Bio-based degradation of emerging endocrine-disrupting and dye-based pollutants using cross-linked enzyme aggregates

The effect of low-temperature straw-degrading microbes on winter wheat growth and soil improvement under straw return

The application of straw-degrading microbes (SDMs) with straw returned to the field is an effective measure to improve soil quality, increase yield, and maintain soil microorganisms. However, the utilization of SDMs in winter in north China is limited by the poor effects at low temperatures. This study investigated the effects of a new compound SDM, including a novel low-temperature fungus Pseudogymnoascus sp. SDF-LT, on winter wheat yield, soil improvement, and soil microbial diversity. A 2-year field experiment was conducted in two different soil textures of wheat-maize rotation fields with full corn straw return and application of SDMs at an amount of 67.5 kg hm-2. After 2 years of continuous application of SDMs, the winter wheat yield increased significantly, reaching 9419.40 kg hm-2 in Ningjin (NJSDM) and 9107.25 kg hm-2 in Mancheng (MCSDM). The soil properties have been significantly improved compared with the single straw return group, especially the sandy loam soil, whose quality is relatively low. The analysis of soil microbial diversity showed that SDMs significantly reduced the Chao1, Shannon, Simpson, and observed species of the sandy loam soil in the MCSDM group. The Simpson and Shannon indexes of fungi diversity in the two experimental sites were significantly increased by SDMs. The negative correlation of fungi increased from 47.1 to 48.85% in the SDM groups. The soil-dominant microbes changed in the SDM groups, in which the interactions between microbes were enhanced. These results suggested that the SDMs changed the the soil microbial community structure and its diversity and complexity, which is beneficial for crop growth. Our study provided sufficient evidence for the utilization of low-temperature SDMs with straw return in cold winter, which plays a role in soil improvement, especially for low-quality soils, to increase crop yield.

Combining computational tools and experimental studies towards endocrine disruptors mitigation: A review of biocatalytic and adsorptive processes

The endocrine disruptors (EDCs) are an important group of emerging contaminants, and their mitigation has been a huge challenge due to their chemistry complexity and variety of these compounds. The traditional treatments are inefficient to completely remove EDCs, and adsorptive processes are the major alternative investigated on their removal. Also, the use of EDCs degrading enzymes has been encouraged due to ecofriendly approach of biocatalytic processes. This paper highlights the occurrence, classification, and toxicity of EDCs with special focus in the use of enzyme-based and adsorptive technologies in the elimination of EDCs from ambiental matrices. Numerous prior reviews have focused on the discussions toward these technologies. However, the literature lacks theoretical discussions about important aspects of these methods such as the mechanisms of EDCs adsorption on the adsorbent surface or the interactions between degrading enzymes - EDCs. In this sense, theoretical calculations combined to experimental studies may help in the development of more efficient technologies to EDCs mitigation. In this review, we point out how computational tools such as molecular docking and molecular dynamics have to contribute to the design of new adsorbents and efficient catalytic processes towards endocrine disruptors mitigation.

Heterogeneous biocatalytic system for effective decolorization of textile dye effluent

The current physicochemical methods for decolorizing toxic synthetic dyes are not sustainable to halt the environmental damage as they are expensive and often produce concentrated sludge, which may lead to secondary disposal problems. Biocatalysis (microbes and/or their enzymes) is a cost-effective, versatile, energy-saving and clean alternative. The most common enzymes involved in dye degradation are laccases, azoreductases and peroxidases. Toxic dyes could be converted into less harmful byproducts through the combined action of many enzymes or the utilization of whole cells. The action of whole cells to treat dye effluents is either by biosorption or degradation (aerobic or anaerobic). Using immobilized cells or enzymes will offer advantages such as superior stability, persistence against harsh environmental conditions, reusability and longer half-lives. This review envisages the recent strategies of immobilization and bioreactor considerations with the immobilized system as the effective treatment of textile dye effluents. Packed bed reactors are the most popular heterogeneous biocatalytic reactors for dye decolorization due to their efficiency and cost-effectiveness.

Tyrosinase Immobilization Strategies for the Development of Electrochemical Biosensors-A Review

The development of enzyme biosensors has successfully overcome various challenges such as enzyme instability, loss of enzyme activity or long response time. In the electroanalytical field, tyrosinase is used to develop biosensors that exploit its ability to catalyze the oxidation of numerous types of phenolic compounds with antioxidant and neurotransmitter roles. This review critically examines the main tyrosinase immobilization techniques for the development of sensitive electrochemical biosensors. Immobilization strategies are mainly classified according to the degree of reversibility/irreversibility of enzyme binding to the support material. Each tyrosinase immobilization method has advantages and limitations, and its selection depends mainly on the type of support electrode, electrode-modifying nanomaterials, cross-linking agent or surfactants used. Tyrosinase immobilization by cross-linking is characterized by very frequent use with outstanding performance of the developed biosensors. Additionally, research in recent years has focused on new immobilization strategies involving cross-linking, such as cross-linked enzyme aggregates (CLEAs) and magnetic cross-linked enzyme aggregates (mCLEAs). Therefore, it can be considered that cross-linking immobilization is the most feasible and economical approach, also providing the possibility of selecting the reagents used and the order of the immobilization steps, which favor the enhancement of biosensor performance characteristics.

