Immobilized microbial nanoparticles for biosorption

Effective denitrification from landfill leachate using magnetic PVA/CMC/DE carrier immobilized microorganisms

Ammonia nitrogen (NH4+-N) discharge has caused eutrophication of water bodies and harm to humans and organisms. In this work, polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), diatomite (DE), and Fe3O4 were used to prepare magnetic immobilized carriers by encapsulating microorganisms for the treatment of NH4+-N wastewater. The response surface methodology was used to explore the optimal ratio of the immobilized carriers. The obtained optimal raw material ratio was 99.10 %. The obtained carriers are spherical (4-5 mm in diameter) with a rich honeycombed pore structure. The magnetic carrier improves the ammonia oxidation activity, and the carrier achieved 99.0 % of NH4+-N and 86.7 % of total nitrogen (TN) removal rates from the simulated wastewater (NH4+-N concentration: 300 mg/L) through nitrification and denitrification under aerobic conditions. Upon applied for a 60 days' treatment of landfill leachate (NH4+-N concentration of 300 mg/L), the daily removal rates for NH4+-N and TN reached 93.7 % and 78.3 %, respectively. The analysis of the microbial community showed that the abundances of heterotrophic nitrifying-aerobic denitrifying bacteria including Enterobacter, Pseudomonas, and Bacillus increased with prolonging treatment days, which accelerated nitrification and denitrification, consequently promoting the nitrogen removal effect.

Microalgae-based bioremediation of refractory pollutants: an approach towards environmental sustainability

Extensive anthropogenic activity has led to the accumulation of organic and inorganic contaminants in diverse ecosystems, which presents significant challenges for the environment and its inhabitants. Utilizing microalgae as a bioremediation tool can present a potential solution to these challenges. Microalgae have gained significant attention as a promising biotechnological solution for detoxifying environmental pollutants. This is due to their advantages, such as rapid growth rate, cost-effectiveness, high oil-rich biomass production, and ease of implementation. Moreover, microalgae-based remediation is more environmentally sustainable for not generating additional waste sludge, capturing atmospheric CO2, and being efficient for nutrient recycling and sustainable algal biomass production for biofuels and high-value-added products generation. Hence, microalgae can achieve sustainability's three main pillars (environmental, economic, and social). Microalgal biomass can mediate contaminated wastewater effectively through accumulation, adsorption, and metabolism. These mechanisms enable the microalgae to reduce the concentration of heavy metals and organic contaminants to levels that are considered non-toxic. However, several factors, such as microalgal strain, cultivation technique, and the type of pollutants, limit the understanding of the microalgal removal mechanism and efficiency. Furthermore, adopting novel technological advancements (e.g., nanotechnology) may serve as a viable approach to address the challenge of refractory pollutants and bioremediation process sustainability. Therefore, this review discusses the mechanism and the ability of different microalgal species to mitigate persistent refractory pollutants, such as industrial effluents, dyes, pesticides, and pharmaceuticals. Also, this review paper provided insight into the production of nanomaterials, nanoparticles, and nanoparticle-based biosensors from microalgae and the immobilization of microalgae on nanomaterials to enhance bioremediation process efficiency. This review may open a new avenue for future advancing research regarding a sustainable biodegradation process of refractory pollutants.

Fundamentals of bio-based technologies for selective metal recovery from bio-leachates and liquid waste streams

The number of metal-containing waste streams resulting from electronic end-of life products, metallurgical by-products, and mine tailings to name but a few, is increasing worldwide. In recent decades, the potential to exploit these waste streams as valuable secondary resources to meet the high demand of critical and economically important raw materials has become more prominent. In this review, fundamental principles of bio-based metal recovery technologies are discussed focusing on microbial metabolism-dependent and metabolism-independent mechanisms as sustainable alternatives to conventional chemical metal recovery methods. In contrast to previous reviews which have partially addressed this topic, a special focus will be given on how fundamental principles of bio-based recovery technologies can influence the selectivity and specificity of metal recovery. While conventional methods for metal recovery show benefits in terms of economic affordability, bio-based recovery technologies offer advantages in terms of efficiency and environmentally friendliness. Modifications and adaptations in the processes of biosorption, bioaccumulation and bioelectrochemical systems are highlighted, further emphasizing the application of metal-binding peptides and siderophores to increase selectivity in the recovery of metals. Single metal solutions or mixtures with a low complexity have been the focus of previous studies and reviews, but this does not reflect the nature of complex industrial effluents. Therefore, key challenges that arise when dealing with complex polymetallic solutions are addressed and the focus is set on optimizing bio-based technologies to recover metals efficiently and selectively from bio-leachates or liquid waste streams.

Advances in immobilized microbial technology and its application to wastewater treatment: A review

The use of immobilized microbial technology in wastewater treatment has drawn extensive attention due to its advantages of high colony density, rapid reaction speed, and good stability. Immobilization carriers are the core of immobilization technology. This review summarizes the types of immobilization carriers and their advantages and disadvantages, focusing on the potential for utilizing novel immobilization carriers (composite carriers, nanomaterials, metal-organic frameworks (MOFs), and biochar materials) in wastewater applications. The basic principles and technical advantages and disadvantages of novel immobilization methods (layer-by-layer self-assembly (LBL) and electrostatic spinning) are then summarized. Additionally, the research progress and application characteristics of immobilized anaerobic ammonia oxidizing (Anammox) and aerobic denitrifying (AD) bacteria for enhanced wastewater nitrogen removal are discussed. Finally, the current challenges of immobilized microbial technology are discussed, and its future development trends are summarized and prospected. This review provides guidance and theoretical support for the practical engineering application of immobilized microbial technology.

