Activity of xylose reductase from Candida mogii grown in media containing different concentrations of rice straw hydrolysate

Xylose reductase (XR) activity was evaluated in extracts of Candida mogii grown in media containing different concentrations of rice straw hydrolysate. Results of X Ractivity were compared to xylitol production and a similar behavior was observed for these parameters. Highest values of specific production and productivity were found for xylose reductase (35 U/g of cell and 0.97 U/[g of cell·h], respectively) and for xylitol (5.63 g/g of cell and 0.13 g/[g of cell·h]) in fermentation conducted in medium containing 49.2 g of xylose/L. The maximum value of XR:XD ratio (1.82) was also calculated under this initial xylose concentration with 60 h of fermentation.     

Evaluation of inoculum of Candida guilliermondii grown in presence of glucose on xylose reductase and xylitol dehydrogenase activities and xylitol production during batch fermentation of sugarcane bagasse hydrolysate

The effect of glucose on xylose-xylitol metabolism in fermentation medium consisting of sugarcane bagasse hydrolysate was evaluated by employing an inoculum of Candida guilliermondii grown in synthetic media containing, as carbon sources, glucose (30 g/L), xylose (30 g/L), or a mixture of glucose (2 g/L) and xylose (30 g/L). The inoculum medium containing glucose promoted a 2.5-fold increase in xylose reductase activity (0.582 IU/mg_prot) and a 2-fold increase in xylitol dehydrogenase activity (0.203 IU/mg_prot) when compared with an inoculum-grown medium containing only xylose. The improvement in enzyme activities resulted in higher values of xylitol yield (0.56 g/g) and productivity (0.46 g/[L·h]) after 48 h of fermentation.     

Application of factorial design to the study of xylitol production from eucalyptus hemicellulosic hydrolysate

This study deals with the bioconversion of xylose into xylitol by Candida guilliermondii FTI 20037 using eucalyptus hemicellulosic hydrolysate obtained by acid hydrolysis. The influence of various parameters (ammonium sulfate, rice bran, pH, and xylose concentration) on the production of xylitol was evaluated. The experiments were based on multivariate statistical concepts, with the application of factorial design techniques to identify the most important variables in the process. The levels of these variables were quantified by the response surface methodology, which permitted the establishment of a significant mathematical model with a coefficient determination of R ²=0.92. The best results (xylitol=10.0 g/L, yield factor=0.2 g/g, and productivity=0.1 g/[L·h]) were attained with hydrolysate containing ammonium sulfate (1.1 g/L), rice bran (5.0 g/L), and xylose (initial concentration of 60.0 g/L), after 72 h of fermentation. The pH of fermentation was adjusted to 8.0 and the inoculum level utilized was 3 g/L.     

STUDY OF COMPOSITE MEMBRANE OF CELLULOSE ACETATE OR POLYVINYL ALCOHOL BLENDED WITH METHYLMETHACRYLATE-ACRYLIC ACID COPOLYMER FOR PERVAPORATION SEPARATION*

In this paper, methylmethacrylate-acrylic acid MMA-AA hydrophilic and hydrophobic copolymerswere prepared by copolymerization for preparing membrane materials. The composite membrane of celluloseacetate (CA) blended with MMA-AA hydrophobic copolymer was used for the separation of methanol frompentane-methanol mixture. When the methanol concentration was only 1 wt% ,the permeate flux stillmaintained at 350 g/m~2h and separation factor was as big as 800. The composite membrane of PVA(polyvinyl alcohol) blended with MMA-AA hydrophilic copolymer was used for the separation of ethanol-water mixture. The permeate flux was increased to 975 g/m~2h at 74℃ and the separation factor reached 3000at 25℃. The PVA/MMA-AA blended membrane surface modified by ammonia plasma was also investigatedfor separating ethanol-water mixture. Both permeate flux and separation factor of the membrane wasimproved. However, there was no obvious difference of plasma treatment time in the interval of 20～40 min.     

