Showing papers in "Environmental Chemistry Letters in 2020"
TL;DR: In this paper, the authors compared the impregnation method with the physical mixing method used in activating with alkali hydroxides and found that the activated carbon obtained through physical mixing had a higher porosity than the activated activated carbon produced by the impravnation method.
Abstract: Activated carbon refers to a wide range of carbonised materials of high degree of porosity and high surface area. Activated carbon has many applications in the environment and industry for the removal, retrieval, separation and modification of various compounds in liquid and gas phases. Selection of the chemical activator agent is a major step controlling the performance and applicability of activated carbon. Here, we review chemical activators used to produce activated carbon. We compare the impregnation method with the physical mixing method used in activating with alkali hydroxides. We selected 81 articles from Google Scholar, PubMed, Scopus, Science Direct, Embase and Medlin databases. Eighteen articles report the activation with potassium hydroxide, 17 with phosphoric acid, 15 with zinc chloride, 11 with potassium carbonate, nine with sodium hydroxide, and 11 with new activating agents. Activation with phosphoric acid is commonly used for lignocellulosic material and at lower temperatures. Zinc chloride generates more surface area than phosphoric acid but is used less due to environmental concerns. Potassium carbonate, in comparison with potassium hydroxide, produces higher yields and a higher surface area for the adsorption of large pollutant molecules such as dyes. Activating with potassium hydroxide in terms of surface area and efficiency shows better results than sodium hydroxide for various applications. Also, the comparison of the physical mixing method and the impregnation method in activation with alkali metals indicates that the activated carbon obtained through physical mixing had a higher porosity than the activated carbon produced by the impregnation method.
422 citations
TL;DR: In this paper, the main strategies for climate change abatement, namely conventional mitigation, negative emissions and radiative forcing geoengineering, are reviewed, and it is evident that conventional mitigation efforts alone are not sufficient to meet the targets stipulated by the Paris agreement; therefore, the utilization of alternative routes appears inevitable.
Abstract: Climate change is defined as the shift in climate patterns mainly caused by greenhouse gas emissions from natural systems and human activities. So far, anthropogenic activities have caused about 1.0 °C of global warming above the pre-industrial level and this is likely to reach 1.5 °C between 2030 and 2052 if the current emission rates persist. In 2018, the world encountered 315 cases of natural disasters which are mainly related to the climate. Approximately 68.5 million people were affected, and economic losses amounted to $131.7 billion, of which storms, floods, wildfires and droughts accounted for approximately 93%. Economic losses attributed to wildfires in 2018 alone are almost equal to the collective losses from wildfires incurred over the past decade, which is quite alarming. Furthermore, food, water, health, ecosystem, human habitat and infrastructure have been identified as the most vulnerable sectors under climate attack. In 2015, the Paris agreement was introduced with the main objective of limiting global temperature increase to 2 °C by 2100 and pursuing efforts to limit the increase to 1.5 °C. This article reviews the main strategies for climate change abatement, namely conventional mitigation, negative emissions and radiative forcing geoengineering. Conventional mitigation technologies focus on reducing fossil-based CO2 emissions. Negative emissions technologies are aiming to capture and sequester atmospheric carbon to reduce carbon dioxide levels. Finally, geoengineering techniques of radiative forcing alter the earth’s radiative energy budget to stabilize or reduce global temperatures. It is evident that conventional mitigation efforts alone are not sufficient to meet the targets stipulated by the Paris agreement; therefore, the utilization of alternative routes appears inevitable. While various technologies presented may still be at an early stage of development, biogenic-based sequestration techniques are to a certain extent mature and can be deployed immediately.
391 citations
TL;DR: In this article, a review of microplastics occurrence, transport, raw polymers and additives, toxicity and methods of removal is presented, including physical sorption and filtration, biological removal and ingestion, and chemical treatments.
