Bioremediation for Environmental Pollutants

Chemical elements with an atomic mass unit ranging from 63.5 – 200.6 (relative atomic mass) and a relative density exceeding 5.0 are generally termed as heavy metals. Since they are non-biodegradable inorganic contaminants, physical and chemical methods of degradation are ineffective. Heavy metals cannot be degraded easily due to their physical and chemical properties, such as the rate of oxidation & reduction reactions, rate of solubility, formation of complexes with other metal ions, etc. They are flexible, and easily accumulated in the environment. In the case of bioaccumulation, they are highly lethal to the organisms. The process of removal of toxic and hazardous material from the environment using plants and microorganisms is termed bioremediation. The disposal of toxic contaminants using plants is termed phytoremediation. Microbial bioremediation consists of the removal of toxic elements with the application of microorganisms during which the toxic substance is converted into either end products or nontoxic and non-hazardous forms or recovery of metals. 

The unorganized dumping of effluents along with different wastes directly into the water and soil has resulted in the rise of the concentration of many harmful metals, chemicals, and other gases in the environment. Widely known heavy metals triggering pollution issues are Lead (Pb), Chromium (Cr), Mercury (Hg), Cadmium (Cd), Copper (Cu), Arsenic (As) and Selenium (Se), as these heavy metals are generally found in the effluents of fertilizers, metallurgy, electroplating, and electronics industries. A number of physical-chemical reactions such as acid-base, oxidationreducing, precipitation- dissolution, solubilization and ion-exchange processes occur and affect metal speciation. The physical methods used for heavy metals removal include magnetic separation, electrostatic separation, mechanical screening method, hydrodynamic classification, gravity concentration, flotation, and attrition scrubbing. The chemical methods used for eliminating heavy metals are chemical precipitation, coagulation and flocculation processes and the heavy metals are therefore removed as sludge. Electro-deposition, membrane filtration, electro-flotation and electrical oxidation are the various electrochemical treatment methods that are used to remove heavy metals from wastewater. Bioremediation is a biological method of eliminating toxins from the environment by using biological microbial bacteria such as Pseudomonas and Sphingomonas. Examples of bioremediation technologies include field farming, bioleaching, phytoremediation, bioventing, bioreactor, bio-stimulation and composting. Bioremediation is a natural process and is quite applicable as a waste treatment process for contaminated soils. The microbes present in the solution or soil can degrade the pollutants. It can also prove to be less expensive than other technologies that are used for clean-up of hazardous waste and are also useful for the destruction of a wide variety of contaminants as many hazardous compounds can be transformed into harmless products.

The pulp and papermaking industry, being a large consumer of natural resources, i.e., wood and water, has become one of the largest sources of pollution to the environment. Wastewater generated during various stages of the pulp and papermaking process continues to be toxic in nature even after secondary treatment. The effluent water contains not only various toxic chemicals such as volatile organic compounds but also heavy metals like copper, mercury, iron, zinc aluminium, etc. Even at very low concentrations, most of the heavy metals are toxic and deadly in nature. Prolonged exposure to heavy metals causes various diseases in humans and animals either through skin contact, inhalation, or via consuming food materials.
Treatment of pulp and paper industry wastewater by conventional methods is not efficient due to its complex nature. These conventional methods, either physical, biological, chemical or a combination of these methods are also not environmentally safe and economically viable. Complete degradation of heavy metals is not possible by the application of a single method. The generation of a huge volume of toxic sludge is an ongoing and major problem. Therefore bioremediation methods are preferred as they are highly efficient, cost effective, eco-friendly in nature, there is no secondary waste created in the environment and metabolize the highly toxic heavy metals into degradable, less toxic components with the help of microbes.
This chapter focuses on Micro-Bioremediation methods using algae, fungi, yeasts and bacteria as the most preferred medium to treat wastewater generated by the pulp and paper industry. These are further also used to reduce toxic organic compounds.