A comprehensive review on removal of pollutants from wastewater through microbial nanobiotechnology -based solutions

Increasing wastewater pollution owing to the briskly rising human population, rapid industrialization, and fast urbanization has necessitated highly efficient wastewater treatment technologies. Although several methods of wastewater treatments are in practice, expensiveness, use of noxious chemicals, generation of unsafe by-products, and longer time consumption restrain their use to a great extent. Over the last few decades, nanotechnological wastewater treatment approaches have received widespread recognition globally. Microbially fabricated nanoparticles reduce the utilization of reducing, capping, and stabilizing agents, and exhibit higher adsorptive and catalytic efficiency than chemically synthesized nanomaterials. The present review comprehensively summarizes the applications of microbial nanotechnology in the removal of a wide range of noxious wastewater pollutants. Moreover, prospects and challenges associated with the integration of nanotechnology with other biological treatment technologies including algal-membrane bioreactor, aerobic digestion, microbial fuel cells, and microbial nanofiber webs have also been briefly discussed.

Clay-polymer hybrid hydrogels in the vanguard of technological innovations for bioremediation, metal biorecovery, and diverse applications

Polymeric hydrogels are among the most studied materials due to their exceptional properties for many applications. In addition to organic and inorganic-based hydrogels, "hybrid hydrogels" have been gaining significant relevance in recent years due to their enhanced mechanical properties and a broader range of functionalities while maintaining good biocompatibility. In this sense, the addition of micro- and nanoscale clay particles seems promising for improving the physical, chemical, and biological properties of hydrogels. Nanoclays can contribute to the physical cross-linking of polymers, enhancing their mechanical strength and their swelling and biocompatibility properties. Nowadays, they are being investigated for their potential use in a wide range of applications, including medicine, industry, and environmental decontamination. The use of microorganisms for the decontamination of environments impacted by toxic compounds, known as bioremediation, represents one of the most promising approaches to address global pollution. The immobilization of microorganisms in polymeric hydrogel matrices is an attractive procedure that can offer several advantages, such as improving the preservation of cellular integrity, and facilitating cell separation, recovery, and transport. Cell immobilization also facilitates the biorecovery of critical materials from wastes within the framework of the circular economy. The present work aims to present an up-to-date overview on the different "hybrid hydrogels" used to date for bioremediation of toxic metals and recovery of critical materials, among other applications, highlighting possible drawbacks and gaps in research. This will provide the latest trends and advancements in the field and contribute to search for effective bioremediation strategies and critical materials recovery technologies.

Chitosan-coated manganese ferrite nanoparticles enhanced Rhodotorula toruloides carotenoid production

The present study aims to analyze the interaction between Rhodotorula toruloides and magnetic nanoparticles and evaluate their effect on carotenoid production. The manganese ferrite nanoparticles were synthesized without chitosan (MnFe2O4) and chitosan coating (MnFe2O4-CS) by the co-precipitation method assisted by hydrothermal treatment. XRD (X-ray diffraction), Magnetometry, Dynamic Light Scattering (DLS) and FTIR (Fourier-Transform Infrared Spectroscopy), are used to characterize the magnetic nanoparticles. The crystallite size of MnFe2O4 was 16 nm for MnFe2O4 and 20 nm for MnFe2O4-CS. The magnetic saturation of MnFe2O4-CS was lower (39.6 ± 0.6 emu/g) than the same MnFe2O4 nanoparticles (42.7 ± 0.3 emu/g), which was attributed to the chitosan fraction presence. The MnFe2O4-CS FTIR spectra revealed the presence of the characteristic chitosan bands. DLS demonstrated that the average hydrodynamic diameters were 344 nm for MnFe2O4 and 167 nm for MnFe2O4-CS. A kinetic study of cell immobilization performed with their precipitation with a magnet demonstrated that interaction between magnetic nanoparticles and R. toruloides was characterized by an equilibrium time of 2 h. The adsorption isotherm models (Langmuir and Freundlich) were fitted to the experimental values. The trypan blue assay was used for cell viability assessment. The carotenoid production increased to 256.2 ± 6.1 µg/g dry mass at 2.0 mg/mL MnFe2O4-CS. The use of MnFe2O4-CS to stimulate carotenoid yeast production and the magnetic separation of biomass are promising nanobiotechnological alternatives. Magnetic cell immobilization is a perspective technique for obtaining cell metabolites.

Immobilization of Coprinus comatus with magnetic alginate hydrogel microsphere for improving the antioxidant activity of fermentation products

Coprinus comatus is an edible mushroom and its fermented product possesses antioxidant activity. In this study, to further enhance the antioxidant activity and improve the reusability of the strain, calcium alginate hydrogel was used as the carrier for embedding and immobilizing Coprinus comatus. The effects of CaCl2 concentration, sodium alginate concentration, microsphere diameter, and the amount of magnetic particle on the antioxidant activity of fermented products were investigated. The results showed that the magnetic immobilized microsphere prepared by 2.50% CaCl2, 2.00% sodium alginate and 0.50% Fe3O4 had the best fermentation antioxidant activity (EC50 was 0.43 ± 0.01 mg/mL) when the diameter was 5 mm, which increased by 24.56% compared to the initial activity. Besides, the microsphere showed strong reusability, the antioxidant activity was still better than the free strain after being used five times. This study not only enhanced the antioxidant activity of Coprinus comatus fermented product through immobilization, but also provided an effective method for microbial fermentation.

