The History And Uses Of Bioremediation

The History And Uses Of Bio amendsThe past decade has shown, in greater or lesser degree, our c atomic number 18lessness and negligence in utilize our subjective resources. The line of work associated with taint of natural resources be prominently change magnitude in many countries. polluted surroundings gener aloney result from production, mathematical function, and disposal of hazardous substances from industrial activities. The problem is world-wide, and the estimated number of soil sites is signifi bunst. It is now widely recognized that polluted environment is a latent threat to human health, and its continual disc all overy over recent years has led to international efforts to remedy many of these sites, to alter the site to be redeveloped for drill.To bioremediate, means to economic consumption living things to eliminate environmental contamination much(prenominal) as foul shit or groundwater. rough micro beings that live in grime and groundwater naturall y eat certain chemicals that argon harmful to people and the environment. The microorganisms be able to change these chemicals into water and righteous gases, such as vitamin C dioxide. Plants john also be apply to clean up ground, water or station this is called phytoremediationBioremediation is an option that offers the misadventure to destroy or render harmless various contaminants using natural biological activity. As such, it uses relatively low-cost, low-technology techniques, which generally sire a bun in the oven a high public acceptance and substructure often be carried knocked out(p) on site. It will non always be suitable, however, as the cuckold of contaminants on which it is effective is limited, the time eggshells compound argon relatively long, and the residual contaminant levels achievable whitethorn not always be appropriate. Although the methodologies employed ar not technically complex, considerable experience and expertise may be postulate to design and implement a successful bioremediation program, repayable to the penury to thoroughly assess a site for suit top executive and to optimise chequers to achieve a satisfactory result.Bioremediation has been employ at a number of sites worldwide Here, we intended to assist by providing a straightforward, pragmatic view of the paradees involved in bioremediation, the pros and cons of the technique, and the issues to be considered when dealing with a proposal for bioremediation.HISTORYBioremediation has been describe as a treat business leader technology that uses biological activity to reduce the preoccupancy or toxicity of a pollutant. It usually uses surgical operationes by which microorganisms transform or degrade chemicals in the environment (King 1). This use of microorganisms (mainly bacterium) to destroy or transform hazardous contaminants is not a new idea. Microorganisms accommodate been apply since 600 B.C. by the Romans and differents to treat their wastewater. Although this same technology is still usedtoday to treat wastewater it has been expand to treat an array of early(a) contaminants. Infact, bioremediation has been used commercially for close to 30 years. The first commercial use of a bioremediation system was in 1972 to clean up a Sun Oil pipeline spill in Ambler, PennsylvaniaCONVENTIONAL STRATEGIES OF REMEDIATIONThe conventional techniques used for remediation ready been to dig up pollute soil and pull out it to a landfill, or to cap and take the contaminated areas of a site. The methods have nigh drawbacks. The first method simply moves the contamination elsewhere and may make believe signifi gitt risks in the barb, handling, and bring of hazardous material.Additionally, it is very difficult and more and more expensive to find new landfill sites for the final disposal of the material. The cap and contain method is only an temporary solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability.A better approach than these traditional methods is to completely destroy the pollutants if possible, or at least to transform them to innocuous substances. whatsoever technologies that have been used are high-temperature incineration and various types of chemical decomposition (e.g., base-catalyzed dechlorination, UV oxidation).They end be very effective at reducing levels of a range of contaminants, tho have several drawbacks, principally their technological complexity, the cost for small-scale application, and the overleap of public acceptance, especially for incineration that may outgrowth the exposure to contaminants for both(prenominal) the workers at the site and nearby residents.Conventional ways of BioremediationDig up and remove it to a landfillRisk of jab, handling and transport of hazardous material actually expensive to find an other(a) land to final ly dispose these materials tough and contain the contaminated area.Maintain it in the same land however isolate itOnly an temporary solutionRequires monitoring and maintenance of isolation barriers for a long timeBetter approachesDestroy them completely, if contingent transfigure them in to harmless substancesDrawbacksTechnological complexityThe cost for small scale application expensiveLack of public acceptance especially in incinerationIncineration gene range more toxic compoundsMaterials rel tranquillized from imperfect incineration cause un coveted imbalance in the atmosphere. Ex. Ozone depletionFall back on earth and pollute more