Abstract: The production of fossil fuel-derived, synthetic plastics is continually increasing, while poor plastic waste management has recently induced severe pollution issues. Microplastics are plastic particles smaller than 5 mm. Microplastics are ubiquitous and slowly-degrading contaminants in waters and soils. Microplastics have long residence time, high stability, high potential of being fragmented and can adsorb other contaminants. Many aquatic species contain microplastics, which are in particular easily accumulated by planktonic and invertebrate organisms. Then, microplastics are transferred along food chains, leading to physical damages, decrease in nutritional diet value and exposure of the living organism to pathogens. Raw plastics contain chemical additives such as phthalates, bisphenol A and polybrominated diphenyl ethers that may induce toxic effects after ingestion by living organisms. Furthermore, the adsorption capability of microplastics makes them prone to carry several contaminants. Methods to remove microplastics from water and other media are actually needed. Here, we review microplastics occurrence, transport, raw polymers and additives, toxicity and methods of removal. Removal methods include physical sorption and filtration, biological removal and ingestion, and chemical treatments. Mechanisms, efficiency, advantages, and drawbacks of various removal methods are discussed.
264 citations
TL;DR: The properties, applications and toxicity of metal and non-metal-based nanoparticles are reviewed and exposure to nanoparticles could induce the production of reactive oxygen species (ROS), which is a predominant mechanism leading to toxicity.
Abstract: Nanotechnology has recently found applications in many fields such as consumer products, medicine and environment Nanoparticles display unique properties and vary widely according to their dimensions, morphology, composition, agglomeration and uniformity states Nanomaterials include carbon-based nanoparticles, metal-based nanoparticles, organic-based nanoparticles and composite-based nanoparticles The increasing production and use of nanoparticles result in higher exposure to humans and the environment, thus raising issues of toxicity Here we review the properties, applications and toxicity of metal and non-metal-based nanoparticles Nanoparticles are likely to be accumulated in sensitive organs such as heart, liver, spleen, kidney and brain after inhalation, ingestion and skin contact In vitro and in vivo studies indicate that exposure to nanoparticles could induce the production of reactive oxygen species (ROS), which is a predominant mechanism leading to toxicity Excessive production of ROS causes oxidative stress, inflammation and subsequent damage to proteins, cell membranes and DNA ROS production induced by nanoparticles is controlled by size, shape, surface, composition, solubility, aggregation and particle uptake The toxicity of a metallic nanomaterial may differ depending on the oxidation state, ligands, solubility and morphology, and on environmental and health conditions
243 citations
TL;DR: In this article, the authors review aqueous chromium species, their toxicity and methods to remove Cr such as membrane filtration, chemical precipitation, ion exchange, adsorption electrocoagulation, electrochemical reduction, electrodialysis, electrodeionization, photocatalysis and nanotechnology.
Abstract: Chromium is a potentially toxic and carcinogenic metal originating from natural processes and anthropogenic activities such as the iron steel, electroplating and leather industries. Therefore, chromium should be removed from wastewater to avoid environmental pollution and to recycle chromium in the context of the future circular economy. Here we briefly review aqueous Cr species, their toxicity and methods to remove Cr such as membrane filtration, chemical precipitation, ion exchange, adsorption electrocoagulation, electrochemical reduction, electrodialysis, electrodeionization, photocatalysis and nanotechnology.
241 citations
TL;DR: Green methods for the fabrication of quantum dots, and biomedical and biotechnological applications are reviewed.
Abstract: Carbon and graphene quantum dots are prepared using top-down and bottom-up methods. Sustainable synthesis of quantum dots has several advantages such as the use of low-cost and non-toxic raw materials, simple operations, expeditious reactions, renewable resources and straightforward post-processing steps. These nanomaterials are promising for clinical and biomedical sciences, especially in bioimaging, diagnosis, bioanalytical assays and biosensors. Here we review green methods for the fabrication of quantum dots, and biomedical and biotechnological applications.
239 citations
TL;DR: In this article, a review of cellulose production methods, properties and applications focusing on the food industry, biomedical materials and electronic devices is presented, and the increase in the number of publications on nanocellulose is also discussed.
