Bioremediation

BIOREMEDIATION Bioremediation is such type of technology in which microorganism, fungi, bacteria, plant and there is use to convert polluted condition in to original condition. Through bioremediation process microorganism act on pollutant or on chemicals due to which pollution occur and help that thing to come back in its original condition. Bioremediation is an option to offers the possibility to destroy or renders various harmful thing through natural biological activity. PRINCIPLES OF BIOREMEDIATION Bioremediation is the field of environmental biotechnology . y definition bioremediation is the use of microorganism, to degrade environment pollutant in to less toxic form. in this microorganism may be indigenous to a contaminant area or may be isolated from different area and brought to that area. Microorganisms start utilizing toxic substance and convert in to non toxic form from toxic form. In bioremediation metabolic process is also involved through which different enzyme release and act on toxic substances or on contaminants due to this biodegradation occur. When microorganism bought to contaminated or polluted site to enhance degradation that process is called bioaugmentation. For bioremediation to be effective, microorganism must enzymatically attack the pollutants and converts them in to non toxic form. n Bioremediation has its limitation, some contaminants such as chlorinated organic compound and aromatic hydrocarbon are resistant to microbial attack . bioremediation techniques are typically more economical than traditional method. FACTORS OF BIOREMEDIATION These factors include the existence of a microbial population capable of degrading the pollutants, the availability of contaminants to the microbial population, the environment factor (soil,temperature,pH,the presence of oxygen or other electron acceptor, and nutrients. ) MICROBIAL POPULATION FOR BIOREMEDIATION PROCESS Microorganism isolated from from any environment condition. microbes adapt nd grow at subzero temperatures ,as well as extreme heat, in water with excess of oxygen and in anaerobic condition,with the presence of hazardous condition or hazardous compound or any waste stream. the main requirements are an energy source and a carbon source. because of microbes and other biological system ,these can be used to degrade or remediate environmental hazards. Microbes can be divide in to groups according to their activity and condition. Anaerobic- in the absence of oxygen. naerobic bacteria cannot used frequently as a aerobic bacteria. There is an increa sing interest in anaerobic bacteria use for bioremediation of polychlorinated biphenyls (PCBs)in river sediment,ination of dechlorination of solvent trichloroethylene(TCE),and chloroform Lingninolytic fungi-fungi such as the white rot fungus phanaerochaete chrysosporium have the ablity to degrade an extremely diverse range of persistent or toxic environmental pollutants. Common substrate used include starw,sawdust,or corn cobs. Methylotrophs-aerobic bacteria that grow utilizing methane for carbon and energy. the initialenzyme in the pathway for aerobic degradation,methane monooxygenase,has a broad substrate range and active against a wide range of compounds ,including the chlorinated aliphatics trichloroethylene and 1,2-dichloroethane For degradationnit is necessary that bacteria and contaminant in proper contact and in proper amount. Class of contaminants |Specific examples |Aerobic |Anaerobic |More potential sources | |Chlorinated solvents |Trichloroethylene | |+ |Drycleaners | | |Perchloroethylene | | |Chemical manufacture Electrical | |Polychlorinated biphenyls |4-Chlorobiphenyl | |+ |manufacturing Power station | | |4,4-Dichlorobiphenyl | | |Railway yards Timber treatment | | | | | |Landfills | |Chlorinated phenol |Pentachlorophenol | |+ | | |â€Å"BTEX† Benzene Toluene |+ |+ |Oil production and storage | | |Ethylbenzene Xylene | | |Gas w ork sites | | | | | |Airports | | | | | |Paint manufacture Port | | | | | |facilities Railway yards | | | | | |Chemical manufacture | |Polyaromatic hydrocarbons |Naphthalene Antracene |+ | |Oil production and storage | |(PAHs) |Fluorene Pyrene | | |Gas work sites Coke plants | | |Benzo(a)pyrene | | |Engine works Landfills | | | | | |Tar production and storage | | | | | |Boiler ash dump sites Power | | | | | |stations | | |Atrazine Carbaryl | | |Agriculture | | |Carbofuran Coumphos | | |Timber treatment plants | | |Diazinon Glycophosphate | | |Pesticide manufacture | |Pesticides |Parathion Propham |+ |+ |Recreational areas Landfills | | |2,4-D | | | | ENVIRONMENTAL FACTORS Nutrients Although the microorganisms are present in contaminated soil, they cannot necessarily be there in the numbers required for bioremediation of the site. Their growth and activity must be stimulated. Biostimulation usually involves the addition of nutrients and oxygen to help indigenous microorgan- isms. These nutrients are the basic building blocks of life and allow microbes to create the necessary enzymes to break down the contaminants. All of them will need nitrogen, phosphorous, and carbon (e. g. , see Table 2). Carbon is the most basic element of living forms and is needed in greater quantities than other elements. In addition to hydrogen, oxygen, and nitrogen it constitutes about 95% of the