Specific Adhesion of 3T3‐L1 Fibroblast onto Uridine‐Containing Polystyrene

A hydrophobic 96‐well multiplate was incubated with aqueous poly(uridine 5′‐p‐styrenesulfonate) (PUSS). Analysis of the PUSS‐coated surface indicated that the surface incubated at higher polymer concentration (50 mg·mL^–1) was hydrophilic while the surface incubated at lower polymer concentration (1 mg·mL^–1) was hydrophobic. Adhesion of 3T3‐L1, which has GalTase on the cell membrane, on the hydrophobic PUSS‐coated surface was greater than on the non‐coated surface. 3T3‐L1 adhesion on the hydrophilic PUSS‐coated surface was even greater. On the other hand, the adhesion of HeLa cells, which did not show GalTase on the cell membrane, on the hydrophilic surface was quite weak. It may well be said that the 3T3‐L1 adhesion on the hydrophilic PUSS‐coated surface was GalTase‐mediated.     

Ethanol production in a membrane bioreactor

Pilot plant trials were conducted in a corn wet mill with a 7000-L membrane recycle bioreactor (MRB) that integrated ceramic microfiltration membranes in a semi-closed loop configuration with a stirred-tank reactor. Residence times of 7.5–10 h with ethanol outputs of 10–11.5% (v/v) were obtained when the cell concentration was 60–100 g/L drywt of yeast, equivalent to about 10⁹−10¹⁰ cells/mL. The performance of the membrane was dependent on the startup mode and pressure management techniques. A steady flux of 70 L/(m²·h) could be maintained for several days before cleaning was necessary. The benefits of the MRB include better productivity; a clear productstream containing no particulates or yeast cells, which should improve subsequent stripping and distillation operations; and substantially reduced stillage handling. The capital cost of the MRB is $21–$34/(m³·yr) ($0.08–$0.13/[gal·yr]) of ethanol capacity. Operating cost, including depreciation, energy, membrane replacement, maintenance, labor, and cleaning, is $4.5–9/m³ ($0.017–$0.034/gal) of ethanol.     

Channel regulation of TFC membrane with hydrophobic carbon dots in forward osmosis

Zero-dimensional carbon dots have emerged as important nanofillers for the separation membrane due to their small specific size and rich surface functional groups. This study proposed a strategy based on hydrophobic carbon dots (HCDs) to regulate water channels for an efficient forward osmosis (FO) membrane. Thin-film composite (TFC) membranes with superior FO performance are fabricated by introducing HCDs as the nanofiller in the polyacrylonitrile support layer. The introduction of HCDs promotes the formation of the support layer with coherent finger-like hierarchical channels and micro-convex structure and an integrated polyamide active layer. Compared to the original membrane, TFC-FO membrane with 10 wt% HCDs exhibits high water flux (15.47 L m⁻² h⁻¹) and low reverse salt flux (2.9 g m⁻² h⁻¹) using 1 mol/L NaCl as the draw solution. This improved FO performance is attributed to the lower structural parameters of HCDs-induced water channels and alleviated internal concentration polarization. Thus, this paper provides a feasible strategy to design the membrane structure and boost FO performance.     

Fabrication and Performance of a Low Operating Pressure Nanofiltration Poly（vinyl chloride） Hollow Fiber Membrane

A low operating pressure nanofiltration membrane is prepared by interfacial polymerization between m-phenylenediamine(MPDA) and trimesoyl chloride(TMC) using PVC hollow fiber membrane as supporting.A series of PVC nanofiltration membranes with different molecular weight cutoff(MWCO) can be obtained by controlling preparation conditions.Chemical and morphological characterization of the membrane surface was carried out by FTIR-ATR and SEM.MWCO was characterized by filtration experiments.The preparation conditions were investigated in detail.At the optimized conditions(40 min air-dried time,aqueous phase containing 0.5% MPDA,0.05% SDS and 0.6% acid absorbent,oil phase containing 0.3% TMC,and 1 min reaction time),under 0.3 MPa,water flux of the gained nanofiltration membrane reaches 17.8 L/m2·h,and the rejection rates of methyl orange and MgSO4 are more than 90% and 60%,respectively.     