Abstract: Cellulose is the main structural component of plant cell walls. Cellulose is a fibrous, water-insoluble substance and is considered to be the most abundant bio-derived polymer on earth. From an industrial perspective, plant cellulose has been the mainstay of the wood industries for the past 100 years. The hierarchical organization and semicrystalline nature of cellulose found in plant fibers allows the extraction of nanofibers and nanocrystals using mechanical and chemical top-down de-structuring strategies. Bacterial cellulose has also been increasingly investigated. Bacterial cellulose is composed of cellulose nanofibers secreted extracellularly by some bacteria; bacterial cellulose is therefore obtained using bottom-up synthesis. The unique nanofibrillar structure of bacterial cellulose confers excellent physical and mechanical properties such as high porosity, high elastic modulus and high crystallinity. Research on nanocellulose is accelerating due actual fossil fuel issues such as CO2 emissions, plastic pollution and lack of renewable energy. Nanocellulose materials are non-toxic, biodegradable and recyclable, with no adverse effects on health and the environment. Here, we review cellulose production methods, properties and applications, focusing on the food industry, biomedical materials and electronic devices. We compare vegetal nanocellulose and bacterial cellulose. The increase in the number of publications on nanocellulose is also discussed.
157 citations
TL;DR: In this paper, a review of microplastic contamination in freshwater systems with focus on adsorption of heavy metals is presented, where the authors find that microplastics may adsorb and carry other aquatic pollutants such as heavy metals, and combined toxic effects include endocrine disrupting and reduced predatory behavior of aquatic carnivores.
Abstract: The worldwide contamination of waters by microplastics is an emerging health and environmental issue. Despite being relatively inert, microplastics may adsorb and carry other aquatic pollutants such as heavy metals. Adsorption of heavy metals onto microplastics is a spontaneous process controlled by the microplastic surface. Marine microplastics have been well discussed, yet there are actually a few reviews on microplastics in freshwater. Here, we review microplastic contamination in freshwater systems with focus on adsorption of heavy metals. We present microplastic abundance, distribution, impact of microplastic size, affinity for heavy metals and combined toxic effects of the co-occurrence of microplastic and heavy metals. Remarkably, the concentration of metals on polystyrene and polyvinyl chloride was 800 times higher than in the surrounding environment. Combined toxic effects include endocrine disrupting and reduced predatory behavior of aquatic carnivores.
153 citations
TL;DR: In this article, the synthesis of chalcones and their biological activities with focus on structure-activity relationships are discussed, and the properties, biosynthesis and structural diversity of natural chalcone are reviewed.
Abstract: Chalcone is an aromatic ketone that forms the central core of many important biological compounds, which are known as chalcones. Chalcones are the biogenetic precursors of flavonoids and isoflavonoids, which are abundant in plants. Chalcones are active lead molecules in medicinal chemistry for the discovery of new drugs. Here, we review properties, biosynthesis and structural diversity of natural chalcones. Then, we present the synthesis of chalcones and their biological activities with focus on structure–activity relationships. Pharmaceutically important and patented chalcones are also discussed.
142 citations
TL;DR: Hemp is a high-yielding annual industrial crop grown providing fibers from hemp stalk and oil from hemp seeds as mentioned in this paper, which has been used for the production of apparels, fabrics, papers, cordages and building materials.
Abstract: The hemp plant Cannabis sativa Linn, referring to industrial hemp, is a high-yielding annual industrial crop grown providing fibers from hemp stalk and oil from hemp seeds. Although hemp is a niche crop, hemp production is currently undergoing a renaissance. More than 30 countries grow hemp, with China being the largest hemp producing and exporting country. Europe and Canada are also important actors in the global hemp market. Traditionally, hemp as a fiber plant has been used for the production of apparels, fabrics, papers, cordages and building materials. The hurds, as waste by-product of fiber production, were used for bedding of animals, the seeds for human nutrition, e.g., as flour, and the oil for a wide range of purposes, from cooking to cosmetics. Hemp has also been an important crop throughout human history for medicine. Other more recent applications include materials for insulation and furniture, automotive composites for interior applications and motor vehicle parts, bioplastics, jewelry and fashion sectors, animal feed, animal bedding, and energy and fuel production. Foods containing hemp seed and oil are currently marketed worldwide for both animal and human nutrition. They also find applications in beverages and in neutraceutical products. Hemp oil is also used for cosmetics and personal care items, paints, printing inks, detergents and solvents. It is estimated that the global market for hemp consists of more than 25,000 products. Currently, the construction and insulation sector, paper and textile industries, and food and nutrition domains are the main markets while the cosmetics and automotive sector are growing markets. Innovative applications, e.g., in the medical and therapeutic domains, cosmeceuticals, phytoremediation, acoustic domain, wastewater treatment, biofuels, biopesticides and biotechnology, open new challenges. Hemp is also the object of numerous fundamental studies. This review presents and discusses the traditional and new uses of industrial hemp.
