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Separation of monosaccharides and monovalent salts is important in the biorefinery and food industry. Nanofiltration (NF) technology is promising for this purpose but its poor selectivity still needs to be addressed. In this work, the separation of monosaccharides and monovalent salts by NF is improved by regulating the surface charge and pore size distribution of polyamide NF membranes. The carboxyl groups on the polyamide membrane are selectively activated by N-(3-Dimethylaminopropyl)-N′-ethyl carbodiimide (EDC) and N-hydroxy succinimide (NHS), and subsequently molecules with amino groups are grafted on the membrane to reduce the effective pore size and electronegativity. The conditions and grafted molecules are optimized, and polyethyleneimine (600 Da) is selected as the best for enhancing the separation of glucose/fructose and KCl. Such targeted modification is found to reduce the effective mean pore size while maintaining the porosity of the NF270 membrane, due to pore segmentation. This results in a remarkable improvement in glucose/fructose rejection (from 67.96% to 84.14%) and separation factor (from 2.20 to 6.78), with only a 4.70% permeability loss. The modified membrane also maintains separation performance in crossflow filtration and after alkaline cleaning (pH 12), which outperforms the pristine NF270 and those modified by mussel-inspired coating and simple physical adsorption.

Enzymes in living cells are highly dynamic but at the same time regularly confined for achieving efficient metabolism. Inspired by this phenomenon, we have prepared a novel biocatalytic membrane with high enzyme activity and stability by tuning the confinement strength of the membrane to enzyme, which was achieved via modifying the support layer of a polymeric nanofiltration (NF) membrane and reversely filtrating enzyme. A mussel-inspired coating was used to modify the support interior of the NF membrane to enhance charge and steric effects on enzyme, thus stabilizing enzyme in the membrane with little increment in mass transfer resistance for substrate and products (only 20% permeability loss with a high enzyme loading of 1.34 mg/cm2). A suitable confinement strength of the membrane to enzyme could delay the enzyme leakage and endow enzyme with certain mobility for efficient reaction. Thus, the obtained biocatalytic membrane exhibited a negligible decline in BPA removal efficiency for 7 reuse cycles (

A by-product from membrane-mediated molasses refining process mainly contains sucrose, glucose, fructose and KCl, which is an ideal raw material to produce high fructose syrup (HFS) by invertase. Ultrafiltration (UF) membrane can achieve invertase reuse while protein adsorption on the membrane not only decreases the membrane permeability, but also induces enzyme activity loss. In this work, the effect of glucose/fructose and KCl on the catalytic behavior of invertase was investigated. Then the reusability of invertase for sucrose hydrolysis was evaluated by different UF membranes, and mussel-inspired surface modification was employed to further improve the invertase reusability. The results showed that the presence of KCl in the raw materials greatly decreased the reaction rate, and thus desalination and concentration of the raw materials should be conducted before enzymatic hydrolysis to improve the enzymatic hydrolysis efficiency, save energy and reduce reactor volume. Moreover, it was found that the sucrose conversion decline with enzyme reuse by UF was caused by enzyme adsorption in/on the membrane and/or its penetration through the membrane leading to overall enzyme loss in the retentate. A polyether sulfone (PES) membrane with molecular weight cut-off (MWCO) of 10 kDa (UP010) was selected to recycle invertase because it enabled complete invertase retention and relatively high permeate flux. When l-cysteine (Cys) was grafted on the polydopamine-coated UP010 membrane, it could reduce invertase adsorption on the membrane, and thus keep high sucrose conversion (93–95%) in four enzyme reuse cycles because the grafted Cys greatly increased the negative charge and hydrophilicity of the membrane surface. This work not only offered an alternative for HFS production by membrane technology but also developed a novel strategy to construct antifouling surface to retard enzyme adsorption.

Oligodextrans with molecular weight (Mw) within the range of 5.0–8.0kDa have great commercial potential as precursors of iron-dextran for anemia treatment. Traditional oligodextran production consists of sucrose fermentation, acid hydrolysis and ethanol precipitation, which results in an uneven Mw product, hypersaline wastewater discharge and potential safety hazards. In this work, a novel enzymatic membrane reactor (EMR) system to produce oligodextran is proposed, whereby in-situ product recovery can be manipulated to control the Mw distribution of the resulting products. Results showed that the membrane material played an important role in the permeate flux and transmission of oligodextran. Among the tested membranes, a 20kDa polyethersulfone (PES) membrane was found to be optimal for building up the EMR, as it successfully controlled the oligodextran Mw within the desired range with a relatively narrow distribution and high productivity. Moreover, high transmembrane pressures (3 bars) and low stirring rates (160rpm) promoted yields beyond 50% in 120min. Higher permeate fluxes prevented further product hydrolysis and enhanced the yield. However, the resulting concentration polarization (CP) should be minimized to reduce accumulation of large oligodextran molecules on the membrane surface, which might diffuse through the membrane and thus broaden the Mw distribution of the products in the permeate. Both dextranase and dextran caused membrane irreversible fouling. The fouling caused by the enzymes not only favored the enzyme immobilization itself, but also contributed to narrow the membrane pore size distribution. As a result, a higher uniformity of oligodextran products compared with the pristine EMR was obtained, especially at the beginning of operation with EMR (which was improved by 22%). It was concluded that selecting the suitable membrane type and permeate flux, maximizing the shear rate, and narrowing the membrane pore size distribution were effective strate

