Types of Bioremediation

Introduction

Bioremediation techniques have become increasingly effective in restoring polluted environments, making them more cost-effective and sustainable. These techniques involve the use of indigenous and non-indigenous bacteria, which are already present in polluted environments. These microorganisms detoxify, reduce, degrade, mineralize, or transform toxic pollutants into less toxic and stable forms. The efficiency of the process depends on the characteristics of organic or inorganic pollutants, such as agrochemicals, dyes, hydrocarbons, heavy metals, plastics, and nuclear waste. Aerobic bacteria like Bacillus, Arthrobacter, and Achromobacter are commonly used in bioremediation, while anaerobic bacteria like Clostridium and Bacteroidetes are used in various methods.

There are two types of bioremediation, in-situ and ex-situ. In-situ methods treat pollutants at their site, while ex-situ methods involve excavation or transportation. In-situ methods are less expensive and less prone to contamination as they don’t involve the translocation of pollutants. On the other hand, Ex-situ methods treat a wider range of contaminants and are expensive. However, bioremediation’s applicability is limited by a lack of knowledge of control and processes.

Ex-situ bioremediation methods

1: Biopile

In this process, soil from polluted places is excavated and pilled above ground at another site. The air and nutrients are added to the soil to stimulate the growth and activities of microbes. This method is used to remediate volatile, low molecular-weight pollutants in extremely cold environments. The rate of degradation depends on pH, nutrients, temperature, and aeration.

2: Windrows

In this method, there is periodic turning of piled polluted soil to increase degradation through microbes in the soil. In the removal of hydrocarbon, this method is more effective than Biopile treatment. For the remediation of toxic volatiles, this method should not be considered as periodic turning is associated with it.

3: Land Farming

In this technique, polluted soil is placed on a fixed layer above the ground surface for aerobic degradation of pollutants. It is a simple technique, requires low energy, and has minimal environmental impacts. By using this method, large areas of polluted soil can be remediated.

4: Composting

In this process, waste is degraded by microbes at very high temperatures ranging from 55-65°C. In this process, microbes produce heat leading to more solubility of wastes and increased metabolic activity. It has many benefits i.e., enriches the soil, reduces methane emission and the need for chemical fertilizers, and lowers the carbon footprints. But it has limitations too.  This process takes more time (three to six months). The piles smell very bad.

5: Bioreactors

It is a manufactured facility or a vessel that supports a bioactive system. Pollutants can be placed in bioreactors in two phases, either as a dry matter or as a slurry. This technique has many advantages i.e., the controlled bioprocess parameters, and the flexible nature of bioreactor designs.  Limitations include costly and limited space etc.

In Situ Bioremediation Techniques

1: Enhanced in situ bioremediation

• Bioventing

In this In situ technique, airflow is controlled for delivering oxygen to the unsaturated (vadose) zone. This increases the bioremediation by increasing the activities of indigenous microbes. Moreover, nutrients and moisture are also added to enhance the microbial transformation of pollutants to a harmless state.

• Biosparging

Biosparging is a technique similar to bioventing. Unlike bio venting, air is injected into a saturated zone which cause volatile organic compounds to move upward to an unsaturated zone to promote degradation. This technique is widely used for treating aquifers polluted with petroleum products.

• Bioslurping

This technique combines the strategies of vacuum-enhanced pumping and soil vapor extraction. This is used for soil and groundwater remediation. Capillary, saturated, and unsaturated zones are remediated by this process. Also, this method remediates the soil contaminated with volatile and semi-volatile organic compounds

• Phytoremediation

This process involves the use of plants for mitigation of the toxic effects of pollutants. There are several mechanisms such as extraction, degradation, filtration, stabilization, and volatilization, involved in phytoremediation.

2: Intrinsic bioremediation

This type of bioremediation is also known as natural attenuation. In this, pollutants are converted into harmless compounds with the help of microbes which are naturally occurring. This doesn’t involve any human activity.

Conclusion

Bioremediation is an effective way of remediating pollutants. Both in-situ and ex-situ techniques are very important in reducing environmental pollution. These techniques help in restoring our environment. By using these techniques, we can have a clean and green environment.