Biocatalytic membrane: Go far beyond enzyme immobilization

Polydopamine-functionalized polyethersulfone membrane: A paradigm advancement in the field of α-amylase stability and immobilization

Biocatalytic membranes have great potential in various industrial sectors, with the immobilization of enzymes being a crucial stage. Immobilizing enzymes through covalent bonds is a complex and time-consuming process for large-scale applications. Polydopamine (PDA) offers a more sustainable and eco-friendly alternative for enzyme immobilization. Therefore, surface modification with polydopamine as mussel-inspired antifouling coatings has increased resistance to fouling. In this study, α-amylase enzyme was covalently bound to a bioactive PDA-coated polyethersulfone (PES) membrane surface using cyanuric chloride as a linker. The optimal activity of α-amylase enzyme immobilized on PES/PDA membrane was obtained at temperature and pH of 55°C and 6.5, respectively. The immobilized enzyme can be reused up to five reaction cycles with 55 % retention of initial activity. Besides, it maintained 60 % of its activity after being stored for five weeks at 4°C. Additionally, the immobilized enzyme demonstrated increased Michaelis constant and maximum velocity values during starch hydrolysis. The results of the biofouling experiment of various membranes in a dead-end cell demonstrated that the PES membrane's water flux increased from 6722.7 Lmh to 7560.2 Lmh after PDA modification. Although α-amylase immobilization reduced the flux to 7458.5 Lmh due to enhanced hydrophilicity, compared to unmodified membrane. The findings of this study demonstrated that the membrane produced through co-deposition exhibited superior hydrophilicity, enhanced coating stability, and strong antifouling properties, positioning it as a promising candidate for industrial applications.

Tuning the Properties of Polyvinylidene Fluoride/Alkali Lignin Membranes to Develop a Biocatalytic Membrane Reactor for an Organophosphorus Pesticide Degradation

It has been observed that the immobilization of a phosphotriesterase enzyme (PTE) onto polyvinylidene fluoride (PVDF) membranes significantly decreased the enzyme activity, and this negative effect was attributed to the hydrophobic character of the membrane. The indirect indication of this reason was that the same enzyme immobilized on other membrane materials bearing hydrophilic character showed better performance. In this work, we provide direct evidence of the mechanism by immobilizing a PTE on a PVDF membrane hydrophilized by blending it with alkali lignin (AL). The PTE was immobilized on PVDF membrane by a covalent bond with the same procedure used in earlier studies to attribute changes in enzyme activity solely to the wettability properties (and not to the material chemistry). The activity of the PTE immobilized on the PVDF membrane hydrophilized with AL was 50% higher than that of the enzyme immobilized on the PVDF hydrophobic membrane. Further improvements of the membrane structure tailored for the development of a biocatalytic membrane reactor (BMR) were also promoted. In particular, the performance of the BMR was studied as a function of the thickness of the membrane, which allowed us to modulate the residence time into the enzyme-loaded membrane pores while maintaining the flow rate through the pores at a constant.

Biocatalytic PEI-PSS membranes through aqueous phase separation: influence of casting solution pH and operational temperature

Biocatalytic membranes combine the separation properties of membranes and the catalytic abilities of enzymes, holding great promise for industries where both purification and conversion are required. In this work, polyelectrolyte complex membranes incorporated with lysozyme were prepared using polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS) through a one-step and mild pH shift aqueous phase separation (APS) approach. The effects of lysozyme addition and casting solution pH on the membrane properties were studied. All the membranes, both with and without added lysozyme, exhibited asymmetric structures with relatively dense top surfaces and porous cross-sections with finger-like macrovoids. The incorporation of lysozyme did not significantly influence the structure and permeability of the formed membranes. The PEI-PSS biocatalytic membranes exhibited temperature dependent enzymatic activity. The activity strongly increased with increased operational temperature, with the highest activity of 4.30 ± 0.15 U cm-2 at 45 °C. This indicates a responsive effect, where a higher temperature leads to some swelling of the polyelectrolyte complex membrane, making the enzyme more accessible to the used substrate. Moreover, the biocatalytic membranes demonstrate desirable enzymatic stability, maintaining 60% activity even after 60 days of storage. This study validates the potential of the water-based APS process as a straightforward approach for integrating enzymes into responsive biocatalytic membranes.

