Water Pollution and Remediation: Heavy Metals

Anthropogenic rare earth elements widely used in high-technology applications are prevalent in the aquatic environment, thus constituting emerging contaminants. Yet reviews on the anthropogenic sources, behavior, and potential health risks of rare earth elements remain limited. The current chapter seeks to (1) highlight anthropogenic sources, behavior, and human intake pathways of rare earth elements, (2) discuss the human and ecological health and exposure risks of rare earth elements, (3) present a conceptual outline for assessing and mitigating health risks, and (4) identify the key thematic areas for further research.

Anthropogenic hotspot sources of rare earth elements include wastes and wastewaters from medical facilities, rare earth elements mining and mineral processing, high-technology electrical and electronic industries, petroleum refineries, rare earth elements-enriched fertilizers and livestock feeds, and recycling plants for postconsumer electronic and electrical goods. The dissemination of rare earth elements from sources into the various environmental compartments is controlled by anthropogenic (industrial discharges) and hydrological processes. Human exposure occurs via occupational inhalation in rare earth elements-based industries, ingestion of contaminated food, and medical applications including magnetic resonace imaging. To date, evidence exists documenting rare earth elements in human body parts including the brain, hair, nails, milk, serum, and sperms. High concentrations of rare earth elements reduce plant growth and nutritional quality, impaired biochemical function in plants, and induce neurotoxicity, acute and chronic health effects, and genotoxicity in aquatic animals. The uptake, partitioning, and bioaccumulation of rare earth elements may also occur along the trophic levels in aquatic ecosystems. Human health risks include (1) severe damage to nephrological systems and nephrogenic systemic fibrosis induced by gadolinium-based contrast agents used in medical applications, (2) induced sterility and anti-testicular effects in males, (3) dysfunctional neurological disorder and reduced intelligent quotient, (3) fibrotic tissue injury, (4) pneumoconiosis, and (5) oxidative stress and cytotoxicity. In developing countries, the health risks of rare earth elements may be considerably high due to the following: (1) weak and poorly enforced environmental and public health regulations, (2) overreliance on untreated drinking water, and (3) lack of human health surveillance systems for early detection and treatment of human health effects. However, limited empirical data exist to establish the relationship between rare earth elements in the aquatic environments and their health effects. A conceptual outline for assessing and mitigating the health risks and thematic areas for further research were highlighted.

Heavy metals are high atomic weight elements that consist five times higher density than water. The widespread use of heavy metals in scientific, agricultural, domestic, industrial, and medical applications accelerated their distribution into water bodies through the environment. The extreme toxicity of heavy metals and their adverse effects on human health have raised concerns for the removal of heavy metals from different water bodies. Considering the severe toxicity, mercury, cadmium, chromium, arsenic, and lead were identified as priority heavy metal pollutants and categorized as human carcinogens by United States Environmental Protection Agency. Over the past few years, zerovalent iron nanoparticles have emerged as potential alternatives for the removal of heavy metals from water and wastewater streams. The superior reactivity and large surface area of zerovalent iron nanoparticles provided greater versatility for the in situ remediation of heavy metals. Therefore, this chapter presents a detailed discussion on the advances reported for the heavy metal remediation using zerovalent iron nanoparticles. It begins with the fate and transport of heavy metals into water bodies and their impact on human health and environment. Additionally, preparation methods, characterization techniques, and inherent applications of zerovalent iron nanoparticles toward the removal of heavy metals from different water bodies are extensively described following the risk assessment studies. Finally, concluding remarks and future prospects that support the effective remediation of heavy metals using zerovalent iron nanoparticles are summarized.

Water is vital for sustenance of life and smooth living. The reliable and safe supply of water is a prime necessity of the most important determinants of human health. The treatment of water is essential to remove contaminants and undesirable components and reduce their concentration to make water fit for its desired end use. It is critical for human health as consumption of unsafe water may cause several ailments classified as waterborne or water-related in common terms.

In this chapter, salient water treatment technologies have been reviewed, which may include photovoltaic, electrocoagulation, oxidation-enriched, membrane-based, deionization, and nanotechnology-inspired approaches for converting raw or effluent water fit for specific purposes and minimization of pollution load. We quite often gather the information regarding advantages and disadvantages of available technologies for water purification and strides for innovation to have suitable models at economical price range. The suitability of technology depends on source, characteristics of water, total dissolved solids, and contaminants present and intrinsic as well as extrinsic factors.

