Preface

Life on Earth relies on the gifts of nature. Water is one such gift, without which we and the other creatures on the planet cannot exist. The essential role of water has long been recognized and was worshipped in many countries and civilizations, including ancient India, Egypt, Iran, Greece, Rome, Israel, Syria, Jordan, and Mongolia. Water has been paid high esteem in ancient Indian culture to the extent that it is regarded as “God”. Indeed, water is considered sacred in all religions: Christians, Muslims, and Hindus sprinkle holy water on a newborn child. This recognition of the importance of water has led to quotes in their holy books such as “God gives life to a substance by means of water” (Islam: The Holy Quran 21:30), “Whoever believes in me, a stream of living water will pour from within him” (Christianity: John 7:38), and “The life has been created in water” (Hinduism: Atharvaveda, Asthagarideyam).

In his quest to quench a seemingly insatiable hunger, modern man has played havoc with nature and its precious gifts. Out of the total enormous quantity of water available on the Earth, barely a small fraction of it is potable and it is one of the most scarce commodities in some parts of the world. On the other hand, in many other places the gross abuse of water has threatened the very process of obtaining pure potable water from the hydrosphere. The curse of modern industrialization is that while extracting some useful and meaningful substances, significant amounts of pollutants are released into the environment. This is how we have heavily polluted the water, air, and soil. Inadequate access to clean water is one of the most pervasive problems afflicting people throughout the world. Problems with water are expected to grow worse in the coming decades. Global water scarcity is likely to affect even those regions currently considered water-rich. Unless new ways to supply clean water are found, this situation will inevitably eventually lead to wars for water.

The ancient civilizations, knowing water as a vital element for life, were very particular to maintain it pure and free from any kind of pollution. The “Manu Smriti”, an Indian scripture, stresses at several places the importance to keep water clean. The “Padma Purana” forcefully condemns the person who pollutes water resources. The need for pure water resulted in the development of water purification methods. These methods provided the foundation for the development of modern-day methods of purifying water. Ancient civilizations that developed early water purification methods include those located in Africa, Asia, especially India and the Middle East, and Europe. On the American continent, archeological evidence suggests that the ancient Mayan civilization used an aqueduct technology, similar to that used by the Romans much later, to provide water to urban residents. Methods to assess and maintain water quality and treatment methods for impure water are explained in the Vedas and in Ayurveda, the oldest known health care system. Varahamihira, an ancient Indian scientist, presented methods for obtaining potable water from a contaminated source using plants, metals, and heat. Ayurveda prescribed a water purification method for drinking purposes by using various flowers and fruits. Ayurveda, as per “Sushutra Sutra”, also prescribed a few other substances like clearing nuts, Gomedka, lotus bulbs, moss, pearls, thick cloth, etc., with which impurities, including suspended ones, could be removed from water.

– Sushruta Sutra 45.13

Much later, in 2000 BC, the Indians and Greeks started boiling water, sand, and gravel filtration, and straining methods for the purification of water. The main driving force for the earliest water treatment processes was perhaps the taste and turbidity of water. At that time the concept of microorganisms or chemical contaminants was probably unknown. After 1500 BC, the coagulation process, in which a chemical, alum, was used for suspended particle settlement, had been started in ancient Egypt. Pictures of this purification technique were found on the walls of the tombs of Amenophis II and Ramses II. After 500 BC, Hippocrates, the father of modern medicine, discovered the healing powers of water. He invented the practice of sieving water, and created the first bag filter, which was called the “Hippocratic sleeve”. The main purpose of the bag was to trap sediments that caused bad tastes or odors in water. Later, in the year 1627, water treatment history continued as Sir Francis Bacon started experimenting with seawater desalination through an unsophisticated form of sand filtration. He did not get the desired success but his work did pave the way for further experimentation by other scientists. In the 1700s the first water filters made of wool, sponge, and charcoal came into existence. In 1804 the first actual municipal water treatment plant based on slow sand filtration was designed by Robert Thom in Scotland. In the 19th century, the effect of disinfectants, such as chlorine, was discovered. In 1854, during the time of a cholera outbreak, John Snow, a British scientist, applied chlorine to purify water, and this established the route for water disinfection. Along with this, ion exchangers were also developed for water softening. In the late 1890s, America started building large sand filters for water to protect public health. In 1902, calcium hypochlorite and ferric chloride were mixed in a drinking water supply in Belgium, resulting in both coagulation and disinfection. In 1906, ozone was used as a disinfectant for the first time in France. In the 1970s, people became aware about water pollution due to organic chemicals, including pesticide residues and industrial sludge. Many techniques such as aeration, flocculation, and activated carbon adsorption were used to combat water pollution. In the 1980s, membrane development for water treatment was added to the list.