weight of cells. Table 2 Composition of a microbial cell. ElementPercentageElementPercentage |Carbon |50 |Sodium |1 | |Nitrogen |14 |Calcium |0,5 | |Oxygen |20 |Magnesium |0,5 | |Hydrogen |8 |Chloride |0,5 | |Phosphorous |3 |Iron |0,2 | |Sulfur |1 |All others |0,3 | |Potassium |1 | | | ENVIRONMENTAL FACTORS Nutrients Although the microorganisms are present in contaminated soil, they cannot necessarily be there in the numbers required for bioremediation of the site. Their growth and activity must be stimulated. Biostimulation usually involves the addition of nutrients and oxygen to help indigenous microorgan- isms. These nutrients are the basic building blocks of life and allow microbes to create the necessary enzymes to break down the contaminants. All of them will need nitrogen, phosphorous, and carbon (e. g. , see Table 2). Carbon is the most basic element of living forms and is needed in greater quantities than other elements. In addition to hydrogen, oxygen, and nitrogen it constitutes about 95% of the weight of cells. Table 2 Composition of a microbial cell. ElementPercentageElementPercentage Carbon |50 |Sodium |1 | |Nitrogen |14 |Calcium |0,5 | |Oxygen |20 |Magnesium |0,5 | |Hydrogen |8 |Chloride |0,5 | |Phosphorous |3 |Iron |0,2 | |Sulfur |1 |All others |0,3 | |Potassium |1 | | | Microbial growth and activity are readily affected by pH, temperature, and moisture. Although microorganisms have been also isolated in extreme conditions, most of them grow optimally over a nar- row range, so that it is important to achieve optimal conditions. If the soil has too much acid it is possible to rinse the pH by adding lime. Temperature affects bio- chemical reactions rates, and the rates of many of them double for each 10  °C rise in temperature. Above a certain temperature, however, the cells die. Plastic covering can be used to enhance solar warming in late spring, summer, and autumn. Available water is essential for all the living organisms, and irrigation is needed to achieve the optimal moisture level. The amount of available oxygen will determine whether the system is aerobic or anaerobic. Hydrocarbons are readily degraded under aerobic conditions, whereas chlorurate compounds are degraded only in anaerobic ones. To increase the oxygen amount in the soil it is possible to till or sparge air. In some cases, hydrogen peroxide or magnesium peroxide can be introduced in the environment. Soil structure controls the effective delivery of air, water, and nutrients. To improve soil structure, materials such as gypsum or organic matter can be applied. Low soil permeability can impede move- ment of water, nutrients, and oxygen; hence, soils with low permeability may not be appropriate for in situ clean-up techniques. BIOREMEDIATION STRATEGIES Different techniques are employed depending on the degree of saturation and aeration of an area. In situ techniques are defined as those that are applied to soil and groundwater at the site with minimal distur- bance. Ex situ techniques are those that are applied to soil and groundwater at the site which has been removed from the site via excavation (soil) or pumping (water). Bioaugmentation techniques involve the addition of microorganisms with the ability to degrade pollutants. In situ bioremediation These techniques [11,12] are generally the most desirable options due to lower cost and less disturbance since they provide the treatment in place avoiding excavation and transport of contaminants. In situ treatment is limited by the depth of the soil that can be effectively treated. In many soils effective oxy- gen diffusion for desirable rates of bioremediation extend to a range of only a few centimeters to about 30 cm into the soil, although depths of 60 cm and greater have been effectively treated in some cases. The most important land treatments are: Bioventing is the most common in situ treatment and involves supplying air and nutrients through wells to contaminated soil to stimulate the indigenous bacteria. Bioventing employs low air flow rates and provides only the amount of oxygen necessary for the biodegradation while minimizing volatiliza- tion and release of contaminants to the atmosphere. It works for simple hydrocarbons and can be used where the contamination is deep under the surface. In situ biodegradation involves supplying oxygen and nutrients by circulating aqueous solutions through contaminated soils to stimulate naturally occurring bacteria to degrade organic contaminants. It can be used for soil and groundwater. Generally, this technique includes conditions such as the infil- tration of water-containing nutrients and oxygen or other electron acceptors for groundwater treatment. Biosparging. Biosparging involves the injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contam- inants by naturally occurring bacteria. Biosparging increases the mixing in the saturated zone and there- by increases the contact between soil and groundwater. The ease and low cost of installing small-diam- eter air injection points allows considerable flexibility in the design and construction of the system. Bioaugmentation. Bioremediation frequently involves the addition of microorganisms indigenous or exogenous to the contaminated sites. Two factors limit the use of added microbial cultures in a land treatment unit: 