Wall-Immobilized Biocatalyst vs. Packed Bed in Miniaturized Continuous Reactors: Performances and Scale-Up

Sustainable biocatalysis syntheses have gained considerable popularity over the years. However, further optimizations - notably to reduce costs - are required if the methods are to be successfully deployed in a range of areas. As part of this drive, various enzyme immobilization strategies have been studied, alongside process intensification from batch to continuous production. The flow bioreactor portfolio mainly ranges between packed bed reactors and wall-immobilized enzyme miniaturized reactors. Because of their simplicity, packed bed reactors are the most frequently encountered at lab-scale. However, at industrial scale, the growing pressure drop induced by the increase in equipment size hampers their implementation for some applications. Wall-immobilized miniaturized reactors require less pumping power, but a new problem arises due to their reduced enzyme-loading capacity. This review starts with a presentation of the current technology portfolio and a reminder of the metrics to be applied with flow bioreactors. Then, a benchmarking of the most recent relevant works is presented. The scale-up perspectives of the various options are presented in detail, highlighting key features of industrial requirements. One of the main objectives of this review is to clarify the strategies on which future study should center to maximize the performance of wall-immobilized enzyme reactors.

Immobilized enzymatic membrane surfaces for biocatalytic organics removal and fouling resistance

This research reported on the immobilization of environmentally friendly enzymes, such as horseradish peroxidase (HRP) and laccase (L), along with the hydrophilic zwitterionic compound l-DOPA on nano-filtration (NF) membranes. This approach introduced biocatalytic membranes, leveraging combined effects between membranes and enzymes. The aim was to systematically assess the efficacy of the enzymatic modified membrane (HRP-NF) in degrading colors in the wastewater, as well as enhancing the membrane resistance toward organic fouling. The enzymatic immobilized membrane demonstrated 96.3 ± 1.8% to 96.6 ± 1.9% removal of colors, and 65.2 ± 1.3% to 67.2 ± 1.3% removal of TOC. This result was underpinned by the insights obtained from the radical scavenger coumarin, which was employed to trap and confirm the formation of PRs through the reaction of enzymes and H2O2. Furthermore, membranes modified with enzymes exhibited significantly improved antifouling properties. The HRP-NF membrane experienced an 8% decline in flux, while the co-immobilized HRP-L-NF membrane demonstrated as low as 6% flux decline, contributed by the synergistic effect of increased hydrophilicity and biocatalytic effects. These findings confirmed that the immobilized enzymatic surface has added function of degrading contaminants in addition to separation function of nanofiltration membrane. These l-DOPA-immobilized enzymatic membranes offered a promising hybrid biocatalytic membrane to eliminate dyes and mitigate membrane fouling, which can be applied in many industrial and domestic water and wastewater treatment.

An enzymatic continuous-flow reactor based on a pore-size matching nano- and isoporous block copolymer membrane

Continuous-flow biocatalysis utilizing immobilized enzymes emerged as a sustainable route for chemical synthesis. However, inadequate biocatalytic efficiency from current flow reactors, caused by non-productive enzyme immobilization or enzyme-carrier mismatches in size, hampers its widespread application. Here, we demonstrate a general-applicable and robust approach for the fabrication of a high-performance enzymatic continuous-flow reactor via integrating well-designed scalable isoporous block copolymer (BCP) membranes as carriers with an oriented and productive immobilization employing material binding peptides (MBP). Densely packed uniform enzyme-matched nanochannels of well-designed BCP membranes endow the desired nanoconfined environments towards a productive immobilized phytase. Tuning nanochannel properties can further regulate the complex reaction process and fortify the catalytic performance. The synergistic design of enzyme-matched carriers and efficient enzyme immobilization empowers an excellent catalytic performance with >1 month operational stability, superior productivity, and a high space-time yield (1.05 × 105 g L-1 d-1) via a single-pass continuous-flow process. The obtained performance makes the designed nano- and isoporous block copolymer membrane reactor highly attractive for industrial applications.

