The role of clays, clay minerals and clay-based materials for nitrate removal from water systems: A review
Excessive use of nitrogenous fertilizers has led to increased nitrate concentrations in groundwater that pose a threat to human health, via nitrate-contaminated potable water, and contribute to eutrophication. The elimination of nitrate from water systems has been thoroughly examined; however, unconventional and low-cost technologies are greatly needed. Clays and clay minerals are widely-used for environmental applications, mostly due to their non-toxicity, worldwide abundance, low cost and physicochemical properties (high surface area, ion exchange capacity, high sorption and catalytic properties). Most are used for the degradation of cationic pollutants, nevertheless, they can be equally efficient at anionic decontamination, depending on the modification process they have undergone, or the materials they are combined with. This review aims to assemble the available literature research on the application of clays and clay minerals as well as the mechanisms that lead to successful removal of nitrate from water. The main characteristics of clays and clay minerals in nitrate uptake are evaluated and the known shortcomings of their application discussed, leading to suggestions for further research.
Preparation of porous adsorbent via Pickering emulsion template for water treatment: A review
Porous materials as emerging potential adsorbents have received much more attention because they are capable of capturing various pollutants with fast adsorption rate, high adsorption capacity, good selectivity and excellent reusability. In order to prepare porous materials with decent porous structure, Pickering emulsion template method has been proved to be one of the most effective technologies to create pore structure. This paper reviewed comprehensively the latest research progress on the preparation of porous materials from various Pickering emulsions and their applications in the decontamination of pollutants (e.g., heavy metal ions, organic pollutants) and in the oil/water separation. It was expected that the summaries and discussions in this review will provide insights into the design and fabrication of new efficient porous adsorbents, and also give us a better understanding of the subject.
Bio-inspired and biomaterials-based hybrid photocatalysts for environmental detoxification: A review
New materials tend to revolutionize scientific community and human race on a larger level. Scientists worldwide have not just been working on some wondrous materials with superior properties but have progressively focused on greener bio-inspired or bio-compatible materials for sustainable development. An increasing number of researchers have been working on using biomaterials as a part of photocatalysts for stability, bio-compatibility, generation of more reactive oxygen species and enhancement of optical absorption. In this review we have focussed on photocatalysts based on biopolymers, biochar, carbons, enzymes and proteins. This review presents various types of bio-inspired nanomaterials and their use as sustainable photocatalysts for degrading various venomous pollutants. The effect of pyrolysis temperature, temperature gradient, feedstock and synthetic route of biochar and carbon on the properties and final performance of derived photocatalysts has also been discussed. The increase in surface area, active adsorption sites, electron shuttling & reservoir properties, high visible absorption, charge separation and biocompatibility have also been elaborated. As far as photocatalytic performance is considered such bio-based photocatalysts are often questioned for their stability under such conditions and poor activity as compared to pure metal-based catalysts. These limitations can be overcome by choice of materials, modifications, new designing routes and coupling of biological methods and photocatalysis for removal of pollutants even from water from waste water treatment plants. Suitable modification to biomolecules as functionalisation has been reported for better adsorption of pollutants. The role of biomaterials in generation of reactive oxygen species, recombination suppression, interactions with pollutants, optical absorption, separation of charge carriers, shuttling and electron flow has also been elaborately explained. The concerns, challenges and future opportunities are also included in this review.
Hydroxyapatite, a multifunctional material for air, water and soil pollution control: A review
Hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ), a calcium phosphate biomaterial, is a very promising candidate for the treatment of air, water and soil pollution. Indeed, hydroxyapatite (Hap) can be extremely useful in the field of environmental management, due in one part to its particular structure and attractive properties, such as its great adsorption capacities, its acid-base adjustability, its ion-exchange capability and its good thermal stability. Moreover, Hap is able to constitute a valuable resource recovery route. The first part of this review will be dedicated towards presenting Hap's structure and defining properties that result in its viability as an environmental remediation material. The second will focus on its use as adsorbent for wastewater and soil treatment, while indicating the mechanisms involved in this remediation process. Finally, the last part will impart all findings on Hap's applications in the field of catalysis, whether it be as catalyst, as photocatalyst, or as active phase support. Hence, all of the above will have served in showcasing the benefits gained by employing hydroxyapatite in air, water and soil clean-up.
Optimization and organic fouling behavior of zwitterion-modified thin-film composite polyamide membrane for water reclamation: A comprehensive study
Membrane fouling can hinder the widespread application of thin film composite (TFC) reverse osmosis (RO) for water treatment. This study evaluated a novel zwitterion-grafted TFC RO as a mean to address organic fouling for water reclamation. The membrane exhibited the best permeability at the grafting condition of 45 °C in 1 h. This modified membrane consistently possessed improved antifouling ability irrespective of organic foulants. Among individual foulants, surfactant Dodecyl Trimethyl Ammonium Chloride (DTAC) posed the worst fouling potential due to its low molecular weight and positive charge, whereas fouling induced by other substances were relatively analogous and minor. In the mixture of DTAC and proteins, the former played a key role in governing the membrane fouling. While, their interplay affected membrane fouling, the fouling extent varied upon the membrane materials. The extended Derijaguin, Landau, Verwey and Overbeek (xDLVO) theory was unable to fully describe the interactions between surfactant foulants and the membrane materials. The complementary use of quartz crystal microbalance with dissipation (QCM-D), otherwise, concurred the fouling potential and gave the plausible interpretation for fouling mechanisms by providing insightful information of foulant layer on the polyamide-coated sensor. This study provided critical insights of organic foulants’ behavior on TFC RO membrane and offered the promising industrial implication of the novel membrane.
