Introduction

Growing environmental pollution stresses the environmental resources like soil and water majorly, and such pollution occurs due to mining and excessive use of pesticides and fertilizers. The rising pollution causes the need for eco-friendly, low-cost, and more efficient techniques to decrease pollution and pollutants from the environment. One of the cost-effective and efficient methods or techniques employed in treating contaminated or polluted sites is bioremediation. In this technique, microbes remove or transform organic or inorganic pollutants from the contaminated site, even in low concentrations. In the bioremediation technique, different microbes and methods are used to detoxify and convert toxic substances into less toxic substances. The bioremediation technique is promising due to its energy efficiency and cost-effectivity.

What Is Bioremediation?

Bioremediation is a biotechnology branch that uses different living microbes such as fungi, bacteria, aerobes, or anaerobes to convert the highly toxic substance into less toxic substances present in the water and soil. For example:-  landfarming, bio-venting, landfarming, bioaugmentation, composting, bioreactor, biostimulation, and rhizofiltration. Microbes used in the bioremediation process are  Mycobacterium, Achromobacter, Bacillus, Alcaligenes, Pseudomonas, Corynebacterium Flavobacterium, Nitrosomonas, Arthrobacter Xanthobacter, etc.

How Bioremediation Works

In the bioremediation process, those microbes used can withstand toxic contaminants and consume those toxic substances organic or inorganic, either accumulated inside the microbial biomass or converted those pollutants into less harmful substances by digesting or transforming toxicants by changing the composition of contaminant and making contaminant-free soil and water. Various factors affect the activities of microbes that introduce into the contaminated area of soil, like pH, temperature, moisture, oxygen presence or absence, and carbon.

Such limiting factors must be suitable according to the microbes introduced or available native microbes to increase the growth of microbes. Microbes work in a different environment like aerobic and anaerobic; in an aerobic environment, microbes need oxygen supply for the detoxification process, while in the case of the anaerobic environment, microbes work in the absence of oxygen. For example, bio-venting is the aerobic process in which the air is forcefully introduced into the soil that stimulates the growth of native bacteria. In contrast, bio-sparging air is employed in water to raise the activity of microbes and anaerobically (landfills).

Bioremediation Categories

Bioremediation is broadly divided into two significant categories named in-situ and ex-situ. Such a process is employed based on suitability or effectiveness.

In-Situ:- It is one of the categories of bioremediation that occurs in its original contaminated site. The disturbance is not or less required. It is less expensive than ex-situ; bio-venting, bio-sparging, and phytoremediation are examples. These methods are implemented and enhanced with little effort and don’t require heavy equipment to treat the contaminated site. This method is suitable for heavy metals, hydrocarbon, and chlorinated solvent treatments.

Ex-situ:- This is an off-site method which means the contaminant or pollutant is removed from its original site and treated on another site. After excavation from the original contaminated site, the polluted site is treated on different sites. It is continuously considered that based on the type of pollutant, contaminant concentration, and geographical location. Example of ex-situ bioremediation:- Bio-piling, land farming, composting.

This technique is expensive due to remote location treatment, needs heavy equipment. Bio-piling is used to treat non-chlorinated VOCs and petroleum-contaminated. Composting treats organic waste like food waste or agriculture waste which takes time because it is an aging process. The excavated soil biologically detoxifies in land-farming by spreading it to stimulate the aerobic microbes process.

Bioremediation Techniques

Bioaugmentation: In this method, the microbes are added externally, either the native spices or exotic species, to treat the polluted site. This process works along with other bioremediation methods such as bio-sparging or bio-venting. There is a factor that limits this process, which is the addition of the exotic microbial species because they are competing with native or indigenous species, limiting the process of bioremediation.

Bio sparging: It is a similar method to bio-venting in which air is introduced to subsurface soil to increase the activities of microbes that stimulate the removal of pollutants from the site. While, in the case of bio-venting, the air is introduced into the water zone, which makes the volatile compound upward movement to biodegrade. The efficiency of bio-sparging is affected by two factors: the degradability of pollutants and the permeability of the soil. In bio-venting, the bio-sparging process is similar to in-situ air sparging, which depends on the increased rate of airflow for pollutant volatilization, biodegradation stimulated by bio-sparging. This process is mainly used in the treatment of petroleum-contaminated aquifers.

Bio-venting: It is a controlled airflow in-situ process to introduce air to the unsaturated water zone that raises the native microbial activity for detoxification. This process can be enhanced by adding moisture or nutrients to the polluted site. In bio-venting, amendments are made by adding nutrients and moisture to increase bioremediation and convert the pollutant into a less harmful substance.

Benefits Of Bioremediation

Bioremediation is an eco-friendly technique for the detoxification process because it does not use any machine, energy, or chemical substance. In this process, the polluted site is treated with the help of microbes (bacteria or fungi). It is a natural self, own going process. This process requires less time. The microbes convert more harmful substances into less harmful and accumulate inside their biomass. This process doesn’t disturb nature and natural activity and does not release any hazardous substance. Some nutrient addition is required to fasten the process. It is cheap and less expensive.

Future Of Bioremediation

Bioremediation uses microbes to treat polluted sites without producing any harmful by-products, making it an economic practice. Various methods are available for the bioremediation process, which is used according to the pollutant, site, microbes availability, and feasibility. Many microbes are present, which can be used in the bioremediation process with different methods to enhance bioremediation, like bio-stimulation and bioaugmentation. Different genetically modified microbes or bacteria are currently used to treat polluted soil and water.

These Genetically modified microbes are designed to act on target and degrade them, but they are not used widely because they can mutate fast and produce different strains that can produce adverse effects on polluted sites. The bio-surfactant chemical used is also nature friendly with biodegradability properties, but their use is not economical. Nanotechnology is also used with bioremediation that enhances the effect of bioremediation and reduces cost and time. Genetically modified microbes make bioremediation promising due to its target specificity and increase the effectiveness of bioremediation.