Eric Lichtfouse

Efficient microwave degradation of humic acids in water using persulfate and activated carbon

Humic acids are complex mixtures of organic molecules of different sizes, molecular weights and functional groups such as phenols, carboxyls, quinones and amino acids. Humic acids occur ubiquitously in media where organic matter is decomposing, such as waters, soils, sediments and organic wastes. The presence of humic acids in untreated water inhibits the oxidation of target pollutants through competing reactions and generates toxic disinfection by-products during the classical disinfection method of chlorination. There is therefore a need for alternative methods that remove humic acids. Here, degradation of humic acids at 10xa0mg/L was tested using 1000xa0W microwave irradiation assisted by 0.25–1.2xa0mM persulfate, with granular activated carbon at 10–50xa0g/L, at pH 3.0–12.0. In 90s, the highest removal of humic acids, of 75%, and humic acids mineralization, of 41%, was obtained using 1000xa0W microwave, 50xa0g/L granular activated carbon and 0.5xa0mM persulfate at pH 8.0. Under the same conditions without persulfate, removal was only 42% and mineralization 24%. Removal was lower than 7% using either persulfate or microwave alone. High removal with microwave, persulfate and granular activated carbon may be explained by enhanced generation of SO4·− and ·OH radicals and also by better trapping/encapsulation/binding of humic acids in the granular activated carbon matrix.

Adsorption-Oriented Processes Using Conventional and Non-conventional Adsorbents for Wastewater Treatment

The removal of contaminants from wastewaters is a matter of great interest in the field of water pollution. Amongst the numerous techniques of contaminant removal, adsorption using solid materials (named adsorbents) is a simple, useful and effective process. The adsorbent may be of mineral, organic or biological origin. Activated carbon is the preferred material at industrial scale and is extensively used not only for removing pollutants from wastewater streams but also for adsorbing contaminants from drinking water sources (e.g. rivers, lakes or reservoirs). However, its widespread use is restricted due to high cost. In the last three decades, numerous approaches have been studied for the development of cheaper and more effective adsorbents capable to eliminate pollutants at trace levels. This chapter gives a general overview of liquid-solid adsorption processes using conventional and non-conventional materials for pollutant removal. It outlines some of the principles of adsorption and proposes a classification for the different types of materials. Finally, the chapter discusses different mechanisms involved in the adsorption phenomena.

Wastewater Treatment: An Overview

During the last 30 years, environmental issues, especially concerning the chemical and biological contamination of water, have become a major concern for both society and public authorities, but more importantly, for the whole industrial world. Any activities whether domestic or agricultural but also industrial produce wastewaters or effluents containing undesirable contaminants which can also be toxic. In this context, a constant effort must be made to protect water resources. In general, conventional wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove insoluble particles and soluble contaminants from effluents. This chapter briefly discusses the different types of effluents, gives a general scheme of wastewater treatment, and describes the advantages and disadvantages of technologies available.

Treatment of organic pollutants by homogeneous and heterogeneous Fenton reaction processes

Nowadays, the water ecosystem is being polluted due to the rapid industrialization and massive use of antibiotics, fertilizers, cosmetics, paints, and other chemicals. Chemical oxidation is one of the most applied processes to degrade contaminants in water. However, chemicals are often unable to completely mineralize the pollutants. Enhanced pollutant degradation can be achieved by Fenton reaction and related processes. As a consequence, Fenton reactions have received great attention in the treatment of domestic and industrial wastewater effluents. Currently, homogeneous and heterogeneous Fenton processes are being investigated intensively and optimized for applications, either alone or in a combination of other processes. This review presents fundamental chemistry involved in various kinds of homogeneous Fenton reactions, which include classical Fenton, electro-Fenton, photo-Fenton, electro-Fenton, sono-electro-Fenton, and solar photoelectron-Fenton. In thexa0homogeneous Fenton reaction process, thexa0molar ratio of iron(II) and hydrogen peroxide, and thexa0pH usually determine the effectiveness of removing target pollutants and subsequently their mineralization, monitored by a decrease in levels of total organic carbon or chemical oxygen demand. We present catalysts used in heterogeneous Fenton or Fenton-like reactions, such as H2O2–Fe3+(solid)/nano-zero-valent iron/immobilized iron and electro-Fenton-pyrite. Surface properties of heterogeneous catalysts generally control the efficiency to degrade pollutants. Examples of Fenton reactions are demonstrated to degrade and mineralize a wide range of water pollutants in real industrial wastewaters, such as dyes and phenols. Removal of various antibiotics by homogeneous and heterogeneous Fenton reactions is exemplified.

Hemp-Based Materials for Metal Removal

With the increasing focus on renewable materials and sustainability issues, the development of non-conventional materials from natural resources and possessing complexing properties is currently an area of extensive research due to their potential applications in biosorption processes for pollutant removal. Among them, the hemp plant, an annual high yielding industrial crop grown for its fibres and seeds, is one of the most promising material for biosorption of metal ions from diluted waste streams. In this chapter, an extensive list of hemp-based biosorbent literature has been compiled and discussed. After a brief description of hemp and its properties and applications, the chapter gives a general overview of liquid-solid biosorption processes for metal removal from aqueous solutions onto hemp-based materials.