High photosynthetic productivity of green microalga Chlorella sorokiniana

The batch culture of a newly isolated strain of a green microalga, Chlorella sorokiniana, was carried out using a conical helical tubular photobioreactor. The isolate was capable of good growth at 40°C under an airstream enriched with 10% CO₂. The maximum photosynthetic productivity was 34.4g of dry biomass/(m² of installation area · d) (12-h light/12-h dark cycle) when the cells were illuminated with an average photosynthetic photon flux density (photosynthetically active radiation ([PAR] 400–700 nm) simulating the outdoors in central Japan (0.980 mmol photons/[m²·s]). This corresponded to a photosynthetic efficiency of 8.67% (PAR), which was defined as the percentage of the light energy recovered as biomass (394 kJ/[reactor·d]) to the total light energy received (4545 kJ/[reactor·d]). A similarly high photosynthetic efficiency (8.12% [PAR]) was also attained in the combined presence of 10% CO₂, 100 ppm of NO, and 25 ppm of SO₂. Moreover, good photosynthetic productivity was also obtained under high temperature and high light intensity conditions (maximum temperature, 46.5°C; 1.737 mmol photons/[m²·s]), when simulating the strong irradiance of the midday summer sun. This strain thus appears well suited for practical application for converting CO₂ present in the stack gases emitted by thermal power plants and should be feasible even during the hot summer weather.     

Fouling and protein adsorption effect of low-temperature plasma treatment of membrane surfaces

Adsorption of proteins and the effect of the chemical nature of membrane surfaces on protein adsorption were investigated using¹⁴C-tagged albumin and several microporous membranes (polyvinilydene fluoride, PVDF; nylon; polypropylene, PP; and polycarbonate, PC). The membrane surfaces were modified by exposing them to low-temperature plasma of several different monomers (n-butane, oxygen, nitrogen alone or as mixtures) in a radiofrequency plasma reactor. Transients in the permeability of albumin solutions through the membranes and changes in flux of distilled water through the membranes before and after adsorption of albumin were used to investigate the role of protein adsorption on membrane fouling. The results show that the extent of adsorption of albumin on hydrophobic membranes was considerably more than that on hydrophilic membranes. The hydrophilic membranes were susceptible to electrostatic interactions and less prone to fouling. A pore-blocking model was successfully used to correlate the loss of water flux through pores of defined geometry     

Behavior of extracellular polymers and bio-fouling during hydrogen fermentation with a membrane bioreactor

The characteristics of membrane fouling were investigated by examining the behaviors of extracellular polymer substances (EPSs) produced by hydrogen-producing bacteria during hydrogen fermentation from a submerged membrane bioreactor (MBR). The MBR consisted of a 1.4-L submerged membrane filtration tank and 3-L hydrogen fermenter. An intermittent suction operation was selected to maintain stable filtration performance. The operation of the suction pump was alternately shifted to ON for 7 min followed by OFF for 3 min, with bio-gas sparging at a flow rate of 5.0 L/m²/h (LMH), and manually regulated. Most of the EPS during the continuous hydrogen fermentation using an MBR had accumulated in the reactor because they were retained by the membrane by adsorption onto the polymeric membrane surface. The amount of proteins in the EPS extracted was increased to 179 mg/L and that of carbohydrates was increased to 58 mg/L. Cu²⁺, Mg²⁺, Zn²⁺ in the EPS were increased in the range of 1.6–3.3 mg/L. The high concentration of EPS that is produced has a higher chelation potential in the formation of ligand complexes with metals or cations than that in a conventional continuous stirred tank reactor (CSTR). The EPS directly affected the decrease in the permeate flux, which resulted in the clogging of the membrane.     