Screening and isolation of cold-adapted cellulose degrading bacterium: A candidate for straw degradation and De novo genome sequencing analysis

Degradation of crop straw in natural environment has been a bottleneck. There has been a recent increase in the exploration of cold-adapted microorganisms as they can solve the problem of corn straw degradation under low temperatures and offer new alternatives for the sustainable development of agriculture. The study was conducted in low-temperature (10°C) and high-efficiency cellulose-degrading bacteria were screened using carboxymethyl cellulose (CMC) selection medium and subjected to genome sequencing by the third-generation Pacbio Sequl and the second-generation Illumina Novaseq platform, and their cellulase activity was detected by 3,5-dinitrosalicylic acid (DNS) method. The results showed that the low-temperature (10°C) and high-efficiency cellulose-degrading bacterium Bacillus subtilis K1 was 4,060,823 bp in genome size, containing 4,213 genes, with 3,665, 3,656, 2,755, 3,240, 1,261, 3,336 and 4,003 genes annotated in the non-redundant protein sequence database (NR), Pfam, clusters of orthologous groups of proteins (COGs), Genome Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Annotation databases, respectively. In addition, a large number of lignocellulose degradation-related genes were annotated in the genome. The cellulose activity of B. subtilis K1 was higher, exhibiting the highest activity of endo-β-glucanase (24.69 U/ml), exo-β-glucanase (1.72 U/ml) and β-glucosaccharase (1.14 U/ml). It was found that through adding cold-adapted cellulose-degrading bacteriaK1 in the corn straw composting under 6°C (ambient temperature), the average temperature of straw composting was 58.7°C, and higher 86.7% as compared to control. The HA/FA was higher 94.02% than the control and the lignocellulose degradation rate was lower 18.01-41.39% than the control. The results provide a theoretical basis for clarifying the degradation potential of cold-adapted cellulose-degrading bacteria and improving the cellulose degradation efficiency.

Endocrine disrupting chemicals (EDCs) in environmental matrices: Occurrence, fate, health impact, physio-chemical and bioremediation technology

Endocrine disrupting chemicals (EDCs) are an emerging category of toxicity that adversely impacts humans and the environment's well-being. Diseases like cancer, cardiovascular risk, behavioral disorders, autoimmune defects, and reproductive diseases are related to these endocrine disruptors. Because these chemicals exist in known sources such as pharmaceuticals and plasticizers, as well as non-point sources such as agricultural runoff and storm water infiltration, the interactive effects of EDCs are gaining attention. However, the efficiency of conventional treatment methods is not sufficient to fully remediate EDCs from aqueous environments as the occurrence of EDC bioremediation and biodegradation is detected in remediated drinking water. Incorporating modification into current remediation techniques has to overcome challenges such as high energy consumption and health risks resulting from conventional treatment. Hence, the use of advanced psychochemical and biological treatments such as carbon-based adsorption, membrane technology, nanostructured photocatalysts, microbial and enzyme technologies is crucial. Intensifying environmental and health concerns about these mixed contaminants are primarily due to the lack of laws about acute concentration limits of these EDCs in municipal wastewater, groundwater, surface water, and drinking water. This review article offers evidence of fragmentary available data for the source, fate, toxicity, ecological and human health impact, remediation techniques, and mechanisms during EDC removal, and supports the need for further data to address the risks associated with the presence of EDCs in the environment. The reviews also provide comprehensive data for biodegradation of EDCs by using microbes such as fungi, bacteria, yeast, filamentous fungi, and their extracellular enzymes.

Emerging contaminants of high concern for the environment: Current trends and future research

Wastewater is contaminated water that must be treated before it may be transferred into other rivers and lakes in order to prevent further groundwater pollution. Over the last decade, research has been conducted on a wide variety of contaminants, but the emerging contaminants are those caused primarily by micropollutants, endocrine disruptors (EDs), pesticides, pharmaceuticals, hormones, and toxins, as well as industrially-related synthetic dyes and dye-containing hazardous pollutants. Most emerging pollutants did not have established guidelines, but even at low concentrations they could have harmful effects on humans and aquatic organisms. In order to combat the above ecological threats, huge efforts have been done with a view to boosting the effectiveness of remediation procedures or developing new techniques for the detection, quantification and efficiency of the samples. The increase of interest in biotechnology and environmental engineering gives an opportunity for the development of more innovative ways to water treatment remediation. The purpose of this article is to provide an overview of emerging sources of contaminants, detection technologies, and treatment strategies. The goal of this review is to evaluate adsorption as a method for treating emerging pollutants, as well as sophisticated and cost-effective approaches for treating emerging contaminants.

Carrier-Free Cross-linked Laccase Crystals for Biocatalytic Degradation of Textile Industrial Effluents

Herein, laccase from Trametes versicolor was used to fabricate carrier-free cross-linked laccase crystals (CLLCs) and deployed as a robust catalyst for waste effluent treatment. The surface morphology and involvement of functional group attributes of CLLCs were scrutinized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). As fabricated CLLCs were subjected to kinetic characterization by assessing the effects of pH environment, thermal profile, and substrate (determination of K_m and V_max) on the activity. A fully characterized CLLCs fraction was used to treat synthetic dyes containing waste effluents taken from various industries, i.e., Chenab Textile Industry, M-tax, Sitara, and National Silk & Rayon Mills. Degradation profile revealed 36.8%, 27.6%, 39.9%, and 26.4% degradation of Chenab Textile Industry, M-tax, Sitara, and National Silk & Rayon Mills, respectively, by the free form of laccase, whereas the biocatalytic activity of CCLCs led to 78.6%, 75.6%, 85.5%, and 63.3% degradation of those effluents. The decrease in peak and mass region alongside the presence of new peaks in GC-MS affirms the effective decolorization of contaminated waste effluents. CLLCs retained over 70% and 50% of their degradation activity after 3 and 5 cycles, respectively. In conclusion, CLLCs might represent a robust bioprocess to improve the usability of laccase for various synthetic dyes containing waste effluents to diminish environmental pollution from the dye-based industries.

Nanohybrids-assisted photocatalytic removal of pharmaceutical pollutants to abate their toxicological effects - A review

Advancement in medication by health care sector has undoubtedly improved our life but at the same time increased the chemical burden on our natural ecosystem. The residuals of pharmaceutical products become part of wastewater streams by different sources such as excretion after their usage, inappropriate way of their disposal during production etc. Hence, they are serious health hazards for human, animal, and aquatic lives. Due to rapid urbanization, the increased demand for clean drinking water is a burning global issue. In this regard it is need of the present era to explore efficient materials which could act as photocatalyst for mitigation of pharmaceuticals in wastewater. Nanohybrid as photocatalyst is one of the widely explored class of materials in photocatalytic degradation of such harmful pollutants. Among these nanohybrids; metal based nanohybrids (metals/metal oxides) and carbon based nanohybrids (carbon nanotubes, graphene, fullerenes etc.) have been explored to remove pharmaceutical drugs. Keeping in view the increasing harmful impacts of pharmaceuticals; the sources of pharmaceuticals in wastewater, their health risk factors and their mitigation using efficient nanohybrids as photocatalysts have been discussed in this review.