Deep degradation of atrazine in water using co-immobilized laccase-1-hydroxybenzotriazole-Pd as composite biocatalyst

The efficient and green removal technology of refractory organics such as atrazine in water has been an important topic of research in water treatment. A novel membrane composite biocatalyst Lac-HBT-Pd/BC as prepared for the first time by co-immobilizing laccase, mediator 1-hydroxybenzotriazole (HBT) and metal Pd on functionalized bacterial cellulose (BC) to investigate the removal of atrazine and degradation of its intermediates under mild ambient conditions. It was found that atrazine could be completely degraded in 5 h by the catalysis of Lac-HBT-Pd/BC, and the removal rate of degradation intermediates from atrazine was about 85% after continuous catalysis, which achieved deep degradation of atrazine. The effect of electrochemical activity and radical stability of the membrane composite biocatalysts loaded with Pd was investigated. The possible degradation pathways were proposed by identifying and analyzing the deep degradation products of atrazine. The Lac-HBT-Pd/BC demonstrated deep degradation of atrazine and favorable reusability as well as considerable adaptability to various water qualities. This work provides an important reference for preparing new kinds of biocatalysts to degrade refractory organic pollutants in water.

Biocatalytic Membranes for Carbon Capture and Utilization

Innovative carbon capture technologies that capture CO₂ from large point sources and directly from air are urgently needed to combat the climate crisis. Likewise, corresponding technologies are needed to convert this captured CO₂ into valuable chemical feedstocks and products that replace current fossil-based materials to close the loop in creating viable pathways for a renewable economy. Biocatalytic membranes that combine high reaction rates and enzyme selectivity with modularity, scalability, and membrane compactness show promise for both CO₂ capture and utilization. This review presents a systematic examination of technologies under development for CO₂ capture and utilization that employ both enzymes and membranes. CO₂ capture membranes are categorized by their mode of action as CO₂ separation membranes, including mixed matrix membranes (MMM) and liquid membranes (LM), or as CO₂ gas-liquid membrane contactors (GLMC). Because they selectively catalyze molecular reactions involving CO₂, the two main classes of enzymes used for enhancing membrane function are carbonic anhydrase (CA) and formate dehydrogenase (FDH). Small organic molecules designed to mimic CA enzyme active sites are also being developed. CO₂ conversion membranes are described according to membrane functionality, the location of enzymes relative to the membrane, which includes different immobilization strategies, and regeneration methods for cofactors. Parameters crucial for the performance of these hybrid systems are discussed with tabulated examples. Progress and challenges are discussed, and perspectives on future research directions are provided.

Study of Membrane-Immobilized Oxidoreductases in Wastewater Treatment for Micropollutants Removal

The development of efficient strategies for wastewater treatment to remove micropollutants is of the highest importance. Hence, in this study, we presented a rapid approach to the production of biocatalytic membranes based on commercially available cellulose membrane and oxidoreductase enzymes including laccase, tyrosinase, and horseradish peroxidase. Effective enzyme deposition was confirmed based on Fourier transform infrared spectra, whereas results of spectrophotometric measurements showed that immobilization yield for all proposed systems exceeded 80% followed by over 80% activity recovery, with the highest values (over 90%) noticed for the membrane-laccase system. Further, storage stability and reusability of the immobilized enzyme were improved, reaching over 75% after, respectively, 20 days of storage, and 10 repeated biocatalytic cycles. The key stage of the study concerned the use of produced membranes for the removal of hematoporphyrin, (2,4-dichlorophenoxy)acetic acid (2,4-D), 17α-ethynylestradiol, tetracycline, tert-amyl alcohol (anesthetic drug), and ketoprofen methyl ester from real wastewater sampling at various places in the wastewater treatment plant. Although produced membranes showed mixed removal rates, all of the analyzed compounds were at least partially removed from the wastewater. Obtained data clearly showed, however, that composition of the wastewater matrix, type of pollutants as well as type of enzyme strongly affect the efficiency of enzymatic treatment of wastewater.

