**5. Bioremediation**

Remediation means to get rid of an issue and if it is associated with taking care of an ecological issue like soil and groundwater contamination is called bio-remediation. Bioremediation is a mechanism which utilizes the living microorganisms to reduce natural contaminations or to anticipate contamination [9]. It is an evolution towards elimination of toxins from the climate in this way reestablishing the first characteristic environmental factors and forestalling further contamination. Bioremediation also can be a permanent in situ solution for contamination instead of simply translocating the problem. Remediation of heavy metals, metalloids, or other inorganic pollutants from soil or water can be done by this technique [10]. It is a cost-effective, efficient, novel, eco-friendly, and solar-driven technology with good public acceptance as compared with other engineering techniques.

**A. Based on applied strategies**: bioremediation techniques applied on the basis of strategies can be classified in two categories. Ex-situ bioremediation. In-situ bioremediation.

**5.1 Ex-situ bioremediation**

Ex-situ as name suggests its mean to remove contamination mat to a remote treatment location. This classification is not much popular because it involves the big task of excavating polluted soil and transports it to offsite. The basic principal of ex situ remediation is to introducing the correct soil oxygen, moisture and nutrient conditions on offsite [11]. However, Ex situ bioremediation process poses a hazard to spreading contamination or risking an accidental spill during transport [12]. There are two technique classes can be applied explained bellow.

## *5.1.1 Slurry phase*

This technique involves the process of combining contaminated soil with water and other additives in a large bio-reactor and mixed to keep the indigenous microorganisms in contact with the contaminants. Essential nutrients, oxygen are added

and the conditions in the bio-reactor are ensured at optimum environment for the micro-organisms to degrade the contaminants. After completion of the treatment, the water is removed from the solids -wastewater is disposed and further treated if still contaminated. Slurry-phase is a relatively rapid process compared to other biological treatment processes specifically for contaminated clays [13]*.*