Ligninolytic enzymes in Basidiomycetes and their application in xenobiotics degradation

Variety of microorganisms have already proven their capabilities for degradation of wide range of wastes with anthropogenic nature. These pollutants, both liquid and solids, also include so called xenobiotics like phenol and its derivatives, PAHs, dyes, pesticides, pharmaceuticals, etc. Xenobiotics as bisphenol A (BPA), chlorhexidine (CHX), octenidine (OCT), other disinfectants and antiseptics have high ecotoxicological impact. Moreover, they can also impair our quality of life and our health interfering different metabolic and hormone receptors pathways in human body. Chemical treatment of such wastes is not a viable option because of its poor socio-economics and environmental merits. Therefore, applying effective, ecofriendly and cheap treatment methods is of great importance. Basidiomycetes are extensively investigated for their abilities to degrade numerous pollutants and xenobiotics. Through their extracellular ligninolytic enzymes they are capable of reducing or completely removing wide range of hazardous compounds. These enzymes can be categorized in two groups: oxidases (laccase) and peroxidases (manganese peroxidase, lignin peroxidase, versatile peroxidase). Due to the broad substrate specificity of the secreted enzymes Basidiomycetes can be applied as a powerful tool for bioremediation of diverse xenobiotics and recalcitrant compounds.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Textile Dye Biodecolorization by Manganese Peroxidase: A Review

Wastewater emissions from textile factories cause serious environmental problems. Manganese peroxidase (MnP) is an oxidoreductase with ligninolytic activity and is a promising biocatalyst for the biodegradation of hazardous environmental contaminants, and especially for dye wastewater decolorization. This article first summarizes the origin, crystal structure, and catalytic cycle of MnP, and then reviews the recent literature on its application to dye wastewater decolorization. In addition, the application of new technologies such as enzyme immobilization and genetic engineering that could improve the stability, durability, adaptability, and operating costs of the enzyme are highlighted. Finally, we discuss and propose future strategies to improve the performance of MnP-assisted dye decolorization in industrial applications.

Biocatalytic remediation of industrial pollutants for environmental sustainability: Research needs and opportunities

An increasing quantum of pollutants from various industrial sector activities represents a severe menace to environmental & ecological balance. Bioremediation is gaining flow globally due to its cost-effective and environment-friendly nature. Understanding biodegradation mechanisms is of high ecological significance. Application of microbial enzymes has been reported as sustainable approach to mitigate the pollution. Immobilized enzyme catalyzed transformations are getting accelerated attention as potential alternatives to physical and chemical methods. The attention is now also focused on developing novel protein engineering strategies and bioreactor design systems to ameliorate overall biocatalysis and waste treatment further. This paper presents and discusses the most advanced and state of the art scientific & technical developments about biocatalytic remediation of industrial pollutants. It also covers various biocatalysts and the associated sustainable technologies to remediate various pollutants from waste streams. Enzyme production and immobilization in bioreactors have also been discussed. This paper also covers challenges and future research directions in this field.

Enzyme-Loaded Flower-Shaped Nanomaterials: A Versatile Platform with Biosensing, Biocatalytic, and Environmental Promise

As a result of their unique structural and multifunctional characteristics, organic-inorganic hybrid nanoflowers (hNFs), a newly developed class of flower-like, well-structured and well-oriented materials has gained significant attention. The structural attributes along with the surface-engineered functional entities of hNFs, e.g., their size, shape, surface orientation, structural integrity, stability under reactive environments, enzyme stabilizing capability, and organic-inorganic ratio, all significantly contribute to and determine their applications. Although hNFs are still in their infancy and in the early stage of robust development, the recent hike in biotechnology at large and nanotechnology in particular is making hNFs a versatile platform for constructing enzyme-loaded/immobilized structures for different applications. For instance, detection- and sensing-based applications, environmental- and sustainability-based applications, and biocatalytic and biotransformation applications are of supreme interest. Considering the above points, herein we reviewed current advances in multifunctional hNFs, with particular emphasis on (1) critical factors, (2) different metal/non-metal-based synthesizing processes (i.e., (i) copper-based hNFs, (ii) calcium-based hNFs, (iii) manganese-based hNFs, (iv) zinc-based hNFs, (v) cobalt-based hNFs, (vi) iron-based hNFs, (vii) multi-metal-based hNFs, and (viii) non-metal-based hNFs), and (3) their applications. Moreover, the interfacial mechanism involved in hNF development is also discussed considering the following three critical points: (1) the combination of metal ions and organic matter, (2) petal formation, and (3) the generation of hNFs. In summary, the literature given herein could be used to engineer hNFs for multipurpose applications in the biosensing, biocatalysis, and other environmental sectors.

Application of immobilized mycelium-based pellets for the removal of organochlorine compounds: a review

Organochlorines have diverse structures and applications and are included in the list of persistent organic pollutants (POPs) due to their toxicity and environmental persistence. The reduced capacity of conventional wastewater treatment plants to remove these compounds encourages the development of cost-effective and efficient remediation approaches. Fungal biotechnology can contribute to the development of these technologies through their enzymatic machinery but faces several drawbacks related to the use of dispersed mycelium. In this sense, investigations concerning the degradation of organochlorines using immobilized fungi demonstrated an increase in contaminant removal efficiency compared with degradation by free cells. Despite this interest, the mechanisms of immobilized fungi have not been comprehensively reviewed. In this paper, recent advances of laboratory and field studies in organochlorine compounds removal by fungi are reviewed, focusing on the role of immobilization techniques. Firstly, the mechanisms of organochlorines bioconversion by fungi and the factors affecting enzyme activity are elucidated and discussed in detail. Then, the main targeted compounds, fungi, technics, and materials used for immobilization are discussed, as well as their advantages and limitations. Furthermore, critical points for future studies of fungi immobilization for organochlorine removal are proposed.

