**2.1 Ex situ bioremediation**

Ex situ bioremediation involves the excavation of contaminants and transporting them to the treatment sites above the ground. Indigenous microorganisms in the soil act as the remediating agents provided other environmental factors are kept monitored. This method can be tailored by changing the decay conditions and maintaining the optimum conditions required for microorganisms to work efficiently. In some conditions, the amendments are added to the soil. There are various types of ex situ techniques that include, biopiles, composting, windrow, landfarming, and slurry reactors [10].

*De*merits associated with ex situ bioremediation are its being expensive in terms of excavation and solid handling, fractionation and screening, and treatment till final

#### *Recent Applications of Bioremediation and Its Impact DOI: http://dx.doi.org/10.5772/intechopen.104959*

disposal. The contaminant may be either solid or liquid. On the basis of phases of contaminant material, ex situ method can be a solid phase or slurry phase. In case of the solid phase method; waste in the form of solid-like agricultural waste or domestic, sewage sludge, industrial waste, and municipal solid waste are treated to get compost, which is further employed for the conditioning of soil. Treatment is done prior to compost formation to enhance the biological treatment potential. Various physicochemical and biological factors of the site under study are considered for this purpose. Organic material thus presents or added to the soil act as the source of carbon for microorganisms. Depending on the availability of oxygen and suitable working pH the enzymes secreted by microorganisms detoxify the surrounding area. Applying ex situ treatment to a site that has some compositional limitations or nutrient deficiency for microbial activity needs tailoring of the site by adding site-specific compost. Adjusting pH and water availability to the bioremediating site ensures the efficiency of microbial colonies at ex situ operating sites. The slurry phase method is applicable to municipal wastewater. In this method supply of air, maintenance of proper pH, temperature, micronutrients are needed for the growth of microbial colonies [11].

#### **2.2 In situ bioremediation**

In situ bioremediation is the subsurface treatment of contaminants by the biological system of that area. These are considered sustainable methods as they do not require any excavation and transportation of contaminants. Some in situ bioremediation techniques like biosparging, phytoremediation, and bioventing, have been enhanced to get good outcomes for onsite decontamination while some other techniques like natural attenuation or intrinsic bioremediation proceed without any enhancement. In situ bioremediation techniques have been successfully used to treat chemically contaminated sites like; as industrial effluents dumping sites containing dyes, chlorinated solvents, hydrocarbons polluted sites, and heavy metals [12–14].

In situ bioremediation works with the abatement of contaminants by disrupting the minimum area and is a continuous and economical treatment method for soil and water. It can be intrinsic or engineered. Intrinsic bioremediation involves the conversion of contaminant to nontoxic form by the microbial communities naturally present in soil and water. The detoxifying potential of these microbial communities must be tested in laboratories so that outcomes can be configured accordingly. Various working conditions or requirements are there for intrinsic bioremediation to be fruitful. Annual water flow through the area understudy determines the presence of various minerals and pH of that soil which in turn tells about the working of microbes under such conditions. The presence of heavy metals hindered the growth of microorganisms present in the soil and water. The time of exposure of microorganisms to the contaminant is also an important parameter that should be studied at a pilot scale before conducting the bioremediation on a wide surface area. Although intrinsic bioremediation shows very promising decontamination results, but the limiting factor is when working conditions and environmental factors/site conditions do not favor microbial growth. In such cases, engineered bioremediation replaces intrinsic bioremediation. This type of bioremediation technique accelerates the growth of microbial colonies by providing suitable physicochemical growth conditions. The availability of oxygen, nutrients, and electron acceptors like sulfates and nitrates increase the onsite growth of microbes. I*n situ* bioremediation is laborious as compared to other methods. The outcomes of this method are highly environment-dependent. Continuous

availability and replacement of nutrients must be ensured for efficient working genetically engineered microorganisms [11].
