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{{Short description|Process used to treat contaminated media such as water and soil}}
{{Short description|Process used to treat contaminated media such as water and soil}}
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{{Pollution sidebar|Soil}}
{{Pollution sidebar|Soil}}
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'''Bioremediation''' broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for degrading environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings.<ref name="yuvraj 305 318">{{cite book |vauthors = Yuvraj |chapter = Microalgal Bioremediation: A Clean and Sustainable Approach for Controlling Environmental Pollution |date=2022 |volume=1|pages=305–318| title = Innovations in Environmental Biotechnology |place=Singapore |publisher=Springer Singapore |language=en |doi=10.1007/978-981-16-4445-0_13 |isbn=978-981-16-4445-0 }}</ref> <ref>{{cite journal |last1=Bayat |first1=Zeynab |last2=Akbari |first2=Nazanin |last3=Hassanshahian |first3=Mehdi |last4=Cappello |first4=Simone |last5=Salehinasab 1 |first5=Ali |title=Screening of Biosurfactant-producing Bacteria from Symbiotic Microbes with Gastropods in the Persian Gulf |journal=Research in Biotechnology and Environmental Science |date=2022 |volume=1 |issue=1 |page=1-5 |url=https://rbes.rovedar.com/article_160292.html}}</ref>
The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment.<ref name="yuvraj 305 318"/> In comparison to conventional physicochemical treatment methods bioremediation may offer considerable advantages as it aims to be sustainable, eco-friendly, cheap, and scalable.<ref name="yuvraj 305 318"/>
'''Bioremediation''' broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi in [[mycoremediation]], and plants in [[phytoremediation]]), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings.<ref name="yuvraj 305 318">{{cite book |vauthors = Yuvraj |chapter = Microalgal Bioremediation: A Clean and Sustainable Approach for Controlling Environmental Pollution |date=2022 |volume=1|pages=305–318| title = Innovations in Environmental Biotechnology |place=Singapore |publisher=Springer Singapore |language=en |doi=10.1007/978-981-16-4445-0_13 |isbn=978-981-16-4445-0 }}</ref> The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment.<ref name="yuvraj 305 318"/> In comparison to conventional physicochemical treatment methods bioremediation may offer advantages as it aims to be sustainable, eco-friendly, cheap, and scalable.<ref name="yuvraj 305 318"/>
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Most bioremediation is inadvertent, involving native organisms. Research on bioremediation is heavily focused on stimulating the process by inoculation of a polluted site with organisms or supplying nutrients to promote the growth. In principle, bioremediation could be used to reduce the impact of byproducts created from anthropogenic activities, such as industrialization and agricultural processes.<ref>{{cite journal
|volume=1 |year=2022 |pages= 305–318 |journal=Applied Catalysis B: Environmental |title=Potential Applications of Oxidative Enzymes and Phenoloxidase-like Compounds in Wastewater and Soil Treatment: A Review |first1=Nelson |last1=Durán |first2=Elisa |last2=Esposito |issue=2
|doi=10.1016/S0926-3373(00)00168-5}}</ref><ref>{{cite book |vauthors = Singh N, Kumar A, Sharma B |chapter = Role of Fungal Enzymes for Bioremediation of Hazardous Chemicals |date=2019 |volume=3 |pages=237–256 |title = Fungal Biology |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-25506-0_9 |isbn=978-3-030-25506-0 |s2cid = 210291135}}</ref> Bioremediation could prove less expensive and more sustainable than other [[Environmental remediation|remediation]] alternatives.<ref>{{cite web |date=June 2011 |title=Green Remediation Best Management Practices: Sites with Leaking Underground Storage Tank Systems. EPA 542-F-11-008 |url=https://www.epa.gov/sites/production/files/2015-04/documents/ust_gr_fact_sheet.pdf|publisher=EPA}}</ref>


⚫
Most bioremediation is inadvertent, involving native organisms. Research on bioremediation is heavily focused on stimulating the process by inoculation of a polluted site with organisms or supplying nutrients to promote their growth. [[Environmental remediation]] is an alternative to bioremediation.<ref>{{cite web |date=June 2011 |title=Green Remediation Best Management Practices: Sites with Leaking Underground Storage Tank Systems. EPA 542-F-11-008 |url=https://www.epa.gov/sites/production/files/2015-04/documents/ust_gr_fact_sheet.pdf|publisher=EPA}}</ref>
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UNICEF, power producers, bulk water suppliers and local governments are early adopters of low cost bioremediation, such as aerobic bacteria tablets which are simply dropped into water.<ref>{{cite web |date=June 2022 |title=Ageing infrastructure gets bio boost |url=https://bedfordviewedenvalenews.co.za/494020/aging-infrastructure-to-get-bio-boost/ |publisher=CAXTON}}</ref>


While organic pollutants are susceptible to [[biodegradation]], heavy metals cannot be degraded, but rather oxidized or reduced. Typical bioremediations involves oxidations.<ref>{{cite journal | vauthors = Duran N, Esposito E | title = Potential Applications of Oxidative Enzymes and Phenoloxidase-like Compounds in Wastewater and Soil Treatment: A Review |journal=Applied Catalysis B: Environmental
Organic pollutants are generally more susceptible to [[biodegradation]] than heavy metals. Typical bioremediations involves oxidations. Oxidations enhance the water-solubility of organic compounds and their susceptibility to further degradation by further oxidation and hydrolysis. Ultimately biodegradation converts hydrocarbons to [[carbon dioxide]] and water.<ref name="EPA_2013" /> For heavy metals, bioremediation offers few solutions. Metal-containing pollutant can be removed or reduced with varying bioremediation techniques.<ref name="Kapahi_2019">{{cite journal |vauthors = Kapahi M, Sachdeva S |title = Bioremediation Options for Heavy Metal Pollution |journal = Journal of Health and Pollution |volume = 9 |issue = 24 |pages = 191203 |date = December 2019 |pmid = 31893164 |pmc = 6905138 |doi = 10.5696/2156-9614-9.24.191203 }}</ref> The main challenge to bioremediations is rate: the processes are slow.<ref name="Norris_1993"/>
|volume=1 |issue=2 |year=2022 |pages= 305–318 |doi=10.1016/S0926-3373(00)00168-5 }}</ref><ref>{{cite book |vauthors = Singh N, Kumar A, Sharma B |title = Recent Advancement in White Biotechnology Through Fungi |series = Fungal Biology |chapter = Role of Fungal Enzymes for Bioremediation of Hazardous Chemicals |date=2019 |volume=3 |pages=237–256 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-25506-0_9 |isbn=978-3-030-25506-0 |s2cid = 210291135}}</ref> Oxidations enhance the water-solubility of organic compounds and their susceptibility to further degradation by further oxidation and hydrolysis. Ultimately biodegradation converts hydrocarbons to [[carbon dioxide]] and water.<ref name="EPA_2013" /> For heavy metals, bioremediation offers few solutions. Metal-containing pollutant can be removed, at least partially, with varying bioremediation techniques.<ref name="Kapahi_2019">{{cite journal |vauthors = Kapahi M, Sachdeva S |title = Bioremediation Options for Heavy Metal Pollution |journal = Journal of Health and Pollution |volume = 9 |issue = 24 |page = 191203 |date = December 2019 |pmid = 31893164 |pmc = 6905138 |doi = 10.5696/2156-9614-9.24.191203 }}</ref> The main challenge to bioremediations is rate: the processes are slow.<ref name="Norris_1993"/>


