Green Solutions for Degradation of Pollutants

The chemical compounds that have been identified as dangerous to the environment, ecosystem and human health are classified as Emerging Pollutants (EPs). EPs include a variety of compounds such as dyes, pesticides, antibiotics, drugs, endocrine disruptors, hormones, industrial wastes and chemicals, and microplastics. These pollutants are malignant and non-biodegradable in nature, so they are responsible for the unhealthy and unsustainable environment. The occurrence of these pollutants has raised global concerns not only in various environmental matrices (air, water, and soil) but also in biological systems due to their toxic nature. These pollutants get accumulated in the environment and ecosystem and cause intensified environmental problems, global warming, deterioration of soil quality, the greenhouse effect, and ecological imbalance. Consequently, they affect the quality of life and the maintenance of the environment on a global level. Recent research indicates that if this trend is continued, situations will worsen in the near future. Sustainable solutions, such as bioremediation, nano-bioremediation, microbial degradation etc., are becoming increasingly important for the removal of these EPs as an efficient tool for sustainable development and pollution control. Therefore, the main aim of this chapter is to assess the current threats and future challenges associated with emerging pollutants so that focus can be drawn on sustainable green solutions for a greener and healthier environment. 

The rise in environmental pollution is a major issue of concern in the current times. Due to globalization and the Industrial Revolution in the 20th century, pollution has become a problem for the world's population. Numerous factors, including unchecked human activity, careless use of petroleum products, industrial waste emissions, poor waste management, release of toxic organic by-products, and increased use of pesticides, insecticides and fertilizers have contributed to increased pollution and its detrimental effects on the planet Earth. For all forms of life, organic molecules are known to have the potential to be carcinogenic and poisonous. To reduce organic pollutants and dispose of industrial waste properly, several techniques have been put forth and put into action, but some of them are either not relevant or have not produced the expected outcomes. For the past few decades, research has been focused on finding biological methods of degradation of complex organic contaminants. Numerous microbial species obtained from polluted native environments have been shown to digest hazardous, complex organic chemicals and can be used to effectively biodegrade contaminated areas. The development of recombinant DNA technologies has revitalized the area of bioremediation by enabling the emergence of microorganisms and entire microbial communities that contain novel genes and enzymes with improved efficiencies. This chapter discusses the significance of isolating efficient indigenous microbial species, different factors that affect the distribution of pollutants in the soil matrix, biodegradation pathways, and physiological factors that affect the efficiency of biodegradation for complete mineralization. In addition to these, efforts to enhance the biodegradation potential of microbes through multiple pathways have also been highlighted. 

Nanomaterials (NMs)-based technology is a powerful tool in the current scenario because of their size and unique physicochemical properties. Green synthesized NMs are promising in creating new and vital products that are beneficial to the environment, industry, and humans. Due to its simplicity, nontoxicity, and environmentally benign advantages, the synthesis of metal nanoparticles (NPs) using green techniques has received a lot of attention recently. Every day, attention is drawn to recycling waste and putting it to good use. NPs are easily manufactured in a green, energy-free manner using plant extracts that are not intended for human consumption. Metal-based NPs are widely used due to their applications, including medicine, biomedical sciences, biosensing, food, cosmetics, and electronics. NPs produced from novel synthesis techniques using plant extracts have remarkable qualities. In the synthesis of NPs via the green approach, many metals such as silver, gold, copper, zinc, manganese, nickel, and magnesium are used due to their unique physical and optical properties. In this chapter, the authors have reported the mechanisms of various green methods of synthesis of NPs, their biological and environmental applications along with their challenges and prospects.

A biological process termed bioremediation transforms waste into a form that can be used and reused by other microbes. Recent research has revealed that xenobiotic pollution and other associated refractory substances pose a serious threat to both human health and the environment. Many contaminants, including heavy metals, polychlorinated biphenyls, plastics and different agrochemicals, are prevalent in the environment because of their toxicity and inability to biodegrade. The key objective of bioremediation is the degradation of pollutants and their transformation into less harmful forms. Depending on several variables like cost, kind and concentration of the contaminant and other considerations, ex-situ or in-situ bioremediation may be used. Bioremediation can be done with the help of microorganisms that can withstand all circumstances due to their metabolic potential. Microbes have a tremendous nutritional capacity, making them useful in the bioremediation of environmental contaminants. With the complete and coordinated activity of microorganisms, bioremediation is significantly involved with the decomposition, expulsion, immobility or decontamination of different chemical pollutants and physically dangerous chemicals from the natural atmosphere. Enzymatic processes and other techniques, including bioventing, bioaugmentation, biostimulation, biopiles and bioattenuation, are widely used throughout the world based on their characteristics, benefits and drawbacks. This chapter aims to portray the current advancements in green bioremediation methods, how various contaminants are broken down by microorganisms and what the future holds for bioremediation in terms of lowering global pollution levels.

