Bioremediation Approaches for Recalcitrant Pollutants: Potentiality, Successes and Limitation

1. Introduction

Environmental contamination due to anthropogenic and natural sources is increasing day by day because of increase in human population, industrialization and urbanization. The paradox for the public, scientists, academicians and politicians is how to tackle the contaminants that jeopardize the environment. Human activities to a greater extent and natural processes to some extent cause serious issues of polluting soil and aquatic environments by releasing a large number of organic chemical substances such as petroleum hydrocarbons, phenolic compounds, halogenated and nitroaromatic compounds, phthalate esters, solvents and pesticides, endocrine disrupting chemicals, toxic heavy metals etc. Organic pollutants comprise a potential group of chemicals which can be dreadfully hazardous to human health. Many of these are recalcitrant. As they persist in the environment, they are capable of long range transportation, bioaccumulation, in human and animals, and biomagnifications in food chain (Nair et al., 2008).Most of the compounds belong to groups that are widespread and are generally persistent and/or toxic. The term “bioremediation” has been used to describe the process of using microorganisms to degrade or remove hazardous components of the wastes from the environment. Biodegradation and its application in bioremediation of organic pollutants have benefited from the biochemical and molecular studies of microbial processes. Biodegradation is defined as the biologically catalyzed reduction in complexity of chemical compounds. It is based on two processes: growth and co-metabolism. In growth, an organic pollutant is used as sole source of carbon and energy and it results in the complete degradation of the pollutant molecules. Co-metabolism can be defined as the transformation of a pollutant by a microorganism incapable of using the pollutant as a sole source of energy or of one of its constituent elements in the presence of a growth substrate that is used as primary carbon and energy source (Basak et al, 2014). Biotransformation of organic contaminants in the natural environment, which is defined as transformation of recalcitrant toxic organic pollutant into the lesser one, has been extensively studied to understand microbial ecology, physiology and evolution for their potential in bioremediation. Bioremediation has considerable strength and certain limitations too. Remediation, achieved whether by biological, chemical or a combination of both means, is the only option as the problem of pollution is to be solved without transferring to the future. As the knowledge mandate and complexities vary for different bioremediation treatments, a better understanding of the principles together with the limitations of bioremediation aids in maximizing the benefits and minimizing the cost of treatments. In this chapter we shall be critically reviewing (i) the potentiality, (ii) successes, the advances made thus far and the requisite foci of research on maximizing the biodegradation of pollutants, and (iii) limitations of bioremediation techniques in removing toxic pollutants from the environments.