1) nonindigenous cultures rarely compete well enough with an indigenous population to develop and sustain useful population levels and 2) most soils with long-term exposure to biodegrad- able waste have indigenous microorganisms that are effective degrades if the land treatment unit is well managed. Ex situ bioremediation Ex situ bioremediation These techniques involve the excavation or removal of contaminated soil from ground. Landfarming is a simple technique in which contaminated soil is excavated and spread over a pre- pared bed and periodically tilled until pollutants are degraded. The goal is to stimulate indigenous biodegradative microorganisms and facilitate their aerobic degradation of contaminants. In general, the practice is limited to the treatment of superficial 10–35 cm of soil. Since landfarming has the potential to reduce monitoring and maintenance costs, as well as clean-up liabilities, it has received much atten – leum hydrocarbons they are a refined version of landfarming that tend to control physical losses of the contaminants by leaching and volatilization. Biopiles provide a favorable environment for indigenous aerobic and anaerobic microorganisms. Bioreactors. Slurry reactors or aqueous reactors are used for ex situ treatment of contaminated soil and water pumped up from a contaminated plume. Bioremediation in reactors involves the pro- cessing of contaminated solid material (soil, sediment, sludge) or water through an engineered con- tainment system. A slurry bioreactor may be defined as a containment vessel and apparatus used to cre- ate a three-phase (solid, liquid, and gas) mixing condition to increase the bioremediation rate of soil- bound and water-soluble pollutants as a water slurry of the contaminated soil and biomass (usually indigenous microorganisms) capable of degrading target contaminants. In general, the rate and extent of biodegradation are greater in a bioreactor system than in situ or in solid-phase systems because the contained environment is more manageable and hence more controllable and predictable. Despite the advantages of reactor systems, there are some disadvantages. The contaminated soil requires pre treat- ment (e. g. , excavation) or alternatively the contaminant can be stripped from the soil via soil washing or physical extraction (e. g. , vacuum extraction) before being placed in a bioreactor. Table 4 summarizes the advantages and disadvantages of bioremediation. Table 4 Summary of bioremediation str ategies. Technology |Examples |Benefits |Limitations |Factors to consider | |In situ |In situ bioremediation |Most cost efficient |Environmental constraints |Biodegradative abilities of | | |Biosparging Bioventing |Noninvasive Relatively |Extended treatment time |indigenous microorganisms | | |Bioaugmentation |passive Natural attenuation |Monitoring difficulties |Presence of metals and | | | |processes | |other inorganics Environmental| | | |Treats soil and water | |parameters Biodegradability of| | | | | |pollutants Chemical solubility| | | | | |Geological factors | | | | | |Distribution of pollutants | |Ex situ |Landfarming Composting |Cost efficient |Space requirements |See above | | |Biopiles |Low cost |Extended treatment time | | | | |Can be done on site |Need to control abiotic | | | | | |loss | | | | |Mass transfer problem | | | | | |Bioavailability limitation| | |Bioreactors |Slurry reactors |Rapid degradation kinetic |Soil requires excavation |See above Bioaugmentation | | |Aqueous reactors |Optimized environmental |Relatively high cost |Toxicity of amendments Toxic | | | |parameters |capital |concentrations of contaminants| | | |Enhances mass transfer |Relatively high operating | | | | |Effective use of inoculants |cost | | | | |and surfactants | | | Advantages of bioremediation †¢Bioremediation is a natural process and is therefore perceived by the public as an acceptable waste treatment process for contaminated material such as soil. Microbes able to degrade the con- taminant increase in numbers when the contaminant is present; when the contaminant is degrad- ed, the biodegradative population declines. The residues for the treatment are usually harmless products and include carbon dioxide, water, and cell biomass. †¢Theoretically, bioremediation is useful for the complete destruction of a wide variety of contam- inants. Many compounds that are legally considered to be hazardous can be transformed to harm- less products. This eliminates the chance of future liability associated with treatment and dispos- al of contaminated material. †¢Instead of transferring contaminants from one environmental medium to another, for example, from land to water or air, the complete destruction of target pollutants is possible. †¢Bioremediation can often be carried out on site, often without causing a major disruption of nor- mal activities. This also eliminates the need to transport quantities of waste off site and the poten- tial threats to human health and the environment that can arise during transportation. Bioremediation can prove less expensive than other technologies that are used for clean-up of hazardous waste. Disadvantages of bioremediation †¢Bioremediation is limited to those compounds that are biodegradable. Not all compounds are sus- ceptible to rapid and complete degradation. †¢There are