In this study, the biocatalytic membranes were prepared by ‘reverse filtration’ of laccase and subsequently various mussel-inspired coating strategies: single dopamine (DA) deposition, DA/polyethyleneimine (PEI) co-deposition, and DA/Cu2+ co-deposition, where nanofiltration (NF) membranes were used as the matrix to further exploit the potential of the biocatalytic membranes. such prepared biocatalytic membranes were enzymatically active on both sides, making it possible to construct a bifacial enzymatic membrane reactor (EMR) for highly efficient micro-pollutants removal (taking bisphenol A (BPA) as an example). Compared with the single polydopamine (PDA) coated membrane, the biocatalytic membranes prepared by DA/PEI and DA/Cu2+ co-depositions exhibited much better performances in terms of enzyme loading, activity and permeability as well as the stability of immobilized enzyme. The BPA removal efficiency was highest for the EMR with the PDA/Cu2+ coated membrane attributed to copper-enhanced electron transfer, while it was lowest for the EMR with the PDA/PEI coated membrane due to the high diffusional resistance of the dense PDA/PEI layer. Meanwhile, the mechanism for performance deterioration of biocatalytic membrane during BPA treatment was revealed, and it was found that the trade-off between BPA removal efficiency and long-term stability could be broken by applying the bifacial EMR with PDA/Cu2+ coated membrane in flow-through mode, since the pressure-induced convective mass transfer improved the substrate accessibility to enzyme together with products removal.

The pervaporation (PV) performance of a thin-film silicalite-1 filled PDMS/PAN composite membrane was investigated in the continuous acetone–butanol–ethanol (ABE) production by a fermentation–PV coupled process. Results showed that continuous removal of ABE from the broth at three different dilution rates greatly increased both the solvent productivity and the glucose utilization rate, in comparison to the control batch fermentation. The high solvent productivity reduced the acid accumulation in the broths because most acids were reassimilated by cells for ABE production. Therefore, a higher total solvent yield of 0.37 g/g was obtained in the fermentation–PV coupled process, with a highly concentrated condensate containing 89.11–160.00 g/L ABE. During 268 h of the fermentation–PV coupled process, the PV membrane showed a high ABE separation factor of more than 30 and a total flux of 486–710 g/m2h. Membrane fouling was negligible for the three different dilution rates. The solution-diffusion model, especially the mass transfer equation, was proved to be applicable to this coupled process.

Background: Succinic acid is one of the key platform chemicals which can be produced via biotechnology process instead of petrochemical process. Biomass derived bio-oil have been investigated intensively as an alternative of diesel and gasoline fuels. Bio-oil could be fractionized into organic phase and aqueous phase parts. The organic phase bio-oil can be easily upgraded to transport fuel. The aqueous phase bio-oil (AP-bio-oil) is of low value. There is no report for its usage or upgrading via biological methods. In this paper, the use of AP-bio-oil for the production of succinic acid was investigated. Results: The transgenic E. coli strain could grow in modified M9 medium containing 20 v/v% AP-bio-oil with an increase in OD from 0.25 to 1.09. And 0.38 g/L succinic acid was produced. With the presence of 4 g/L glucose in the medium, succinic acid concentration increased from 1.4 to 2.4 g/L by addition of 20 v/v% AP-bio-oil. When enzymatic hydrolysate of corn stover was used as carbon source, 10.3 g/L succinic acid was produced. The obtained succinic acid concentration increased to 11.5 g/L when 12.5 v/v% AP-bio-oil was added. However, it decreased to 8 g/L when 50 v/v% AP-bio-oil was added. GC-MS analysis revealed that some low molecular carbon compounds in the AP-bio-oil were utilized by E. coli. Conclusions: The results indicate that AP-bio-oil can be used by E. coli for cell growth and succinic acid production. © 2013 Wang et al.; licensee BioMed Central Ltd.