139 citations
TL;DR: In this paper, the authors proposed that biofuel from crop residues can be promoted by government subsidies to reduce the fuel price and meet the requirement of industries, transportation and agricultural sectors.
Abstract: Energy demands, pollution and global warming induced by globalization are rising, thus calling for alternative sources of energies. In particular, biofuels are increasingly used for transportation, electric power and heat energy generation. Biofuels can mitigate greenhouse gas emissions by up to 50%. Biofuels are produced from organic matter and waste such as dry lignocellulose, algae, yeast, restaurant greases, food grain, non-food grain and animal fats. Biofuel from crop residues can be promoted by government subsidies to reduce the fuel price and meet the requirement of industries, transportation and agricultural sectors.
TL;DR: Chitosan, a naturally occurring polysaccharide obtained from chitin, has recently drawn attention because chitOSan is non-toxic, biocompatible, biodegradable, stable and sterilizable.
Abstract: Polymers are used in drug delivery devices for drug encapsulation and release. Natural polymers often have advantages such as biocompatibility, biodegradability and biologically recognizable moieties which support cellular activities, compared to synthetic polymers. Chitosan, a naturally occurring polysaccharide obtained from chitin, has recently drawn attention because chitosan is non-toxic, biocompatible, biodegradable, stable and sterilizable. The additional qualities of chitosan are the release rate of drug, easy modification, cross-linking ability with other polymers, antimicrobial properties, gel forming ability, bioadhesion, immunostimulation, activation of macrophages and gas permeability. Here, I review applications of chitosan in drug delivery. The properties of chitin and chitosan, and the mechanisms of drug release are also presented.
TL;DR: Chitosan bound enzymes, as compared to free enzymes, have improved the biocatalytic performances due to exceptionally high operational stability and reusability.
Abstract: Enzymes of industrial importance are primarily employed for biotechnological applications. However, high-cost and instability issues of purified enzymes hamper their usage. Multiple reuses rather than the single use is more cost-effective. A robuster bioprocess is feasible by enzyme immobilization. Performance of immobilized enzymes depends on the nature of support materials. Chitin and its derivatives-based supports offer stability and cost-effective bioprocessing. Chitosan is biocompatible, biodegradable, non-toxic and has multiple functional groups. A variety of supports such as chitosan, chitosan film, chitosan nanoparticle and chitosan nanocomposite are employed for enzyme immobilization. Chitosan bound enzymes, as compared to free enzymes, have improved the biocatalytic performances due to exceptionally high operational stability and reusability. Here we review enzymes immobilized on chitin/chitosan supporting materials with applications ranging from agriculture to drug delivery.
TL;DR: In this article, the efficacy of unmodified and modified carbon nanotubes for the removal of dyes from wastewater has been reviewed and shown that chemical modification leads to an improvement of the adsorption capacity.
Abstract: Contamination of water is calling for new techniques to provide safe and clean water for drinking and other usages. Among existing techniques of wastewater treatment, adsorption is one of the most efficient methods. Recently, carbon nanotube-based adsorbents are attracting research and industrial attention due to their large surface area, cylindrical hollow structure and well-flourished mesopores. Raw carbon nanotubes can be modified and adapted to the intended applications and targeted pollutants. Here we review the efficacy of unmodified and modified carbon nanotubes for the removal of dyes from wastewater. Reports show that chemical modification leads to an improvement of the adsorption capacity. The adsorption of dyes on carbon nanotubes depends on the nature of the adsorbent and adsorbate. Adsorption mechanisms involve van der Waals forces, π–π stacking, hydrophobic interactions, hydrogen bonding and electrostatic interactions. Nonetheless, hydrophobicity and cost actually restrict practical applications.
TL;DR: Alternative technologies for the removal of endocrine disruptors from aqueous matrices are reviewed, with focus on adsorption, membrane separation and biodegradation.