Bioremediation techniques can be classified as (i) ''[[in situ]]'' techniques, which treats polluted sites directly, vs (ii) ''[[ex situ]]'' techniques which are applied to excavated materials.<ref>{{Cite journal |vauthors = Kensa VM |date=2011 |title=Bioremediation - An Overview |url=https://www.icontrolpollution.com/%20peer-reviewed/%20bioremediation-an-overview-37408.html |journal=I Control Pollution |language=en |volume=27 |issue=2 |pages=161–168 |issn=0970-2083}}</ref> In both these approaches, additional nutrients, vitamins, minerals, and pH buffers are added to enhance the growth and metabolism of the microorganisms. In some cases, specialized microbial cultures are added ([[Bioaugmentation|biostimulation]]). Some examples of bioremediation related technologies are [[phytoremediation]], [[bioventing]], bioattenuation, [[biosparging]], [[composting]] (biopiles and [[windrow]]s), and [[landfarming]]. Other remediation techniques include [[thermal desorption]], [[vitrification]], [[air stripping]], [[bioleaching]], [[rhizofiltration]], and soil washing. Biological treatment, bioremediation, is a similar approach used to treat wastes including wastewater, industrial waste and solid waste. The end goal of bioremediation is to remove or reduce harmful compounds to improve soil and water quality.<ref name="Canak_2019">{{Cite journal |vauthors = Canak S, Berezljev L, Borojevic K, Asotic J, Ketin S |date=2019 |title=Bioremediation and "green chemistry" |url= https://www.researchgate.net/publication/332318816 |journal=Fresenius Environmental Bulletin |volume=28 |issue=4 |pages=3056–3064 |via=}}</ref>
Bioremediation techniques can be classified as (i) ''[[in situ]]'' techniques, which treat polluted sites directly, vs (ii) ''ex situ'' techniques which are applied to excavated materials.<ref>{{Cite journal |vauthors=Kensa VM |date=2011 |title=Bioremediation - An Overview |url=https://www.icontrolpollution.com/peer-reviewed/bioremediation-an-overview-37408.html |journal=I Control Pollution |language=en |volume=27 |issue=2 |pages=161–168 |issn=0970-2083}}</ref> In both these approaches, additional nutrients, vitamins, minerals, and pH buffers are added to enhance the growth and metabolism of the microorganisms. In some cases, specialized microbial cultures are added ([[Bioaugmentation|biostimulation]]). Some examples of bioremediation related technologies are [[phytoremediation]], [[bioventing]], bioattenuation, [[biosparging]], [[composting]] (biopiles and windrows), and [[landfarming]]. Other remediation techniques include [[thermal desorption]], [[vitrification]], [[air stripping]], [[bioleaching]], [[rhizofiltration]], and soil washing. Biological treatment, bioremediation, is a similar approach used to treat wastes including wastewater, industrial waste and solid waste. The end goal of bioremediation is to remove harmful compounds to improve soil and water quality.<ref name="Canak_2019">{{Cite journal |vauthors = Canak S, Berezljev L, Borojevic K, Asotic J, Ketin S |date=2019 |title=Bioremediation and "green chemistry" |url= https://www.researchgate.net/publication/332318816 |journal=Fresenius Environmental Bulletin |volume=28 |issue=4 |pages=3056–3064 |via=}}</ref>


== ''In situ'' techniques ==
== ''In situ'' techniques ==
[[File:In Situ Bioremediation.png|thumb|Visual representation showing ''in-situ'' bioremediation. This process involves the addition of oxygen, nutrients, or microbes into contaminated soil to remove toxic pollutants.<ref name="Canak_2019" /> Contamination includes buried waste and underground pipe leakage that infiltrate ground water systems.<ref>{{cite journal | vauthors = Jørgensen KS |title=In Situ Bioremediation|date=2007 | journal = Advances in Applied Microbiology|volume=61|pages=285–305|publisher=Academic Press|language=en|doi=10.1016/S0065-2164(06)61008-3|pmid=17448793|isbn=9780120026630|access-date=}}</ref> The addition of oxygen removes the pollutants by producing carbon dioxide and water.<ref name="Kapahi_2019" />]]
[[File:In Situ Bioremediation.png|thumb|Visual representation showing ''in-situ'' bioremediation. This process involves the addition of oxygen, nutrients, or microbes into contaminated soil to remove toxic pollutants.<ref name="Canak_2019" /> Contamination includes buried waste and underground pipe leakage that infiltrate ground water systems.<ref>{{cite journal | vauthors = Jørgensen KS |title=In Situ Bioremediation|date=2007 | journal = Advances in Applied Microbiology|volume=61|pages=285–305|publisher=Academic Press|language=en|doi=10.1016/S0065-2164(06)61008-3|pmid=17448793|isbn=978-0-12-002663-0}}</ref> The addition of oxygen removes the pollutants by producing carbon dioxide and water.<ref name="Kapahi_2019" />]]


