Key Concepts & Self-Assessment20 Key Facts
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#1
Bioremediation uses metabolic enzymes of bacteria, fungi (mycoremediation), algae (phycoremediation), or plants (phytoremediation) to detoxify environmental pollutants into harmless byproducts.
#2
In-situ bioremediation treats contaminants at their original subsurface location without excavation, preserving soil structure and preventing dust exposure.
#3
Ex-situ bioremediation excavates polluted soil or pumps groundwater to above-ground treatment facilities such as biopiles, landfarming beds, or slurry bioreactors.
#4
Biostimulation accelerates indigenous microbial degradation by adding rate-limiting nutrients such as nitrogen, phosphorus, potassium, or electron acceptors (oxygen or nitrate) to the contaminated site.
#5
Bioaugmentation introduces pre-cultured, high-efficiency exogenous or genetically engineered microbial consortia directly into a site when native bacteria cannot break down recalcitrant xenobiotics.
#6
Bioventing is an aerobic in-situ technique that delivers oxygen at low flow rates into the unsaturated (vadose) soil zone to stimulate microbial biodegradation of petroleum fuels while minimizing volatile organic compound emissions.
#7
Biosparging injects pressurized air and nutrients into the saturated zone below the water table to increase dissolved oxygen levels and stimulate groundwater hydrocarbon degradation.
#8
Landfarming is an ex-situ technique in which excavated contaminated soil is spread in thin layers (typically 15 to 45 centimeters) over prepared liners and periodically tilled to aerate indigenous microbes.
#9
Biopiles are engineered ex-situ mounds of excavated soil equipped with internal perforated piping for forced aeration, leachate collection, and moisture regulation.
#10
Indian microbiologist Anand Mohan Chakrabarty developed a genetically engineered strain of Pseudomonas putida in 1971 by transferring four plasmids capable of degrading octane, xylene, camphor, and naphthalene.
#11
In the landmark 1980 U.S. Supreme Court ruling Diamond v. Chakrabarty, Pseudomonas putida became the first genetically modified living organism in history to be granted a utility patent.
#12
TERI (The Energy and Resources Institute), supported by India’s Department of Biotechnology (DBT), developed Oilzapper—a consortium of five immobilized bacterial strains carried on powdered corncob that digests aliphatic and aromatic hydrocarbons.
#13
Following the collision of cargo vessels MSC Chitra and MV Khalijia 3 off the Mumbai coast in August 2010, TERI deployed Oilzapper to remediate oil-slicked mangroves and coastal sediments.
#14
Oilivorous-S is an advanced variant of Oilzapper engineered specifically by TERI and Indian Oil Corporation R&D to degrade high-sulfur oily sludge and heavy asphaltene residues in refinery pits.
#15
Mycoremediation utilizes extracellular ligninolytic enzymes—such as laccase and manganese peroxidase secreted by white-rot fungi like Phanerochaete chrysosporium—to break down persistent aromatic pesticides and dyes.
#16
Phytoremediation uses hyperaccumulator plants such as Indian mustard (Brassica juncea) to absorb lead and chromium, and Chinese brake fern (Pteris vittata) to hyperaccumulate arsenic from groundwater.
#17
Deinococcus radiodurans is a radiation-resistant extremophile bacterium engineered to reduce and immobilize toxic ionic mercury and uranium in mixed radioactive waste environments.
#18
Unlike organic hydrocarbons, heavy metals (lead, mercury, cadmium, arsenic) cannot be degraded into carbon dioxide; microbes instead alter their valence state to decrease solubility and bioavailability.
#19
Ideonella sakaiensis, discovered by Japanese researchers in 2016, secretes two specialized enzymes—PETase and MHETase—that hydrolyze polyethylene terephthalate (PET) plastic into benign terephthalic acid and ethylene glycol monomers.
#20
Optimal aerobic soil bioremediation typically requires a soil moisture content between 40% and 60% of field capacity, a neutral pH range of 6.5 to 7.5, and a Carbon-to-Nitrogen-to-Phosphorus (C:N:P) molar ratio near 100:10:1.
Subject Specialist Commentary
Analytical perspective & practical exam advice from the Master10 academic board
Bioremediation is a recurring favorite in UPSC Prelims and State PSC examinations because it tests both ecological biochemistry and Indian scientific innovation. Candidates frequently confuse in-situ and ex-situ variants: remember that bioventing and biosparging are strictly in-situ subsurface aeration methods, whereas landfarming, windrow composting, and biopiles require excavating the contaminated matrix ex-situ. Beyond this, aspirants must remember that bioventing targets the unsaturated vadose zone, while biosparging targets the saturated aquifer below the water table.
A classic trap in objective multiple-choice questions involves whether microbes can completely destroy heavy metals. Microorganisms can completely mineralize organic compounds (crude oil, benzene, pesticides) into carbon dioxide and water, but they cannot destroy atomic elements like cadmium, mercury, or lead—they can only convert heavy metals into less soluble valence states or sequester them via phytoremediation and biosorption.
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