Cell immobilization and xylitol production using sugarcane bagasse as raw material

Sugarcane bagasse pretreated by three different procedures (with 2% [v/v] polyethyleneimine (PEI), with 2% [w/v] NaOH, or with a sequence of NaOH and PEI) was used as cell immobilization carrier for xylitol production byCandida guilliermondii yeast. Fermentations using these pretreated carriers were performed in semidefined medium and in a hydrolysate medium produced from sugarcane bagasse hemicellulose. Sugarcane bagasse pretreated with NaOH was the best carrier obtained with respect to immobilization efficiency, because it was able to immobilize a major quantity of cells (0.30 g of cells/g of bagasse). Fermentation in semidefined medium using the NaOH-pretreated carrier attained a high efficiency of xylose-to-xylitol bioconversion (96% of the theoretical value). From hydrolysate medium, the bioconversion efficiency was lower (63%), probably owing to the presence of other substances in the medium that caused an inadequate mass transfer to the cells. In this fermentation medium, better results with relation to xylitol production were obtained by using PEI-pretreated carrier (xylose-to-xylitol bioconversion of 81% of the theoretical and volumetric productivity of 0.43 g/[L·h]). The results showed that sugarcane bagasse is a low-cost material with great potential for use as cell immobilization carrier in the fermentative process for xylitol production.     

Mass transfer and benzene removal from air using latex rubber tubing and a hollow-fiber membrane module

A dense-phase latex rubber tube and a polyporous propylene hollow-fiber membrane module (HFMM) were investigated for control of benzene-contaminated gas streams. The abiotic mass flux observed through the latex tube was 3.9–13 mg/(min·m²) for 150 ppm of benzene at various gas and liquid flow rates, while a 100-fold lower mass flux was observed in the HFMM. After seeding with an aromatic-degrading culture enriched from activated sludge, the observed removal was 80% of 150 ppm, corresponding toa mass flux of 45 mg/(min·m²). The observed mass flux through the HFMM during biofiltration also rose, to 0.4 mg/(min·m²). Because the HFMM had a 50-fold higher surface area than the latex tube, the observed ben zene removal was 99.8%. Compared to conventional biofilters, the two reactors had modest elimination capacities, 2.5–18 g/(m³·h) in the latex tube membrane bioreactor and 4.8–58 g/(m³·h) in the HFMM. Although the HFMM had a higher elimination capacity, the gas-phase pressure drop was much greater.     

Enhanced desulfurization performance and swelling resistance of asymmetric hydrophilic pervaporation membrane prepared through surface segregation technique

The severe swelling behavior of most hydrophobic membranes has always been an obstinate problem when separating organic mixtures by pervaporation. In some cases, hydrophilic membranes may be an appropriate alternative. In this study, amphiphilic copolymer Pluronic F127 was employed as a surface modifier to fabricate polyethersulfone (PES) asymmetric pervaporation membranes via surface segregation. The scanning electron microscopy (SEM) photographs showed an asymmetric structure of PES/Pluronic F127 membranes. The Fourier transform-infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and static water contact angle measurements confirmed the hydrophilic modification of the membrane surface. Based on the distinct difference of solubility in water between thiophene and n-octane, the prepared membranes were utilized to remove thiophene from n-octane by pervaporation. The effect of Pluronic F127 content on the pervaporation performance was evaluated experimentally. It has been found that both the permeation flux and enrichment factor exhibited a peak value of approximately 60 wt% of the Pluronic F127 content. The highest enrichment factor was around 3.50 with a permeation flux of 3.10 kg/(m² h) for 500 mg/L sulfur in the feed at 30 °C. The influence of various operating parameters on the pervaporation performance was extensively investigated.     

Yields from glucose, xylose, and paper sludge hydrolysate during hydrogen production by the extreme thermophile Caldicellulosiruptor saccharolyticus

This study addressed the utilization of an industrial waste stream, paper sludge, as a renewable cheap feedstock for the fermentative production of hydrogen by the extreme thermophile Caldicellulosiruptor saccharolyticus. Hydrogen, acetate, and lactate were produced in medium in which paper sludge hydrolysate was added as the sole carbon and energy source and in control medium with the same concentration of analytical grade glucose and xylose. The hydrogen yield was dependent on lactate formation and varied between 50 and 94% of the theoretical maximum. The carbon balance in the medium with glucose and xylose was virtually 100%. The carbon balance was not complete in the paper sludge medium because the measurement of biomass was impaired owing to interfering components in the paper sludge hydrolysate. Nevertheless, >85% of the carbon could be accounted for in the products acetate and lactate. The maximal volumetric hydrogen production rate was 5 to 6 mmol/(L·h), which was lower than the production rate in media with glucose, xylose, or a combination of these sugars (9–11 mmol/[L·h]). The reduced hydrogen production rate suggests the presence of inhibiting components in paper sludge hydrolysate.     