=== Bioventing ===
=== Bioventing ===
Bioventing is a process that increases the oxygen or air flow into the unsaturated zone of the soil, this in turn increases the rate of natural i''n situ'' degradation of the targeted hydrocarbon contaminant.<ref>{{cite journal | vauthors = García Frutos FJ, Escolano O, García S, Babín M, Fernández MD | title = Bioventing remediation and ecotoxicity evaluation of phenanthrene-contaminated soil | journal = Journal of Hazardous Materials | volume = 183 | issue = 1–3 | pages = 806–13 | date = November 2010 | pmid = 20800967 | doi = 10.1016/j.jhazmat.2010.07.098 }}</ref> Bioventing, an aerobic bioremediation, is the most common form of oxidative bioremediation process where oxygen is provided as the electron acceptor for oxidation of [[petroleum]], [[Polycyclic aromatic hydrocarbon|polyaromatic hydrocarbons]] (PAHs), [[phenols]], and other reduced pollutants. Oxygen is generally the preferred electron acceptor because of the higher energy yield and because oxygen is required for some enzyme systems to initiate the degradation process.<ref name="Norris_1993">{{Cite book| authors = Mirza Hasanuzzaman, Majeti Narasimha Vara Prasad |title=Handbook of Bioremediation|year=2020|isbn=978-0-12-819382-2|publisher=Academic Press|doi=10.1016/C2018-0-05109-9|s2cid=127409446 }}</ref> Microorganisms can degrade a wide variety of hydrocarbons, including components of gasoline, kerosene, diesel, and jet fuel. Under ideal aerobic conditions, the biodegradation rates of the low- to moderate-weight [[Aliphatic compound|aliphatic]], [[Alicyclic compound|alicyclic]], and [[Aromatic hydrocarbon|aromatic]] compounds can be very high. As molecular weight of the compound increases, the resistance to biodegradation increases simultaneously.<ref name="Norris_1993" /> This results in higher contaminated volatile compounds due to their high molecular weight and an increased difficulty to remove from the environment.
Bioventing is a process that increases the oxygen or air flow into the unsaturated zone of the soil, this in turn increases the rate of natural ''in situ'' degradation of the targeted hydrocarbon contaminant.<ref>{{cite journal | vauthors = García Frutos FJ, Escolano O, García S, Babín M, Fernández MD | title = Bioventing remediation and ecotoxicity evaluation of phenanthrene-contaminated soil | journal = Journal of Hazardous Materials | volume = 183 | issue = 1–3 | pages = 806–13 | date = November 2010 | pmid = 20800967 | doi = 10.1016/j.jhazmat.2010.07.098 | bibcode = 2010JHzM..183..806F }}</ref> Bioventing, an aerobic bioremediation, is the most common form of oxidative bioremediation process where oxygen is provided as the electron acceptor for oxidation of [[petroleum]], [[Polycyclic aromatic hydrocarbon|polyaromatic hydrocarbons]] (PAHs), [[phenols]], and other reduced pollutants. Oxygen is generally the preferred electron acceptor because of the higher energy yield and because oxygen is required for some enzyme systems to initiate the degradation process.<ref name="Norris_1993">{{Cite book |author=Mirza Hasanuzzaman |author2=Majeti Narasimha Vara Prasad |title=Handbook of Bioremediation|year=2020|isbn=978-0-12-819382-2|publisher=Academic Press|doi=10.1016/C2018-0-05109-9|s2cid=127409446 }}</ref> Microorganisms can degrade a wide variety of hydrocarbons, including components of gasoline, kerosene, diesel, and jet fuel. Under ideal aerobic conditions, the biodegradation rates of the low- to moderate-weight [[Aliphatic compound|aliphatic]], [[Alicyclic compound|alicyclic]], and [[Aromatic hydrocarbon|aromatic]] compounds can be very high. As molecular weight of the compound increases, the resistance to biodegradation increases simultaneously.<ref name="Norris_1993" /> This results in higher contaminated volatile compounds due to their high molecular weight and an increased difficulty to remove from the environment.


Most bioremediation processes involve oxidation-reduction reactions where either an electron acceptor (commonly oxygen) is added to stimulate oxidation of a reduced pollutant (e.g. hydrocarbons) or an electron donor (commonly an organic substrate) is added to reduce oxidized pollutants (nitrate, [[perchlorate]], oxidized metals, chlorinated solvents, explosives and propellants).<ref name="EPA_2013">{{Cite book|url=https://www.epa.gov/sites/production/files/2015-04/documents/introductiontoinsitubioremediationofgroundwater_dec2013.pdf|title=Introduction to In Situ Bioremediation of Groundwater|publisher=US Environmental Protection Agency|year=2013|pages=30}}</ref> In both these approaches, additional nutrients, vitamins, minerals, and pH buffers may be added to optimize conditions for the microorganisms. In some cases, specialized microbial cultures are added ([[bioaugmentation]]) to further enhance biodegradation.
Most bioremediation processes involve oxidation-reduction reactions where either an electron acceptor (commonly oxygen) is added to stimulate oxidation of a reduced pollutant (e.g. hydrocarbons) or an electron donor (commonly an organic substrate) is added to reduce oxidized pollutants (nitrate, [[perchlorate]], oxidized metals, chlorinated solvents, explosives and propellants).<ref name="EPA_2013">{{Cite book|url=https://www.epa.gov/sites/production/files/2015-04/documents/introductiontoinsitubioremediationofgroundwater_dec2013.pdf|title=Introduction to In Situ Bioremediation of Groundwater|publisher=US Environmental Protection Agency|year=2013|page=30}}</ref> In both these approaches, additional nutrients, vitamins, minerals, and pH buffers may be added to optimize conditions for the microorganisms. In some cases, specialized microbial cultures are added ([[bioaugmentation]]) to further enhance biodegradation.