Laccase immobilization in polyelectrolyte multilayer membranes for 17α-ethynylestradiol removal: Biocatalytic approach for pharmaceuticals degradation

Enzymatic membrane reactors equipped with multifunctional biocatalytic membranes are promising and sustainable alternatives for removal of micropollutants, including steroid estrogens, under mild conditions. Thus, in this study an effort was made to produce novel multifunctional biocatalytic polyelectrolyte multilayer membranes via polyelectrolyte layer-by-layer assembly with laccase enzyme immobilized between or into polyelectrolyte layers. In this study, multifunctional biocatalytic membranes are considered as systems composed of commercially available filtration membrane modified by polyelectrolytes and immobilized enzymes, which are produced for complex treatment of water pollutants. The multifunctionality of the proposed systems is related to the fact that these membranes are capable of micropollutants removal via simultaneous catalytic conversion, membrane adsorption and membrane rejection making remediation process more complex, however, also more efficient. Briefly, cationic poly-l-lysine and polyethylenimine as well as anionic poly(sodium 4-styrenesulfonate) polyelectrolytes were deposited onto NP010 nanofiltration and UFX5 ultrafiltration membranes to produce systems for removal of 17α-ethynylestradiol. Images from scanning electron microscopy confirm effective enzyme deposition, whereas results of zeta potential measurements indicate introduction of positive charge onto the membranes. Based on preliminary results, four membranes with over 70%, activity retention produced using polyethylenimine in internal and entrapped mode, were selected for degradation tests. Systems based on UFX5 membrane allowed over 60% 17α-ethynylestradiol removal within 100 min, whereas NP010-based systems removed over 75% of estrogen within 150 min. Further, around 80% removal of 17α-ethynylestradiol was possible from the solutions at concentration up to 0.1 mg/L at pH ranging from 4 to 6 and at the pressure up to 3 bar, indicating high activity of the immobilized laccase over wide range of process conditions. Produced systems exhibited also great long-term stability followed by limited enzyme elution from the membrane. Finally, removal of over 70% and 60% of 17α-ethynylestradiol, respectively by NP010 and UFX5 systems after 8 cycles of repeated use indicate high reusability potential of the systems and suggest their practical application in removal of micropollutants, including estrogens.

Bioinspired Lipase Immobilized Membrane for Improving Hesperidin Lipophilization

Lipophilization is a promising way to improve the bioavailability of flavonoids. However, the traditional enzymatic esterification methods are time-consuming, and present low yields and purity. Herein, a novel membrane-based lipophilization technology-bioinspired lipase immobilized membranes (BLIMs), including CAL-B@PES, CAL-B@PDA/PES and GA/CAL-B@PDA/PES- were fabricated to improve the antioxidant flavanone glycoside hesperidin lipophilization. Via reverse filtration, PDA coating and GA crosslinking, Candida antarctica lipase B (CAL-B) was stably immobilized on membrane to fabricate BLIMs. Among the three BLIMs, GA/CAL-B@PDA/PES had the greatest enzyme activity and enzyme loading, the strongest tolerance of changes in external environmental conditions (temperatures, pH, heating time, storage time and numbers of cycles) and the highest hesperidin esterification efficiency. Moreover, the optimal operating condition for GA/CAL-B@PDA/PES fabrication was the CAL-B concentration of 0.36 mg/mL, operation pressure of 2 bar, GA concentration of 5% and crosslinking time of 1 h. Afterwards, the hesperidin esterification process did not affect the micromorphology of BLIM, but clearly improved the BLIM permeability and esterified product efficiency. The present study reveals the fabrication mechanism of BLIMs and offers insights into the optimizing strategy that governs the membrane-based lipophilization technology process.