or less other environmentDioxin production due to burning of plastics leads to cancerMay increase the exposure to contaminants, for both workers and nearby residentsPRINCIPLES OF BIOREMEDIATIONFigure 1 Bioremediation Triangle in that respect are trey substantial components take aimed for bioremediation. These three components are microorganis ms, nourishment, and nutrients. These three main components shown in Figure 1 are known as the bioremediation triangle. Microorganisms are found al close to everywhere on earth with the exception of active volcanoes. So a wish of food and nutrients are unremarkably the missing ingredients that prevent successful bioremediation. Microorganisms find the food they eat in the soil or water where they live. However, if a contaminant is present it can become an do-gooderal food source for the microorganisms. The contaminant serves two useable purposes for the microbes. First, the contaminant provides a source of carbon needed for growth. Second,the microbes obtain elan vital by breaking chemical bonds and transferring electrons away from the contaminant. This is known as an oxidoreducing reaction. The contaminant that loses electrons is oxidized and the chemical that gains the electrons(electron acceptor) is reduced. The energy gained from the electron transfer is used along with t he carbon and some electrons to produce more cells. Microbes generally use atomic number 8as an electron acceptor but nit judge, sulfate, iron, and CO2 are also commonly used. The use of type O as an electron acceptor is called aerobiotic ventilation. The study byproducts of aerobic internal cellular respiration are carbon dioxide, water, and an increase in the microbe population. Anaerobic respiration uses nit rate, sulfate, iron, or CO2 as the electron acceptor instead of atomic number 8. Anaerobic respiration can occur after the oxygen has been depleted by aerobic respiration or where there is not sufficient oxygen in the first place. The process of anaerobiotic degradation has been ignored for many years. However, of late it has been gaining more attentionThere are also several nutrients that moldiness be accessible to the microorganisms for bioremediation to be successful. These include wet, nitrogen, phosphorus, and other trace subdivisions. Microorganisms like ot her organisms need wet to survive and grow.In addition, microbes depend on the moisture to transport food to them since they do not have mouths. The optimal moisture case for microbes in the vadose zone has been dressd to be between 10 and 25% (King 16). Besides moisture, nitrogen (ammonia)and phosphorus (orthophosphate) are two major nutrients needed for the microorganisms. The microorganisms also require minor elements such as sulfur, potassium, magnesium,calcium, manganese, iron, cobalt, copper, nickel, and zinc (King 19). However, these minor elements are usually available in the environment in sufficient gets where nitrogen and phosphorus may be lacking and need to be added. There are many contaminants susceptible to bioremediation. Petroleum hydrocarbons, in particular, benzene, toluene, ethylbenzene, and xylene (BTEX), the major components of gasoline, have been bio turbulent using this technology. In addition, alcohols, ketones, and esters are heartyspring established as being biodegradable by microorganisms. Many other contaminants are emerging as treatable using bioremediation such as halogenated aliphatics, halogenated aromatics, polychlorinated biphenyls, and nitroaromatics.FACTORS touching BIOREMEDIATIONThe factors impact bioremediation can be divided into chase categories.Microbial factorsenvironmental factorsMicrobial FactorsMicroorganisms can be isolated from al almost any environmental conditions. Microbes will adapt and grow at subzero temperatures, as healthy as extreme heat, desert conditions, in water, with an purposeless of oxygen, and in anaerobic conditions, with the mien of hazardous compounds or on any waste stream. The main requirements are an energy source and a carbon source. Because of the adaptability of microbes and other biological systems, these can be used to degrade or remediate environmental hazards. We can subdivide these microorganisms into the following groupsAerobicAnaerobicLigninolytic FungiMethylotrophsAer obicThese microbes have often been reported to degrade pesticides and hydrocarbons, both alkanes and polyaromatic compounds. Many of these bacteria use the contaminant as the sole source of carbon and energy.Examples of aerobic bacteria recognized for their degradative abilities are Pseudomonas, Alcaligenes, Sphingomonas, Rhodococcus, and Mycobacterium.AnaerobicAnaerobic bacteria are not as frequently used as aerobic bacteria. There is an increasing reside in anaerobic bacteria used for bioremediation of polychlorinated biphenyls (PCBs) in river drink down payments, dechlorination of the upshot trichloroethylene (TCE), andchloroform.Ligninolytic fungiFungi such as the white decomposition reaction fungus Phanaerochaete chrysosporium have theability to degrade an extremely diverse range of brutal or toxic environmental pollutants. Common substrates used include straw, truism dust, or corn cobs.MethylotrophsAerobic bacteria that grow utilizing methane for carbon and energy. The sign enzyme in the pathway for aerobic degradation, methane monooxygenase, has a broad substrate range and is active against a wide range of compounds, including the chlorinated