some concerns that the products of biodegradation may be more persistent or toxic than the parent compound. †¢Biological processes are often highly specific. Important site factors required for success include the presence of metabolically capable microbial populations, suitable environmental growth con- ditions, and appropriate levels of nutrients and contaminants. It is difficult to extrapolate from bench and pilot-scale studies to full-scale field operations. †¢Research is needed to develop and engineer bioremediation technologies that are appropriate for sites with complex mixtures of contaminants that are not evenly dispersed in the environment. Contaminants may be present as solids, liquids, and gases. †¢Bioremediation often takes longer than other treatment options, such as excavation and removal of soil or incineration. †¢Regulatory uncertainty remains regarding acceptable performance criteria for bioremediation. There is no accepted definition of â €Å"clean†, evaluating performance of bioremediation is difficult, and there are no acceptable endpoints for bioremediation treatments. PHYTOREMEDIATION Although the application of microbe biotechnology has been successful with petroleum-based con- stituents, microbial digestion has met limited success for widespread residual organic and metals pol- lutants. Vegetation- based remediation shows potential for accumulating, immobilizing, and transform- ing a low level of persistent contaminants. In natural ecosystems, plants act as filters and metabolize substances generated by nature. Phytoremediation is an emerging technology that uses plants to remove contaminants from soil and water [14–16]. The term â€Å"phytoremediation† is relatively new, coined in 1991. Its potential for encouraging the biodegradation of organic contaminants requires further research, although it may be a promising area for the future. We can find five types of phytoremediation techniques, classified based on the contaminant fate: phytoextraction, phytotransformation, phytostabilization, phytodegradation, rhizofiltration, even if a combination of these can be found in nature. Phytoextraction or phytoaccumulation is the process used by the plants to accumulate contami- nants into the roots and aboveground shoots or leaves. This technique saves tremendous remediation cost by accumulating low levels of contaminants from a widespread area. Unlike the degradation mech- anisms, this process produces a mass of plants and contaminants (usually metals) that can be transport- ed for disposal or recycling. Phytotransformation or phytodegradation refers to the uptake of organic contaminants from soil, sediments, or water and, subsequently, their transformation to more stable, less toxic, or less mobile form. Metal chromium can be reduced from hexavalent to trivalent chromium, which is a less mobile and noncarcinogenic form. Phytostabilization is a technique in which plants reduce the mobility and migration of contami- nated soil. Leachable constituents are adsorbed and bound into the plant structure so that they form a stable mass of plant from which the contaminants will not reenter the environment. Phytodegradation or rhizodegradation is the breakdown of contaminants through the activity existing in the rhizosphere. 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. Rhizodegradation is a symbiotic rela- tionship that has evolved between plants and microbes. Plants provide nutrients necessary for the microbes to thrive, while microbes provide a healthier soil environment. Rhizofiltration is a water remediation technique that involves the uptake of contaminants by plant roots. Rhizofiltration is used to reduce contamination in natural wetlands and estuary areas. In Table 5, we can see an overview of phytoremediation applications. Table 5 Overview of phytoremediation applications. TechniquePlant mechanismSurface medium PhytoextractionUptake and concentration of metal viaSoils direct uptake into the plant tissue with subsequent removal of the plants PhytotransformationPlant uptake and degradation of organicSurface water, groundwater compounds PhytostabilizationRoot exudates cause metal to precipitateSoils, groundwater, mine tailing and become less available PhytodegradationEnhances microbial degradation inSoils, groundwater within rhizosphere rhizosphere RhizofiltrationUptake of metals into plant rootsSurface water and water pumped PhytovolatilizationPlants evaportranspirate selenium, mercury,Soils and groundwater and volatile hydrocarbons Vegetative capRainwater is evaportranspirated by plantsSoils to prevent leaching contaminants from disposal sites Phytoremediation is well suited for use at very large field sites where other methods of remedia- tion are not cost effective or practicable; at sites with a low concentration of contaminants where only polish treatment is required over long periods of time; and in conjunction with other technologies where vegetation is used as a final cap and closure of the site. There are some limitations to the technology that it is necessary to consider carefully before it is selected for site remediation: long duration of time for remediation, potential contamination of the vegetation and food chain, and difficulty establishing and maintaining vegetation at some sites with high toxic levels. .