Synergistic action of laccase treatment and membrane filtration during removal of azo dyes in an enzymatic membrane reactor upgraded with electrospun fibers

Nowadays, the increasing amounts of dyes present in wastewaters and even water bodies is an emerging global problem. In this work we decided to fabricate new biosystems made of nanofiltration or ultrafiltration membranes combined with laccase entrapped between polystyrene electrospun fibers and apply them for decolorization of aqueous solutions of three azo dyes, C.I. Acid Yellow 23 (AY23), C.I. Direct Blue 71 (DB71) and C.I. Reactive Black 5 (RB5). Besides effective decolorization of the permeate stream, the biosystems also allowed removal of dyes from the retentate stream as a result of enzymatic action. The effect of pH and applied pressure on decolorization efficiencies was investigated, and pH 5 and pressure of 2 bar gave the highest removal efficiencies of 97% for AY23 and 100% for both DB71 and RB5 from permeate solutions while decolorization of retentate for RB5 reached 65% under these conditions. Almost 100% decolorization of all dyes was achieved after three consecutive enzyme membrane cycles. Decolorization was shown to be due to the synergistic action of membrane separation and bioconversion. The biocatalytic action also enabled significant reduction of permeate and retentate toxicity, which is one of the biggest environmental health issues for these types of streams.

Biomolecule-Enabled Liquid Separation Membranes: Potential and Recent Progress

The implementation of membrane surface modification to enhance the performance of membrane-based separation has become a favored strategy due to its promise to address the trade-off between water permeability and salt rejection as well as to improve the durability of the membranes. Tremendous work has been committed to modifying polymeric membranes through physical approaches such as surface coating and ontology doping, as well as chemical approaches such as surface grafting to introduce various functional groups to the membrane. In the context of liquid separation membranes applied for desalination and water and wastewater treatment, biomolecules have gained increasing attention as membrane-modifying agents due to their intriguing structural properties and chemical functionalities. Biomolecules, especially carbohydrates and proteins, exhibit attractive features, including high surface hydrophilicity and zwitterionic and antimicrobial properties that are desired for liquid separation membranes. In this review, we provide an overview of the recent developments in biomolecule-enabled liquid separation membranes. The roles and potentials of some commonly explored biomolecules in heightening the performance of polymeric membranes are discussed. With the advancements in material synthesis and the need to answer the call for more sustainable materials, biomolecules could serve as attractive alternatives for the development of high-performance composite membranes.

Regenerable temperature-responsive biocatalytic nanofiltration membrane for organic micropollutants removal

Biocatalytic nanofiltration membranes (BNMs) exhibit great potentials in organic micropollutants removal attributed to its synergistic effect between enzyme catalysis and membrane separation. However, the difficulties in regeneration of the BNMs halted their economic practicality. Inspired by cell membranes with stimuli-responsive channels, we have developed the temperature-responsive BNMs with nanogating function by poly(N-isopropyl acrylamide) (PNIPAM) modification. PNIPAM modification increases the geometric confinement of the support layer to enzymes, thus improving enzyme loading, inhibiting enzyme leakage, and preventing membrane permeability decline caused by enzyme excess migration and aggregation. By optimizing the concentration of reaction monomers, modification time, and strategies, the PNIPAM-based BNMs show high bisphenol A (BPA) removal efficiency and long-term stability. Furthermore, the PNIPAM-polyethyleneimine-based BNMs can be easily regenerated at 38°C, and the laccase activity and BPA removal efficiency are fully recovered. This work would promote the real application of BNMs in bioconversion, drug delivery, and biosensors.

Biocatalytic membranes for combating the challenges of membrane fouling and micropollutants in water purification: A review

Over the last few years, the list of water contaminants has grown tremendously due to many anthropogenic activities. Various conventional technologies are available for water and wastewater treatment. However, micropollutants of emerging concern (MEC) are posing a great threat due to their activity at trace concentration and poor removal efficiency by the conventional treatment processes. Advanced technology like membrane technology can remove MEC to some extent. However, issues like the different chemical properties of MEC, selectivity, and fouling of membranes can affect the removal efficiency. Moreover, the concentrate from the membrane filtration may need further treatment. Enzymatic degradation of pollutants and foulants is one of the green approaches for removing various contaminants from the water as well as mitigating membrane fouling. Biocatalytic membranes (BCMs), in which enzymes are immobilized on membranes, combines the advantages of membrane separation and enzymatic degradation. This review article discussed various commonly used enzymes in BCMs for removing MEC and fouling. The majorly used enzymes were oxidoreductases and hydrolases for removing MEC, antifouling, and self-cleaning ability. The various BCM synthesis processes based on entrapment, crosslinking, and binding have been summarized, along with the effects of the addition of the nanoparticles on the performances of the BCMs. The scale-up, commercial viability, challenges, and future direction for improving BCMs have been discussed and shown bright possibilities for these new generation membranes.

