Thanks to the rising pollution, the level of contaminants everywhere is rioting. Moreover, the increasing population has, indirectly, put a massive burden on natural resources. By virtue of “Bioremediation Technology,” a major chunk of environmental pollutants can be taken care of. Broadly known as “the Pollution Solution,” the utilization of micro-organisms to break down hazardous and toxic substances into less toxic and non-toxic products is what is known as bioremediation. According to Cornell University, “Bioremediation provides a technique for cleaning up pollution by enhancing the same biodegradation processes that occur in nature.” Although the environment sees a lot of bioremediation around it, scientists have developed a strategy to expedite this exercise through Bioremediation Technology owing to its long-living and enduring gains. So, today, we are going to have a look at some real-life examples of bioremediation.
What is Bioremediation?
It is well clear that microorganisms have an inherent ability to break down complex substances into simpler ones. In addition to this, microorganisms also absorb loads of inorganic substances. The microorganisms have also found their wonderful utilization in yet another process for pollution treatment known as “Bioremediation.”
Speaking in broad terms, Bioremediation Technology makes use of micro-organisms. These micro-organisms degrade toxic and hazardous environmental pollutants into less toxic and non-toxic products. Both aerobic and anaerobic microorganisms are involved in the process and use this breakdown as a source of energy. Bioremediation technology aims to curtail certain environmental pollutants and, in turn, their vandalizing traits.
Factors Influencing Bioremediation
Before getting to real-life examples of bioremediation technology, let’s have a look at the major factors influencing this process. The various intrinsic and extrinsic factors need to be in optimization so that the process of bioremediation is successful.
1. Nature and Concentration of Contaminant
The nature of the contaminant and its concentration forms one of the limiting factors in bioremediation. The contaminants with large quantities of heavy metal impurities limit the process of bioremediation because such impurities inhibit the growth of microorganisms. In addition to the nature of the contaminant, a high concentration of contaminant in a particular bioremediating site affects the growth and enzymatic functions of the microorganisms.
2. Nutrient Availability
For the bioremediation process to work in its full bloom, the presence of essential nutrients for the optimum functioning of microorganisms is very important. Various nutrients like nitrates and phosphates, and other electron transport systems need to be in prime attendance in soil or water environments where the process of bioremediation takes place.
3. Factors Associated with Contaminated Site
The pH of soil and water is an indicator of the species of microorganisms present in it. The pH is responsible for causing a change in the chemical composition of the soil or water environment. The optimum pH range for the microorganisms to work in a bioremediation site is between 5 to 9. Optimum pH is crucial for not only the functioning of enzymes but also their existence.
Temperature is the underlying determining for the moisture content and chemical composition of the bioremediating site. A temperature between 20°C and 40°C is optimum for the orderly performance and functioning of the microorganisms.
3.3 O2 Availability and Moisture Content
The presence of oxygen is an important factor since it is responsible for ensuring certain oxidative and reducing properties in the bioremediating soil and water environment. The type of soil present in the site affects the aeration of the site. Retention of moisture and aeration of the soil is critical. Soils rich in gravel and sand aerate the site well and also retains moisture. Whereas, clayey and organically-rich soil fails to aerate the site properly, thereby, limiting the availability of oxygen to the microorganisms and hampering their functioning.
Examples of Bioremediation
The increasing population has had limiting effects on all types of ecosystems. This has led to devastating effects on the environment and given birth to pollution and other negative anthropogenic activities. Bioremediation aims to break down/degrade/convert more hazardous substances into less hazardous substances. Bioremediation involves two approaches: in-situ and ex-situ. The process of bioremediation can either occur naturally or can be induced by the administration of fertilizers (biostimulation) or the addition of similar strains of microorganisms. Now that we know why bioremediation is crucial for the environment, we shall begin our discussion of examples of bioremediation;
1. Application to Different States of Matter
The process of bioremediation can be applied to different states of matter in the environment. Generally, the native soil microflora is exploited for the process. For the remediation of metal-contaminated soils, the toxic removal properties of higher plants are steered accordingly.
Application of bioremediation to different states of matter:
- Solid: sediment, soils, and sludge.
- Liquid: groundwater, surface water, and industrial wastewater.
- Gas: industrial air emissions.
- Sub-Surface Environment: saturated and vadose zones.
In this form of bioremediation, fungi are used. This type of bioremediation is comparatively less expensive and does not require elaborate equipment. Not only can fungi successfully take over both biotic and abiotic surfaces, but they also serve as an excellent source to remove toxic pollutants/substances from the environment. Saprotrophic and biotrophic fungi are most commonly used in the process of bioremediation. In addition, basidiomycetes is also utilized extensively.
- Fungi present freely in the soil remove toxic substances.
- Fungi present in symbiotic association with the roots of plants (ectomycorrhizal and endomycorrhiza) remove harmful substances.
- Since fungi are decomposers, they break down dead and decaying organic matter.
- The production and secretion of special acids and enzymes by fungal hyphae break down lignin (white-rot fungi) and cellulose (brown-rot fungi).
- The process of microfiltration employed by fungal mycelium removes toxic substances.
- Various pollutants in soil and water, hydrocarbons, aromatic and petroleum compounds, and oils are degraded and broken down by fungi.
- A variety of heavy metals present in soil are mobilized by Mushroom Agaricus, Amanita, Cortinarius, Boletus, Leccinum, Suillus, and Phellinus.
In this process, a variety of plants are involved which are responsible for environmental cleanup.
- Phytovolatilization: In this process, contaminants from the soil are absorbed by plants and released in an unstable form into the gaseous atmosphere through transpiration.