aliphatics trichloroethylene and 1,2-dichloroethane.For degradation it is incumbent that bacteria and the contaminants be in contact. This is not easily achieved, as uncomplete the microbes nor contaminants are uniformly spread in the soil. Some bacteria are mobile and exhibit a chemotactic response, sensing the contaminant and moving toward it. other microbes such as fungi grow in a thready form toward the contaminant. It is possible to call down the mobilization of the contaminant utilizing some surfactants such as sodium dodecyl sulphate (SDS)Microbes are used to degrade gasoline, the most common contaminant of groundwater in the United States. Adding powdered seaweed to DDT-contaminated soil boosts the cleanup spot activity of DDT-eating microbes. In one test site, 80% of the DDT was outside after six weeks. Microbes and fungi are used in air filters to control odours from sewage treatment plants and in the paint industry. A gene for a protein found in rat livers that binds with toxic metals has been inserted in both tobacco plants and algae. With this gene, the tobacco plant and the algae are able to convey several hundred times more toxic metal compounds from soil or water compared to plants without the gene. One particular microbe degrades polycyclic aromatic hydrocarbons (PAHs), which are cancer-causing petroleum by-products. The microbes, called simply sulfate-reducers, are able to attack PAHs in the sediment of Boston Harbor where scientists thought the contaminant could not be tough due to lack of oxygen.Examples of microbes used for bioremediation includeDeinococcus radiodurans bacteria have been genetically modified to digest solvents and heavy metals, as well as toluene and ionic mercury from highly radioactive nuclear waste.Geobacter sufurreducens bacteria can t urn uranium dissolved in groundwater into a non-soluble, collectable form.Dehalococcoides ethenogenes bacteria are being used in ten states to clean up chlorinated solvents that have been linked to cancer. The bacteria are naturally found in both soil and water and are able to digest the solvents much faster than using traditional clean-up methods.Thermus brockianus, found in Yellowstone National Park, produces an enzyme that breaks down hydrogen peroxide 80,000 times faster than current chemicals in use.Alcaligenes eutrophus, naturally degrades 2,4-D, the third most widely used herbicide in the U.S.Some contaminants potentially suitable for bioremediation.Class of contaminantsSpecific examplesAerobicAnaerobic dominance sourcesChlorinated solventsTrichloroethylene+DrycleanersPerchloroethyleneChemical manufacturePolychlorinated biphenyls4-Chlorobiphenyl+Electrical manufacturing4,4DichlorobiphenylPower station railway system yardsChlorinated phenolPentachlorophenol+ tonus treatmentLa ndfillsBTEXBenzene++Oil production and computer memoryToluene turgidity work sitesEthylbenzeneAirportsXylenePaint manufacture air facilitiesRailway yardsChemical manufacturePolyaromatic hydrocarbonsNaphthalene+Oil production and depot(PAHs)AntraceneGas work sitesFluoreneCoke plantsPyreneEngine worksBenzo(a)pyreneLandfillsTar production and storageBoiler ash dump sitesPower stationsPesticidesAtrazine++AgricultureCarbarylTimber treatmentCarbofuranPesticide manufactureCoumphosRecreational areasENVIRONMENTAL FACTORS1. NutrientsAlthough 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 endemic microorganisms. These nutrients are the basic building blocks of life and get microbes to create the necessary enzymes to break down the contaminants. All of them will need nitrogen, phosphorous, and carbon (e.g., see Table below).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.Phosphorous and sulphur contribute with 70% of the remainders. The nutritional requirement of carbon to nitrogen ratio is 101, and carbon to phosphorous is 301.3. Environmental requirementsOptimum environmental conditions for the degradation of contaminants are reported in Table belowParametersCondition required for microbic activityOptimum value for an oil degradationSoil moisture25-28% of water holding capacity30-90%Soil pH5.5-8.86.5-8.0Oxygen matterAerobic, minimum air-filled center space of 10%10-40%Nutrient contentN and p for microbial growthCNP = 100101Temperature (C)15-4520-30ContaminantsNot too toxicHydrocarbon 5-10% of ironical weight of soilHeavy metalsTotal content 2000 ppm700 ppmType of soilLow clay or silt content4. Envir onmental conditions affecting degradationMicrobial growth and activity are readily impact by pH, temperature, and moisture. Although microorganisms have been also isolated in extreme conditions, most of them grow optimally over a narrow range, so that it is all important(p) to achieve optimal conditions.If the soil has too much acid it is possible to rinse the pH by adding lime. Temperature affects biochemical reactions rates, and the rates of many of them soprano 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 dissolute nether aerobic conditions, whereas chlorurate compounds are degraded only in anaerobic ones. To in crease 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 permeableness can impede movement of water, nutrients, and oxygen hence, soils with low permeability may not be appropriate for in situ clean-up techniques.STRATEGIES AND TECHNIQUES INVOLVED IN BIOREMEDIATIONBasically two types of techniques are involved in BioremediationIn situ Bioremediation (at the site)Ex situ Bioremediation (away