Abstract: Rising anthropogenic activities have increased waste production and, in turn, the concentration of contaminants in waters. In particular, endocrine disruptors are natural and synthetic contaminants that cause many health problems. Endocrine disruptors bioaccumulate and alter the endocrine systems of both humans and wildlife. Endocrine disruptors are health hazards even at low concentrations. Their recalcitrant properties make the current water and wastewater management system inefficient for their removal. Hence, new removal methods need to be designed and employed. Here, we review alternative technologies for the removal of endocrine disruptors from aqueous matrices, with focus on adsorption, membrane separation and biodegradation. The efficiency, materials, methods, advantages and disadvantages of these treatments are analysed and compared. The main endocrine disruptors include parabens, bisphenols, phthalates, estradiols, nonylphenols and some pesticides.
TL;DR: In this article, the use of natural banana peel for the biosorption of pollutants from water is discussed, and the factors controlling pollutants removal, and regeneration and reuse of the biosorbent.
Abstract: Pollution of environmental waters and ecosystems is increasing. Adsorption is an effective technique for water decontamination, but is limited by the cost of commercial adsorbents such as activated carbon. Research has thus focused on the recycling and transformation of biowaste as low-cost, biodegradable adsorbents. In particular, banana peel is promising for commercial use due to its wide availability and efficiency. Here, we review the use of natural banana peel for the biosorption of pollutants from water. We discuss the factors controlling pollutants removal, and the regeneration and reuse of the biosorbent. pH of 5.0 to 7.0 is favorable for the removal of cationic pollutants, while pH of 2.0 to 4.0 is suitable for anionic pollutants. Generally, higher pollutant concentration induces lower removal, whereas higher banana peel dosage induces higher removal. Banana peel exhibits efficient removal of pollutants at various temperatures, with adsorption capacities mostly within 1–100 mg/g. Nitric acid is the most efficient eluent for heavy metal desorption from banana peel. Most studies showed efficient biosorbent reuse up to five cycles and above. We also discuss the thermodynamics, kinetics and isotherms of the adsorption process.
TL;DR: This work reviews the synthesis and applications of biopolymeric nanomaterials for photocatalytic degradation of azo dyes, and focuses on conducting biopolymers incorporating metal, metal oxide, metal/metal oxide and metal sulphide for improved biodegradation.
Abstract: Pure and drinkable water will be rarer and more expensive as the result of pollution induced by industrialisation, urbanisation and population growth. Among the numerous sources of water pollution, the textile industry has become a major issue because effluents containing dyes are often released in natural water bodies. For instance, about two years are needed to biodegrade dye-derived, carcinogenic aromatic amines, in sediments. Classical remediation methods based upon physicochemical reactions are costly and still generate sludges that contain amine residues. Nonetheless, recent research shows that nanomaterials containing biopolymers are promising to degrade organic pollutants by photocatalysis. Here, we review the synthesis and applications of biopolymeric nanomaterials for photocatalytic degradation of azo dyes. We focus on conducting biopolymers incorporating metal, metal oxide, metal/metal oxide and metal sulphide for improved biodegradation. Biopolymers can be obtained from microorganisms, plants and animals. Unlike fossil-fuel-derived polymers, biopolymers are carbon neutral and thus sustainable in the context of global warming. Biopolymers are often biodegradable and biocompatible.
TL;DR: Biofuel production from microalgae is reviewed, including cultivation, harvesting, drying, extraction and conversion of microalgal lipids, which can be achieved by two-stage culture strategies, which is a win–win approach because it solves the conflicts between cell growth and biomass accumulation.
Abstract: The shortage of fossil fuels is actually a major economic issue in the context of increasing energy demand. Renewable energies are thus gaining in importance. For instance, microalgae-based fuels are viewed as an alternative. Microalgae are microscopic unicellular plants, which typically grow in marine and freshwater environments. They are fast growing, have high photosynthetic efficiency, and have relatively small land requirement and water consumption in comparison with conventional land crops biofuels. Nonetheless, selling biofuels is still limited by high cost. Here, we review biofuel production from microalgae, including cultivation, harvesting, drying, extraction and conversion of microalgal lipids. Cost issues may be solved by upstream and downstream measures: (1) upstream measures, in which highly productive strains are obtained by strain selection, genetic engineering and metabolic engineering, and (2) downstream measures, in which high biofuels yields are obtained by enhancing the cellular lipid content and by advanced conversion of microalgal biomass to biofuels. Maximum biomass and high biofuels production can be achieved by two-stage culture strategies, which is a win–win approach because it solves the conflicts between cell growth and biomass accumulation.