Some engineering parameters for Propionic acid fermentation coupled with Ultrafiltration

The effect of circulation rate on permeate flux, the energy requirements for heating or cooling, the reactor homogeneity, and cell activity are discussed for a continuous culture system with cell recycle. The fermentation system was a continuous stirred-tank reactor with an ultrafiltration membrane unit for cell recycle. The membranes have a tubular configuration and are composed of a carbon support coated with zirconium oxide. The permeate flux obtained for a long-run fermentation with Propionibacterium acidi-propionici was higher when the circulation rate was increased: 5.13 L/m²-h for a circulation rate of 0.810 m³/h and 7.09 L/m²-h for 1.104 m³/h. The temperature rise inside the fermenter for different circulation rates was studied, allowing determination of the need of input or output of energy for temperature control. Residence time distribution studies showed that, with a circulation rate of 0.606 m³/h, the dead volume was 9.2%, whereas at 1.104 m³/h the reactor behavior was almost ideal. The influence of the circulation rate on loss of cell activity is also discussed, and rheological studies are suggested as an indirect indicator of cell viability. We hereby express our recognition for the ongoing collaborations with James Gaddy (University of Arkansas) and Gerard Goma (INSA, Toulouse, France).     

Performance of solvent-resistant membranes for non-aqueous systems: solvent permeation results and modeling

Membrane processes like reverse osmosis (RO) and nanofiltration (NF) can be low energy consuming operations as compared to the traditional chemical engineering unit operations and have been widely used for aqueous systems. Since such membrane processes are low energy consuming operations, their use in non-aqueous systems would offer considerable energy savings. Thus, the study is directed towards development and experimental verification of membrane materials and transport models to explain permeation properties of non-aqueous solvent systems. The understanding of polymer–solvent interactions is critical towards the development of suitable materials and also the prediction of the transport mechanisms.Pure solvent permeation studies were conducted to understand the mechanism of solvent transport through polymeric membranes. Different membrane materials (hydrophilic and hydrophobic) as well as different solvents (polar and non-polar) were used for the study. Pure solvent fluxes for hydrophilic membranes used showed that polar solvents (methanol, ethanol, iso-propanol) had a significantly higher flux (8–10 times) than that of the non-polar solvents (pentane, hexane, octane). On the contrary, the non-polar solvent flux was two to four times that of the polar solvents for hydrophobic membranes. For example, hexane flux at ∼13 bar through a hydrophobic silicone based NF membrane was ∼0.6×10⁻⁴ cm³/cm² s. And that through a hydrophilic aromatic polyamide based NF membrane was ∼6×10⁻⁴ cm³/cm² s. A simple model based on a solution-diffusion approach is proposed for predicting the pure solvent permeation through hydrophobic polymeric membranes. The model uses molar volume and viscosity of the solvent as parameters for predicting the pure solvent permeability. The model reasonably predicts the pure solvent permeation (R²=0.89, S.E.∼4%) for hydrophobic membranes. The model has also been experimentally verified using high solution temperatures and also literature experimental data. To extend the predictions to different membranes (hydrophilic and hydrophobic), surface energy and sorption values have been used as a parameter along with the solvent physical properties.     