from the site)In situ BioremediationIn situ techniques are defined as those that are applied to soil and groundwater at the site with minimal disturbance. These techniques are generally the most desirable options due to lower cost and less disturbances 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 toughened. In many soils effective oxygen diffusion for desirable rates of bioremediation extend to a range of only a hardly a(prenominal) centimetres to about 30 cm into the soil, although depths of 60 cm and greater have been effectively treated in some cases.In situ Bioremediation typesBioventing is the most common in situ treatment and involves supplying air and nutrients done and through wells to contaminated soil to stimulate the indigenous bacteria. Bioventing employs low air fertilize rates and provides only the amount of oxygen necessary for the biodegradation while minimizing volatilization 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 stimula te naturally occurring bacteria to degrade organic contaminants. It can be used for soil and groundwater. Generally, this technique includes conditions such as the infiltration of water-containing nutrients and oxygen or other electron acceptors for groundwater treatment.Biosparging involves the injection of air under imperativeness below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by naturally occurring bacteria. Biosparging increases the mixing in the thoroughgoing(a) zone and thereby increases the contact between soil and groundwater. The ease and low cost of installing small-diameter air injection points allows considerable flexibility in the design and construction of the systemBioaugmentation. 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) nonind igenous cultures rarely deal well enough with an indigenous population to develop and sustain reusable population levels and 2) most soils with long-term exposure to biodegradable waste have indigenous microorganisms that are effective degrades if the land treatment unit is well managed.Ex situ bioremediationEx situ techniques are those that are applied to soil and groundwater at the site which has been upstage from the site via excavation (soil) or pumping (water). These techniques involve the excavation or removal of contaminated soil from ground.Ex situ Bioremediation typesThese 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 prepared get it on and periodically tilled until pollutants are degraded. The goal is to stimulate indigenous biodegradative microorganisms and press forward their aerobic degradation of contaminants. In general, the practice is limit ed to the treatment of frivolous 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 attention as a disposal alternative.Composting is a technique that involves combining contaminated soil with nonhazardous organic amendants such as manure or agricultural wastes. The presence of these organic materials supports the outgrowth of a rich microbial population and elevated temperature characteristic of composting.Biopiles are a hybrid of landfarming and composting. Essentially, engineered cells are constructed as air composted piles. typically used for treatment of surface contamination with petroleum hydrocarbons they are a gauzy version of landfarming that tend to control somatogenetic losses of the contaminants by take away and volatilization. Biopiles provide a favorable environment for indigenous aerobic and anaerobic microorganisms.Bioreactors Slurry reactors or aqueous reactor s are used for ex situ treatment of contaminated soil and water pumped up from a contaminated plume. Bioremediation in reactors involves the processing of contaminated solid material (soil, sediment, sludge) or water through an engineered containment system. A slurry bioreactor may be defined as a containment vessel and apparatus used to create 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 corrupting 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-treatment (e.g., excavation) or alternatively the contaminant can be scanty from the soil via soil washing or physical extraction (e.g., hoover extraction) before being placed in a bioreactor.Monitoring bioremediationThe process of bioremediation can be monitored indirectly by measuring the Oxidation reducing Potential or redox in soil and groundwater, together with pH, temperature, oxygen content, electron acceptor/donor concentrations, and concentration of breakdown products (e.g. carbon dioxide). This table shows the (decreasing) biological breakdown rate as function of the redox potential.Process responseRedox potential (Eh in mV)AerobicO2 + 4e + 4H+ 2H2O600 400AnaerobicDenitrification2NO3 + 10e + 12H+ N2 + 6H2O five hundred 200Manganese IV reduction MnO2 + 2e + 4H+ Mn2+ + 2H2O 400 200 contract III reductionFe(OH)3 + e + 3H+ Fe2+ + 3H2O300 100Sulfate reductionSO42 + 8e +10 H+ H2S + 4H2O0 one hundred fiftyFermentation2CH2O CO2 + CH4150 220Types of BioremediationBioremediation techniques can be subdivided into vari ous based on following factors found on type of atmosphere in which Bioremediation takes place it can be divided into two typesEngineered BioremediationIntrinsic BioremediationBased on Type of organism being used for BioremediationMycoremediationPhytoremediationENGINEERED BIOREMEDIATIONFactors effecting engineered bioremediationContact between the microbes and the substrateProper physical environmentNutrientsOxygenAbsence of toxic