TL;DR: In this paper, the authors discuss the applications and benefits of using ethylene scavengers in packages and improve the efficiency of these scavengers using atmospheric packaging tools, which can prolong the shelf life and retain the original food quality.
Abstract: Many fruits and vegetables are sensitive to ethylene, which upon prolonged exposure induces the deterioration of food quality, such as change in taste, odour and colour, or microbial growth. Therefore, ethylene scavengers in packages can be used to limit ethylene accumulation. Ethylene scavengers extend the shelf life and retain the original food quality. Here, we review ethylene scavenging systems such as potassium carbonate, palladium, natural clays, titanium dioxide-based, electron-deficient dienes and trienes. Ethylene scavenging is done by chemical reactions and physical adsorption. We then discuss the applications and benefits of ethylene scavengers in packages. The efficiency of ethylene scavengers is improved using atmospheric packaging tools.
TL;DR: In this article, the authors review mechanisms and applications of carbon-based nanomaterials for the adsorption and photocatalytic removal of organic and inorganic pollutants in wastewaters.
Abstract: The deterioration of water quality by pollutants is a major health issue. Actual remediation methods are limited, and, as a consequence, there is a need for new remediation technologies. In particular, nanomaterials of unique properties have been recently developed for remediation. Here, we review mechanisms and applications of carbon-based nanomaterials for the adsorption and photocatalytic removal of organic and inorganic pollutants in wastewaters. Nanomaterials allow enhanced adsorption due to strong interactions between pollutants and adsorption sites. In photocatalysis, enhanced efficiency is attributed to the improved light harvesting and reduced recombination of photo-induced electrons and holes.
TL;DR: Experiments reveal that excessive glyphosate use induces stress on crops and on non-target plants, and is toxic for mammalians, microorganisms and invertebrates, and the long half-life period of glyphosate and its metabolites under different environmental conditions is a major concern.
Abstract: The herbicide glyphosate is widely used to control weeds in grain crops. The overuse of glyphosate has induced issues such as contamination of surface water, decreased soils fertility, adverse effects on soil microbiota and possible incorporation in food chains. Here we review biochemical, agricultural, microbiological and analytical aspects of glyphosate. We discuss uptake, translocation, toxicity, degradation, complexation behaviour, analytical monitoring techniques and resistance emergence in crops. We provide data of glyphosate toxicity on different ecosystems. Experiments reveal that excessive glyphosate use induces stress on crops and on non-target plants, and is toxic for mammalians, microorganisms and invertebrates. The long half-life period of glyphosate and its metabolites under different environmental conditions is a major concern. Development of analytical methods for the detection of glyphosate is important because glyphosate has no chromophoric or fluorophoric groups.
TL;DR: In this article, a review of green solvents employed for carbon capture, with emphasis on ionic liquids, deep eutectic and liquid polymers, is presented.
Abstract: Global warming is a critical issue resulting partly from increasing carbon dioxide emissions. Technologies have been developed to capture carbon dioxide followed by storage or utilization, yet techniques are limited by the use of toxic solvents and the generation of harmful by-products. Research in green chemistry has designed green solvents which are non-toxic, efficient and environmentally friendly. Here we review green solvents employed for carbon capture, with emphasis on ionic liquids, deep eutectic solvents and liquid polymers. Solvent performance depends on temperature, density and viscosity. Deep eutectic solvents appear as the most advanced solvents with capacities reaching up to 4.292 g CO2 per g of solvent. Ionic liquids have shown CO2 uptakes of 4.72 mol of CO2/mol of solvent, but are less efficient on average. Liquid polymers display capacities of up to 1.357 mol of CO2/mol of solvent.
TL;DR: The types and biosynthesis of microalgal lipids are reviewed, and genetic engineering and manipulation of cultivation conditions for enhancing lipid production are discussed, with focus on green techniques.