Microorganisms immobilized hydroxyethyl cellulose/luffa composite sponge for selective adsorption and biodegradation of oils in wastewater

The highly efficient removal of oils such as oils or dyes from wastewater has aroused wide concern and is of great significance for clean production and environmental remediation. The synthesis of a novel aerogel (designated as HEC/LS) is reported herein, achieved through a sol-gel method followed by freeze-drying utilizing loofa and hydroxyethyl cellulose as the raw materials. The new HEC/LS aerogel exhibits excellent porosity and specific surface area, with a porosity of 88.70 %, a total pore area of 0.607 m2 g-1, and a specific surface area of 230 m2 g-1. The prepared HEC/LS aerogel exhibits exceptional hydrophilicity and self-floatability, facilitating its rapid absorption of water up to 21 times its own weight within a mere 3 s. Additionally, it demonstrates good adsorption performance for methylene blue (MB), with a maximum adsorption capacity of 83.30 mg g-1. Subsequently, a new hydrophobic microorganisms-loaded composite aerogel (namely, Bn-HEC/LS) was obtained by doping microorganisms into the as-prepared HEC/LS in multiple enrichment followed by a hydrophobic and oleophilic surface modification. Based on its rich porous structure and oleophilic wettability, the as-synthesized Bn-HEC/LS exhibits excellent selective adsorption and degradation properties for the oil contamination, the diesel oil could be selectively absorbed in the Bn-HEC/LS and degraded by the loaded microorganisms. Among them, B5-HEC/LS displays the highest removal efficiency of 94.50 % within 180 h, while free microorganisms and HEC/LS aerogels show degradation efficiencies of only 21.70 % and 48.10 %, respectively. The fixation of microorganisms in the aerogel increases their number within the material and enhances the relative microorganisms removal capacity. The hydrophobic and lipophilic modifications improve the selective adsorption performance of the aerogel on diesel oil, resulting in a significantly high removal rate of Bn-HEC/LS for diesel oil. The results indicate that the immobilization of microorganisms into aerogel improves the activity of microorganisms, and the hydrophobic and oleophilic modification enhances the selective adsorption performance of aerogel to diesel oil, thus resulting in a very high removal rate of Bn-HEC/LS for diesel oil. This study is expected to provide a now possibility for the green and efficient bioremediation of oils.

Removal of food dyes using biological materials via adsorption: A review

It is alarming that synthetic food dyes (FD) are widely used in various industries and that these facilities discharge their wastewater into the environment without treating it. FDs mixed into industrial wastewater pose a threat to the environment and human health. Therefore, removing FDs from wastewater is very important. This review explores the burgeoning field of FD removal from wastewater through adsorption using biological materials (BMs). By synthesizing a wealth of research findings, this comprehensive review elucidates the diverse array of BMs employed, ranging from algae and fungi to agricultural residues and microbial biomass. Furthermore, this review investigates challenges in practical applications, such as process optimization and scalability, offering insights into bridging the gap between laboratory successes and real-world implementations. Harnessing the remarkable adsorptive potential of BMs, this review presents a roadmap toward transformative solutions for FD removal, promising cleaner and safer production practices in the food and beverage industry.

Applications and synergistic degradation mechanisms of nZVI-modified biochar for the remediation of organic polluted soil and water: A review

Increasing organic pollution in soil and water has garnered considerable attention in recent years. Nano zero-valent iron-modified biochar (nZVI/BC) has been proven to remediate the contaminated environment effectively due to its abundant active sites and unique reducing properties. This paper provides a comprehensive overview of the application of nZVI/BC in organic polluted environmental remediation and its mechanisms. Firstly, the review introduced primary synthetic methods of nZVI/BC, including in-situ synthesis (carbothermal reduction and green synthesis) and post-modification (liquid-phase reduction and ball milling). Secondly, the application effects of nZVI/BC were discussed in remediating soil and water polluted by antibiotics, pesticides, polycyclic aromatic hydrocarbons (PAHs), and dyes. Thirdly, this review explored the mechanisms of the adsorption and chemical degradation of nZVI/BC, and synergistic degradation mechanisms of nZVI/BC-AOPs and nZVI/BC-Microbial interactions. Fourth, the factors that influence the removal of organic pollutants using nZVI/BC were summarized, encompassing synthesis conditions (raw materials, pyrolysis temperature and aging of nZVI/BC) and external factors (reagent dosage, pH, and coexisting substances). Finally, this review proposed future challenges for the application of nZVI/BC in environmental remediation. This review offers valuable insights for advancing technology in the degradation of organic pollutants using nZVI/BC and promoting its on-site application.

Dynamic immobilization of bacterial cells on biofilm in a polyester nonwoven chemostat

Cell immobilization plays an important role in biocatalysis for high-value products. It is necessary to maintain the viability of immobilized cells for bioconversion using viable cells as biocatalysts. In this study, a novel polyester nonwoven chemostat was designed for cell immobilization to investigate biofilm formation and the dynamic balance between adsorption and desorption of cells on polyester nonwoven. The polyester nonwoven was suitable for cell immobilization, and the cell numbers on the polyester nonwoven can reach 6.5 ± 0.38 log CFU/mL. After adding the polyester nonwoven to the chemostat, the fluctuation phenomenon of free bacterial cells occurred. The reason for this phenomenon was the balance between adsorption and desorption of bacterial cells on the polyester nonwoven. Bacterial cells could adhere to the surface of polyester nonwoven via secreting extracellular polymeric substances (EPS) to form biofilms. As the maturation of biofilms, some dead cells inside the biofilms can cause the detachment of biofilms. This process of continuous adsorption and desorption of cells can ensure that the polyester nonwoven chemostat has lasting biological activity.