CDs (Carbon dots) are a new group of zero-dimensional luminescent nanomaterials. They have drawn a lot of attention due to their excellent properties, for example, easy preparation, strong optical properties, low toxicity, significant biocompatibility, low cost, facile functionalization, tunable porous structures and high specific surface area. CDs have found many applications in the fields of bioimaging, sensing, catalysis, optoelectronics and energy conversion. Recently, CDs have demonstrated promising applications in the control of environmental pollution and remediation. CDs have been applied for environmental pollutants sensing, adsorption of contaminants, membrane-based separation, photocatalytic degradation of pollutants, and antimicrobial coatings for protection. In this chapter, we have discussed the classification of CDs, synthesis, properties and applications of CDs in environmental pollution control and environmental protection measures.

Science has undergone a revolution with the development of nanotechnology. The vast applications of nanoparticles (NPs) have greatly helped every area of technology. Nanomaterials (NMs) can be created via a range of physical and chemical practices along with the use of ultrasound and microwave heating processes, but green synthesis has drawn great attention, especially when it involves the use of microbes or plant extracts. Green synthesis is a recent and advanced method to make NPs because it is simpler, cheaper, more reproducible and environmentally friendly than other approaches. When compared to other classical methods of NP synthesis, plants produce NPs that are more stable and simpler to scale up and have a variety of applications. This chapter has reviewed and discussed various applications of green synthesized NPs along with the latest developments in the eco-friendly synthesis of gold, silver, copper, palladium, iron, and iron oxide NPs. Due to the widespread use of nanoscale metals in different industries, including engineering, medicine, and the environment, the topic of nanoscale metal synthesis is currently relevant. The bulk of nanoscale metals is currently produced chemically, which has unintended effects like environmental contamination and serious health issues. To overcome these challenges, green synthesis can be used as a commercial chemical method to decrease metal ions from the environment. Green synthesis is more advantageous than classical chemical synthesis because it improves environmental quality and is also safe for human health.

Nanotechnology has gained significant attention in the fields of biotechnology and biomedicine and has been widely used in drug delivery, imaging, diagnosis, and sensing. Nanoparticles (NPs) are submicron-sized particles that have unique properties due to their high surface area-to-volume ratio. NPs have gained significant attention in recent years due to their potential applications in biotechnology and biomedicine, including drug delivery, imaging, diagnosis, and sensing. Microalgae are photosynthetic microorganisms that are widely distributed in aquatic environments. Recently, microalgae have been explored as a potential source of NPs due to their unique chemical and physical properties. Microalgae-derived NPs have several advantages over chemically synthesized NPs, including lower toxicity, biocompatibility, and eco-friendliness. In this chapter, we have discussed the various types of NPs produced by microalgae, their synthesis and characterization methods, and their different domains of applications, with a special focus on environmental remediation. Additionally, we have highlighted the challenges and prospects of using microalgae-derived NPs. 

In the current scenario, dangerous refractory organic and inorganic pollutants are continuously released into the environment as a result of industrialization that poses a significant threat on a global scale. One of the greatest challenges that needs to be solved is the effective management of various pollutants and waste. Despite their effectiveness, traditional treatment methods have several drawbacks, such as the fact that they are time-consuming and target-specific. As a result, it directs the search for a suitable replacement. Researchers are paying close attention to the novel technique of nano-bioremediation to remove pollutants from various contaminated locations. This approach combines the benefits of bioremediation and nanotechnology to develop a remediation process that is quicker, more productive, and less harmful to the environment than either approach individually. This chapter summarizes the green synthesis methods of various nanomaterials (NMs) along with an explanation of the remediation methodology, its mechanism, and prospective applications in environmental remediation. Additionally, the removal and valorzsation of waste materials using green nanotechnology supported by microbes and enzymes are highlighted. This chapter also discusses the multiple constraints of nanobioremediation as well as the factors responsible for the efficiency of NMs.

Chromium is a major component that is responsible for environmental stress. It also has profound effects on the health of living beings because trace amounts of chromium in the environment have been linked to serious health problems in humans and plants. The dangers to human health, bioavailability, plant response to chromium toxicity, and phytoextraction storage in plants are issues of major concern. Understanding and optimizing the phytoextraction process would be immensely beneficial to know about metabolic pool changes that occur in plants in response to Cr toxicity. Therefore, the removal of chromium from the environment is necessary due to its toxic nature. However, the removal of chromium from the environment is a daunting task. Physico-chemical and biological techniques are either too expensive or inefficient to be widely implemented to eradicate chromium from the contaminated soil and environment. The challenges of widespread implementation can be met by adopting integrated approaches, which are currently under consideration. The removal of chromium from the environment can be more economical and sustainable using phytoremediation technology.

