Nanomaterials for Water Remediation

Ajay Kumar Mishra, Chaudhery M. Hussain, Shivani B. Mishra, Ajay Kumar Mishra, Chaudhery M. Hussain, Shivani B. Mishra

• Publisher: De Gruyter
• Year: 2020
• ISBN:
  9783110634556
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Environmental Science

The capability to generate potable water from polluted sources is growing in importance as pharmaceuticals, microplastics and waste permeate our soil. Nanotechnology allows for improvements in water remediation technologies by taking advantage of the unique properties of materials at this small scale.

1 Nanocellulose and nanochitin for water remediation by adsorption of heavy metals

Y. K. Dasan

Department of Fundamental and Applied Sciences, Universiti Teknologi Petronas Malaysia, Perak Darul Ridzuan, Malaysia

A. H. Bhat

Department of Fundamental and Applied Sciences, Universiti Teknologi Petronas Malaysia, Perak Darul Ridzuan, Malaysia

Imran Khan

CICECO-Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Aveiro, Portugal

1.1 Introduction

The rapidly growing world population and accelerated industrialization have led to a large number of severe environmental problems including water pollution. In terms of the World Health Organization (WHO) drinking water quality guidelines, one-sixth of the population or almost 1.2 billion people living in developing countries are still without access to clean drinking water, while about 2.6 billion people comprising about 400 million children under 5 years old and elderly people do not have access to basic sanitation facilities [1, 2].

In addition, 3.7% of the annual health burden worldwide is caused by unsafe water and lack of sanitation facilities. Among all the water pollutants, heavy metal contaminations are posing a serious threat to human society. Three categories of heavy metals such as toxic metals, precious metals, and radionuclides are of environmental concern. A substantial amount of various toxic metals is released into the water system by many types of industries, such as mining and smelting of minerals, surface finishing industry, energy and fuel production, fertilizer and pesticide industry and application, metallurgy, iron and steel, electroplating, electrolysis, electro-osmosis, leatherworking, photography, electric appliance manufacturing, aerospace and atomic energy installation. For example, mining industries release heavy metal ions such as lead (Pb²⁺), mercury (Hg²⁺), silver (Ag⁺), chromium (Cr³⁺), arsenic (As⁵⁺), cadmium (Cd²⁺), palladium (Pd²⁺), zinc (Zn²⁺), and aluminum (Al³⁺) to the environment. The recovery of these valuable metal ions after removal is also an issue that needs to be further addressed [3, 4, 5]. Silver, copper, and iron are the target metals in this chapter, since all of them belong to the most common pollutants in industrial effluents. Silver ions can be released into groundwater and surface water by many industrial operations such as mining, photographic processing, and electroplating in mirror industry. Industries such as dyeing, paper, petroleum, copper brass plating, and copper–ammonium rayon discharge Cu²⁺ containing wastewater. Short-term exposure to copper ions can result in gastrointestinal distress, and long-term exposure leads to liver or kidney damage [6].

1.2 Current water remediation techniques and their limitation

Numerous conventional methods are readily available for removal of heavy metal ions and improve the effluent quality produced from industrial wastewater such as chemical precipitation, ion exchange, membrane separation, adsorption, electrochemical techniques, and biosorption. In this section, we will discuss about the available treatment methods and their pros and cons.

1.2.1 Chemical precipitation

Chemical precipitation is an effective method for removal of metal ions from wastewater stream by precipitating the metal in an insoluble form. The resulting metal precipitates then settled in a pond and/or a clarifier [7]. The most commonly used chemical precipitation techniques include hydroxide and sulfide precipitation. Chemical precipitation with hydroxide is preferred, as the process involved is relatively simple, is of low cost, and is easy to control the pH. The optimum pH for effective precipitation is in the pH range of 8.0–11.0. In industrial settings, lime is the favored base in hydroxide precipitation [8]. Equation (1.1) represents the conceptual mechanism of heavy metal removal by hydroxide precipitation:

(1.1)${\mathrm{M}}^{\mathrm{n}+}+n(\mathrm{O}{\mathrm{H}}^{-})⟷\mathrm{M}(\mathrm{O}\mathrm{H}{)}_{\mathrm{n}}\downarrow$

In general, the addition of coagulants such as alum, iron salts, and organic polymers enhances the hydroxide precipitation process [8]. A coagulant destabilizes the suspended particles and makes them flocculate together into larger aggregates that can settle out of solution [9]. On the other hand, metal sulfide precipitates have lower metal ion leach out as compared to hydroxide precipitates. Therefore, sulfide precipitation process has the ability to attain higher treatment efficiency with better thickening and dewatering characteristic sludge. However, this sulfide treatment method produces toxic H₂S fumes due to the acidic nature of heavy metal and sulfide precipitants. Hence, this sulfide precipitation process must be conducted in a neutral or basic medium [8, 10].Equation (1.2) represents the conceptual mechanism of heavy metal removal by sulfide precipitation [11].

(1.2)${\mathrm{M}}^{2+}+{\mathrm{S}}^{2-}\to \mathrm{M}\mathrm{S}\to \downarrow$

Carbonate precipitation is well known for calcium hardness removal from water. Recently, the precipitation of metal carbonates was proposed for heavy metal removal. This acts as an alternative technique to reduce the large sludge volume that is produced through hydroxide precipitation. Moreover, it facilitates the settling and filtration process [10]. Equation (1.3) represents the conceptual mechanism of heavy metal removal by carbonate precipitation [11]:

(1.3)${\mathrm{M}}^{2+}+{\mathrm{C}\mathrm{O}}_3^{2-}\to \mathrm{M}\mathrm{C}{\mathrm{O}}_3\downarrow$

Despite its simplicity and extensive usage, metal precipitation requires the large amount of chemicals in order to achieve the acceptable level concentration before discharging. Furthermore, precipitation process results in excessive sludge production, which contains toxic metals, thus increasing the cost of sludge disposal. Apart from this, the slow metal precipitation and the long-term environmental impacts of sludge disposal make the process a little tricky [12, 13].

Flotation is a technique of using bubble attachment or carrier to separate solid or dispersed liquids from a liquid phase. The carrier can be activated coal, polymeric resin, mineral particles, or a by-product having good sorption properties [14]. There are five different kinds of flotation processes available: (i) vacuum air flotation, (ii) dispersed air flotation, (iii) electroflotation, (iv) dissolved air flotation, and (v) biological flotation. Among them, dissolved air flotation is the one most frequently used for the removal of heavy metal ions. In dissolved air flotation, metal impurities were separated by foaming in adsorptive bubble separation process [13].

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Table of contents

• Title Page
• Copyright
• Contents
• Preface
• List of contributors
• 1 Nanocellulose and nanochitin for water remediation by adsorption of heavy metals
• 2 Waste-derived nanocarbons: a cleaner approach toward water remediation
• 3 Black but gold: carbon nanomaterials for waste water purification
• 4 Characterization of eco-friendly bentonite materials and their applications
• 5 Removal of ammonium from aquatic environment using bentonite and its modified forms
• 6 Ion-imprinted thermosensitive macroporous cryogels for cadmium removal
• 7 Ag and Au nanoparticles for detection of heavy metals in water
• Index