition of substrate to lipase, the yield of butyl oleate and ethyl oleate were only 24.9% and 3.3%, respectively. In contrast, 75% and 11.8% of butyl oleate and ethyl oleate were obtained, respectively, at the end of the fed-batch esterification. The novel integration process provides a promising strategy for in situ upgrading ABE products.

Integrated in situ gas stripping-salting-out process for high-titer acetone-butanol-ethanol production from sweet sorghum bagasse

BACKGROUND

The production of biobutanol from renewable biomass resources is attractive. The energy-intensive separation process and low-titer solvents production are the key constraints on the economy-feasible acetone-butanol-ethanol (ABE) production by fermentation. To decrease energy consumption and increase the solvents concentration, a novel two-stage gas stripping-salting-out system was established for effective ABE separation from the fermentation broth using sweet sorghum bagasse as feedstock.

RESULTS

The ABE condensate (143.6 g/L) after gas stripping, the first-stage separation, was recovered and introduced to salting-out process as the second-stage. K₄P₂O₇ and K₂HPO₄ were used, respectively. The effect of saturated salt solution temperature on final ABE concentration was also investigated. The results showed high ABE recovery (99.32%) and ABE concentration (747.58 g/L) when adding saturated K₄P₂O₇ solution at 323.15 K and 3.0 of salting-out factor. On this condition, the energy requirement of the downstream distillation process was 3.72 MJ/kg of ABE.

CONCLUSIONS

High-titer cellulosic ABE production was separated from the fermentation broth by the novel two-stage gas stripping-salting-out process. The process was effective, which reduced the downstream process energy requirement significantly.

Performance enhancement of a polydimethylsiloxane membrane for effective n-butanol pervaporation by bonding multi-silyl-functional MCM-41

In the current work, MCM-41/polydimethylsiloxane (PDMS) mixed matrix membrane (MMM) was prepared for effective n-butanol pervaporation from a model aqueous solution. In order to improve the compatibility between MCM-41 and PDMS, different types of silane coupling agents including n-propyltrimethoxysilane (PTMS), n-octyltrimethoxysilane (OTMS), n-dodecyltrimethoxysilane (DTMS) and n-hexadecyltrimethoxysilane (HDTMS) were used to modify the MCM-41. The results showed that the highest n-butanol separation performance was achieved by bonding 20 wt% of PTMS-modified MCM-41 with PDMS. Under these conditions, total flux of 1476 g m-2 h-1 was obtained when separating a 1.5 wt% n-butanol aqueous solution at 55 °C. The total flux increased by nearly 40% compared to the pure PDMS membrane with no obvious changes of the n-butanol separation factor at the same time. The curing process of the casting solution was also significantly improved after MCM-41 modification.