Bioremediation and Phytoremediation
Bioremediation and Phytoremediation.
The industrialization has led to an increase in the use and release of harmful chemicals into the environment, which negatively affects aquatic life, soil, groundwater, animals, and humans. Bioremediation and Phytoremediation, which use living organisms to decompose these chemicals, are known as Bioremediation. It is urgently needed as a solution. There is an urgent need for measures for the effective decomposition of these harmful chemicals in the environment. Bioremediation involves multiple processes involving using certain microorganisms to decompose harmful xenobiotics much more cost-effectively and efficiently as compared to conventional remediation technologies. This article describes all types of bio and phytoremediation method which plays an important role in the reduction of these chemicals.
The process of breaking down harmful chemicals such as herbicides, pesticides, refrigerants, polyaromatic hydrocarbons, metallic waste, petroleum oil, rubber, plastic waste, and many others, also known as ‘Xenobiotics’, with the help of living organisms or their products like microorganism, plants, enzymes, immobilized cells, by degradation, mineralization or detoxification. The increasing global demand for these chemicals and their unregulated and unsafe use can cause a huge trauma to the environment. Bioremediation is a better option than conventional techniques like incineration, adsorption, landfilling, chemical oxidation, flocculation, and pyrolysis because conventional techniques are time-consuming, costly, and not environmentally friendly. Bioremediation technique has been applied to clean up oil spills, lagoons, rivers, groundwater, and soil.
Principle of Bioremediation:
The living organisms mainly microorganisms and plants break down and detoxify the harmful pollutants into simpler biodegradable products and produce clean fuel like CO2, H2O, and biomass. The microorganism used can belong to the native contaminated site i.e., indigenous, or can be exogenous to the contaminated sites. Microorganisms obtain their nutrition from pollutants by utilizing them as their energy source. Sometimes a single species of microbes is enough to decompose a certain pollutant but sometimes, the synergic action of several species of enzymes is required to decompose a contaminant.
Biodegradation depends upon:
- Environmental conditions.
- Type and nature of pollutant.
- Solubility of pollutants.
- Bioavailability of pollutants to microbes.
Microorganisms involved in Bioremediation:
Microorganisms inhabiting harsh environmental conditions like hot sulfur springs, thermal lakes, salt lakes, glaciers, and volcano active areas also where most other life forms couldn’t survive. Microbes inhibiting such areas possess exceptionally active and enzymatic properties of decomposing harmful materials via either an aerobic process or an anaerobic process. Microbes use harmful pollutants as their energy source and convert them into less toxic and simpler forms. Major Bacterial species involved in bioremediation are Pseudomonas, Mycobacterium, Alcaligens, and Sphingomonas. Fungal species like Phanerochaete chrysosporium.
Types of Bioremediations:
Bioremediation is broadly categorized into two types i.e., In situ and Ex situ bioremediation based on origin, transportation, and removal of pollutants from contaminated sites.
In situ Bioremediation:
This type of remediation is the most convenient, natural, and preferred method. It involves the remediation of contaminants at their native pollutant site without any transportation or excavation or disturbance. This technique is further divided into two categories; Intrinsic and Enhanced.
In situ, bioremediation is convenient, and cost-effective because no cost of extra transportation is involved but it is time-consuming and less controllable than the ex-situ remediation technique.
1. Intrinsic bioremediation: This method is the passive remediation of harmful pollutants without any human involvement. The remediation is carried out by various aerobic and anaerobic microorganisms indigenous to the site of a pollutant without any disturbance but the progress of the decomposing reactions occurring is regularly monitored for sustainable and successful decomposition.