There have been several new developments in the water treatment field in the last three decades. Conventional methods for water treatment can address the issues of disinfection, decontamination, and desalination. These water treatment methods are heavily dependent on large supplies of chemicals and energy. They also require huge operational complexity and are focused on large systems requiring considerable infusion of capital, engineering expertise, and infrastructure, all of which precludes their use in many parts of the world. Materials commonly used in these technologies are sediment filters, activated carbon, water softeners, ion exchangers, ceramics, activated alumina, organic polymers, and many hybrid materials.

Environmental considerations demand the development of strong, economically viable and eco-friendly replacements for conventional methods. Such interventions should be based upon renewable materials which are economical and which tend to degrade naturally if ever released in the environment. It is also important to develop technologies which consume less energy and have minimal effect on global warming. Green remediation is the practice of minimizing the environmental footprint of cleanup actions. It considers all environmental effects of cleaning up a contaminated site. Green and sustainable remediation of water is a rapidly growing field of interest to one and all: governmental agencies, corporations, academia, environmental consultants, public interest groups, and individuals. With the advancement of science in the 21st century, scientists are now able to create lighter and stronger materials for remediation of contaminated water which are not detrimental to our environment. Sources for such green materials include a wide range, from inorganic to organic to hybrid and from plant biomass to animal biomass, non-porous to porous, microbial to antimicrobial, and from solids to liquids.

In light of the above considerations, a focused set of articles covering a range of green materials for water remediation has been included in this book. Chapter 1 discusses the guidelines being followed for materials to be used for water remediation. It also discusses the directives given by the various world authorities in this regard. The information in this chapter provides the basic starting knowledge to new researchers in the field.

Chapter 2 presents a generalized and yet comprehensive view of available green technologies covering all biological and chemical methods, as well as their processes and applications for metal remediation. Chapter 3 gives a compilation of studies done by researchers on plant biomass-based materials as treatment agents for the removal of heavy metals from wastewater. The major advantages of biosorption over conventional treatment methods include low cost, minimization of chemical and/or biological sludge, no additional nutrient requirement, regeneration of the biosorbent, and the possibility of metal recovery. The author also discusses the types of mechanisms involved in the process. Chapter 4 evaluates the application of plant and animal polysaccharides as flocculants in effluent treatment.

Chapter 5 is a review of the application of zeolites in wastewater treatment. A brief overview on water softening and recent applications for removal of ammonia from wastewater are given in the chapter. Immobilization of organic complexing agents on the surface of an inorganic or organic solid support is usually aimed at modifying the surface with certain target functional groups that can be exploited for specific metal extraction. Chapter 6 presents functionalized silica gel, an organic–inorganic hybrid material, for metal remediation. Ease of synthesis of these green materials is discussed, along with methods based on solid-phase extraction using them for the separation and preconcentration of metal ions in polluted water resources.

Chapter 7 presents nanotechnologies developed rapidly in the past decade for water remediation. It gives an account of various types of nanomaterials evaluated/being evaluated as functional materials for water purification, e.g. metal-containing nanoparticles, carbonaceous nanoparticles, nanocrystalline zeolites, photocatalysts, magnetic nanoparticles, and dendrimers.

Chapter 8 emphasizes the potential of ionic liquids in many separation processes. Ionic liquids have been emerging as “green” solvents in separation processes due to many fascinating properties and having the potential to replace conventional solvents. Moreover, the required properties in extraction systems, i.e. hydrophobicity, polarity, efficiency, and selectivity, can be tailor-made using ionic liquids. They are used for simple biphasic liquid–liquid extractions, liquid-phase micro-extractions, ionic liquid-based solid-phase micro-extractions, thin layer chromatographic and high-performance liquid chromatographic methods, electro-migration methods, gas–liquid chromatographic methods, and supported ionic liquid membrane separations.

Chapter 9 describes the composition and structure of periphyton biofilms studied in recent years along with two aspects of their application, firstly in the purification of water and secondly in phosphorus release from sediments, cyanobacterial blooms, and periphyton biofilms. Periphyton communities are often used as monitors of ecosystem health and indicators of contamination in aquatic ecosystems. They are largely phototrophic benthic microbial biofilms. Owing to their microporous structure, complex composition, and extracellular polymeric substances, periphyton biofilms are applied in water and wastewater treatment. Chapter 10 describes the importance of microorganisms, especially green algae, in water remediation processes. Using green algae for the treatment of textile wastewater is slowly making a mark in the field of water treatment. The mechanism involved and factors affecting biosorption and the parameters used for predicting the efficacy of the use of viable green algae are discussed.

Chapter 11 describes green materials that exhibit ion-exchange properties and can undergo surface modification with positively charged surfactants. This property gives them efficiency for oxo anion removal from water. This process of surface modification shows high promise for a fraction of the cost of commercially available ion-exchange media.

All chapters of the book comprise fundamental information about the various types of promising green materials used for water remediation. The use of such materials will lead to a better and more sustainable way of treating polluted water. The book may be of use to students and researchers in this field.

Anuradha Mishra

James H. Clark