- Rhizodegradation: Mycorrhiza refers to the symbiotic relationship between plant roots and fungi. The contaminants which are rich in proteins and enzymes are degraded by microorganisms and plants in the rhizosphere.
- Phytoextraction: Plant roots absorb contaminants from water and drive them to the upper parts of plants.
- Phytostabilization: Certain plant species soak up contaminants from soil and water.
In this process, heavy metals or radionuclides are absorbed by plants from the soil or water. This process exploits the utility of different types of algae. The organisms which have the ability to absorb more-than-usual amounts of contaminants from the soil are called “hyperaccumulators.” It is interesting to note that different plants have the ability to absorb different elements. The different elements absorbed by different parts of a plant are accumulated in various parts of a plant body.
- Removal of Arsenic: The removal of arsenic is facilitated by Sunflower (Helianthus annuus) and Chinese Brake fern (Pteris vittata). In this case, the Chinese Brake Fern acts as a hyperaccumulator. The absorbed arsenic is accumulated in the leaves of the fern.
- Removal of Cadmium, Copper, and Zinc: Heavy metal elements like cadmium, copper, and zinc are removed efficiently by Willow (Salix). Willow exhibits a wonderfully high property of transporting heavy metals from root to shoot. In addition to the aforesaid, this common plant also aids in large biomass production. Therefore, its utilization has also found a way to the production of energy in a biomass-fuelled power plant.
- Removal of Cadmium and Zinc: Another plant called Alpine pennycress (Thlaspi caerulescens) helps in the removal of cadmium and zinc. Alphine pennycress acts as a hyperaccumulator for these heavy metal elements. However, copper affects the growth of this plant.
- Removal of Lead: Plants and trees like Indian Mustard (Brassica juncea), Hemp Dogbane (Apocynum cannabinum), Ragweed (Ambrosia artemisiifolia), and Poplar are a great help for removing lead from the environment and accumulating it in their biomass.
- Removal of Sodium Chloride: Extremely high levels of groundwater has led to the generation of saline fields. The extraction of sodium chloride from soil and water is facilitated by plants like barley and/or sugar beets. Various salt-tolerant varieties (moderately halophytic) of other plants also serve the same purpose.
- Removal of Other Heavy Metals: The transgenic plants which contain genes for bacterial enzymes assist in the easy removal of selenium, mercury, and other organic pollutants including polychlorinated biphenyls (PCBs).
Just like the terrestrial ecosystem, the marine ecosystem is also vulnerable to accumulating pollutants. Usually known as “Wonder Organisms,” microalgae accomplish bioremediation in marine ecosystems by employing two mechanisms, namely, bioassimilation and biosorption. Algae can successfully establish their colonies in polluted water and sequester various pollutants. Such colonies of microalgae are known as “algal blooms.” Industrial waste of any and all types is usually disposed off in the water. The presence of various chemical pollutants in water is capable of entering the food chain and causing harm.
- Various pollutants from water are sequestered by algal blooms.
- The algal biomass also works as an efficient biosorbent after their harvest and lipid/protein extraction.
- The pesticides which are released in the water can also be removed by algal blooms.
6. Bioremediation by Microorganisms
As we have seen that various chemical pollutants can be effectively removed by microorganisms, these microorganisms are capable of adopting active as well as passive approaches for the same.
- Researchers are working diligently to construct genetically modified organisms to enhance the process of bioremediation, for example Deinococcus radiodurans. The absorption of substances like mercury and complex aromatic hydrocarbon like toluene can easily be facilitated by this genetically modified organism.
- The water is usually made unfit for human purposes by oil spills resulting in a vandalizing impact on the food chain and food web. Not only this but a large number of lives are also lost because of the same reason. Microorganisms excellently remediate dangers like oil spills and leave no chance to conserve the environment.
- The bioremediation of soil, air, and water is also eased by protozoa, mites, isopods, and collembolan.
- Microorganisms are added to the soil by the process of bioaugmentation. The exercise whereby pollutants are degraded by modification, addition, reduction, or genetic engineering of the microbial colonies is known as biostimulation.
7. Bioremediation by Nematodes
The presence of heavy metals and other toxic substances in the sea and other aquatic ecosystems is often detected by nematode parasites. In addition, the heavy metals in fish are also remediated by these nematodes. In addition to the function of bioremediation, nematode parasites are also involved in cleaning, nutrient mobilization, nitrification, enzyme activation, etc.
- Echinocephalus sp. can effectively bioaccumulate heavy toxic metals in the muscles and guts of fish.
- Ascaris sp. bioremediate various heavy metals in Liza vaigiensis.
- Other nematode species like Caenorhabditis elegans, Plectus acuminatus, Heterocephalobus pauciannulatus naturally bioremediate heavy metals in aquatic ecosystems.
8. Other Examples of Bioremediation
- Crime Scene Cleanup: Bioremediation is employed to clean blood and other bodily fluids to contain the spread of infections like hepatitis, HIV, and MRSA. Such infections can pose serious health risks. Apart from using conventional methods like the usage of bleach and ammonia, various enzyme cleaners are also utilized to clean up crime scenes.
- Cleanup of Contaminated Soil: Various human activities have led to the contamination of soil and groundwater to a large extent. Various microorganisms are exploited for remediating harmful chemical pollutants.
Bioremediation can be referred to as nature’s way of healing itself and employing secret agents for cleaning up the harm done to the environment by certain human anthropogenic activities. The cleaning abilities of microorganisms like algae, bacteria, fungi, nematodes, etc. work wonders for various ecosystems. The process of bioremediation, because of its applications, has found its way to home and other commercial setups.