2. Enhanced bioremediation: This type of in situ bioremediation involves the progress of remediation at polluted sites by excavation or the addition of nutrients, air, and microbes to enhance microbial growth for the biodegradation process. It is further categorized into several types bioaugmentation, bioventing, biostimulation, biosparging, etc.
a. Biostimulation: As the name suggests this technique involves stimulation or enhancement of microbial activity by the addition of nutrients, cofactors, enzymes, and oxygen in adequate amounts. This technique is used to treat heavy metal-contaminated sites and hydrocarbons.
b. Bioaugmentation: Sometimes various microbial species require synergic action to decompose a contaminant or recalcitrant pollutants. So, introducing exogenous microbial species or genetically modified microorganisms to a particular contaminated site enhances the rate of biodegradation. But sometimes, exogenous microbes compete with indigenous microbes for nutrients. This technique is used to treat municipal wastewater or contaminated groundwater.
c. Bioventing: In this technique, low oxygen and low amount of nutrients are provided to promote the controlled growth of microorganisms at contaminated sites. Providing low oxygen to microbes in the soil is done to reduce exposure to volatile contaminated chemicals in the environment. This technique is mostly used for the biodegradation of low-molecular-weight hydrocarbons, spilled petroleum oil or products, and volatile pollutants from the soil.
d. Bioslurping: This process involves multiple techniques to treat the contaminated sites like vacuum enhanced pumping, bioventing, and soil vapor extraction, for the removal of soil and groundwater pollutants by supplying oxygen indirectly and enhancing microbial biodegradation. But sometimes this technique reduces the permeability of soil due to which oxygen due not reaches sufficiently for the aerobic microorganism which leads to a reduction in their activity.
e. Biosparging: The air provided to the subsurface of soil leads to the rising of volatile pollutants towards the topmost layer of soil for biodegradation by microbes present there. This process is dependent upon two factors soil permeability and biodegradability of pollutants. But this technique is most suitable for volatile pollutants like benzene, xylene, and toluene.
Ex situ Bioremediation:
Opposite to in situ, Ex situ bioremediation involves the excavation or transport of pollutants from their native contaminated site to the site where biodegradation is carried out. On the basis of the cost involved, transportation, location, and degree of pollution bioremediation are classified into many types; bioreactors, landfarming, biopilling, and biofilters.
1. Biopilling: Also known as the Heap technique. This process involves testing contaminated soil in the laboratory for pollution check, mechanical separation and homogenization of soil, creating piles of soil, and adding nutrients and air to enhance microbial activity. Sometimes, additional exogenous microbes are also added. This technique is a combination of composting and landfarming. The technique is used to treat soil contaminated with low-molecular-weight pollutants and petroleum hydrocarbons. The technique is dependent upon pH, temperature, and nutrient control.
2. Landfarming: In this technique, the contaminated soil layer is removed from its site, spread, and tilled by forming a layer of thickness 8-40 cm over another fixed upper surface of the soil to allow biodegradation by aerobic microbes. This is done to provide nutrients, proper air, and irrigation for the enhanced activity of microorganisms. A neutral pH is necessary to maintain. This technique offers advantages like it is simple and cheap as less equipment, low cost, and low maintenance are required for its operation.
3. Bioreactors: Use of reactor under controlled conditions to carry out remediation. Specially engineered containers designed to carry out bioremediation of solid waste. Dependent on factors such as controlled bioaugmentation, supply of nutrients, mass transfer, availability of pollutants, and optimized reaction conditions.
4. Biofilters: Thin layers of microbes are embedded in columns and gaseous waste is passed through them. Mainly used to treat gaseous waste.
The new advanced technique involves plants and their parts for the remediation of contaminated soil and groundwater. Plants possess an uptake mechanism for the clearance of contaminated material from the site. Roots uptake the pollutants along with water and minerals which are further translocated to shoots and leaves by the xylem and phloem. Phytoremediation methods potentially degrade, accumulate, immobilize, and transform contaminants by acting as a biofilter and metabolizing the pollutant. It is a cost-effective and innovative alternative method to conventional techniques.
Types of Phytoremediation:
Phytoremediation is classified on the basis on the pollutant type, such as elemental, organic compound, accumulation, degradation, stabilization, volatilization, transformation, filtration, and a combination of these processes.