Unveiling antibacterial and antioxidant activities of zinc phosphate-based nanosheets synthesized by Aspergillus fumigatus and its application in sustainable decolorization of textile wastewater

BACKGROUND

The development of an environment-friendly nanomaterial with promising antimicrobial and antioxidant properties is highly desirable. The decolorization potentiality of toxic dyes using nanoparticles is a progressively serious worldwide issue.

METHODS

The successful biosynthesis of zinc nanoparticles based on phosphates (ZnP-nps) was performed using the extracellular secretions of Aspergillus fumigatus. The antibacterial activity of the biosynthetic ZnP-nps was investigated against Gram-negative bacteria and Gram-positive bacteria using the agar diffusion assay method. The antioxidant property for the biosynthetic nanomaterial was evaluated by DPPH and H2O2 radical scavenging assay.

RESULTS

Remarkable antibacterial and antiradical scavenging activities of ZnP-nps were observed in a dose-dependent manner. The minimum inhibitory concentration (MIC) for Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli was 25 µg/ml, however, the MIC for Bacillus subtilis was 12.5 µg/ml. The maximum adsorptive performance of nanomaterial was respectively achieved at initial dye concentration of 200 mg/L and 150 mg/L using methylene blue (MB) and methyl orange (MO), where sorbent dosages were 0.5 g for MB and 0.75 g for MB; pH was 8.0 for MB and 4.0 for MO; temperature was 30 °C; contact time was 120 min. The experimental data was better obeyed with Langmuir's isotherm and pseudo-second-order kinetic model (R2 > 0.999). The maximum adsorption capacity (qmax) of MB and MO dyes on nanomaterial were 178.25 mg/g and 50.10 mg/g, respectively. The regenerated nanomaterial, respectively, persist > 90% and 60% for MB and MO after 6 successive cycles. The adsorption capacity of the prepared zinc phosphate nanosheets crystal toward MB and MO, in the present study, was comparable/superior with other previously engineered adsorbents.

CONCLUSIONS

Based on the above results, the biosynthesized ZnP-nanosheets are promising nanomaterial for their application in sustainable dye decolorization processes and they can be employed in controlling different pathogenic bacteria with a potential application as antiradical scavenging agent. Up to our knowledge, this is probably the first study conducted on the green synthesis of ZnP-nanosheets by filamentous fungus and its significant in sustainable dye decolorization.

Improving rhamnolipids production using fermentation-foam fractionation coupling system: cell immobilization and waste frying oil emulsion

This work focused on the development of an inexpensive carbon source and the improvement of the fermentation-foam fractionation coupling system. The rhamnolipids production capacity of waste frying oil (WFO) was evaluated. The suitable bacterial cultivation of seed liquid and the addition amount of WFO was 16 h and 2% (v/v), respectively. A combined strategy of cell immobilization and oil emulsion avoid cell entrainment inside foam and improves the oil mass transfer rate. The immobilization conditions of bacterial cells into alginate-chitosan-alginate (ACA) microcapsules were optimized using the response surface method (RSM). Under the optimal conditions, rhamnolipids production using batch fermentation with immobilized strain reached 7.18 ± 0.23% g/L. WFO was emulsified into a fermentation medium using rhamnolipids as emulsifier (0.5 g/L). By monitoring dissolved oxygen, 30 mL/min was selected as a suitable air volumetric flow rate for fermentation-foam fractionation coupling operation. The total production and recovery percentage of rhamnolipids were 11.29 ± 0.36 g/L and 95.62 ± 0.38%, respectively.

More effective application of biochar-based immobilization technology in the environment: Understanding the role of biochar

In recent years, biochar-based immobilization technology (BIT) has been widely used to treat different environmental issues because of its cost-effectiveness and high removal performance. However, the complexity of the real environment is always ignored, which hinders the transfer of the BIT from lab-scale to commercial applications. Therefore, in this review, the analysis is performed separately on the internal side of the BIT (microbial fixation and growth) and on the external side of the BIT (function) to achieve effective BIT performance. Importantly, the internal two stages of BIT have been discussed concisely. Further, the usage of BIT in different areas is summarized precisely. Notably, the key impacts were systemically analyzed during BIT applications including environmental conditions and biochar types. Finally, the suggestions and perspectives are elucidated to solve current issues regarding BIT.

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment

Efficient wastewater treatment accompanied by sustainable "nutrients/pollutants waste-wastewater-resources/energy nexus" management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.

Immobilized enzyme for screening and identification of anti-diabetic components from natural products by ligand fishing

Diabetes is a chronic metabolic disease caused by insufficient insulin secretion and insulin resistance. Natural product is one of the most important resources for anti-diabetic drug. However, due to the extremely complex composition, this research is facing great challenges. After the advent of ligand fishing technology based on enzyme immobilization, the efficiency of screening anti-diabetic components has been greatly improved. In order to provide critical knowledge for future research in this field, the application progress of immobilized enzyme in screening anti-diabetic components from complex natural extracts in recent years was reviewed comprehensively, including novel preparation technologies and strategies of immobilized enzyme and its outstanding application prospect in many aspects. The basic principles and preparation steps of immobilized enzyme were briefly described, including entrapment, physical adsorption, covalent binding, affinity immobilization, multienzyme system and carrier-free immobilization. New formatted immobilized enzymes with different carriers, hollow fibers, magnetic materials, microreactors, metal organic frameworks, etc., were widely used to screen anti-diabetic compositions from various natural products, such as Ginkgo biloba, Morus alba, lotus leaves, Pueraria lobata, Prunella vulgaris, and Magnolia cortex. Furthermore, the challenges and future prospects in this field were put forward in this review.