Increasing population has raised the demand for food grains, which compels the producers for the heavy use of pesticides to meet the demand for sufficient production of food grains. Heavy utilization of pesticides polluted soil, water, plant, animal, food grains, etc. Additionally, that much utilization of pesticides has also created several legal and illegal contaminated sites across the world, which are continuously polluting the environment. There are several methods available for pesticide treatment, but the bioremediation method has been more promising than the others. Bioremediation of pesticides is carried out through either ex situ or in situ methods using different organisms like bacteria, fungi and higher plants. The pesticides degradation using bacteria, fungi and higher plants is called bacterial degradation, mycodegradation and phytodegradation, respectively. Present review discusses different methods, mechanisms and recent tools used for the bioremediation of pesticides.

The low toxicity, biodegradability, powerful surface activity, and the functionality under extreme conditions (pH, salinity and temperature) make the surfactants produced by micro-organisms (bacteria, fungi, and yeasts) best surfaceactive molecules that can replace hazardous and non degradable chemical surfactants in different industries and fields. In recent decades, there has been growing interest in the use of biosurfactants for bioremediation of environmental pollution and biodegradation of various categories of hydrophobic pollutants and waste due to their eco-friendly and low-cost properties. This chapter presents the classification, the characteristics, and the potential uses of biosurfactants in the solubilization and enhancing the biodegradation of low solubility compounds.

The most problematic issue related to textile wastewater is dyes. The occurrence of toxic and carcinogenic compounds in textile dyes creates aesthetic problems and affects the aquatic ecosystem. Dyestuff removal methods include physical, chemical, and biological-based technology. For a more environmentally friendly process that is low cost, produces less sludge, and needs a lesser amount of chemicals, biological treatment is preferable technology. To get maximum effectiveness and efficiency, integrations/ hybrids consisting of several technologies are commonly used. This chapter is dedicated to exploring the potential of biological technology to remove dyes from wastewater, especially dyes used in textile industries. This chapter briefly discusses dyes' characteristics, their utilization, and toxicity. Deeper reviews about the biodegradation potential of dyes are elaborated, along with a discussion about biodegradation mechanisms and reviews of either lab-scale or fullscale applications of biological-based technology for dyes treatment. Lastly, this chapter also gives future insight into the biological treatment of dyes.

Advancement in industrialization and urbanization has caused an influx of contaminants into the environment polluting the soil, water, and air. These contaminants come in various forms and structures, including heavy metals, petroleum hydrocarbons, industrial dyes, pharmaceutically active compounds, pesticides, and many other toxic chemicals. The presence of these pollutants in the environment poses a serious threat to living things, including humans. Various conventional methods have been developed to tackle this menace, though effective, are however not safe for the ecosystem. Interestingly, bioremediation has offered a cheap, effective, and environmentally safe method for the removal of recalcitrant pollutants from the environment. White-rot fungi (WRF), belonging to the basidiomycetes, have shown class and proven to be an excellent tool in the bioremediation of the most difficult organic pollutants in the form of lignin. White-rot fungi possess extracellular lignin modified enzymes (LMEs) made up of laccases (Lac), manganese peroxidase (MnP), lignin peroxidase (LiP), and versatile peroxidase (VP) that are not specific to a particular substrate, causes opening of aromatic rings and cleavage of bonds through oxidation and reduction among many other pathways. The physiology of WRF, nonspecificity of LMEs coupled with varying intracellular enzymes such as cytochrome P450 removes pollutants through biodegradation, biosorption, bioaccumulation, biomineralization, and biotransformation, among many other mechanisms. The application of WRF on a laboratory and pilot scale has provided positive outcomes; however, there are a couple of limitations encountered when applied in the field, which can be overcome through improvement in the genome of promising strains.

In the recent decade, membrane technology has gained immense interest in water purification, wastewater treatment, and water desalination. However, the major drawback which destroys the efficiency of membrane technology is fouling. Membrane fouling arises due to the non-specific interaction between fouling species and membrane surface. This major drawback can be overcome by preparation of antifouling membranes. Although there are various techniques involved in water filtration i.e. microfiltration, ultrafiltration, and nanofiltration. However, in this book chapter, we shall emphasize antifouling nanofiltration membranes, recent developments and future prospects. Further, we shall discuss the various fouling types, its consequences, mechanisms affecting fouling, challenges, and modification approaches in the antifouling membrane technology.