Bio-based and cost effective method for phenolic compounds removal using cross-linked enzyme aggregates

This work aimed at presenting a green method using a new source of peroxidase isolated from Raphanus sativus var. niger (RSVNP) in immobilized form, for the treatment of wastewater. To ensure stability and enzymatic activity in the biodegradation process, RSVNP was immobilized as a cross-linked enzyme aggregate (CLEAs). With more than 29% of recovered activity and 85% aggregation yield, acetone was selected as the best precipitating agent. The formed protein aggregates required 2% (v/v) of glutaraldehyde (GA) concentration and a ratio of 9:1 (v/v) enzyme (E) amount to cross-linker (E/GA). Compared to the free enzyme, RSVNP-CLEAs were found more chemically and thermally stable and exhibited good storage stability for more than 8 weeks. In addition, RSVNP-CLEAs were evaluated for their ability to remove phenol and p-cresol from aqueous solution by varying several operating conditions. A maximal yield (98%) of p-cresol conversion was recorded after 40 min; while 92% of phenol was degraded after 1 h duration time. The reusability of RSVNP-CLEAs was tested, displaying 71% degradation of phenol in the third batch carried out and more than 54% was achieved for p-cresol after four successive reuses in the presence of hydrogen peroxide at 2 mM concentration.

White rot fungi can be a promising tool for removal of bisphenol A, bisphenol S, and nonylphenol from wastewater

Endocrine-disrupting chemicals (EDC) are a wide group of chemicals that interfere with the endocrine system. Their similarity to natural steroid hormones makes them able to attach to hormone receptors, thereby causing unfavorable health effects. Among EDC, bisphenol A (BPA), bisphenol S (BPS), and nonylphenol (NP) seem to be particularly harmful. As the industry is experiencing rapid expansion, BPA, BPS, and NP are being produced in growing amounts, generating considerable environmental pollution. White rot fungi (WRF) are an economical, ecologically friendly, and socially acceptable way to remove EDC contamination from ecosystems. WRF secrete extracellular ligninolytic enzymes such as laccase, manganese peroxidase, lignin peroxidase, and versatile peroxidase, involved in lignin deterioration. Owing to the broad substrate specificity of these enzymes, they are able to remove numerous xenobiotics, including EDC. Therefore, WRF seem to be a promising tool in the abovementioned EDC elimination during wastewater treatment processes. Here, we review WRF application for this EDC removal from wastewater and indicate several strengths and limitations of such methods.

Persistence, ecological risks, and oxidoreductases-assisted biocatalytic removal of triclosan from the aquatic environment

Triclosan (TCS) has been immensely employed in health care products and consumer items, as an active agent with fungicidal and bactericidal potentialities, such as soaps, sanitizers, tubes of toothpaste, deodorants, skin creams, and so on for over last five decades. The ultimate excretory route of TCS ends in our water matrices, thus has been frequently detected with ecological and human-health related matters and hazards. Bioactive residues of TCS reach into the key atmosphere compartment through numerous routes, such as (1) scarce or ineffective elimination or degradation throughout the treatment practices, (2) abandoned landfill leachates, (3) leakage from the discarded TCS-containing materials, and so on. Such persistence and occurrence of TCS or its degraded but bioactive residues have growing attentions. Its complete removal and/or effective prevention are still challenging tasks for safeguarding the environment. Owing to the highly effective catalytic and stability potential, enzyme-based bio-degradation approaches are considered an evocative substitute for TCS mitigation from environmental matrices. As compared to enzymes in their pristine form, immobilized enzymes, with unique catalytic, stability, selectivity, and reusability profile, are of supreme and strategic interest in environmental biotechnology. Herein, an effort has been made to signify the novel bio-catalytic and bio-degradation potentialities of various oxidoreductases, including laccases, and peroxidases including soybean peroxidase, versatile manganese peroxidase, and horseradish peroxidase with suitable examples. Following a brief introduction, the focus is given to the presence of TCS in the key atmosphere compartments. Potential sources, acquaintance, and hazardous influence of TCS are also discussed with recent and relevant examples. The second half shows the TCS removal/degradation potentialities of soluble enzyme-based catalytic systems and immobilized-enzyme-based catalytic systems. Finally, the concluding remarks, along with possible future directions are given in this significant research arena.

From Laboratory Tests to the Ecoremedial System: The Importance of Microorganisms in the Recovery of PPCPs-Disturbed Ecosystems

The presence of a wide variety of emerging pollutants in natural water resources is an important global water quality challenge. Pharmaceuticals and personal care products (PPCPs) are known as emerging contaminants, widely used by modern society. This objective ensures availability and sustainable management of water and sanitation for all, according to the 2030 Agenda. Wastewater treatment plants (WWTP) do not always mitigate the presence of these emerging contaminants in effluents discharged into the environment, although the removal efficiency of WWTP varies based on the techniques used. This main subject is framed within a broader environmental paradigm, such as the transition to a circular economy. The research and innovation within the WWTP will play a key role in improving the water resource management and its surrounding industrial and natural ecosystems. Even though bioremediation is a green technology, its integration into the bio-economy strategy, which improves the quality of the environment, is surprisingly rare if we compare to other corrective techniques (physical and chemical). This work carries out a bibliographic review, since the beginning of the 21st century, on the biological remediation of some PPCPs, focusing on organisms (or their by-products) used at the scale of laboratory or scale-up. PPCPs have been selected on the basics of their occurrence in water resources. The data reveal that, despite the advantages that are associated with bioremediation, it is not the first option in the case of the recovery of systems contaminated with PPCPs. The results also show that fungi and bacteria are the most frequently studied microorganisms, with the latter being more easily implanted in complex biotechnological systems (78% of bacterial manuscripts vs. 40% fungi). A total of 52 works has been published while using microalgae and only in 7% of them, these organisms were used on a large scale. Special emphasis is made on the advantages that are provided by biotechnological systems in series, as well as on the need for eco-toxicological control that is associated with any process of recovery of contaminated systems.