Effects of Diamond Nanoparticles Immobilisation on the Surface of Yeast Cells: A Phenomenological Study

An interesting development of biotechnology has linked microbial cell immobilisation with nanoparticles. The main task of our research was to reveal the possible influences of differently electrically charged diamond nanoparticles upon physiological characteristics of the yeast Saccharomyces cerevisiae. It was revealed that the adverse impact of these nanoparticles can manifest not only against prokaryotes, but also against eukaryotic yeast cells. However, the obtained results also indicate that it is possible to reduce and, most likely, completely eliminate the dangerous effects of nanoparticles to cells by using special physical approaches. Comparison of non-arylated and arylated nanoparticles showed that in terms of changes in the physiological activity of cells, which are important to biotechnology and biomedicine, the selection of certain nanoparticles (non-arylated or arylated) may be necessary in each specific case, depending on the purpose of their use.

Development of multifarious carrier materials and impact conditions of immobilised microbial technology for environmental remediation: A review

Microbial technology is the most sustainable and eco-friendly method of environmental remediation. Immobilised microorganisms were introduced to further advance microbial technology. In immobilisation technology, carrier materials distribute a large number of microorganisms evenly on their surface or inside and protect them from external interference to better treat the targets, thus effectively improving their bioavailability. Although many carrier materials have been developed, there have been relatively few comprehensive reviews. Therefore, this paper summarises the types of carrier materials explored in the last ten years from the perspective of structure, microbial activity, and cost. Among these, carbon materials and biofilms, as environmentally friendly functional materials, have been widely applied for immobilisation because of their abundant sources and favorable growth conditions for microorganisms. The novel covalent organic framework (COF) could also be a new immobilisation material, due to its easy preparation and high performance. Different immobilisation methods were used to determine the relationship between carriers and microorganisms. Co-immobilisation is particularly important because it can compensate for the deficiencies of a single immobilisation method. This paper emphasises that impact conditions also affect the immobilisation effect and function. In addition to temperature and pH, the media conditions during the preparation and reaction of materials also play a role. Additionally, this study mainly reviews the applications and mechanisms of immobilised microorganisms in environmental remediation. Future development of immobilisation technology should focus on the discovery of novel and environmentally friendly carrier materials, as well as the establishment of optimal immobilisation conditions for microorganisms. This review intends to provide references for the development of immobilisation technology in environmental applications and to further the improve understanding of immobilisation technology.

Biosorption of heavy metals by microorganisms: Evaluation of different underlying mechanisms

Globally, ecotoxicologists, environmental biologists, biochemists, pathologists, and other experts are concerned about environmental contamination. Numerous pollutants, such as harmful heavy metals and emerging hazardous chemicals, are pervasive sources of water pollution. Water pollution and sustainable development have several eradication strategies proposed and used. Biosorption is a low-cost, easy-to-use, profitable, and efficient method of removing pollutants from water resources. Microorganisms are effective biosorbents, and their biosorption efficacy varies based on several aspects, such as ambient factors, sorbing materials, and metals to be removed. Microbial culture survival is also important. Biofilm agglomerates play an important function in metal uptake by extracellular polymeric molecules from water resources. This study investigates the occurrence of heavy metals, their removal by biosorption techniques, and the influence of variables such as those indicated above on biosorption performance. Ion exchange, complexation, precipitation, and physical adsorption are all components of biosorption. Between 20 and 35 °C is the optimal temperature range for biosorption efficiency from water resources. Utilizing living microorganisms that interact with the active functional groups found in the water contaminants might increase biosorption efficiency. This article discusses the negative impacts of microorganisms on living things and provides an outline of how they affect the elimination of heavy metals.

Immobilization of Biomass Materials for Removal of Refractory Organic Pollutants from Wastewater

In the field of environmental science and engineering, microorganisms, enzymes and algae are promising biomass materials that can effectively degrade pollutants. However, problems such as poor environmental adaptability, recycling difficulties, and secondary pollution exist in the practical application of non-immobilized biomass materials. Biomass immobilization is a novel environmental remediation technology that can effectively solve these problems. Compared with non-immobilized biomass, immobilized biomass materials have the advantages of reusability and stability in terms of pH, temperature, handling, and storage. Many researchers have studied immobilization technology (i.e., methods, carriers, and biomass types) and its applications for removing refractory organic pollutants. Based on this, this paper reviews biomass immobilization technology, outlines the mechanisms and factors affecting the removal of refractory organic pollutants, and introduces the application of immobilized biomass materials as fillers for reactors in water purification. This review provides some practical references for the preparation and application of immobilized biomass materials and promotes further research and development to expand the application range of this material for water purification.

Critical Review on Nanomaterials for Enhancing Bioconversion and Bioremediation of Agricultural Wastes and Wastewater

Anaerobic digestion (AD), microalgae cultivation, and microbial fuel cells (MFCs) are the major biological processes to convert organic solid wastes and wastewater in the agricultural industry into biofuels, biopower, various biochemical and fertilizer products, and meanwhile, recycle water. Various nanomaterials including nano zero valent irons (nZVIs), metal oxide nanoparticles (NPs), carbon-based and multicompound nanomaterials have been studied to improve the economics and environmental sustainability of those biological processes by increasing their conversion efficiency and the quality of products, and minimizing the negative impacts of hazardous materials in the wastes. This review article presented the structures, functionalities and applications of various nanomaterials that have been studied to improve the performance of AD, microalgae cultivation, and MFCs for recycling and valorizing agricultural solid wastes and wastewater. The review also discussed the methods that have been studied to improve the performance of those nanomaterials for their applications in those biological processes.

Biosorption optimization of lead(II) and cadmium(II) ions by two novel nanosilica-immobilized fungal mutants

AIMS

This study aims at immobilization of fungal mutants on nanosilica-carriers for designing efficient biosorbents as a significant new technology for decontamination practices and maximizing their heavy metal (HM) sorption proficiency through the experimental design methodology.

