- Bioremediation is the use of microorganisms (bacteria and fungi) to degrade the environmental contaminants into less toxic forms.
- The microorganisms may be indigenous to a contaminated area or they may be isolated from elsewhere and brought to the contaminated site.
- The process of bioremediation can be monitored indirectly by measuring the Oxidation Reduction Potential or redox soil and groundwater, together with pH, temperature, oxygen content, electron acceptor/donor concentrations, and concentration of
breakdown products (e.g. carbon dioxide).
In situ bioremediation
- In situ — It involves treatment of the contaminated material at the site.
- Bioventing: supply of air and nutrients through wells to contaminated soil to stimulate the growth of indigenous bacteria. It is used for simple hydrocarbons and can be used where the contamination is deep under the surface.
- Biosparging: Injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by naturally occurring bacteria
- Bioaugmentation: Microorganisms are imported to a contaminated site to enhance the degradation process.
- Using bioremediation techniques, TERI has developed a mixture of bacteria called ‘Oilzapper and Oilivorous-S’ which degrades the pollutants of oil-contaminated sites, leaving behind no harmful residues. This technique is not the only environment-friendly, but also highly cost-effective.
Ex situ bioremediation
- Ex situ — involves the removal of the contaminated material to be treated elsewhere.
- Landfarming: contaminated soil is excavated and spread over a prepared bed and periodically tilled until pollutants are degraded. The goal is to stimulate indigenous biodegradative microorganisms and facilitate their aerobic degradation of contaminants.
- Biopiles: it is a hybrid of land farming and composting. Essentially, engineered cells are constructed as aerated composted piles. Typically used for the treatment of surface contamination with petroleum hydrocarbons.
- Bioreactors: it involves the processing of contaminated solid material (soil, sediment, sludge) or water through an engineered containment system.
- Composting: Composting is nature’s process of recycling decomposed organic materials into a rich soil known as compost.
Advantages and Disadvantages of bioremediation
Advantages of bioremediation
- Useful for the complete destruction of a wide variety of contaminants.
- The complete destruction of target pollutants is possible.
- Less expensive.
Disadvantages of bioremediation
- Bioremediation is limited to those compounds that are biodegradable. Not all compounds are susceptible to rapid and complete degradation.
- Biological processes are often highly specific.
- It is difficult to extrapolate from the bench and pilot-scale studies to full-scale field operations.
- Bioremediation often takes a longer time than another treatment process.
- Phytoremediation is the use of plants to remove contaminants from soil and water. Natural phytoremediation is carried out by mangroves, estuarine vegetation, and other wetland vegetation.
- Phytoextraction/phytoaccumulation: plants accumulate contaminants into the roots and aboveground shoots or leaves.
- Phytotransformation/photodegradation on the uptake of organic contaminants from soil, and their transformation to more stable, less toxic, less mobile form.
- Phytostabilization: plants reduce the mobility and migration of contaminated soil. Leachable constituents are adsorbed and bound into the plant structure.
- Rhizodegradation: breakdown of contaminants through the activity existing in the rhizosphere (region of soil in the vicinity of plant roots). This activity is due to the presence of proteins and enzymes produced by the plants or by soil organisms such as bacteria, yeast, and fungi.
- Rhizofiltration: the water remediation technique that involves the uptake of contaminants by plant roots. Rhizofiltration is used to reduce contamination in natural wetlands and estuary areas (E.g. Mangroves).
- Mycoremediation: fungi are used to decontaminate the area.
- Mycofiltration: using fungal mycelia to filter toxic waste and microorganisms.
- The bacterium Deinococcus radiodurans has been used to detoxify toluene and ionic mercury which are released from radioactive nuclear waste.