compoundsSources of microorganismsFrom contaminated plain stitch sites(with varying environmental conditions subzero temperatures or extreme heat, desert conditions or in water, with excess of oxygen or in anaerobic conditions, with presence of hazardous compounds or on any waste stream)From culture collectionsGenetically Engineered Microorganisms (GEMs)Electro kinetically enhanced bioremediation (EEB) is a method of engineered bioremediation of soil contaminated by such organic compounds as solvents and petroleum products. As depicted schematically in th e figure, EEB involves the utilization of controlled flows of liquids and gases into and out of the ground via wells, in conjunction with electrokinetic transport of matter through pores in the soil, to provide reagents and nutrients that enhance the natural degradation of contaminants by indigenous and/or introduced microorganisms.The operational parameters of an EEB setup can be tailored to obtain the coveted flows of reagents and nutrients in variably textured and layered soils of variable hydraulic permeability and of moisture content that can range from saturation down to as little as about 7 percent. A major lovely feature of EEB is the ability to control the movements of charged anionic and cationic as well as noncharged chemical species.The basic components of electrokinetic enhancement of bioremediation are the following* Ions are transported by electromigration that is, with minimum transport of liquid through the soil. The ions of interest include nutrient agents, elect ron donors (e.g., lactate) or electron acceptors (e.g., nitrate or sulfate) added to the soil. Electromigration is utilized as an efficient mode of electrokinetic transport in vadosezone soils.* water supply in soil is pumped (horizontally or vertically, depending on the positions of electrode wells) by bring on electro-osmotic flow. Whereas the hydraulic flow used in older methods decreases with decreasing pore size and is thus not effective for treating tightly packed soil, electro-osmotic flow is less restricted by tight packing. Electro-osmosis is utilized to enhance the transport of both ions and such noncharged particles as micro-organisms, by moving water from anodes (positive electrodes) toward cathodes (negative electrodes).* ionophoresis induced in soil under an applied galvanic theme is used to control the transport and/or distribution of micro-organisms throughout the treated soil volume. The beneficial effect of electrophoresis can be increase or otherwise modifie d by use of electro-osmotic flushing of the soil.* The applied electric current can be utilized to heat the soil to the optimum temperature for bioremediation.* The gaseous and liquid products of electrolysis of water in the soil are removed from electrode wells and mixed and reinjected into the ground as needed to maintain the pH of the soil within a range favorable for bioremediation.DisadvantagesMostly GEMs do not work the way we expectLab strains become food source for soil protozoaInability of GEMs to contact the compounds to be degradedFailure of GEMs to survive/compete indigenous microorganisms. Mostly due to lack / decreased activity of House Keeping Genes.INTRINSIC BIOREMEDIATIONIt is a natural attenuation process that leads to the decrease in contaminant levels in a particular environment due to unmanaged physical, chemical and biological processes.Conversion of environmental pollutants into the harmless forms through the innate capabilities of naturally occurring microbia l population is called inbred bioremediation. However, there is increasing interest on intrinsic bioremediation for control of all or some of the contamination at waste sites. The intrinsic i.e. essential capacity of microorganism, to metabolize the contaminants should be tested at laboratory and field levels before use for intrinsic bioremediation. Through site monitoring programmes emanation of intrinsic bioremediation should be recorded time to time. The conditions of site that favours intrinsic bioremediation are ground water flow throughout the year, carbonate minerals to buffer sulkiness produced during biodegradation supply of electron acceptors and nutrients for microbial growth and absence of toxic compounds. The other environmental factors such as pH concentration, temperature and nutrient availability determine whether or not biotransformation takes place. Bioremediation of waste mixtures containing metals such as Hg, Pb, As and nitrile at toxic concentration can cre ate problem (Madsen, l99l).The ability of surface bacteria to degrade a given mixture of pollutants in ground water is dependent on the type and concentration of compounds, electron acceptor and duration of bacteria exposed to contaminants. Therefore, ability of indigenous bacteria degrading contaminants can be determined in laboratory by plate count and macrocosm studiesExample Microbes in Hudson River mud developed an ability to partially degrade PCB (Poly Chlorinated Biphenyls)Process occurs in two steps fond(p) dehalogenation of PCBs occurs naturally under anaerobic conditionsLess chlorinated residuesThen mud is aerated to promote the complete degradationof these less chlorinated residuesMYCOREMEDIATIONMycoremediation is a form of bioremediation, the process of using fungi to return an environment (usually soil) contaminated by pollutants to a less contaminated state. The term Mycoremediation was coined by Paul Stam