Approaches for oxygen addition below the water table include recirculating aerated water through the treatment zone, addition of pure oxygen or peroxides, and [[air sparging]].<ref name="Leeson_2002" /> Recirculation systems typically consist of a combination of injection wells or galleries and one or more recovery wells where the extracted groundwater is treated, oxygenated, amended with nutrients and re-injected.<ref name="EPA_2017">{{cite web | publisher = United States Environmental Protection Agency (USEPA) | date = 2017 | title = How To Evaluate Alternative Cleanup Technologies For Underground Storage Tank Sites. A Guide For Corrective Action Plan Reviewers. | work = EPA 510-B-17-003 | url = https://www.epa.gov/sites/production/files/2014-03/documents/tum_ch5.pdf }}</ref> However, the amount of oxygen that can be provided by this method is limited by the low solubility of oxygen in water (8 to 10&nbsp;mg/L for water in equilibrium with air at typical temperatures). Greater amounts of oxygen can be provided by contacting the water with pure oxygen or addition of [[hydrogen peroxide]] (H<sub>2</sub>O<sub>2</sub>) to the water. In some cases, slurries of solid calcium or magnesium peroxide are injected under pressure through soil borings. These solid peroxides react with water releasing H<sub>2</sub>O<sub>2</sub> which then decomposes releasing oxygen. Air sparging involves the injection of air under pressure below the water table. The air injection pressure must be great enough to overcome the hydrostatic pressure of the water and resistance to air flow through the soil.<ref name="Leeson_2002">{{Cite book|title=Air Sparging Design Paradigm| vauthors = Leeson A |publisher= Battelle | location = Columbus OH |year=2002| url = https://apps.dtic.mil/sti/pdfs/ADA492279.pdf| archive-url = https://web.archive.org/web/20170620003120/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA492279| url-status = live| archive-date = June 20, 2017}}</ref><ref name="EPA_2017" />
Approaches for oxygen addition below the water table include recirculating aerated water through the treatment zone, addition of pure oxygen or peroxides, and [[air sparging]].<ref name="Leeson_2002" /> Recirculation systems typically consist of a combination of injection wells or galleries and one or more recovery wells where the extracted groundwater is treated, oxygenated, amended with nutrients and re-injected.<ref name="EPA_2017" /> However, the amount of oxygen that can be provided by this method is limited by the low solubility of oxygen in water (8 to 10&nbsp;mg/L for water in equilibrium with air at typical temperatures). Greater amounts of oxygen can be provided by contacting the water with pure oxygen or addition of [[hydrogen peroxide]] (H<sub>2</sub>O<sub>2</sub>) to the water. In some cases, slurries of solid calcium or magnesium peroxide are injected under pressure through soil borings. These solid peroxides react with water releasing H<sub>2</sub>O<sub>2</sub> which then decomposes releasing oxygen. Air sparging involves the injection of air under pressure below the water table. The air injection pressure must be great enough to overcome the hydrostatic pressure of the water and resistance to air flow through the soil.<ref name="Leeson_2002">{{Cite book|title=Air Sparging Design Paradigm| vauthors = Leeson A |publisher= Battelle | location = Columbus OH |year=2002| url = https://apps.dtic.mil/sti/pdfs/ADA492279.pdf| archive-url = https://web.archive.org/web/20170620003120/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA492279| url-status = live| archive-date = June 20, 2017}}</ref><ref name="EPA_2017" />


=== Biostimulation ===
=== Biostimulation ===
[[File:Bioremediation at INL.jpg|thumb|An example of biostimulation at the Snake River Plain Aquifer in Idaho. This process involves the addition of whey powder to promote the utilization of naturally present bacteria. Whey powder acts as a substrate to aid in the growth of bacteria.<ref name = "Mora_2008">{{Cite journal| vauthors = Mora RH, Macbeth TW, MacHarg T, Gundarlahalli J, Holbrook H, Schiff P |date=2008|title=Enhanced bioremediation using whey powder for a trichloroethene plume in a high-sulfate, fractured granitic aquifer |journal=Remediation Journal|language=en|volume=18|issue=3|pages=7–30|doi=10.1002/rem.20168|issn=1520-6831}}</ref> At this site, microorganisms break down the carcinogenic compound [[trichloroethylene]] (TCE), which is a process seen in previous studies.<ref name = "Mora_2008" />]]
[[File:Bioremediation at INL.jpg|thumb|An example of biostimulation at the Snake River Plain Aquifer in Idaho. This process involves the addition of whey powder to promote the utilization of naturally present bacteria. Whey powder acts as a substrate to aid in the growth of bacteria.<ref name = "Mora_2008">{{Cite journal| vauthors = Mora RH, Macbeth TW, MacHarg T, Gundarlahalli J, Holbrook H, Schiff P |date=2008|title=Enhanced bioremediation using whey powder for a trichloroethene plume in a high-sulfate, fractured granitic aquifer |journal=Remediation Journal|language=en|volume=18|issue=3|pages=7–30|doi=10.1002/rem.20168|bibcode=2008RemJ...18c...7M |issn=1520-6831}}</ref> At this site, microorganisms break down the carcinogenic compound [[trichloroethylene]] (TCE), which is a process seen in previous studies.<ref name = "Mora_2008" />]]


Bioremediation can be carried out by bacteria that are naturally present. In biostimulation, the population of these helpful bacteria can be increased by adding nutrients.<ref name="Kapahi_2019" /><ref>{{cite journal |last1=Kalantary |first1=Roshanak Rezaei |last2=Mohseni-Bandpi |first2=Anoushiravan |last3=Esrafili |first3=Ali |last4=Nasseri |first4=Simin |last5=Ashmagh |first5=Fatemeh Rashid |last6=Jorfi |first6=Sahand |last7=Ja’fari |first7=Mahsa |title=Effectiveness of biostimulation through nutrient content on the bioremediation of phenanthrene contaminated soil |journal=Journal of Environmental Health Science and Engineering |date=December 2014 |volume=12 |issue=1 |pages=143 |doi=10.1186/s40201-014-0143-1 |pmid=25610635 |access-date=|pmc=4301987 }}</ref>
Bioremediation can be carried out by bacteria that are naturally present. In biostimulation, the population of these helpful bacteria can be increased by adding nutrients.<ref name="Kapahi_2019" /><ref>{{cite journal | vauthors = Kalantary RR, Mohseni-Bandpi A, Esrafili A, Nasseri S, Ashmagh FR, Jorfi S, Ja'fari M | title = Effectiveness of biostimulation through nutrient content on the bioremediation of phenanthrene contaminated soil | journal = Journal of Environmental Health Science & Engineering | volume = 12 | issue = 1 | pages = 143 | date = December 2014 | pmid = 25610635 | pmc = 4301987 | doi = 10.1186/s40201-014-0143-1 | bibcode = 2014JEHSE..12..143K | doi-access = free }}</ref>