MATERIALS AND RESULTS

Endophytic fungal mutant strains, Chaetomium globosum El26 mutant and Alternaria alternata S5 mutant were heat inactivated then immobilized, each separately, on nanosilica (NSi) carriers to formulate two separated nano-biosorbents. The formulated NSi-Chaetomium globosum El26 mutant (NSi-Chae El26 m) was investigated for Pb⁺² uptake while, the formulated NSi-Alternaria alternata S5 mutant (NSi-Alt S5 m) was investigated for Cd⁺² uptake, each through a batch equilibrium protocol. Before and after the metal sorption process, the designed nano-biosorbents were characterized via scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier Transform Infrared analysis. Sorption pH, contact time, sorbent concentration, and initial HM concentration, were statistically optimized using a Box-Behnken design (BBD). Results showed that NSi-Chae El26 m was efficient in Pb⁺² uptake with maximum biosorption capacities of 199.0 while, NSi-Alt S5 m was efficient in Cd⁺² uptake with maximum biosorption capacities of 162.0 mg∙g^-1 . Moreover, the equilibrium data indicated that the adsorption of Pb⁺² and Cd⁺² by the tested nano-biosorbents fitted to the Freundlich isotherm.

CONCLUSIONS

The formulated nano-biosorbents resulted in higher HM biosorption of metal ions from aqueous solution than that obtained by the free fungal biomass. The biosorption statistical modelling described the interactions between the tested sorption parameters and predicted the optimum values for maximum HM biosorption capacity by the two designed nano-biosorbents.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings verify that members of the endophytic fungal genera Alternaria and Chaetomium are suitable to produce nano-biosorbents for decontamination practices after treatment by gamma mutagenesis, heat inactivation, and nanosilica immobilization. Moreover, statistical optimization can assist to evaluate the optimal conditions to produce such bioremediation material.

Microbial adaptation and impact into the pesticide's degradation

The imprudent use of agrochemicals to control agriculture and household pests is unsafe for the environment. Hence, to protect the environment and diversity of living organisms, the degradation of pesticides has received widespread attention. There are different physical, chemical, and biological methods used to remediate pesticides in contaminated sites. Compared to other methods, biological approaches and their associated techniques are more effective, less expensive and eco-friendly. Microbes secrete several enzymes that can attach pesticides, break down organic compounds, and then convert toxic substances into carbon and water. Thus, there is a lack of knowledge regarding the functional genes and genomic potential of microbial species for the removal of emerging pollutants. Here we address the knowledge gaps by highlighting systematic biology and their role in adaptation of microbial species from agricultural soils with a history of pesticide usage and profiling shifts in functional genes and microbial taxa abundance. Moreover, by co-metabolism, the microbial species fulfill their nutritional requirements and perform more efficiently than single microbial-free cells. But in an open environment, free cells of microbes are not much prominent in the degradation process due to environmental conditions, incompatibilities with mechanical equipment and difficulties associated with evenly distributing inoculum through the agroecosystem. This review highlights emerging techniques involving the removal of pesticides in a field-scale environment like immobilization, biobed, biocomposites, biochar, biofilms, and bioreactors. In these techniques, different microbial cells, enzymes, natural fibers, and strains are used for the effective biodegradation of xenobiotic pesticides.

E-waste mining and the transition toward a bio-based economy: The case of lamp phosphor powder

Abstract

Replacement of conventional hydrometallurgical and pyrometallurgical process used in E-waste recycling to recover metals can be possible.

The metallurgical industry has been considered biohydrometallurgical-based technologies for E-waste recycling.

Biorecovery of critical metals from phosphor powder from spent lamps is an example of transition to a bio-based circular economy.

E-waste contains economically significant levels of precious, critical metals and rare-earth elements (REE), apart from base metals and other toxic compounds. Recycling and recovery of critical elements from E-waste using a cost-effective technology are now among the top priorities in metallurgy due to the rapid depletion of their natural resources. This paper focuses on the perceptions of recovery of REE from phosphor powder from spent fluorescent lamps regarding a possible transition toward a bio-based economy. An overview of the worldwide E-waste and REE is also demonstrated to reinforce the arguments for the importance of E-waste as a secondary source of some critical metals. Based on the use of bioprocesses, we argue that the replacement of conventional steps used in E-waste recycling by bio-based technological processes can be possible. The bio-recycling of E-waste follows a typical sequence of industrial processes intensely used in classic pyro- and hydrometallurgy with the addition of bio-hydrometallurgical processes such as bioleaching and biosorption. We use the case study of REE biosorption as a new technology based on biological principles to exemplify the potential of urban biomining. The perspective of transition between conventional processes for the recovery of valuable metals for biohydrometallurgy defines which issues related to urban mining can influence the mineral bioeconomy. This assessment is necessary to outline future directions for sustainable recycling development to achieve United Nations Sustainable Development Goals.

Graphical Abstract

Bacterial Biosorbents, an Efficient Heavy Metals Green Clean-Up Strategy: Prospects, Challenges, and Opportunities

Rapid industrialization has led to the pollution of soil and water by various types of contaminants. Heavy metals (HMs) are considered the most reactive toxic contaminants, even at low concentrations, which cause health problems through accumulation in the food chain and water. Remediation using conventional methods, including physical and chemical techniques, is a costly treatment process and generates toxic by-products, which may negatively affect the surrounding environment. Therefore, biosorption has attracted significant research interest in the recent decades. In contrast to existing methods, bacterial biomass offers a potential alternative for recovering toxic/persistent HMs from the environment through different mechanisms for metal ion uptake. This review provides an outlook of the advantages and disadvantages of the current bioremediation technologies and describes bacterial groups, especially extremophiles with biosorbent potential for heavy metal removal with relevant examples and perspectives.