Synthesis of a three-dimensional network sodium alginate-poly(acrylic acid)/attapulgite hydrogel with good mechanic property and reusability for efficient adsorption of Cu2+ and Pb2+

Water pollution caused by heavy metals has dramatically impacted ecosystems in recent years. For instance, 45.4% of lakes in China are in the category of moderate to high risk of toxic metalxa0pollution, due to excessive mining. There is, therefore, a need for efficient techniques of metal decontamination. Hydrogels are gaining interest as heavy metal adsorbents because of their easy separation, but hydrogel applications are limited due to their poor mechanical property. Here we solve this problem by introducing natural attapulgite into the sodium alginate–poly(acrylic acid) semi-interpenetrating polymer network of thexa0hydrogel. Results show that the compressive stress of thexa0hydrogel with 10% attapulgite, of 1.230 Mpa, was 4.1 times higher than that of purexa0hydrogel, of 0.299xa0MPa. The adsorption capacity of hydrogel with 10% attapulgite was high, of 272.8xa0mg/g for Cu2+ and 391.7xa0mg/g for Pb2+. Even after five cycles of adsorption, the hydrogel with 10% attapulgite still adsorbs 261.7xa0mg/g Cu2+ and 368.1xa0mg/g Pb2+. Our findings thus reveal that network-structured sodium alginate–poly(acrylic acid)/attapulgite hydrogel holds great potential as an efficient and recyclable adsorbent for heavy metal removal.

Conventional and non-conventional adsorbents for wastewater treatment

The removal of contaminants from wastewaters is a major challenge in the field of water pollution. Among numerous techniques available for contaminant removal, adsorption using solid materials, named adsorbents, is a simple, useful and effective process. The adsorbent matter can be mineral, organic or biological. Activated carbon is the preferred, conventional material at the industrial scale. Activated carbon is extensively used not only for removing pollutants from wastewater streams, but also for adsorbing contaminants from drinking water sources, e.g., groundwater, rivers, lakes and reservoirs. However, the widespread use of activated carbon is restricted due to a high cost. In the last three decades, numerous approaches using non-conventional adsorbents have been studied for the development of cheaper and more effective adsorbents to eliminate pollutants at trace levels. This review gives an overview of liquid–solid adsorption processes using conventional and non-conventional adsorbents for pollutant removal. The manuscript outlines the principles of adsorption and proposes a classification for adsorbent materials. Finally, the various mechanisms involved in the adsorption phenomena are discussed.

Glutathione-functionalized melamine sponge, a mimic of a natural antidote, as a quick responsive adsorbent for efficient removal of Hg(II) from aqueous solutions

Minamata disease is caused by methylmercury, which is produced by microorganisms from inorganic mercury ions, Hg(II), in the aquatic environment. Adsorption is a feasible method to remove Hg(II) from waters, but there are some drawbacks when using conventional adsorbents, for example, tedious solid–liquid separation, slow response, and excessive residual levels of mercury. In this work, a novel spongy adsorbent has been developed for Hg(II) removal via surface functionalization of melamine formaldehyde sponge by glutathione. This material mimics a natural antidote that removes trace heavy metals in the human body. Results show that the functionalized sponge displays a 99.99% removal efficiency for low concentrations of Hg(II) of 10xa0mg/L. As a consequence, the residual Hg concentration is lower than 0.005xa0mg/L, which is slightly below the standard for total mercury in drinking water, of 0.006xa0mg/L, formulated by thexa0World Health Organization, and much lower that the discharge regulation standard, of 0.01xa0mg/L, set by the ministry of environmental protection of China. Adsorption kinetic studies indicate that the functionalized sponge has a fast response. Indeed, the adsorption equilibrium can be reached within 10xa0min, and about 80% of total adsorption capacities are reached in 1xa0min. Moreover, the maximum adsorption capacity of the glutathione-functionalized sponge is as high as 240.02xa0mg/g, as shown by adsorption isotherm. Overall our findings disclose the great potential of the developed sponge adsorbent for rapid and efficient removal of Hg(II) from water.

Advantages and disadvantages of techniques used for wastewater treatment

During the last 30xa0years, environmental issues about the chemical and biological contaminations of water have become a major concern for society, public authorities and the industry. Most domestic and industrial activities produce wastewaters containing undesirable toxic contaminants. In this context, a constant effort must be made to protect water resources. Current wastewater treatment methods involve a combination of physical, chemical and biological processes, and operations to remove insoluble particles and soluble contaminants from effluents. This article provides an overview of methods for wastewater treatment, and describes the advantages and disadvantages of available technologies.

CaCu 3 Ti 4 O 12 , an efficient catalyst for ibuprofen removal by activation of peroxymonosulfate under visible-light irradiation

Contamination of waters by pharmaceuticals is a major health issue. Therefore, there is a need for efficient techniques to remove pharmaceutical pollutants. Here, a photo-assisted fenton-like method based on sulfate radicals was tested using CaCu3Ti4O12 with different morphologies as catalyst. Sintering of CaCu3Ti4O12 at 775xa0°C for 6xa0h produced cubic structures with sizes from 2 to 5xa0μm, whereas sintering for 14xa0h produced microfibers, according to scanning electron microscopy. The highest electron paramagnetic resonance signal was observed for 6-h sintering. We evaluated the catalytic efficiency of CaCu3Ti4O12 for ibuprofen degradation with peroxymonosulfate under visible light. Results show that CaCu3Ti4O12 and 0.5xa0mM peroxymonosulfate under visible-light irradiation induced 91.8% removal of ibuprofen in 60xa0min. The Cu+ vacancy on the surface of CaCu3Ti4O12 is essential to activate the sulfate radicals by forming a Cu+–Cu2+ redox couple, which led to the rapid and efficient removal of ibuprofen.