Bacteria can in principle be used to degrade hydrocarbons.<ref>{{cite journal | vauthors = Lee DW, Lee H, Lee AH, Kwon BO, Khim JS, Yim UH, Kim BS, Kim JJ | display-authors = 6 | title = Microbial community composition and PAHs removal potential of indigenous bacteria in oil contaminated sediment of Taean coast, Korea | journal = Environmental Pollution | volume = 234 | pages = 503–512 | date = March 2018 | pmid = 29216488 | doi = 10.1016/j.envpol.2017.11.097 }}</ref><ref>{{cite journal| vauthors = Chen Q, Bao B, Li Y, Liu M, Zhu B, Mu J, Chen Z |date=2020|title=Effects of marine oil pollution on microbial diversity in coastal waters and stimulating indigenous microorganism bioremediation with nutrients |journal=Regional Studies in Marine Science|language=en|volume=39|pages=101395|doi=10.1016/j.rsma.2020.101395|s2cid=225285497 |issn=2352-4855}}</ref> Specific to marine oil spills, nitrogen and phosphorus have been key nutrients in biodegradation.<ref>{{Cite journal| vauthors = Varjani SJ, Upasani VN |date=2017|title=A new look on factors affecting microbial degradation of petroleum hydrocarbon pollutants |journal=International Biodeterioration & Biodegradation|language=en|volume=120|pages=71–83|doi=10.1016/j.ibiod.2017.02.006|issn=0964-8305}}</ref> The bioremediation of hydrocarbons suffers from low rates.
Bacteria can in principle be used to degrade hydrocarbons.<ref>{{cite journal | vauthors = Lee DW, Lee H, Lee AH, Kwon BO, Khim JS, Yim UH, Kim BS, Kim JJ | title = Microbial community composition and PAHs removal potential of indigenous bacteria in oil contaminated sediment of Taean coast, Korea | journal = Environmental Pollution | volume = 234 | pages = 503–512 | date = March 2018 | pmid = 29216488 | doi = 10.1016/j.envpol.2017.11.097 | bibcode = 2018EPoll.234..503L }}</ref><ref>{{cite journal| vauthors = Chen Q, Bao B, Li Y, Liu M, Zhu B, Mu J, Chen Z |date=2020|title=Effects of marine oil pollution on microbial diversity in coastal waters and stimulating indigenous microorganism bioremediation with nutrients |journal=Regional Studies in Marine Science|language=en|volume=39|page=101395|doi=10.1016/j.rsma.2020.101395|bibcode=2020RSMS...3901395C |s2cid=225285497 |issn=2352-4855}}</ref> Specific to marine oil spills, nitrogen and phosphorus have been key nutrients in biodegradation.<ref>{{Cite journal| vauthors = Varjani SJ, Upasani VN |date=2017|title=A new look on factors affecting microbial degradation of petroleum hydrocarbon pollutants |journal=International Biodeterioration & Biodegradation|language=en|volume=120|pages=71–83|doi=10.1016/j.ibiod.2017.02.006|bibcode=2017IBiBi.120...71V |issn=0964-8305}}</ref> The bioremediation of hydrocarbons suffers from low rates.


Bioremediation can involve the action of [[microbial consortium]]. Within the consortium, the product of one species could be the substrate for another species.<ref>{{cite book | vauthors = Paniagua-Michel J, Fathepure BZ | chapter = Microbial Consortia and Biodegradation of Petroleum Hydrocarbons in Marine Environments|date=2018 | title =Microbial Action on Hydrocarbons|pages=1–20| veditors = Kumar V, Kumar M, Prasad R |place= Singapore|publisher=Springer Singapore|language=en|doi=10.1007/978-981-13-1840-5_1|isbn=978-981-13-1839-9 }}</ref>
Bioremediation can involve the action of [[microbial consortium]]. Within the consortium, the product of one species could be the substrate for another species.<ref>{{cite book | vauthors = Paniagua-Michel J, Fathepure BZ | chapter = Microbial Consortia and Biodegradation of Petroleum Hydrocarbons in Marine Environments|date=2018 | title =Microbial Action on Hydrocarbons|pages=1–20| veditors = Kumar V, Kumar M, Prasad R |place= Singapore|publisher=Springer Singapore|language=en|doi=10.1007/978-981-13-1840-5_1|isbn=978-981-13-1839-9 }}</ref>