In recent decades, enormous research efforts have been made on the development of promising, effective, and eco-friendly treatment technologies for the removal of recalcitrant toxic organic contaminants. Huge attention has been received on the treatment processes based on oxidative removal of organic pollutants through hydroxyl radicals generated by various electrochemical advanced oxidation processes.

This chapter reviews the fundamentals of various electrochemical advanced oxidation processes like anodic oxidation, electro-Fenton process, peroxi-coagulation, anodic-Fenton, Fered–Fenton process, hybrid processes including photo-electro-Fenton, solar photo-electro-Fenton, and sono-electro-Fenton process. It also reviews the electrochemical-based treatment of real effluents from different industries such as textile, paper mill industry, and tannery as well as domestic and urban effluents and landfill leachate. The strong potential of various electrochemical advanced oxidation processes indicated that these technologies can be demonstrated as the promising processes for the treatment of various real effluents to meet the regulatory norms.

Environment conservation through cleaning up of xenobiotics is a global concern. Different technologies have been tried to remove pollutants from the water environment. Among them adsorption is one of the prime candidates. In this chapter, we have discussed the removal of heavy metals: arsenic, lead, cadmium, and chromium using unconventional low-cost novel sorbents, e.g., waste materials, biochar, industrial wastes, nanomaterials, and metal–organic frameworks. We have majorly focused on the introduction of unconventional adsorbents with their maximum adsorption capacity to their target metals from an aqueous environment. Besides the commercial adsorbents such as activated carbon, the unconventional adsorbents showed promising capability to remove metals from water. However, the holistic approach of the multidisciplinary involvement is needed to make these unconventional materials an industrial scale adsorbent to clean up the metals at the source/discharge points.

Desalination is the technology to provide energy, fresh water, and food security concurrently for the remote, coastal, and energy-lacking countries. In this chapter, we have discussed various techniques and problems of thermal and membrane desalination techniques such as electrodialysis, reverse osmosis, ultrafiltration, and nanofiltration, membrane distillation, and various integrated methods. However, these methods are expensive and energy-intensive, with massive carbon-footprints, and have a serious problem of membrane fouling. Moreover, these technologies are often not sustainable for implementation in many energy-and-water-starved developing countries.

We have, therefore, concentrating on research and progress of nanomaterials and energy-efficient membrane development to overcome membrane fouling and scaling prevention. We have also focused on the modification of membrane process such as forward osmosis. We have also discussed the integration of renewable energies such as solar desalination and hybrid power generation such as nuclear desalination to reduce carbon footprint and enhance cost-effectiveness to obtain fresh water. From the viewpoint of water–energy nexus, choosing the right types of desalination techniques and processes should be strategically planned, designed, and implemented to achieve water security.

The environment has been seriously polluted by heavy metals and metalloids, and it has become one of the most severe problems today. This affects human health, plants, aquatics, air, and soil. Heavy metals are mainly naturally occurring compounds, but anthropogenic activities increase their concentration level in different environmental compartments. The remediation of heavy metals and metalloids is extremely needed as the high level of contamination, caused by the heavy metals, poses serious threats to the environment.

In past years, various technologies for the remediation of heavy metals and metalloids in contaminated water have been extensively studied. In this book chapter, we have discussed about the heavy metals and metalloids which contaminate water; described their harmful effects on human health, plants, and aquatic environments; and presented several nanotechnologies as well as nanomaterials used in heavy metal and metalloid remediation of contaminated water.

The twentieth century has witnessed a rapid industrialization of chemical processes. It has facilitated in improvising living style of humans but other side effluents from the industries adversely polluting the water. The industrial wastewater has to be treated to avoid the water pollution and water scarcity around the world. A single treatment technology that leads to zero water pollutant discharge from industry appears to be unrealistic; thus the combination of different technologies will be the new approach to deal efficiently with the present condition of wastewater treatment. In this chapter, such hybrid technologies are discussed with the different case studies. Effective use of hydrodynamic cavitation techniques in combination with the micro-/ultrafiltration, use of photocatalysis combined with ultrafiltration and use of novel adsorbent materials like hydrogels, shows improvement in the removal of pollutants from the industrial wastewater. This article also endorses the inclusion of energy and water reuse plan within the treatment scheme and accordingly proposes a conceptual industrial wastewater treatment system.