Treatment of dairy wastewater by immobilized microbial technology using polyurethane foam as carrier

The development of dairy industry is accompanied by large volumes of wastewater production, which is threaten to human's health and the biosphere. In this study, synthetic dairy wastewater was treated by immobilized microbial technology using polyurethane foam as carrier. Batch experiments were conducted to determine the effects of different operational parameters, and an up-flow immobilized microbial reactor was built to investigate long-term performance of the system. Batch experiments showed that COD, TN and NH₃-N dropped from 1932, 51.33 and 51.42 mg·L^-1 to 75.3, 5.17 and 4.54 mg·L^-1 after 48 h, respectively, at the optimum conditions (25 °C, pH 6.0). Besides, the reactor can remove 97.33% of COD, 96.46% of TN and 99.55% of NH₃-N with HRT of 24 h, which the average volume load was 1.93 kg COD·(m³·d)^-1. The analysis of microbial community determined that dominant bacteria at genus level were Acinetobacter, Fusibacter, Nannocystis and norank _f_NS9_marine_group.

Immobilized enzymes and cell systems: an approach to the removal of phenol and the challenges to incorporate nanoparticle-based technology

The presence of phenol in wastewater poses a risk to ecosystems and human health. The traditional processes to remove phenol from wastewater, although effective, have several drawbacks. The best alternative is the application of ecological biotechnology tools since they involve biological systems (enzymes and microorganisms) with moderate economic and environmental impact. However, these systems have a high sensitivity to environmental factors and high substrate concentrations that reduce their effectiveness in phenol removal. This can be overcome by immobilization-based technology to increase the performance of enzymes and bacteria. A key component to ensure successful immobilization is the material (polymeric matrices) used as support for the biological system. In addition, by incorporating magnetic nanoparticles into conventional immobilized systems, a low-cost process is achieved but, most importantly, the magnetically immobilized system can be recovered, recycled, and reused. In this review, we study the existing alternatives for treating wastewater with phenol, from physical and chemical to biological techniques. The latter focus on the immobilization of enzymes and microorganisms. The characteristics of the support materials that ensure the viability of the immobilization are compared. In addition, the challenges and opportunities that arise from incorporating magnetic nanoparticles in immobilized systems are addressed.

Microbial Technologies Employed for Biodegradation of Neonicotinoids in the Agroecosystem

Neonicotinoids are synthetic pesticides widely used for the control of various pests in agriculture throughout the world. They mainly attack the nicotinic acetylcholine receptors, generate nervous stimulation, receptor clot, paralysis and finally cause death. They are low volatile, highly soluble and have a long half-life in soil and water. Due to their extensive use, the environmental residues have immensely increased in the last two decades and caused many hazardous effects on non-target organisms, including humans. Hence, for the protection of the environment and diversity of living organism's the degradation of neonicotinoids has received widespread attention. Compared to the other methods, biological methods are considered cost-effective, eco-friendly and most efficient. In particular, the use of microbial species makes the degradation of xenobiotics more accessible fast and active due to their smaller size. Since this degradation also converts xenobiotics into less toxic substances, the various metabolic pathways for the microbial degradation of neonicotinoids have been systematically discussed. Additionally, different enzymes, genes, plasmids and proteins are also investigated here. At last, this review highlights the implementation of innovative tools, databases, multi-omics strategies and immobilization techniques of microbial cells to detect and degrade neonicotinoids in the environment.

Selective Adsorption and Efficient Degradation of Petroleum Hydrocarbons by a Hydrophobic/Lipophilic Biomass Porous Foam Loaded with Microbials

Highly efficient elimination of petroleum pollution is of great importance for addressing environmental issues and social sustainability. In this study, we demonstrate a novel strategy for efficient elimination of petroleum pollution by selective adsorption of it by an ultralight hydrophobic/lipophilic microorganism-loaded biomass porous foam (BTS-MSFT4@MTMS) followed by a green degradation of adsorbates under mild conditions. The porous structure of biomass porous foam (MSFT) could provide plenty of room for immobilization of Bacillus thuringiensis (BTS), while a simple surface modification of the MSFT load with a BTS strain (BTS-MSFT4) by methyltrimethoxysilane (MTMS) could change its wettability from hydrophilic to lipophilic, which makes selective adsorption of hydophobic petroleum pollution from water for biodegradation possible. As expected, using a petroleum n-hexadecane solution with a concentration of 3% as a model oily wastewater, the as-prepared BTS-MSFT4@MTMS possesses both a superior selective adsorption of ca. 99% and high degradation activity with a high degradation rate of up to 86.65% within 8 days under the conditions of 37 °C, 120 r min^-1, and pH = 7, while the degradation rates for the BTS-MSFT4 and the free BTS strain were measured to be only 81.62 and 65.65%, respectively, under the same conditions. In addition, the results obtained from the study on environment tolerance show that the BTS-MSFT4@MTMS exhibits a strong tolerance under different conditions with various pHs, temperatures, and initial concentrations. Compared with the existing methods for removal of petroleum pollution by direct adsorption of petroleum pollution via superoleophilic porous materials or applying free microorganisms for biodegradation only, which suffers the drawbacks of low selectivity or poor efficiency, our method has great advantages of cost-effectiveness, scalable fabrication, and high efficiency without secondary pollution. Moreover, such a two-in-one strategy by integration of both selective adsorption and biodegradation into biodegradable BTS-MSFT4@MTMS may particularly have great potential for practical application in environmental remediation.