Anaerobic bioremediation can in principle be employed to treat a range of oxidized contaminants including chlorinated [[ethylene]]s ([[Tetrachloroethylene|PCE]], [[Trichloroethylene|TCE]], [[Dichloroethene|DCE]], [[Vinyl chloride|VC)]], chlorinated [[ethane]]s ([[Trichloroethane|TCA]], [[Dichloroethane|DCA]]), chloromethanes ([[Carbon tetrachloride|CT]], [[Chloroform|CF]]), chlorinated cyclic hydrocarbons, various energetics (e.g., [[perchlorate]],<ref>{{cite book| vauthors = Coates JD, Jackson WA |title=In situ bioremediation of perchlorate in groundwater|date=2008|publisher=Springer|isbn=978-0-387-84921-8| veditors = Stroo H, Ward CH |location=New York|pages=29–53|chapter=Principles of Perchlorate Treatment|series=SERDP/ESTCP Environmental Remediation Technology|doi=10.1007/978-0-387-84921-8_3}}</ref> [[RDX]], [[TNT]]), and [[nitrate]].<ref name="Kapahi_2019" /> This process involves the addition of an electron donor to: 1) deplete background electron acceptors including oxygen, nitrate, oxidized iron and manganese and sulfate; and 2) stimulate the biological and/or chemical reduction of the oxidized pollutants. [[Hexavalent chromium]] (Cr[VI]) and uranium (U[VI]) can be reduced to less mobile and/or less toxic forms (e.g., Cr[III], U[IV]). Similarly, reduction of sulfate to sulfide (sulfidogenesis) can be used to precipitate certain metals (e.g., [[zinc]], [[cadmium]]). The choice of substrate and the method of injection depend on the contaminant type and distribution in the aquifer, hydrogeology, and remediation objectives. Substrate can be added using conventional well installations, by direct-push technology, or by excavation and backfill such as [[permeable reactive barrier]]s (PRB) or biowalls.<ref>{{cite web | vauthors = Gavaskar A, Gupta N, Sass B, Janosy R, Hicks J | title = Design guidance for application of permeable reactive barriers for groundwater remediation. | publisher = Battelle | location = Columbus OH | date = March 2000 | url = https://www.researchgate.net/publication/265150942 }}</ref> Slow-release products composed of edible oils or solid substrates tend to stay in place for an extended treatment period. Soluble substrates or soluble fermentation products of slow-release substrates can potentially migrate via advection and diffusion, providing broader but shorter-lived treatment zones. The added organic substrates are first fermented to hydrogen (H<sub>2</sub>) and volatile fatty acids (VFAs). The VFAs, including acetate, lactate, propionate and butyrate, provide carbon and energy for bacterial metabolism.<ref name="Kapahi_2019" /><ref name="EPA_2013" />
Anaerobic bioremediation can in principle be employed to treat a range of oxidized contaminants including chlorinated [[ethylene]]s ([[Tetrachloroethylene|PCE]], [[Trichloroethylene|TCE]], [[Dichloroethene|DCE]], [[Vinyl chloride|VC)]], chlorinated [[ethane]]s ([[Trichloroethane|TCA]], [[Dichloroethane|DCA]]), chloromethanes ([[Carbon tetrachloride|CT]], [[Chloroform|CF]]), chlorinated cyclic hydrocarbons, various energetics (e.g., [[perchlorate]],<ref>{{cite book| vauthors = Coates JD, Jackson WA |title=In Situ Bioremediation of Perchlorate in Groundwater |date=2008|publisher=Springer|isbn=978-0-387-84921-8| veditors = Stroo H, Ward CH |location=New York|pages=29–53|chapter=Principles of Perchlorate Treatment|series=SERDP/ESTCP Environmental Remediation Technology|doi=10.1007/978-0-387-84921-8_3}}</ref> [[RDX]], [[TNT]]), and [[nitrate]].<ref name="Kapahi_2019" /> This process involves the addition of an electron donor to: 1) deplete background electron acceptors including oxygen, nitrate, oxidized iron and manganese and sulfate; and 2) stimulate the biological and/or chemical reduction of the oxidized pollutants. The choice of substrate and the method of injection depend on the contaminant type and distribution in the aquifer, hydrogeology, and remediation objectives. Substrate can be added using conventional well installations, by direct-push technology, or by excavation and backfill such as [[permeable reactive barrier]]s (PRB) or biowalls.<ref>{{cite web | vauthors = Gavaskar A, Gupta N, Sass B, Janosy R, Hicks J | title = Design guidance for application of permeable reactive barriers for groundwater remediation. | publisher = Battelle | location = Columbus OH | date = March 2000 | url = https://www.researchgate.net/publication/265150942 }}</ref> Slow-release products composed of edible oils or solid substrates tend to stay in place for an extended treatment period. Soluble substrates or soluble fermentation products of slow-release substrates can potentially migrate via advection and diffusion, providing broader but shorter-lived treatment zones. The added organic substrates are first fermented to hydrogen (H<sub>2</sub>) and volatile fatty acids (VFAs). The VFAs, including acetate, lactate, propionate and butyrate, provide carbon and energy for bacterial metabolism.<ref name="Kapahi_2019" /><ref name="EPA_2013" />


=== Bioattenuation ===
=== Bioattenuation ===
Numerous chemical, physical, and biological processes that lessen the bulk, toxicity, volume, or concentration of pollutants are referred to as bioattenuation. These procedures involve the transformation of pollutants as well as aerobic and anaerobic biodegradation, sorption, volatilization, and chemical or biological stabilization. Since there are no other remedial treatments that may be used, the duration is not a limiting issue and is typically applied to sites with low concentrations of contaminants. <ref>Vásquez-Murrieta, M. S., Hernández-Hernández, O. J., Cruz-Maya, J. A., Cancino-Díaz, J. C., & Jan-Roblero, J. (2016). Approaches for Removal of PAHs in Soils: Bioaugmentation, Biostimulation and Bioattenuation. Soil Contamination - Current Consequences and Further Solutions. https://doi.org/10.5772/64682</ref> During bioattenuation, biodegradation occurs naturally with the addition of nutrients or bacteria. The indigenous microbes present will determine the metabolic activity and act as a natural attenuation.<ref name="Ying_2018">{{cite book | vauthors = Ying GG | chapter = Chapter 14 - Remediation and Mitigation Strategies|date=2018 | title = Integrated Analytical Approaches for Pesticide Management|pages=207–217|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-816155-5.00014-2|isbn=978-0-12-816155-5}}</ref> While there is no anthropogenic involvement in bioattenuation, the contaminated site must still be monitored.<ref name="Ying_2018" />
During bioattenuation, biodegradation occurs naturally with the addition of nutrients or bacteria. The indigenous microbes present will determine the metabolic activity and act as a natural attenuation.<ref name="Ying_2018">{{cite book | vauthors = Ying GG | chapter = Chapter 14 - Remediation and Mitigation Strategies|date=2018 | title = Integrated Analytical Approaches for Pesticide Management|pages=207–217|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-816155-5.00014-2|isbn=978-0-12-816155-5}}</ref> While there is no anthropogenic involvement in bioattenuation, the contaminated site must still be monitored.<ref name="Ying_2018" />