Abstract: Rise in human population and gradual decline in fossil fuels are increasing the demand for fuels and causing an upsurge in fuel prices and global warming. Concomitantly, consumers have raised their health awareness by taking various supplements, e.g. omega-3 fatty acids, thus calling for advanced nutraceuticals. Both issues are addressed by recent research on microalgae, which can be easily cultivated to produce lipidic biofuels and active drugs. Here, we reviewed the types and biosynthesis of microalgal lipids. We discuss genetic engineering and manipulation of cultivation conditions for enhancing lipid production. We present techniques for lipid extraction, with focus on green techniques. We also discuss the technical and economic challenges in manufacturing microalgae-based biofuels and other bioproducts at the industrial scale. Last, the market potentials and further research directions for future commercialization of microalgae lipids are discussed.
TL;DR: In this paper, a review of the mechanical and barrier properties of composite films based on chitosan is presented, and the major points are: (1) compared with synthetic plastic films, an important limitation of CHITOSAN-based films is their mechanical properties, especially their capacity to elongation; (2) CHITO is a polymer that allows an easy combination with other polysaccharides, plasticizers, proteins and lipids; (3) this allows to develop mixed components and modify the film-properties according to the nature of the food to be
Abstract: Chitosan is an alternative to synthetic polymers for food packaging. The mechanical and barrier properties of pure chitosan films are promising. Chitosan properties can be modified by combining chitosan with other components such as plasticizers, other polysaccharides, proteins and lipids. Here we review mechanical and barrier properties of composite films based on chitosan. The major points are: (1) compared with synthetic plastic films, an important limitation of chitosan-based films is their mechanical properties, especially their capacity to elongation; (2) chitosan is a polymer that allows an easy combination with other polysaccharides, plasticizers, proteins and lipids; (3) this allows to develop mixed components and modify the film properties according to the nature of the food to be packaged.
TL;DR: In this article, a review of the conversion of algal biomass into energy by fast, slow, microwave and catalytic pyrolysis is presented, along with a classification of algae, including macroalgae and microalgae.
Abstract: Climate change issues are calling for the design of renewable sources of energy. In particular, biomass energy from algae is encouraging because production of algae at the commercial scale can be done successfully with various techniques. Here, we review the conversion of algal biomass into energy by fast, slow, microwave and catalytic pyrolysis. The article details algae classification; cultivation of macroalgae and microalgae; pyrolysis parameters; production of biochar, bio-oil and biogas; and types of pyrolysis.
TL;DR: In this paper, the authors present recent experimental findings on the synthesis of magnetic adsorbents, focusing on magnetization methods, the main aspects of adsorption and adsorbent regeneration.
Abstract: Environmental pollution by toxic metals causes serious health complications, thus requiring advanced remediation methods for waters and effluents. In particular, chitosan-based magnetic materials have been recently developed to remove metals from aqueous solutions, industrial wastewater and water from lakes and rivers. Here, we review the adsorption of lead (Pb), cadmium (Cd), mercury (Hg) and arsenic (As) using magnetic chitosan. The manuscript presents recent experimental findings on the synthesis of magnetic adsorbents, focusing on magnetization methods, the main aspects of adsorption and adsorbent regeneration. The major findings are: (1) Kinetic patterns are mostly correlated by pseudo-second-order equations. (2) Langmuir isotherm model provides satisfactory estimations of monolayer capacity, the highest reported values being 341.7 mg/g for lead, 152 mg/g for mercury, 321.9 mg/g for cadmium and 65.5 mg/g for arsenic. (3) Most magnetic chitosan-based adsorbents keep their magnetic features and adsorption efficiency in consecutive adsorption–desorption runs. Overall, most chitosan-based magnetic adsorbents provide effective uptake of toxic metals ions from aqueous media and have a high degree of reusability.
TL;DR: The review provides important information on the role of different root exudates to subsist Cd stress in plants naturally, particularly by reducing the dependence on synthetic amendments to enhance Cd-tolerance and its aquisition in plants.