Overview of Recent Advances in Immobilisation Techniques for Phenol Oxidases in Solution

Over the past two decades, phenol oxidases, particularly laccases and tyrosinases, have been extensively used for the removal of numerous pollutants in wastewaters due to their broad substrate specificity and their ability to use readily accessible molecular oxygen as the essential cofactor. As for other enzymes, immobilisation of laccases and tyrosinases has been shown to improve the performance and efficiency of the biocatalysts in solution. Several reviews have addressed the enzyme immobilisation techniques and the application of phenol oxidases to decontaminate wastewaters. This paper offers an overview of the recent publications, mainly from 2012 onwards, on the various immobilisation techniques applied to laccases and tyrosinases to induce and/or increase the performance of the biocatalysts. In this paper, the emphasis is on the efficiencies achieved, in terms of structural modifications, stability and resistance to extreme conditions (pH, temperature, inhibitors, etc.), reactivity, reusability, and broad substrate specificity, particularly for application in bioremediation processes. The advantages and disadvantages of several enzyme immobilisation techniques are also discussed. The relevance and effectiveness of the immobilisation techniques with respect to wastewater decontamination are critically assessed. A perspective on the future directions for large-scale application of the phenol oxidases in immobilised forms is provided.

Laccases and peroxidases: The smart, greener and futuristic biocatalytic tools to mitigate recalcitrant emerging pollutants

Various organic pollutants so-called emerging pollutants (EPs), including active residues from pharmaceuticals, pesticides, surfactants, hormones, and personal care products, are increasingly being detected in numerous environmental matrices including water. The persistence of these EPs can cause adverse ecological and human health effects even at very small concentrations in the range of micrograms per liter or lower, hence called micropollutants (MPs). The existence of EPs/MPs tends to be challenging to mitigate from the environment effectively. Unfortunately, most of them are not removed during the present-day treatment plants. So far, a range of treatment processes and degradation methods have been introduced and deployed against various EPs and/or MPs, such as ultrafiltration, nanofiltration, advanced oxidation processes (AOPs) and enzyme-based treatments coupled with membrane filtrations. To further strengthen the treatment processes and to overcome the EPs/MPs effective removal dilemma, numerous studies have revealed the applicability and notable biocatalytic potentialities of laccases and peroxidases to degrade different classes of organic pollutants. Exquisite selectivity and unique catalytic properties make these enzymes powerful biocatalytic candidates for bio-transforming an array of toxic contaminants to harmless entities. This review focuses on the use of laccases and peroxidases, such as soybean peroxidase (SBP), horseradish peroxidase (HRP), lignin peroxidase (LiP), manganese peroxidase (MnP), and chloroperoxidase (CPO) as a greener oxidation route towards efficient and effective removal or degradation of EPs/MPs.

Biodegradability of Dental Care Antimicrobial Agents Chlorhexidine and Octenidine by Ligninolytic Fungi

Chlorhexidine (CHX) and octenidine (OCT), antimicrobial compounds used in oral care products (toothpastes and mouthwashes), were recently revealed to interfere with human sex hormone receptor pathways. Experiments employing model organisms—white-rot fungi Irpex lacteus and Pleurotus ostreatus—were carried out in order to investigate the biodegradability of these endocrine-disrupting compounds and the capability of the fungi and their extracellular enzyme apparatuses to biodegrade CHX and OCT. Up to 70% ± 6% of CHX was eliminated in comparison with a heat-killed control after 21 days of in vivo incubation. An additional in vitro experiment confirmed manganese-dependent peroxidase and laccase are partially responsible for the removal of CHX. Up to 48% ± 7% of OCT was removed in the same in vivo experiment, but the strong sorption of OCT on fungal biomass prevented a clear evaluation of the involvement of the fungi or extracellular enzymes. On the other hand, metabolites indicating the enzymatic transformation of both CHX and OCT were detected and their chemical structures were proposed by means of liquid chromatography–mass spectrometry. Complete biodegradation by the ligninolytic fungi was not achieved for any of the studied analytes, which emphasizes their recalcitrant character with low possibility to be removed from the environment.

Recent development in the application of immobilized oxidative enzymes for bioremediation of hazardous micropollutants - A review

During the past several years, abundant progresses has been made in the development of immobilized oxidative enzymes with focus on finding new support materials, improving the immobilization methods and their applications. Nowadays, immobilized oxidative enzymes are broadly accepted as a green way to face the challenge of high amounts of micropollutants in nature. Among all oxidative enzymes, laccases and horseradish peroxidase were used frequently in recent years as they are general oxidative enzymes with ability to oxidize various types of compounds. Immobilized laccase or horseradish peroxidase are showed better stability, and reusability as well as easy separation from reaction mixture that make them more favorable and economic in compared to free enzymes. However, additional improvements are still essential such as: development of the new materials for immobilization with higher capacity, easy preparation, and cheaper price. Moreover, immobilization methods are still need improving to become more efficient and avoid enzyme wasting during immobilization and enzyme leakage through working cycles.

Environmentally responsive and anti-bugs textile finishes - Recent trends, challenges, and future perspectives

Bugs, such as microorganisms and insects, are present in the environment and sometimes can be health-hazardous if the living environment is not maintained following proper hygienic regulations. In the present scenario of increasing public awareness, environmental consciousness, and growing demand for easy-care, and disinfected textiles, the manufacturing of protective and easy-to-care textiles has become a key necessity of the modern world. Comfortable, clean, hygienic, antimicrobial, and insect repelling properties of textile goods are gaining the accelerating research momentum as a basic requirement to produce multifunctional textiles. These functional finishes have numerous applications such as in-home textiles, bed nets, and tenting, camping gear as well as in military uniforms. Synthetic antimicrobial and insect repellents are quite effective against insects and microscopic organisms but are slightly toxic to the human being and the environment. To overcome these problems, researchers are considering natural agents for functional finishes, but their effectiveness is less durable to textile material. Besides needful advantages, the excessive use of dyes in finishing processes heavily required washing cycles and ultimately release various types of hazardous dyes or wasteful effluents in the environment. This review reports the chemical composition and recent developments in textile finishes, particularly antimicrobial and insect repellent textile finishes. A large number of commonly used antimicrobial agents (i.e. chitosan, zwitterionic compounds, silver and silver-based compounds, titanium dioxide nanoparticles, imidazolium salts, triclosan and quaternary ammonium salts) and insect repellent textile finishes (i.e. N‑N‑diethyl‑m‑toluamide, permethrin, cypermethrin, pyrethrum, picaridin, bioallethrin, citriodiol and essential oils) have been presented. Finally, the review is wrapped up with major research gaps/challenges, concluding remarks, and future opportunities in this area of research.