1. Phytoextraction: In this method, Plants uptake pollutants through roots and accumulate the pollutant in roots, shoots, and leaves. After the complete accumulation of pollutants, the parts are disposed of or recycled. This method is used to treat metal-contaminated sites. Especially water-soluble metals like Lead (Pb). This method is also known as Phytoaccumulation or Rhizoaccumulation. Microbes involved are Rhizophora spp, Rumex crispus, and Sedum alfredii.
2. Phytodegradation: In this method, the degradation of contaminants by enzymes produced by soil and microbes inhabiting plants. In phytodegradation, Plants utilize organic contaminants for metabolism and convert them into less toxic forms. This degradation is based on the symbiotic relationship between plants and microbes. The microbes involved are Pueraria, and Elodea canadensis.
3. Phytostabilization: As the name suggests, stabilizing the pollutant present in water or soil from its further dispersal. There are many methods of enhancing Phytostabilization, one of them is by the use of soil amendments to immobilize metals or metalloids and acclimatize plant species that are tolerant to high levels of metals. Microbes involved are Anthyllis vulneraria, and Festuca arvernensis.
4. Phytotransformation: Conversion of toxic and harmful pollutants into nontoxic and harmless forms by accumulation by plants. Microbes involved are Cannas.
5. Rhizofilteration: This method involves clarification of contaminated Groundwater by plants. Similar to Phytoextraction, Plants uptake contaminants along with the water and accumulate it into shoots and leaves by xylem and phloem. The plants need to be acclimatized in the contaminated area. The plant accumulates the contaminants until its roots reach saturation. After attaining saturation, the plant roots are disposed of safely and the site is treated properly. Microbes involved are Brassica juncea, Aruna donax, Eichornia crassipes, Plectranthus amboinicus, and Carex penduta.
6. Phytovolatilization: In this process, Plants accumulate volatile organic components by their roots and translocate them into shoots. The volatile contaminants get converted into a gaseous phase and vaporize into the air. The microbes involved are Liriodendron tulipifera.
Advantages of Bioremediation:
- Permanently eliminate pollutants.
- Can be coupled with the physical and chemical conventional techniques.
- Large-scale application.
- Environmentally friendly.
- Increase soil fertility.
- Prevent soil erosion.
- Help in the recovery of precious metals.
Disadvantages of Bioremediation:
- Not applicable to radioactive and recalcitrant chemicals.
- Sometimes, microbes also produce toxic by-products by utilizing pollutants.
- Require site-specific treatment.
- Toxicity to plants.
Q.No.1 What are the various factors affecting bioremediation?
Various factors are Microbial growth until critical biomass is achieved Microbial population diversity, Induction of enzymes, environmental conditions, substrate specificity, aerobic/ anaerobic process, and bioavailability of pollutants
What are the advantages of In situ bioremediation over Ex situ bioremediation?
Low cost of operation, easy control, and monitoring, no heavy equipment needed, application of aerobic and anaerobic techniques together or individually, Natural process, no cost of transportation involved.
Describe any important example of bioremediation used in real life.
The Alaska oil spill cleanup is a good example of the use of bioremediation. Alcanivorax bacterial species were involved. It was a three-year project (1989-1992) and cost more than $3.8 billion and 1000 of manpower. It was a complex project that also involved migrating the aquatic life from the affected area to a safer region.
Is bioremediation safe?
Bioremediation is safe, sustainable method as compared to conventional techniques of landfilling, incineration, chemical detoxification, and pyrolysis. Less energy requirement and cost-effective operation are major advantages of bioremediation. The byproducts of bioremediation are clean fuels like water, carbon dioxide, and biomass. Also provides fertility and important minerals to the soil, boosting the plant’s yield.
What are the major limitations of bioremediation?
Bioremediation is the time-consuming slow process of treating pollutants. Specific microbes are required for the remediation of some specific pollutants. Sometimes microbes utilize pollutants and produce toxic by-products.
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