1
Green Chemistry for Water Remediation

Syed Wazed Ali*, Satyaranjan Bairagi and Swagata Banerjee

Department of Textile and Fiber Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India

Abstract

With the curve of industrialization growing exponentially, the quality index of natural resources is facing a deteriorating trend. Water is one of the most abundantly available natural resources that is being exploited tremendously by humans. Gallons of water are consumed in our day-to-day activities, starting from industrial to household. This exploitation has proved to be a boomerang for them and, hence, ways are being sought to recover, reuse, and preserve this natural resource. Treatment of wastewater has been a subject of interest for a long time, and techniques have been established for the same. However, the chemical treatments of wastewater often adversely affect the environment. The by-products of these processes are often toxic and pose serious health hazards. Hence, a concept like green chemistry has come into the picture for the remediation of water resources. It has proved to be one of the key tools to achieve sustainability by providing appropriate solutions to existing problems. It helps to avoid the toxic by-products of conventional techniques and enhances ecofriendly wastewater treatment approaches. This chapter deals with the various principles of green chemistry in brief and the methods of water remediation in detail. Various chemical treatments of water using green technology have been discussed in detail. Various challenges faced in the path of treatment have also been highlighted.

Keywords: Green chemistry, water remediation, eco-friendly

1.1 Introduction

It has been stated by the World Health Organization (WHO) that a person consumes about 50 to 100 liters of water daily to fulfil their essential needs and maintain their health. The right to acquire a sufficient and nontoxic quantity of drinking water applies to every living being in our society ignoring what financial status and society they belong to. It has been surveyed that 13.6% of the world's population is not able to access safe drinking water [1] and on the other hand 2.6 billion people face a shortage of the required hygiene. Earlier in the 21st century, around 600 km3 per year of water was consumed by people staying throughout the world, whereas during the start of this century, the total consumption of drinking water has been elevated to 5300 km3 per year. It has been surveyed that after the year 2060, there will be some stabilization with four billion human beings staying in city areas proving a very high demand for water consumption [2]. Furthermore, the future prediction states that around 1.8 billion living beings will be facing a shortage of water and approximately 66% of the whole population worldwide will live with the problem of water shortage from the year 2025 [3]. It has also been observed that the main cause for such a disaster is the pollution generated by various industries on our natural water resources. The various wastes from industries, households, agriculture, and farming adversely affect our worldwide drinking water resources.

In the upcoming era, the management of water quality can be done by refining the raw water available in our nature, improving the technology related to such raw water treatment, and properly maintaining the network related to the drinking water supply. Also, it has been stated by many researchers that managing, improving, and inventing new technologies related to water supply can give rise to ways that can achieve efficient and pure quality water supply. In this context, scientists have come up with methodologies that can improve the quality of water by using less toxic or environmentally friendly approaches, some of which are elaborated on in the upcoming section of this chapter. Researchers have also added in their studies that such green approaches give rise to improved and less toxic chemicals, minimization of wastes, and less consumption of energy resources [4]. Therefore, from these approaches, the idea of introducing green chemistry for water purification has approached the minds of various scholars. The idea of such introduction to green chemistry is termed by 12 different principles, which can be stated as follows: preventing the generation of wastes, incrementing the rate of reaction conversions, developing less toxic chemicals, developing safe products made with much less toxic chemicals, increasing efficient energy technologies, utilizing renewable feedstocks, eliminating toxic derivatives of chemicals, utilizing catalysts to increase the rate reactions, designing biodegradable chemical-based products, analyzing ways to diminish pollution, and reducing the causes that lead to accidents [5].

1.2 Challenges in Water Remediation

Several green movements have objected to the use of chemicals in water treatment that harms the environment. Some ask for abolishing the use of such chemicals while others aim at replacing them. Chlorine is one such chemical that is used for disinfecting water while having harmful impacts on the surroundings at the same time [6, 7]. Chlorine kills the microorganisms responsible for diseases like cholera, typhoid, hepatitis, etc. At the same time, however, it is responsible for the formation of compounds like chloroform that are carcinogenic. Disinfecting with chloramines helps to prevent the formation of chloroform, but the cyanogen chloride formed as a by-product is toxic. Several reagents have been tried to eliminate the chloroform formation [8].

Water has an organic matter of natural origin and synthetic origin. The naturally present organic matter in water is called natural organic matter while the organic matter added to water due to human activities is called synthetic organic matter. The percentage of synthetic organic matter is less compared to that of natural organic matter; however, synthetic organic matter is more harmful compared to natural organic matter. The Blackfoot disease is a well-known disease in Taiwan that causes numbness and coldness of limbs [9, 10]. It is thought to be due to the presence of fluorinated compounds in water. Humic acid is one such fluorinated compound that causes organ-related diseases. It is a high molecular weight complex molecule that negatively impacts the erythrocytes via the generation of reactive oxygen species [11]. Metals like copper and aluminum are also related to toxicity issues [12, 13].

1.3 Green Chemistry as a Novel Alternative to Conventional Wastewater Treatment

1.3.1 Green Chemistry

The conceptualization of green chemistry was a result of the Pollution Prevention Act, in the year 1990 [4]. It stated the US national policy to eradicate pollution by improvising its design and processes rather than the treatment and disposal of products. In other words, the term green chemistry refers to the design and development of products that would help to reduce or get rid of the production of any hazardous substances [14]. There exists a small line of difference between environmental chemistry and green chemistry. Environmental chemistry deals with environmental pollutants. Green chemistry, on the other hand, aims at designing new techniques and improving existing technologies that would minimize the generation of waste. Green chemistry also includes certain crucial ideas. One is the impact of all raw materials used in product synthesis and not just the principal raw material. The other is the optimization of an efficient process with the least negative impacts. Green chemistry is based on twelve principles that may be stated as under. The "Twelve Principles" related to "Green Chemistry" were introduced in the year 1998 [5]. These principles provide a strong guideline to manufacture ways of different less harmful chemical products and technologies, which apply to almost all life cycle processes, including the raw materials utilized for enhancing the productivity and safeness of the principles used, along with the toxic nature and degradability of different products and chemicals used in this green chemistry approach. Some of them are listed as prevention, atom economy, less hazardous chemical synthesis, designing safer chemicals, safer solvents, and auxiliaries, design for energy efficiency, use of renewable feedstocks, reducing derivatives, catalysis, design for degradation, real-time analysis for pollution prevention and inherently safer chemistry for accident prevention.

Proper waste handling: It aims to prevent waste generation rather than treat and clean them up when produced. It is one of the most important of the twelve different principles of this green chemistry approach. It is always safer to avoid the accumulation of waste other than to clean up after it has been formed. Waste can be defined as anything that has no appreciated importance or the product produced from any damage caused to any energy technology. Also, it has been stated in many studies that wastes can take different forms and can cause an impact on nature in a different way depending on the waste's nature, toxicity, quantity, or the way it has been drained out [15]. When huge quantities of the precursors are utilized in a method of synthesis, then much of them are lost due to the original design of the procedure itself and this generation will give rise to undesirable wastes. One of such examples to minimize waste quantity is to use molecular oxygen, thereby eliminating the requirement for...