Bioaugmentation is an eco-friendly practice, which is the introduction of cultured microbes in the subsurface region for microbial degradation of the contaminants present in the soil or water. The basic approach of this method is to increase the rate or degree of degradation of the contaminants or pollutants by introducing those microbes which degrade the pollutants. Bioaugmentation boosts the microbes’ genetic diversity or gene pool at the contaminated site.
For successful Bioaugmentation process requires appropriate or ideal microbial strains, and the selection of the optimum microbial consortia need to consider some certain feature of microbes like feasibility of cultivation of microbes, fast growth, and ability to survive a wide range of environmental conditions and with stand-in a large concentration of pollutants, which make possible bioaugmentation. There are some other considerable approaches called re-inoculation of soil with the same microbe, in which bacterial strain is isolated from the contaminated site and prepared for pre-adaptation under laboratory conditions and set them back to the same site.
Applications of Bioaugmentation
Removal of Lignin:
This compound is recalcitrant and degraded resistant and is majorly found in wastewater released from the paper and pulp industry. This lignin is present in high amounts of water and is called black liquor. That black liquor is composed of polysaccharides, resinous compounds, and lignin. To effectively remove such compounds from wastewater needs unique microbes to degrade them. The microbes are Comamonas B-9 and Pandoraea B-6 (bacteria), and Aspergillus F-1 used in the bioaugmentation process that removes >50% lignin in the sequencing batch reactor.
These are non-natural dyes, which typically consist of azo and anthraquinone-based molecules and are majorly used in cosmetic and textile dyes, and they account for 2 to 10% of environmental contaminants. Azo dye is the most diverse dye group and is resistant to biodegradation with typical treatment. The removal of acid orange 7 and azo dye takes place using Shewanella sp. XB, in bioaugmentation technique. Some other microbes are used to remove bromoamine acid (BAA) dye by the use of Sphingomonas xenophaga.
Polycyclic Aromatic Hydrocarbons and Heterocyclic Compounds(PAHs):
PAHs are high molecular weight hydrocarbons and act as pollutants, commonly present in petroleum products and found in the waste streams of other industries like organic chemical and coal conversion plants. These compounds sustain for a long period in the environment because they are recalcitrant regarding biodegradation. The bioaugmentation method is used in wastewater of coal gasification plants by using Streptomyces sp., which effectively removes the naphthalene (PAHs).
It is the potential carcinogen compound that is released with wastewater from the tobacco industry, the bioaugmentation technique is used to remove the such compound, in which several microbes are reported which are capable of degrading the nicotine in wastewater, and the microbes are Acinetobacter sp. and Sphingomonas sp. The efficiency in the control reactor is ~10 % to 98% in the Bioaugmented reactor.
Limitations of Bioaugmentation Technology
This bioremediation method successfully gives results regarding wastewater treatment at a laboratory scale, but it is not fully employed at a large scale. This method is used on the surface, groundwater, and soil, with the in-situ removal of chlorinated solvents in the groundwater using the Dehalococcoides group of aerobic microbes. Several factors limit the bioaugmentation technique, such as changes in temperature, nutrient limitation, competition between native and non-native microbes, pH, pollutant load shock on microbes, Bacteriophage infection on working microbes, and protozoa grazing.
Potential Strategy to Improve the Efficiency of Bioaugmentation
Several strategies are used to improve this bioaugmentation technique:-
Immobilized or Entrapped Cells in Bioaugmentation:
In this method, the microbes used are located or entrapped in the semipermeable membrane, which protects the microbes from bacteriophage infection and protozoan grazing. It also stabilizes the physical change by decreasing the minor fluctuation in pH and temperature, preventing the toxic effects of heavy metals, and enhancing biological stability.
Genetically modified Microbes:
The bioaugmentation process is improved by using GM microbes. The microbe’s genes are modified by introducing pollutant degrading genes in their DNA, making them degrade the pollutant. That process increases the efficiency of the biodegradation of microbes. The strains of Pseudomonas sp. and Pseudomonas putida are used to degrade the mono-aromatic compound and are genetically modified. This method shows effective potential regarding bioaugmentation but can hinder the natural ecology of microbes
Nanotechnology in Bioaugmentation:
The use of nanoparticles in treating wastewater is an emerging trend and some other sectors like medicine, agriculture, pharmaceutics, food industry. Various kinds of nanoparticles tested and used, like zinc oxide, gold, and silver nanoparticles, help remove organic and inorganic pollutants from the environment. Usually, the nanomaterial inhibits the growth of bacteria, but in a certain amount or range, the nanomaterial used does not show any effect on bacteria growth, like the Carbon nanotube used to inhibit the Arthrobacter sp. However, the carbon nanotube used less than <25 mg/l with Arthrobacter sp. Fully utilized the atrazine, which is absorbed by the carbon nanotube.
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