Stormwater generated in urbanized areas is generally contaminated with different pollutants such as heavy metals, nutrients, and suspended solids. One of the successful infrastructures in managing stormwater quality in cities is biofiltration system. Biofilters which consist of a layered filter media and vegetation are found successful in removing different classes of pollutants. Filter media of such systems is found to be the main contributor in removing heavy metals; however, its efficiency is highly dependent on material composition and size distribution. This study is aimed to review and discuss different types of filter media and their performances in removing different heavy metals and also the practical limitations of using such material in biofiltration systems. Moreover, other influencing factors in selecting the filter media including infiltration rate, metals accumulation in soil, and the short-term and long-term functionality of the system are discussed.

Nowadays, heavy metals have become threat because of their toxicity and risk associated with exposure to them. In recent years, due to various technological advancements, both type and amount of heavy metals in water have increased gradually. They may enter the body through a variety of media present in our environment, i.e., food chain, air, etc. Furthermore, heavy metals act as barrier in metabolic processes. Exposure to such metals either accidental or occupational causes different kinds of disorders, including cardiovascular disorders, cancer, and neurological disorder which are arising due to consumption of water contaminated by these pollutants. Heavy metals such as cadmium, nickel, and chromium are known to be carcinogenic, as exposure of these heavy metals causes serious hazard to the human health. Some of the heavy metals get accumulated in the environment and are found to be difficult for recycling/degradation, hence leading to enormous increase in health hazard. This chapter provides information about some of the heavy metals and their potential toxicity to the human beings, plants, and environment along with their removal methods as well.

Photocatalysis mediated by semiconductor nanoparticles is a promising technology for water remediation, which takes advantage of solar energy and nanomaterials properties, such as high surface area, effective charge carrier separation, etc. Particularly, metal chalcogenides are advantageous because of their energy band gap in the visible region. Several contaminants can be degraded or removed employing this technology. This chapter summarizes the advances in dyes degradation (as methyl orange, rhodamine B, and methylene blue) and metal reduction (Cr(VI) to Cr(III)) using tin-based compounds. The best degradation rates, and methods developed to improve photocatalytic efficiency, as the design of tin(IV) sulfide (SnS₂) heterostructures, are discussed. Moreover, tin-based compounds have shown antimicrobial properties, which can be combined with their photocatalytic capacity. The progress concerning tin-based compound photocatalysis is bearing this nanotechnology as the next technology to be incorporated in water remediation systems.

The total global production of refined copper in 2017 was approximately 19 million tons, with an annual growth rate of 3.4%. During the copper production process, a large proportion of the accompanying toxic metals end up in the environment. For this reason, there is a significant need for advanced wastewater treatment methods and technologies in order to ensure optimal water quality, eliminate heavy metals and other pollutants from water, and suggest appropriate industrial technology for the treatment of wastewater. Although various techniques for treatment of wastewater contaminated with heavy metals are being applied today, the choice of the most suitable wastewater treatment process depends on some basic commonly accepted parameters which will be discussed in this paper.

The methods and techniques such as adsorption on the new sorbents (biosorbents, agricultural and industrial wastes (lignocellulosic materials) as an ecological adsorbent; nano-adsorbents, activated carbon, carbon nanotubes, graphene, MgO, MnO, ZnO, TiO_2, Fe₃O₄, etc.), nanotechnology, photocatalysis, nano zero-valent iron (nZVI), the use of dimensionally stable anodes in electrolysis, and phytoremediation have proved to be adequate in the treatment of wastewater from the support in particular toxic metals such as copper (Cu), lead (Pb), cadmium (Cd), nickel (Ni), chromium (Cr), arsenic (As), zinc (Zn), and mercury (Hg), from primary and secondary copper production. Sorbents can be regenerated or concentrated by combustion and electrolysis using dimensionally stable anode; metals can be selectively separated and can be returned to the production process. Working principles and the advantages and disadvantages of the mentioned materials and methods for water remediation will be discussed in this paper. Due to their importance of the impact on the living world and on the environment, the toxicity of each of these polluting metals will also be demonstrated. The results show that water is generally polluted and that in the near future, we will have to take the most serious approach to addressing this problem. Great efforts are already being made to come up with the most efficient and inexpensive methods for wastewater treatment. This generally requires combining multiple methods for quality problem-solving, in accordance with the type and concentration of the pollution identified. In addition to engaging experts from the natural sciences, it is also necessary to include a management system and link up ministries of ecology at the state level and international level, in order to approach this problem more efficiently and to preserve rivers that flow through multiple lands and carry with them substances harmful to human health and to the environment and rivers which then flow with these substances into lakes, seas, and oceans.