Abstract: In the past few decades, cadmium (Cd) as soil contaminant is a major problem for the mankind. Cd contamination of soil and food crops is a critical environmental concern as it deteriorates the soil quality and creates threat to the food safety and human health. High Cd concentration in soils pose negative effects on the plants at physiological, structural and molecular levels. Secretion of certain secondary metabolites in the rhizosphere is a survival mechanism adopted by plants to tolerate and encounter Cd toxicity. Under metal-stressed conditions, secretion of root exudates in soil increases the external detoxification strategies of the plants. The secreted phytochemicals are gaseous compounds, inorganic and especially organic in composition. In plants, the role of these metabolites to confront Cd toxicity and induce tolerance under Cd distress is underrated. The review paper focuses on Cd sources, factors that affect its bioavailability, uptake and toxicity in the plants. Furthermore, it also highlights the contemporary progression in our understanding on the mechanisms of root exudation in plants and the effect of Cd toxicity on the root exudation. Finally, the review provides important information on the role of different root exudates to subsist Cd stress in plants naturally, particularly by reducing the dependence on synthetic amendments to enhance Cd-tolerance and its aquisition in plants.
TL;DR: Mechanisms by which pollutants disrupt epigenetic factors are reviewed, focusing on the impact of arsenic, cadmium, nickel, mercury, benzene, bisphenol A, dioxin, hexahydro-1,3,5-trinitro-4-triazine and diethylstilbestrol.
Abstract: Pollution is a major issue impacting the health of life and ecosystems. In particular, some pollutants may alter gene expression by epigenetic mechanisms such as deoxyribonucleic acid (DNA) methylation, histone modifications, and microRNA (miRNA) expression. Epigenetics is the study of heritable changes without alteration in the DNA sequence. In the healthy state, the coordinated actions of interconnected epigenetic factors are responsible for proper cell development and cell regulation. Epigenetic mechanisms are tissue-specific; hence, a pollutant may or may not cause an alteration depending on the type of tissue. Here we review mechanisms by which pollutants disrupt epigenetic factors. We focus on the impact of arsenic, cadmium, nickel, mercury, benzene, bisphenol A, dioxin, hexahydro-1,3,5-trinitro-1,3,5-triazine and diethylstilbestrol. A list of diseases related to epigenetic factors and heavy metals exposure is provided.
TL;DR: In this paper, a review of advanced oxidation processes with focus on ozonation and photocatalysis for the degradation of organic and microbial contaminants in wastewaters is presented, which resulted in faster reaction kinetics, enhanced pollutant degradation with mineralization achieved in most cases, and reduction of toxicity up to 100%.
Abstract: Industrialization is inducing water pollution by pharmaceuticals, fertilizers and cosmetics. Many emerging pollutants are non-biodegradable, toxic and recalcitrant to conventional wastewater treatments, thus calling for improved remediation techniques such as advanced oxidation processes which allow complete mineralization of pollutants. Here we review advanced oxidation processes with focus on ozonation and photocatalysis for the degradation of organic and microbial contaminants in wastewaters. Ozonation efficiency is limited by ozone-resistant pollutants, whereas photocatalysis is slow due to charge recombination, yet photocatalytic ozonation overcomes these limitations. Photocatalytic ozonation indeed shows synergy indices of up to 5.8 for treating wastewaters. This resulted in faster reaction kinetics, enhanced pollutant degradation with mineralization achieved in most cases, and reduction of toxicity up to 100%. We also discuss energy requirements.
TL;DR: In this paper, the authors reviewed the feasibility of membrane separation for biogas upgrading by membrane separation and discussed gas permeation, membrane materials, membrane modules, multi-stage configurations, process configurations, and commercial biOGas plants.
Abstract: Global warming caused by increasing CO2 atmospheric levels is calling for sustainable fuels For instance, biomethane produced by biogas upgrading is a promising source of green energy Technologies to upgrade biogas include chemical absorption, water scrubbing, physical absorption, adsorption, cryogenic separation and membrane separation Historically, water scrubbing was preferred because of the simplicity of this operation However, during the last decade, membrane separation stood out due to its promising economic viability with investment costs of 3500–7500 €/(m3/h) and operational costs of 75–125 €/(m3/h) Here we review biogas upgrading by membrane separation We discuss gas permeation, membrane materials, membrane modules, process configurations and commercial biogas plants Polymeric materials appear as most adequate for membranes aimed to upgrade biogas Concerning membrane modules, hollow fibers are the cheapest (15–9 €/m2) Multistage configurations provide high methane recovery, of 99%, and purity, of 95–99%, compared to single-stage configurations