=== Biosparging ===
=== Biosparging ===
A useful method for removing volatile organic chemicals is biosparging. By slowly infusing air into the aquifer beneath the contaminated zone, biosparging works. The injected air encourages oxygenation of the aquifer at a reasonably near well spacing, which is critical to encourage aerobic biodegradation. <ref>Kao, C., Chen, C., Chen, S., Chien, H., & Chen, Y. (2008). Field and microbiological evaluation of the use of in situ biosparging to remediate a petroleum-hydrocarbon spill site. Chemosphere, 70(8), 1492–1499. https://doi.org/10.1016/j.chemosphere.2007.08.029</ref> Indigenous bacteria are encouraged to accelerate their rate of destruction when oxygen is introduced.<ref name="Disadv-Overview" /> However, biosparging focuses on saturated contaminated zones, specifically related to ground water remediation.<ref>{{cite journal| vauthors = Johnson PC, Johnson RL, Bruce CL, Leeson A |date=2001|title=Advances in In Situ Air Sparging/Biosparging |journal=Bioremediation Journal|volume=5|issue=4|pages=251–266|doi=10.1080/20018891079311|s2cid=131393543|issn=1088-9868}}</ref>
Biosparging is the process of groundwater remediation as oxygen, and possible nutrients, is injected. When oxygen is injected, indigenous bacteria are stimulated to increase rate of degradation.<ref name="Disadv-Overview" /> However, biosparging focuses on saturated contaminated zones, specifically related to ground water remediation.<ref>{{cite journal| vauthors = Johnson PC, Johnson RL, Bruce CL, Leeson A |date=2001|title=Advances in In Situ Air Sparging/Biosparging |journal=Bioremediation Journal|volume=5|issue=4|pages=251–266|doi=10.1080/20018891079311|bibcode=2001BiorJ...5..251J |s2cid=131393543|issn=1088-9868}}</ref>

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UNICEF, power producers, bulk water suppliers, and local governments are early adopters of low cost bioremediation, such as aerobic bacteria tablets which are simply dropped into water.<ref>{{cite web |date=June 2022 |title=Ageing infrastructure gets bio boost |url=https://bedfordviewedenvalenews.co.za/494020/aging-infrastructure-to-get-bio-boost/ |publisher=CAXTON}}</ref>


== ''Ex situ'' techniques ==
== ''Ex situ'' techniques ==


=== Biopiles ===
=== Biopiles ===
Biopiles, similar to bioventing, are used to remove petroleum pollutants by introducing aerobic hydrocarbons to contaminated soils. However, the soil is excavated and piled with an aeration system. This aeration system enhances microbial activity by introducing oxygen under positive pressure or removes oxygen under negative pressure.<ref>{{cite journal | vauthors = Chen R, Zhou Y | title = Measure microbial activity driven oxygen transfer in membrane aerated biofilm reactor from supply side | journal = Environmental Research | volume = 195 | pages = 110845 | date = April 2021 | pmid = 33549616 | doi = 10.1016/j.envres.2021.110845 | bibcode = 2021ER....19510845C | s2cid = 231867176 }}</ref>
In order to improve bioremediation by essentially boosting microbial activity, biopile-mediated bioremediation requires piling excavated tainted soil above ground, followed by nutrient supplementation and occasionally aeration. Aeration, irrigation, nutrient and leachate collecting systems, and a treatment bed are the elements of this technique. Due to its beneficial qualities, such as cost effectiveness, which enables effective biodegradation under the condition that nutrient, temperature, and aeration are sufficiently managed, the application of this specific ex situ technique is being studied more frequently. <ref>Whelan MJ, Coulon F, Hince G, Rayner J, McWatters R, Spedding T,
Snape I (2015) Fate and transport of petroleum hydrocarbons in
engineered biopiles in polar regions. Chemosphere 131:232–240.
doi:10.1016/j.chemosphere.2014.10.088</ref>


=== Windrows ===
=== Windrows ===
[[File:Shell Haven East Site - geograph.org.uk - 591937.jpg|thumb|The former Shell Haven Refinery in Standford-le-Hope which underwent bioremediation to minimize the oil contaminated site. Bioremediation techniques, such as windrows, were used to promote oxygen transfer.<ref name = "Waters_2002">{{Cite book| vauthors = Waters JM, Lambert C, Reid D, Shaw R |title=Redevelopment of the former Shell Haven refinery |publisher=WIT Press|year=2002|isbn=1-85312-918-6|location=Southampton, UK|pages=77–85}}</ref> The refinery has excavated approximately 115,000&nbsp;m<sup>3</sup> of contaminated soil.<ref name = "Waters_2002" />]]
In order to improve ex situ bioremediation, windrows shift the piled polluted soil on a regular basis. This increases the degradation activities of the native and/or transitory hydrocarbonoclastic bacteria present in the polluted soil. It is possible to do bioremediation by assimilation, biotransformation, and mineralization. Periodic turning of polluted soil and the addition of water promote aeration, uniformly distribute pollutants, nutrients, and microbial degradative activities. <ref>Barr D (2002) Biological methods for assessment and remediation of
Windrow systems are similar to compost techniques where soil is periodically turned in order to enhance aeration.<ref>{{Cite book | vauthors = Prasad S, Kannojiya S, Kumar S, Yadav KK, Kundu M, Rakshit A | chapter = Integrative Approaches for Understanding and Designing Strategies of Bioremediation. | veditors = Rakshit A, Parihar M, Sarkar B, Singh HB, Fraceto LF | chapter-url=https://books.google.com/books?id=H-IaEAAAQBAJ&q=bioremediation+windrow&pg=PA37|title=Bioremediation Science: From Theory to Practice|date=2021|publisher=CRC Press|isbn=978-1-000-28046-3|language=en}}</ref> This periodic turning also allows contaminants present in the soil to be uniformly distributed which accelerates the process of bioremediation.<ref>{{cite journal | vauthors = Azubuike CC, Chikere CB, Okpokwasili GC | title = Bioremediation techniques-classification based on site of application: principles, advantages, limitations and prospects | journal = World Journal of Microbiology & Biotechnology | volume = 32 | issue = 11 | page = 180 | date = November 2016 | pmid = 27638318 | pmc = 5026719 | doi = 10.1007/s11274-016-2137-x }}</ref>
contaminated land: case studies. Construction Industry Research
and Information Association, London</ref>