The catastrophic effect of petroleum contamination on the environment is a severe problem of global concern. Bioremediation is probably the easiest and most cost-effective way to treat the contaminants. Several microorganisms ranging from bacteria, fungi, yeast, algae, etc., are known for their ability to biodegrade different hydrocarbons. Hydrocarbon degrading microorganisms are largely known for the release of biosurfactants and other surface-active biopolymers, which decrease the surface tension of oil particles into smaller entities for their easy degradation throughout the respective metabolic cycle. Such biopolymers are encoded by several genes and operon systems which are discussed briefly in this chapter. Information on such genes help in better understanding the molecular events involved in the microbial bioremediation of petroleum hydrocarbon. 

Oil spill contamination occurs due to exploration activities in the deep sea and downstream activities such as oil transportation via pipelines, oil-tankers (marine and terrestrial), re-fineries, finished product storage, distribution, and retail distribution setup. Physico-chemical technologies are accessible for oil spill clean-up, but oil bioremediation technologies are proven to be more affordable and environmentally friendly. The aim of this book chapter is to give deeper knowledge about the bioremediation technology of oil spills. This chapter discusses the nature and composition of crude oil, bioremediation agents and strategies, bioremediation on different matrices (water, soil sludge), application strategy, and future prospect of bioremediation technology.

Hydrocarbons are a common contaminant in both terrestrial and aquatic ecological systems. This is most likely due to the widespread use of hydrocarbons as everyday energy sources and precursors in the majority of chemical manufacturing applications. Because of their physical and chemical properties, most hydrocarbons in the environment are resistant to degradation. Although several derivatives are classified as xenobiotics, their persistence in the environment has induced microorganisms to devise ingenious strategies for incorporating their degradation into existing biochemical pathways. Understanding these mechanisms is critical for microbial utilization in bioremediation technologies. This chapter focuses on recalcitrant and persistent hydrocarbons, describing the reasons for their resistance to biodegradation as well as the effects on ecological systems. Furthermore, aerobic and anaerobic degradation pathways, as well as ancillary strategies developed by various microorganisms in the degradation of hydrocarbon pollutants, are discussed.

Plastic is being used over the entire globe in the form of capsules, microbeads, fibers or microplastics. The waste thus generated has gained concern due to the loss of aesthetic value, the presence of various toxic chemicals such as plasticizers, antioxidants, etc., and the release of greenhouse gases. The small size and slow degradability of microplastics are responsible for their accumulation in the environment and organisms. Plastic degradability can be improved by altering its chemical and physical structure or using better degrading agents. Different types of microorganisms and enzymes are being designed and employed for degrading plastic waste. This chapter gives an overview of the degradation mechanism along with different microbial, plant and animal species responsible for this process. 

The essentiality of plastics in our daily life is inseparable. Almost all industrial sectors utilize plastics either directly or indirectly. But the downside of plastics also increased simultaneously. These materials increased water and soil pollution due to unmanaged discharge. Hence, plastic waste treatment becomes essential for a sustainable and efficient environment. Plastic recycling and degradation are two processes to deal with plastic waste. Out of the three degradation processes, physical, chemical, and biological, biological degradation is near to a sustainable environment. Recent studies revolve around the use of micro-organisms for the degradation of plastics. The present chapter reports the microbial degradation of plastic waste using bacteria and fungi. The discussion also includes the impact of plastic properties and environmental factors on biodegradation.

The increase in the amount of plastic waste, especially microplastics and the environmental pollution caused by it has diverted the research focus of the world into plastic recycling and degradation. Hence in the last decade, different strategies have been adopted to combat this problem. Albeit many physiochemical technologies are there for the degradation of plastics, they give rise to harmful chemicals as by-products. This has shifted the priority of our research to the biodegradation of plastics by microbes. In fact, in the last decade, many microorganisms have been discovered with the ability to degrade many conventional plastics with moderate efficiency but longer duration. The initial part of this chapter discusses the various kinds of plastics present and the methods adopted for the degradation of plastics, with special emphasis on the factors affecting plastic degradation. In the subsequent section, the microbial degradation of different plastics by bacteria and fungi, along with a mechanism, has been outlined. Furthermore, this chapter also briefly discusses the role of enzymes in the degradation of different plastics by microbes and the future of plastic biodegradation.