Innovative method for encapsulating highly pigmented biomass from Aspergillus nidulans mutant for copper ions removal and recovery

Biosorption has been considered a promising technology for the treatment of industrial effluents containing heavy metals. However, the development of a cost-effective technique for biomass immobilization is essential for successful application of biosorption in industrial processes. In this study, a new method of reversible encapsulation of the highly pigmented biomass from Aspergillus nidulans mutant using semipermeable cellulose membrane was developed and the efficiency of the encapsulated biosorbent in the removal and recovery of copper ions was evaluated. Data analysis showed that the pseudo-second-order model better described copper adsorption by encapsulated biosorbent and a good correlation (r2 > 0.96) to the Langmuir isotherm was obtained. The maximum biosorption capacities for the encapsulated biosorbents were higher (333.5 and 116.1 mg g-1 for EB10 and EB30, respectively) than that for free biomass (92.0 mg g-1). SEM-EDXS and FT-IR analysis revealed that several functional groups on fungal biomass were involved in copper adsorption through ion-exchange mechanism. Sorption/desorption experiments showed that the metal recovery efficiency by encapsulated biosorbent remained constant at approximately 70% during five biosorption/desorption cycles. Therefore, this study demonstrated that the new encapsulation method of the fungal biomass using a semipermeable cellulose membrane is efficient for heavy metal ion removal and recovery from aqueous solutions in multiple adsorption-desorption cycles. In addition, this reversible encapsulation method has great potential for application in the treatment of heavy metal contaminated industrial effluents due to its low cost, the possibility of recovering adsorbed ions and the reuse of biosorbent in consecutive biosorption/desorption cycles with high efficiency of metal removal and recovery.

Kinetics and equilibrium study for the biosorption of lanthanum by Penicillium simplicissimum INCQS 40,211

Lanthanum (La) is a light rare-earth element that plays an essential role in manufacturing technological products, clean technologies, medical products, electron cathodes, scintillators, fluorescent lamps, and fertilizers. This study is the first investigation of La³⁺ biosorption using inactive lyophilized biomass from Penicillium simplicissimum INCQS 40,211. The maximum sorption capacity (q_max) for P. simplicissimum was 7.81 mg g^-1. La ³⁺ biosorption followed the Freundlich model, where the biosorption system possibly multilayer coverage of P. simplicissimum by lanthanum ions. The kinetic data for the adsorption process obeyed a pseudo-second-order (R ² > 0.92), indicating chemical sorption. The results indicated that inactive lyophilized biomass from Penicillium simplicissimum INCQS 40211are an excellent candidate for removing light rare-earth elements from aquatic environments.

Temperature-robust and ratiometric G-quadruplex proximate DNAzyme assay for robustly monitoring of uranium pollution and its microbial biosorbents screening

Uranium pollution in environment and food chain is a serious threat to public security and human health. Herein, we proposed a temperature-robust, ratiometric, and label-free bioassay based on G-quadruplex proximate DNAzyme (G4DNAzyme), accommodating us to precisely monitor uranium pollution and biosorption. The proximity of split G-quadruplex probes was proposed to sense UO₂²⁺-activated DNAzyme activity, thus eliminating the use of chemically labeled nucleic acid probes. And the simultaneous monitoring of G-quadruplex and double-stranded structures of DNAzyme probes contributed to a ratiometric and robust detection of UO₂²⁺. Particularly, the separation of enzymatic digestion and fluorescence monitoring endued a robust and highly responsive detection of UO₂²⁺ upon the temperature of enzymatic digestion process ranged from 18° to 41 °C. Consequently, G4DNAzyme assay allowed a robust, label-free and ratiometric quantification of uranium. We demonstrated the feasibility of G4DNAzyme assay for estimating uranium pollution in water and aquatic product samples. Ultimately, G4DNAzyme assay was adopted to serve as the platform to screen bacterial species and conditions for uranium biosorption, promising its roles in uranium associated biosafety control.

Monodisperse Selectively Permeable Hydrogel Capsules Made from Single Emulsion Drops

Capsules are often used to protect chemical and biological entities from the environment, to control the timing and location of their release, or to facilitate the collection of waste. Their performance depends on the thickness and composition of their shells, which can be closely controlled if capsules are made from double emulsion drops that are produced with microfluidics. However, the fabrication of such double emulsions is delicate, limiting throughput and increasing costs. Here, a fast, scalable method to produce monodisperse microcapsules possessing mechanically robust, thin, semipermeable hydrogel shells from single emulsion drops is introduced. This is achieved by selectively polymerizing reagents in close proximity to the drop surface to form a biocompatible 1.6 μm-thick hydrogel shell that encompasses a liquid core. The size-selective permeability of the shell enables the growth of living yeast and bacteria in their cores. Moreover, if capsules are loaded with adsorbents, they can repetitively remove waste products from water. The simplicity and robustness of the capsule fabrication makes the process scalable and cost effective. It has thus the potential to extend the use of calibrated capsules possessing well-defined dimensions to cost sensitive fields, including food, waste water treatment, or oil recovery.

Biosorption: A Review of the Latest Advances

Biosorption is a variant of sorption techniques in which the sorbent is a material of biological origin. This technique is considered to be low cost and environmentally friendly, and it can be used to remove pollutants from aqueous solutions. The objective of this review is to report on the most significant recent works and most recent advances that have occurred in the last couple of years (2019–2020) in the field of biosorption. Biosorption of metals and organic compounds (dyes, antibiotics and other emerging contaminants) is considered in this review. In addition, the use and possibilities of different forms of biomass (live or dead, modified or immobilized) are also considered.