Cultivation of a versatile manganese-oxidizing aerobic granular sludge for removal of organic micropollutants from wastewater

Organic micropollutants (OMPs) are frequently detected in water and wastewater, and have attracted wide attention due to potential adverse effects on ecosystems and human health. In this work, manganese-oxidizing aerobic granular sludge (Mn-AGS) was successfully cultivated and applied to remove OMPs from wastewater. Biogenic manganese (III,IV) oxides (bio-MnO_x) were generated and accumulated to 22.0-28.3 mg Mn/g SS in the final sludge. Neither the addition of allochthonous manganese-oxidizing bacteria (MnOB; Pseudomonas putida MnB1) nor the reduction in hydraulic retention time (HRT) facilitated the cultivation of Mn-AGS. Batch experiments of OMPs degradation indicated that Mn-AGS significantly improved (1.3-3.9 times) degradation rates of most OMPs. Removal rates of bisphenol A (BPA), 17α‑ethinylestradiol (EE2), tetracycline (TC), and chloramphenicol (CAP) were 3.0-12.6 μg/h/g SS by the traditional AGS and 8.0-16.3 μg/h/g SS by Mn-AGS; those of imazethapyr (IM) were relatively high, 64.7 ± 0.1 and 127.8 ± 2.5 μg/h/g SS by AGS and Mn-AGS, respectively. However, degradation of dichlorophenyl phosphine (DCPP) was slower by Mn-AGS than AGS, 9.0 ± 0.4 vs. 21.2 ± 0.9 μg/h/g SS, possibly due to inhibition of microbial activity by bio-MnO_x. This work provides a promising method for treating OMPs in organic wastewater, but the possible inhibition of microbes by bio-MnO_x should be noted.

Designing and modeling of a novel electrolysis reactor using porous cathode to produce H2O2 as an oxidant

The entry of toxic organic pollutants and resistant to biodegradation has increased the concern about human health. The use of advanced oxidation (AO) processes to degrade these pollutants has been developing. One of the AO processes is based on the use of hydrogen peroxide in removing resistant organic pollutants.

This study aimed to develop a new reactor capable of producing H₂O₂ in the solution. Therefore, a porous electrode made of stainless steel with the capability of air injection in the electrode center was used. The 30 cm rod graphite electrodes were also used as an anode electrode in a 4000 ml reactor. The effects of variables, including current density (30–40 mA/cm²), time (10–30 min), and electrolyte concentration (12–17 mM/L) on the amount of H₂O₂ production were evaluated by Box behenken design under response surface methodology using Design expert software. The results of this study showed that H₂O₂ can be produced at the electrode surface of porous cathode under optimal conditions of 36 mA/cm² current density, 16 mM/l electrolyte concentration, in 23 min, and in the amount of 34 ppm. Using a porous cathode electrode causes the maximum contact among the solution, water, and air, and increases the production of H₂O₂.

The release of resistant organic compounds to the waste water is a serious problem to the environment. By the application of the Electro-oxidation (EO)reactor with the ability to produce H₂O₂, this issue is resolved. Furthermore, this technique is applied for non-selective degradation of the toxic organic compounds.

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The electro-oxidation process is a useful method for destruction of persistent organic matter from wastewater.

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Due to use of porous cathode in this method, contact between the electrode and the sewage is at its maximum level which increases the efficiency and speed of sewage treatment.

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This method can produce H₂O₂ as a high potential oxidant that can reduce persistent organic properties of sewage and make the wastewater suitable for biological treatment.

Mitigation of environmental pollution by genetically engineered bacteria - Current challenges and future perspectives

Industries are the paramount driving force for the economic and technological development of society. However, the flourishing industrialization and unimpeded growth of current production unit's result in widespread environmental pollution due to increased discharge of wastes loaded with baleful, hazardous, and carcinogenic contaminants. Physicochemical-based remediation means are costly, create a secondary disposal problem and remain inadequate for pollution mitigating because of the continuous emergence of new recalcitrant pollutants. Due to eco-friendly, social acceptance, and lesser health hazards, microbial bioremediation has received considerable global attention for pollution abatement. Moreover, with the recent advancement in biotechnology and microbiology, genetically engineered bacteria with high ability to remove environmental pollutants are widely used in the fields of environmental restoration, resulting in the bioremediation in a more viable and eco-friendly way. This review summarized the advantages of genetically engineered bacteria and their application in the treatment of a wide variety of environmental contaminants such as synthetic dyestuff, heavy metal, petroleum hydrocarbons, polychlorinated biphenyls, phenazines and agricultural chemicals which will include herbicides, pesticides, and fertilizers. Considering the risk of genetic material exchange by using genetically engineered bacteria, the challenges and limitations associated with the application of recombinant bacteria on contaminated sites are also discussed. An integrated microbiological, biological and ecological acquaintance accompanied by field engineering designs are the desired features for effective in situ bioremediation of hazardous waste polluted sites by recombinant bacteria.

Enrichment of thermophilic and mesophilic microbial consortia for efficient degradation of corn stalk

Six different environmental samples were applied to enrich microbial consortia for efficient degradation of corn stalk, under the thermophilic and mesophilic conditions. The consortium obtained from anaerobic digested sludge under thermophilic condition (TC-Y) had the highest lignocellulose-degrading activity. The CO₂ yield was 246.73 mL/g VS in 23 days, meanwhile, the maximum CO₂ production rate was 15.48 mL/(CO₂·d), which was 28.75% and 52.27% higher than that under mesophilic condition, respectively. The peak value of cellulase activity reached 0.105 U/mL, which was at least 34.61% higher than the other groups. In addition, 49.5% of corn stalk was degraded in 20 days, moreover, the degradation ratio of cellulose, hemicellulose and lignin can reach 52.76%, 62.45% and 42.23%, respectively. Microbial consortium structure analysis indicated that the TC-Y contained the phylum of Gemmatimonadetes, Acidobacteria, Chloroflexi, Planctomycetes, Firmicutes, and Proteobacteria. Furthermore, the Pseudoxanthomonas belonging to GammaProteobacteria might be the key bacterial group for the lignocellulose degradation. These results indicated the capability of degrading un-pretreated corn stalk and the potential for further investigation and application of TC-Y.