β-Galactosidase from Kluyveromyces lactis: Characterization, production, immobilization and applications - A review

A review on the enzyme β-galactosidase from Kluyveromyces lactis is presented, from the perspective of its structure and mechanisms of action, the main catalyzed reactions, the key factors influencing its activity, and selectivity, as well as the main techniques used for improving the biocatalyst functionality. Particular attention was given to the discussion of hydrolysis, transglycosylation, and galactosylation reactions, which are commonly mediated by this enzyme. In addition, the products generated from these processes were highlighted. Finally, biocatalyst improvement techniques are also discussed, such as enzyme immobilization and protein engineering. On these topics, the most recent immobilization strategies are presented, emphasizing processes that not only allow the recovery of the biocatalyst but also deliver enzymes that show better resistance to high temperatures, chemicals, and inhibitors. In addition, genetic engineering techniques to improve the catalytic properties of the β-galactosidases were reported. This review gathers information to allow the development of biocatalysts based on the β-galactosidase enzyme from K. lactis, aiming to improve existing bioprocesses or develop new ones.

An enzymatic membrane reactor for oligodextran production: Effects of enzyme immobilization strategies on dextranase activity

An enzymatic membrane reactor (EMR) with immobilized dextranase provides an excellent opportunity for tailoring the molecular weight (Mw) of oligodextran to significantly improve product quality. However, a highly efficient EMR for oligodextran production is still lacking and the effect of enzyme immobilization strategy on dextranase hydrolysis behavior has not been studied yet. In this work, a functional layer of polydopamine (PDA) or nanoparticles made of tannic acid (TA) and hydrolysable 3-amino-propyltriethoxysilane (APTES) was first coated on commercial membranes. Then cross-linked dextranase or non-cross-linked dextranase was loaded onto the modified membranes using incubation mode or fouling-induced mode. The fouling-induced mode was a promising enzyme immobilization strategy on the membrane surface due to its higher enzyme loading and activity. Moreover, unlike the non-cross-linked dextranase that exhibited a normal endo-hydrolysis pattern, we surprisingly found that the cross-linked dextranase loaded on the PDA modified surface exerted an exo-hydrolysis pattern, possibly due to mass transfer limitations. Such alteration of hydrolysis pattern has rarely been reported before. Based on the hydrolysis behavior of the immobilized dextranase in different EMRs, we propose potential applications for the oligodextran products. This study presents a unique perspective on the relation between the enzyme immobilization process and the immobilized enzyme hydrolysis behavior, and thus opens up a variety of possibilities for the design of a high-performance EMR.

A versatile ceramic capillary membrane reactor system for continuous enzyme-catalyzed hydrolysis

As an alternative to classical batch processes, enzyme-catalyzed hydrolysis can also be carried out continuously. To facilitate this, a continuous ceramic capillary membrane reactor system (CCCMRS) was developed which can be operated with various proteolytic enzymes immobilized on the porous ceramic capillary membranes. This system has several advantages over common batch processes regarding stability, reproducibility and controllability and can easily be adapted to optimal reaction conditions and individual preferences. Two exemplary applications utilizing the CCCMRS were carried out and investigated in long-term stability studies. In the first application the continuous enzymatic cleavage of human IgG into the antibody fragments Fab and Fc by immobilized papain was performed. A total volume of 22 mL of 1 mg mL-1 IgG-solution was enzymatically cleaved over a period of 33.3 h. The antibody cleavage products could be detected in an SEC-HPLC over the whole process time thus indicating long-term stability of the continuous hydrolysis process. The second application investigated the continuous digestion of pea and almond protein isolates by immobilized Alcalase resulting in the generation of a large variety of different peptides. This peptide fingerprint remains constant over a long period of time enabling fractionation and thus making the peptides accessible for further bioactivity studies in sufficient quantities. The constant peptide fingerprint could be shown in the RP-HPLC analysis for all 30 samples with a total volume of 29.7 mL collected over a period of 45 h.