This chapter presents a sequential summary of various solutions for heavy metal remediation adopted over the decades with improved techniques and efficient eco-friendly methods. Heavy metals (specific gravity>5) are released into water bodies due to rapid urbanization and create plenty of environmental problems. A scientific approach gradually being adopted by the researchers always struggles to resolve such issues and thanks to their breakthroughs to solve such problems with innovative avenues and cutting-edge technologies in the modern era. A good variety of methods with emphasis on adsorption technique for heavy metal removal is summarized.

The adsorption process is proved to be the most accepted method for heavy metal removal. Adsorbents or bio sorbents prepared from plants, living and dead biomass, various micro composites, nanocomposites containing carbon alone or blends with metal oxides and/or polymer are summarized in this chapter. Additionally, the use of zeolites and metal–organic frameworks is also discussed herewith. Researchers have authenticated the synthesized or modified adsorbents through various characterization techniques, namely, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and thermogravimetric analysis. The estimation of heavy metals is presented that has been obtained using atomic absorption spectroscopy, batch adsorption, and column techniques. The chapter may be proved as a great support to the future scientists in many ways.

This book chapter summarizes the sources of heavy metals in water, treatment of wastewater, and diseases caused by polluted water due to heavy metals. Commonly, human interaction with heavy metal can occur through various routes, which include ingestion through food or drinks and inhalation of dust or fume. Heavy metals such as lead, mercury, copper, cadmium, zinc, nickel, chromium, and arsenic cause growth problems, nervous system damage, cancer, organ damage, and in extreme cases death. In recent years, both the type and content of heavy metals in water have gradually increased due to fast global development and human activities.

In this chapter, various water purification techniques such as chemical precipitation, lime coagulation, coagulation and flocculation, flotation, ion-exchange process, adsorption, membrane filtration, electrochemical treatment, and phytoremediation have been discussed in detail.

Contamination of surface and underground water resources with heavy metals has been an issue of paramount concern in recent decades. This is attributed to the magnitude of impacts that heavy metals pose to terrestrial and aquatic living organisms on exposure. Furthermore, mining activities and metal processing interventions generate huge volumes of heavy metal-laden streams to different receiving environments. Similarly, the nature of chemical species present in the water bodies depends on the nature and type weathered and host minerals. On that regard, scientists and engineers have developed a number of prudent and pragmatic technologies for the removal of these pollutants from water bodies. Different techniques that rely on different mechanisms and approaches are often employed for the removal of heavy metals from wastewater, and they include neutralization, adsorption, filtration, and phytoremediation, among others. These technologies have been reported to present different advantages and disadvantages on application. This chapter will give an in-depth discuss on different mechanisms and approaches employed for the removal of pollutants from wastewater. Furthermore, sustainable approaches for valorization and beneficiation of waste effluent streams will also be discussed in this chapter, including preliminary challenges of beneficiation. This will impart value to wastewater via the conversion of waste into a resource, thus enabling them to perceive these wastewater streams as a resource not waste. Recovery of heavy metals from wastewater can aid in offsetting the running cost of the treatment process, hence making it self-sustainable and eco-friendly. This will also foster the concept of circular economy and sustainable development. This chapter will also highlight the advances made in terms of acid mine drainage management and heavy metals treatment. In particular, the advancements, failures, challenges, and future research avenues will also be unpacked in this chapter. This will be used as an avenue to guide future research and to identify potential opportunities for future research in wastewater treatment.

In recent years, many researches are focused to use clay and diatomaceous earth like the most and the effective solution to reduce this problem, thanks for their abundance, the cheapness, and the important surface area. This chapter aims to discuss the removal of organic and inorganic pollutants such as dyes (methyl orange, indigo carmine, phenol red, acid brown 75, basic yellow 28, etc.) and heavy metal ions (such as Zn (II), Cd (II), Pb (II), Ni (II), Cr (II), etc.) from water by adsorption on clays and diatomaceous earth. The application of chemical and physical modifications of the functional groups of clay and diatomite enhance their adsorption capacities. The kinetics and the models used to describe the adsorption processes are discussed. The reported results for a variety of clays and diatomite derivatives showed that these materials could be applied successfully for the removal of dyes and heavy metals from wastewater.