Mode of Action, Properties, Production, and Application of Laccase: A Review

Background and Source: Laccase belongs to the blue multi-copper oxidases, which are widely distributed in fungi and higher plants. It is present in Ascomycetes, Deuteromycetes, and Basidiomycetes and found abundantly in white-rot fungi. Applications: Laccase enzymes because of their potential have acquired more importance and application in the area of textile, pulp and paper, and food industry. Recently, it is being used in developing biosensors for detection and removal of toxic pollutants, designing of biofuel cells and medical diagnostics tool. Laccase is also being used as a bioremediation agent as they have been found potent enough in cleaning up herbicides pesticides and certain explosives in soil. Because of having the ability to oxidize phenolic, non-phenolic lignin-related compounds and highly fractious environmental pollutants, laccases have drawn the attention of researchers in the last few decades. Commercially, laccases have been used to determine the difference between codeine and morphine, produce ethanol and are also being employed in de-lignify woody tissues. We have revised patents related to applicability of laccases. We have revised all the patents related to its wide applicability. Conclusion: For fulfillment of these wide applications, one of the major concerns is to develop a system for efficient production of these enzymes at a broad scale. Research in the field of laccases has been accelerated because of its wide diversity, utility, and enzymology. This paper deals with recent trends in implementation of the laccases in all practical possibilities with the help of optimizing various parameters and techniques which are responsible for mass production of the enzyme in industries.

Emerging contaminants of high concern and their enzyme-assisted biodegradation - A review

The widespread occurrence and adverse environmental and health-related impacts of various types of emerging contaminants (ECs) have become an issue of high concern. With ever increasing scientific knowledge, socio-economic awareness, health-related problems and ecological apprehensions, people are more concerned about the widespread ECs, around the globe. Among ECs, biologically active compounds from pharmaceutical, cosmeceutical, biomedical, personal care products (PPCPs), endocrine-disrupting chemicals (EDCs), and flame-retardants are of paramount concern. The presence and persistence of ECs in water bodies are of continued and burning interest, worldwide. Various types of ECs are being discharged knowingly/unknowingly with/without partial treatments into the aquatic environments that pose serious health issues and affects the entire living ecosystem. So far, various approaches have been developed for ECs degradation and removal to diminish their adverse impact. Many previous and/or ongoing studies have focused on contaminants degradation and efficient removal via numerous treatment strategies, i.e. (1) physical, (2) chemical and (3) biological. However, the experimental evidence is lacking to enable specific predictions about ECs mechanistic degradation and removal fate across various in-practice systems. In this context, the deployment oxidoreductases such as peroxidases (lignin peroxidases, manganese-dependent peroxidases, and horseradish peroxidase), aromatic dioxygenases, various oxygenases, laccases, and tyrosinases have received considerable research attention. Immobilization is highlighted as a promising approach to improve enzyme catalytic performance and stabilization, as well as, to protect the three-dimensional structure of the enzyme against the undesirable consequences of harsh reaction environment. This work overviews the current and state-of-the-art critical aspect related to hazardous pollutants at large and ECs in particular by the immobilized oxidoreductase enzymes. The first part of the review focuses on the occurrence, physiochemical behavior, potent sources and significant routes of ECs. Following that, environmentally-related adverse impacts and health-related issues of ECs are discussed in the second part. In the third part, biodegradation and removal strategies with a comparative overview of several conventional vs. non-conventional methods are presented briefly. The fourth part majorly focuses on operational modes of different oxidoreductase enzyme-based biocatalytic processes for the biodegradation and biotransformation of a wide array of harmful environmental contaminants. Finally, the left behind research gaps, concluding remarks as well as future trends and recommendations in the use of carrier-immobilized oxidoreductases for environmental perspective are also discussed.

Environmentally-related contaminants of high concern: Potential sources and analytical modalities for detection, quantification, and treatment

In recent years, emerging contaminants (ECs) of high concern are broadly distributed throughout the environmental matrices because of various industrial practices and anthropogenic inputs, i.e., human-made activities. With ever increasing scientific knowledge, technological advancement, socio-economic awareness, people are now more concern about the widespread distribution of environmentally related ECs of high concern. As, ECs possess serious ecological threats and potential risks to human health and aquatic life, even at minor concentrations. The controlled or uncontrolled discharge and long-term persistence of ECs that includes micro-pollutants, endocrine disruptors (EDs), pesticides, pharmaceuticals, hormones, toxins, and industrially-related synthetic dyes and dyes-containing hazardous pollutants, etc. pose a significant challenge to policy regulators, engineers, and scientific community. The conventional treatment technologies are proved ineffective for the complete elimination and removal of an array of contaminants of emerging environmental concern in various biological and environmental samples. In order to overcome the aforementioned ecological threats, tremendous research efforts have been made to boost the efficiency of remediation techniques or develop new modalities to detect, quantify and treat the samples efficiently. The boom in biotechnology and environmental engineering offers potential opportunities to develop advanced and innovative remediation techniques in the field of water treatment. This review discusses the environmental and health hazards associated with a widespread distribution of micro-pollutants, pesticides, pharmaceuticals, hormones, and industrially-related synthetic dyes and dyes-containing hazardous pollutants, etc. in the water bodies, i.e., surface water, groundwater, and industrial wastewater streams. Life-cycle distribution of emerging (micro)-pollutants with suitable examples from various industrial sources viewpoints is also discussed. The later part of the review focuses on innovative and cost-effective remediation (removal) approaches from phase-changing treatment technologies for these ECs of high concern.