In this chapter, we have discussed the phytoremediation technique as a green solution for the removal of chromium from polluted soil because phytoremediation, and especially phytoextraction, is a viable and sustainable solution to restore chromiumpolluted soil.

Water is the most crucial natural resource required for the survival of humankind, but chemical industries, household activities, foul practices, etc., are responsible for polluting it. This leads us to work on the purification and bioremediation of water contaminants. Diverse techniques have been developed globally for decontamination/purification of water, but owing to their high cost, tediousness and time consumption, it has become necessary to work on those methods that are comparatively cheaper, techno-feasible and employ a green process. In the contemporary world, the use of nanotechnology in the bioremediation of water pollutants revolutionarily provides a way to incorporate functional chemicals in notably reduced quantities to fulfil the desired purpose. Globally, water pollution is primarily caused by the rainwater containing the pollutants present in the air. Industrial and domestic wastewater, which is a major source of toxic heavy metals, industrial dyes, pesticides and insecticides, is used in agriculture. These water pollutants adversely affect the health of human beings as well as the whole ecosystem of the affected region. The employment of nano-materials (NMs) degrades the pollutants from the water source to its standard permissible level. The current chapter comprises a detailed discussion on the immense potential of NMs in the bioremediation of polluted water using different NMs and also provides a comprehensive comparison with other conventional bioremediation methods to make water environmentally non-hazardous. 

Nanotechnology is a multidisciplinary area with a wide range of applications. Recent developments in nanotechnology and nanoscience have also triggered the development of new nanomaterials (NMs), enhancing the hazards to human health and the environment. There has been a rise in interest in creating ecologically friendly techniques for producing metallic nanoparticles (MNPs). The aim is to reduce the harmful effects of synthetic technologies, the chemicals used in association with them, and the derivative products. A useful strategy in green nanotechnology is the utilization of various biomolecules for the fabrication of NPs. MNPs that are inexpensive, energy-efficient, nontoxic, and beneficial to the environment have been produced using biological resources, including bacteria, algae, fungi, and plants. Plant components are mainly employed as capping and reducing agents in green synthesis. MNPs of various sizes and forms have been created using bark, leaves, fruits, and flower extracts. In this chapter, we have addressed the green synthesis of palladium NPs to remove positive ions, negative ions, and dye from wastewater, their potential applications and the directions for future research.

 In the process of purification of water, nanotechnology provides the possibility of an effective removal of pollutants and germs. In recent times, nanoparticles (NPs), nanopowder and nanomembranes have been used for the detection and removal of chemical and biological substances that contain metals like cadmium, copper, lead, mercury, nickel, zinc, etc., nutrients like phosphate, ammonia, nitrate and nitrite, algae, cyanobacterial toxins, viruses, bacteria, parasites, and antibiotics. Commonly, four classes of nanoscale materials that are being evaluated as functional materials for water purification are metal-containing nanoparticles, carbonaceous nanomaterials, dendrimers and zeolites. Carbon nanotubes and nanofibers are also used in the techniques of water purification. Nanomaterials (NMs) give the best results in water treatment in comparison to other techniques because NMs have a high surface area (surface/volume ratio). Silver NPs affect the activated sludge of microorganisms and play an important role in wastewater treatment since they restrain their activity and significantly reduce their number. Carbon nanostructures are widely used as nanoadsorbents for wastewater treatment owing to their abundant availability, costeffectiveness, high chemical and thermal stabilities, high active surface areas, excellent adsorption capacities, and environmentally friendly nature. Due to the high utility of nanotechnology in the treatment of pollutants, this chapter further highlights various fundamental aspects of nanotechnology, such as types, synthesis, applications and future directions for a green and sustainable environment.

In recent years, microplastics (MPs) and nanoplastics (NPs) have become significant environmental concerns due to their persistent nature and potentially harmful effects on ecosystems and human health. Most of the reported materials and methods for the degradation of such toxic pollutants show limitations such as low recovery, high energy consumption and environmental impacts. As a result, more efficient green materials and methods are the need of the hour. Recently, researchers have reported efficient materials for the degradation of MPs and NPs. Hence, in this chapter, a comprehensive overview of eco-friendly initiatives and preventive measures is highlighted. It covers detailed information about the sources of MPs and NPs and their toxic impact on the environment and human health. It also highlights the existing techniques for processing and degradation of MPs and NPs and the potential of green nanomaterials in the degradation of plastics. The authors believe that this information will pave the way for the design and development of new alternate methods for further implementation.