*5.2.1.1 Intrinsic bioremediation*

Intrinsic bioremediation is a process for converting environmental pollutants degrades to non-toxic forms through the immanent abilities of naturally occurring microbial population at the site. This process is usually employed in underground places as such underground petroleum tanks. Intrinsic bioremediation manages the innate capabilities of naturally occurring microbial communities to degrade environmental pollutants without modified or taking any engineering steps to accelerate the process [11]. This technique deals with stimulation of indigenous microbial population by feeding them nutrients and oxygen to increase their metabolic activity.

#### *5.2.1.2 Enhanced (engineered) In situ bioremediation*

As the name suggested this technique involves the introduction of specific microorganism to the contaminated site. Engineered in situ bioremediation accelerates the degradation process by enhancing the physicochemical conditions to increase the growth of microorganism.

#### A.**Bio-venting**

Bio-venting is an in situ remediation technique that uses microorganisms to degrade organic constituents adsorbed on soils [17]. This technique involves regulated stimulation of airflow for increasing oxygen to unsaturated zone for enhances the bioremediation, by increasing activities of indigenous microbes. In the process of bio-venting, amendments are done by adding nutrients and moisture to increase bioremediation to achieve microbial transformation of pollutants to a nontoxic state. This technique has gained popularity among other in situ bioremediation techniques especially in restoring sites polluted with light spilled petroleum products. Bioventing primarily use for the degradation of adsorbed fuel residuals, and also can use in the degradation of volatile organic compounds (VOCs) through biologically active soil.

#### B. **Bioslurping**

Bioslurping technique is the combination of bioventing and vacuum-enhanced pumping of soil and groundwater remediation by indirect provision of oxygen and stimulation of contaminant biodegradation [18]. This technique uses a "slurp" that extends into the free product layer, which draws up liquids (free products and soil gas) from this layer in a manner similar to that of how a straw draws liquid from any vessel. The bioslurping system is constituted by a well connected to an adjustable length called "slurp tube" is installed, and this slurp tube, connected to a vacuum pump, which is lowered into the light nonaqueous phase liquids (LNAPL) layer, and pumping begins to remove free product along with some groundwater. The vacuum-induced negative pressure zone in the well promotes LNAPL flow towards the well and also draws LNAPL trapped in small pore spaces above the water table. This technique used to

remediate soils contaminated with volatile and semi-volatile organic compounds