Peroxidases-assisted removal of environmentally-related hazardous pollutants with reference to the reaction mechanisms of industrial dyes

Environmental protection is one of the most important challenges for the humankind. Increasing number of emerging pollutants resulting from industrial/human-made activities represents a serious menace to the ecological and environmental equilibrium. Industrial dyes, endocrine disrupters, pesticides, phenols and halogenated phenols, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and other xenobiotics are among the top priority environmental pollutants. Some classical remediation approaches including physical, chemical and biological are being employed, but are ineffective in cleaning the environment. Enzyme-catalyzed transformation reactions are gearing accelerating attention in this context as potential alternatives to classical chemical methods. Peroxidases are catalysts able to decontaminate an array of toxic compounds by a free radical mechanism resulting in oxidized or depolymerized products along with a significant toxicity reduction. Admittedly, enzymatic catalysis offers the hallmark of high chemo-, regio-, and enantioselectivity and superior catalytic efficiency under given reaction environment. Moreover, enzymes are considered more benign, socially acceptable and greener production routes since derived from the renewable and sustainable feedstock. Regardless of their versatility and potential use in environmental processes, several limitations, such as heterologous production, catalytic stability, and redox potential should be overcome to implement peroxidases at large-scale transformation and bio-elimination of recalcitrant pollutants. In this article, a critical review of the transformation of different types of hazardous pollutants by peroxidases, with special reference to the proposed reaction mechanisms of several dyes is presented. Following that major challenges for industrial and environmental applications of peroxidases are also discussed. Towards the end, the information is also given on miscellaneous applications of peroxidases, concluding remarks and outlook.

Magnetic nanoparticles as versatile carriers for enzymes immobilization: A review

Enzymes are highly efficient biocatalysts and widely employed in biotechnological sectors. However, lack of (re)-purification and efficient recovery of enzymes are among the most critical and challenging aspects, which render them enormously expensive for industrial exploitability. Aiming to tackle these challenges, magnetic nanoparticles (MNPs) have gained a special place as versatile carriers and supporting matrices for immobilization purposes, owing to the exceptional properties of MNPs, such as large surface area, large surface-to-volume ratio, and mobility and high mass transference. More importantly, they can also be easily separated and recovered by applying an external magnetic field. Apart from their biocompatible micro-environment, the utilization of such MNPs represents a noteworthy green chemistry approach, since it lengthens the biocatalyst lifetime through multiple recovery cycles. According to the literature evidence, various modification and/or functionalization approaches have been developed to produce MNPs for the effective immobilization of a broad variety of industrially important enzymes and biomolecules with improved characteristics. Enzymes immobilized on MNPs displayed a wide-working pH and temperature range, as well as, improved thermal and storage stabilities than that of their pristine counterparts. Co-immobilization of multi-enzymes could also be accomplished through nanoparticle-based approaches. This review presents an updated outlook on the development and characterization of MNPs, in particular, iron-based MNPs-derived nano-constructs as support materials for enzyme immobilization.

Graphene and graphene oxide: Functionalization and nano-bio-catalytic system for enzyme immobilization and biotechnological perspective

Graphene-based nanomaterials have gained high research interest in different fields related to proteins and thus are rapidly becoming the most widely investigated carbon-based materials. Their exceptional physiochemical properties such as electrical, optical, thermal and mechanical strength enable graphene to render graphene-based nanostructured materials suitable for applications in different fields such as electroanalytical chemistry, electrochemical sensors and immobilization of biomolecules and enzymes. The structural feature of oxygenated graphene, i.e., graphene oxide (GO) covered with different functionalities such as epoxy, hydroxyl, and carboxylic group, open a new direction of chemical modification of GO with desired properties. This review describes the recent progress related to the structural geometry, physiochemical characteristics, and functionalization of GO, and the development of graphene-based novel carriers as host for enzyme immobilization. Graphene derivatives-based applications are progressively increasing, in recent years. Therefore, from the bio-catalysis and biotransformation viewpoint, the biotechnological perspective of graphene-immobilized nano-bio-catalysts is of supreme interest. The structural geometry, unique properties, and functionalization of graphene derivatives and graphene-based nanomaterials as host for enzyme immobilization are highlighted in this review. Also, the role of GO-based catalytic systems such as microfluidic bio-catalysis, enzyme-based biofuel cells, and biosensors are also discussed with potential future perspectives of these multifaceted materials.

"Smart" chemistry and its application in peroxidase immobilization using different support materials

In the past few decades, the enzyme immobilization technology has been exploited a lot and thus became a matter of rational design. Immobilization is an alternative approach to bio-catalysis with the added benefits, adaptability to automation and high-throughput applications. Immobilization-based approaches represent simple but effective routes for engineering enzyme catalysts with higher activities than wild-type or pristine counterparts. From the chemistry viewpoint, the concept of stabilization via manipulation of functional entities, the enzyme surfaces have been an important driving force for immobilizing purposes. In addition, the unique physiochemical and structural functionalities of pristine or engineered cues, or insoluble support matrices (carrier) such as mean particle diameter, swelling behavior, mechanical strength, and compression behavior are of supreme interest and importance for the performance of the immobilized systems. Immobilization of peroxidases into/onto insoluble support matrices is advantageous for practical applications due to convenience in handling, ease separation of enzymes from a reaction mixture and the reusability. A plethora of literature is available explaining individual immobilization system. However, current literature lacks the chemistry viewpoint of immobilization. This review work presents state-of-the-art "Smart" chemistry of immobilization and novel potentialities of several materials-based cues with different geometries including microspheres, hydrogels and polymeric membranes, nanoparticles, nanofibers, composite and hybrid or blended support materials. The involvement of various functional groups including amino, thiol, carboxylic, hydroxyl, and epoxy groups via "click" chemistry, amine chemistry, thiol chemistry, carboxyl chemistry, and epoxy chemistry over the protein surfaces is discussed.

Combined Cross-Linked Enzyme Aggregates as Biocatalysts

Enzymes are efficient biocatalysts providing an important tool in many industrial biocatalytic processes. Currently, the immobilized enzymes prepared by the cross-linked enzyme aggregates (CLEAs) have drawn much attention due to their simple preparation and high catalytic efficiency. Combined cross-linked enzyme aggregates (combi-CLEAs) including multiple enzymes have significant advantages for practical applications. In this review, the conditions or factors for the preparation of combi-CLEAs such as the proportion of enzymes, the type of cross-linker, and coupling temperature were discussed based on the reaction mechanism. The recent applications of combi-CLEAs were also reviewed.