Catalytic ozonation for water and wastewater treatment: Recent advances and perspective
Ozonation process has been widely applied in water and wastewater treatment, such as for disinfection, for degradation of toxic organic pollutants. However, the utilization efficiency of ozone is low and the mineralization of organic pollutants by ozone oxidation is ineffective, and some toxic disinfection byproducts (DBPs) may be formed during ozonation process. Catalytic ozonation process can overcome these problems to some extent, which has received increasing attention in recent years. During catalytic ozonation, catalysts can promote O 3 decomposition and generate active free radicals, which can enhance the degradation and mineralization of organic pollutants. In this paper, the history of ozonation application in water treatment was briefly reviewed. The properties of the ozone molecule, the ozonation types and several ozonebased water treatment processes were briefly introduced. Various catalysts for catalytic ozonation, including homogeneous and heterogeneous catalysts, such as metal ions, metal oxidizes, carbonbased materials and their possible catalytic mechanisms were analyzed and summarized in detail. Furthermore, some inconsistent results of previous research on catalytic ozonation were analyzed and discussed. The application of catalytic oxidation for the degradation of toxic organic pollutants, including phenols, pesticides, dyes, pharmaceuticals and others, was summarized. Finally, several key aspects of catalytic ozonation, such as pH effect, the catalyst performance, the catalytic mechanism were proposed, to which more attention should be paid in future study.
Occurrence, impacts and general aspects of pesticides in surface water: A review
A review of the main pesticides employed in agriculture found that the pesticide groups present in the highest amounts are herbicides, fungicides, and insecticides. For this reason, their occurrence in surface waters around the world, as well as their adverse effects on nontarget organisms were reviewed for the period 20122019. Among the most common vegetal herbicides is atrazine, followed by metalochlor, both of which are widelyused on soybean and corn crops. Insecticides are used to control insects by agonizing them. Although they present low toxicity for mammals, they are toxic to ecosystems and impact the environment when present. Fungicides are employed to prevent fungal infections by damaging the cellular membrane, causing damage to nontarget organisms, tebuconazole and carbendazim were the most frequent fungicides identified in surface waters throughout the world. Once pesticides reach water bodies, they can impact the whole ecological food chain, since other animals, including humans, feed on aquatic animals that may be contaminated. Another concern is the mixing of pesticides, in which case the mixture may be more toxic than any one single compound. Because mixtures of pesticides are commonly found in surface water, the need for suitable water treatment is crucial.
Recent advances in controlling denitritation for achieving denitratation/anammox in mainstream wastewater treatment plants
Denitratation (NO 3 NO 2 )anammox is a promising method for anammox application in mainstream wastewater treatment plants (WWTPs) to reduce oxygen and organic matter consumption. Achieving nitrite production via denitratation and controlling denitritation (NO 2 N 2 ) is the basis of the denitratationanammox process. To control denitritation, the denitrifying biocommunity and growth rate are critically reviewed for biocommunity optimization. Then, the shortterm and longterm effects of pH on denitritation were summarized and the possible mechanism was discussed, along with the effect of CN ratio and organic matter type on denitritation. Meanwhile, the strategies for producing nitrite via controlling denitritation are discussed, as well as the processes for achieving nitrogen removal via denitratationanammox in WWTPs. Finally, the practical application of denitratationanammox in a fullscale mainstream WWTP is documented.
Effects of microplastics on wastewater and sewage sludge treatment and their removal: A review
Microplastics are widely used and inevitably released into the environment, which can be easily enriched in wastewater treatment plants. This review assesses their potential effects on wastewater and sludge treatment and the methods for removing microplastics from wastewater and sludge. Firstly, recent advances of the methods for purification and detection of microplastics in wastewater and sewage sludge environment were reviewed. Then, the effects of microplastics on wastewater and sludge treatment and the mechanisms were discussed. It can be seen that when the size of microplastics reached the nanometer level, they infiltrated into the biofilm and produce ROS, which showed acute inhibitory effect on microbial community, key enzymes, metabolic intermediates and final products. Due to their large specific surface area and hydrophobic surface, persistent organic pollutants, metals and pathogens could be easily adsorbed on the surface of microplastics. As various additives were added in the production of plastics, the adsorption of environmental micropollutants and the exudation of additives made the mechanism of microplastics affecting sewage and sludge treatment more complicated. Also, the methods for removing microplastics from wastewater and sludge were reviewed and their removal efficiencies were compared. Finally, the problems that need to be addressed in the future were pointed out, and the key points for future investigation were proposed.
Microwave-responsive catalysts for wastewater treatment: A review
Microwaveassisted catalysis technology has the advantages of high reaction speed, simple equipment and convenient operation, showing broad application prospects in the field of water treatment. A complete understanding of the interactions between microwave and the catalyst can be conducive to the further development of microwaveassisted catalysis technology for application to wastewater treatment. This review first introduces the microwave theory and microwave heating mechanism during microwaveassisted catalysis processes briefly. Microwaveresponsive catalysts are then classified in detail, and common characterization methods of catalysts are also described briefly. Subsequently, the effective parameters, kinetics, and mechanisms and pathways in microwaveassisted catalytic reactions are emphatically discussed. Typical practical cases are also provided to introduce the applications of microwaveresponsive catalysts in the water treatment field. Finally, possible research challenges and directions for microwaveresponsive catalysts applied to wastewater treatment in the future are summarized.