A mussel-induced approach to secondary functional cross-linking 3-aminopropytriethoxysilane to modify the graphene oxide membrane for wastewater purification

Graphene oxide (GO) with one-atom-thick exhibit remarkable molecule sieving properties, but its low permeance flux renders it difficult to be applied in practice as a high-permeance separation membrane. In this study, we design complex membrane from covalently crosslinked GO, polydopamine (PDA), and 3-aminopropytriethoxysilane (APTES) as building blocks to fabricate the high-permeance GO-based membrane via the vacuum filtration method. A branched crosslinking product (PDA/APTES) working as a clamp grasped the hydrophilic functional groups (hydroxyl, epoxy, carboxyl) on GO for improving the GO membrane flux. The interlayer structure of the GO membrane was optimized according to the crosslinker concentration, reaction time, initial pH, and temperature for RGO/PDA/APTES (RGPA) in this study. At the optimized reaction conditions including the crosslinker concentration of 1.4 mL/L, the temperature of 80 °C, the time of 16 h, and the initial pH of 8.5 for RGPA mixture, the interlayer gallery of RGPA membrane was effectively tunes, endowing high flux ranging from 11.98 L m^?2 h^?1 to 1823.97 L m^?2 h^?1. Besides, the RGPA membrane ensured the high rejections to dye solutions such as methylene blue (MB) (>99%) and congo red (CR) (>90%). Meanwhile, the superior reusable performance of the RGPA membrane was achieved, together with the rejections for MB and CR to 96.32% and 93.1% after 4 cycles, respectively. Also, the RGPA membrane possessed superior anti-fouling performances for bovine serum albumin (BSA) aqueous solution and excellent stabilities in harsh conditions (pH 3, 7 and 11). Grafting the crosslinker onto GO nanosheets exhibits the distinct advantages of achieving the high flux, high rejections to dyes, and superior reusable performance of membranes, posing a great application potential for membrane separation technology in wastewater treatment.     

Effects of initial pH on biological synthesis of xylitol using xylose-rich hydrolysate

Sugarcane bagasse, an agricultural residue plentiful in Brazil, was utilized for xylitol production by a biotechnological process. Am edium fermentation prepared with this xylose-rich biomass at an oxygen transfer volmetric coefficient of 10/h¹ and different initial pH value was inoculated with cells of Candida guilliermondii FTI 20037. The maximum values of xylitol and cell volumetric productivities (Q _p=0.56 g/[L·h] and Q _p=0.11 g/[g·h]), xylitol yield factor (Y _p/s=0.79 g/g), and xylose uptake rate (qs=0.197 g/[g·h]) wereattained atp H 7.0 without further pH control. The results show that the yeast performance was influeced by the pH, an im portant bioengineering prameter in this fermentation process.     

Membrane modification to avoid wettability changes due to protein adsorption in an emulsion/membrane bioreactor

This study addresses problems encountered with an emulsion/membrane bioreactor. In this reactor, enzyme- (lipase) catalyzed hydrolysis in an emulsion was combined with two in-line separation steps. One is carried out with a hydrophilic membrane, to separate the water phase, the other with a hydrophobic membrane, to separate the oil phase. In the absence of enzyme, sunflower oil/water emulsions with an oil fraction between 0.3 and 0.7 could be separated with both membranes operating simultaneously. However, two problems arose with emulsions containing lipase. First, the flux through both the hydrophilic and the hydrophobic membranes decreased with exposure to the enzyme. Second, the hydrophobic membrane showed a loss of selectivity demonstrated by permeation of both the oil phase and the water phase through the hydrophobic membrane at low transmembrane pressure. These phenomena can be explained by protein (i.e. lipase) adsorption to the polymer surface within the pores of the membrane. It was proven that lipase was present at the hydrophilic membrane and that this, in part, explains the flux decrease of the hydrophilic membrane. To prevent the observed loss of selectivity with exposure to protein, the hydrophobic polypropylene membrane (Enka) was modified with block copolymers of propylene oxide (PO) and ethylene oxide (EO). These block copolymers act as a steric hindrance for proteins that come near the surface. The modification was successful: After 10 days of continuous operation the minimum transmembrane pressure at which water could permeate through an F 108-modified membrane was 0.5 bar, the same value as that observed in the beginning of the experiment. This indicates that loss of selectivity due to protein adsorption is prevented by the modification of the membrane.