=== Landfarming ===
=== Landfarming ===
{{Main|Landfarming}}
Due to its low cost and little equipment needs, land farming is one of the simplest bioremediation processes. Ex situ bioremediation is what it is generally referred to as, however in other circumstances, in situ bioremediation technology is what it is referred to. The treatment site is at the center of this argument. Whether or whether land farming may be done in situ or ex situ depends in large part on the depth of the pollution. In land farming, dirty soils are often excavated and tilled, although it appears that the method of bioremediation depends on the treatment site. Excavated polluted soil might be considered in situ when it is treated there; otherwise, it is ex situ because it shares more characteristics with other ex situ bioremediation approaches.
[[Landfarming]], or land treatment, is a method commonly used for sludge spills. This method disperses contaminated soil and aerates the soil by cyclically rotating.<ref>{{cite book | vauthors = Kumar V, Shahi SK, Singh S | chapter = Bioremediation: An Eco-sustainable Approach for Restoration of Contaminated Sites|date=2018 | veditors = Singh J, Sharma D, Kumar G, Sharma NR | title = Microbial Bioprospecting for Sustainable Development|pages=115–136|place=Singapore|publisher=Springer|language=en|doi=10.1007/978-981-13-0053-0_6|isbn=978-981-13-0053-0 }}</ref> This process is an above land application and contaminated soils are required to be shallow in order for microbial activity to be stimulated. However, if the contamination is deeper than 5 feet, then the soil is required to be excavated to above ground.<ref name="EPA_2017">{{cite web | publisher = United States Environmental Protection Agency (USEPA) | date = 2017 | title = How To Evaluate Alternative Cleanup Technologies For Underground Storage Tank Sites. A Guide For Corrective Action Plan Reviewers. | work = EPA 510-B-17-003 | url = https://www.epa.gov/sites/production/files/2014-03/documents/tum_ch5.pdf }}</ref> While it is an ''ex situ'' technique, it can also be considered an ''in situ'' technique as Landfarming can be performed at the site of contamination.<ref>{{cite journal | vauthors = Azubuike CC, Chikere CB, Okpokwasili GC | title = Bioremediation techniques-classification based on site of application: principles, advantages, limitations and prospects | journal = World Journal of Microbiology & Biotechnology | volume = 32 | issue = 11 | pages = 180 | date = November 2016 | pmid = 27638318 | pmc = 5026719 | doi = 10.1007/s11274-016-2137-x }}</ref>
<ref>Nikolopoulou M, Pasadakis N, Norf H, Kalogerakis N (2013)
Enhanced ex situ bioremediation of crude oil contaminated
beach sand by supplementation with nutrients and rhamnolipids.
Mar Pollut Bull 77:37–44. doi:10.1016/j.marpolbul.2013.10.038</ref>


== ''In situ'' vs. ''Ex situ'' ==
=== Bioreactor ===
''Ex situ'' techniques are often more expensive because of excavation and transportation costs to the treatment facility, while i''n situ'' techniques are performed at the site of contamination so they only have installation costs. While there is less cost there is also less of an ability to determine the scale and spread of the pollutant. The pollutant ultimately determines which bioremediation method to use. The depth and spread of the pollutantare other important factors.<ref>{{cite journal | vauthors = Azubuike CC, Chikere CB, Okpokwasili GC | title = Bioremediation techniques-classification based on site of application: principles, advantages, limitations and prospects | journal = World Journal of Microbiology & Biotechnology | volume = 32 | issue = 11 | pages = 180 | date = November 2016 | pmid = 27638318 | doi = 10.1007/s11274-016-2137-x | pmc = 5026719 }}</ref>
In a bioreactor, basic materials are transformed into specified products through a sequence of biological reactions. The bioreactor can be operated in a variety of ways, such as batch, fed-batch, sequencing batch, continuous, and multistage. The market economy and capital expenditure have a major role in determining the operating mode. The environment of a bioreactor mimics and preserves the natural environment of cells to provide the best circumstances for growth. In either instance, using a bioreactor to clean polluted soil has various benefits over alternative ex situ bioremediation methods. Polluted samples can be put into a bioreactor as dry matter or slurry. <ref>Mohan SV, Sirisha K, Rao NC, Sarma PN, Reddy SJ (2004)
Degradation of chlorpyrifos contaminated soil by bioslurry
reactor operated in sequencing batch mode: bioprocess monitoring. J Hazard Mater 116:39–48. doi:10.1016/j.jhazmat.2004.
05.037</ref>


==Heavy metals==
==Heavy metals==
Heavy metals become present in the environment due to anthropogenic activities or natural factors.<ref name="Kapahi_2019" /> Arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and mercury (Hg) are five heavy metals that pose risks to environmental ecology and human health because they are carcinogenic and poisonous even in small concentrations.<ref>Leong, Y. K., & Chang, J. S. (2020). Bioremediation of heavy metals using microalgae: Recent advances and mechanisms. Bioresource Technology, 303, 122886. https://doi.org/10.1016/j.biortech.2020.122886</ref> Anthropogenic activities include industrial emissions, electronic waste, and ore mining. Natural factors include mineral weathering, soil erosion, and forest fires.<ref name="Kapahi_2019" /> Heavy metals including cadmium, chromium, lead and uranium are unlike organic compounds and cannot be biodegraded. However, bioremediation processes can potentially be used to reduce the mobility of these material in the subsurface, reducing the potential for human and environmental exposure.<ref>{{Cite journal| vauthors = Ghosh M, Singh SP |date= July 2005|title=A Review on Phytoremediation of Heavy Metals and Utilization of It's by Products | url = https://www.semanticscholar.org/paper/A-review-on-phytoremediation-of-heavy-metals-and-of-Ghosh-Singh/0b6cdc57ea1f70f5b43f649b2efe36a775df410c?p2df |journal=Asian Journal on Energy and Environment|volume=6|issue=4|pages=214–231|doi= 10.15666/AEER/0301_001018|s2cid= 15886743|issn=}}</ref> Heavy metals from these factors are predominantly present in water sources due to runoff where it is uptake by marine fauna and flora.<ref name="Kapahi_2019" />
Heavy metals are introduced into the environment by both anthropogenic activities and natural factors.<ref name="Kapahi_2019" /> Anthropogenic activities include industrial emissions, electronic waste, and mining. Natural factors include mineral weathering, soil erosion, and forest fires.<ref name="Kapahi_2019" /> Heavy metals including cadmium, chromium, lead and uranium are unlike organic compounds and cannot be biodegraded. However, bioremediation processes can potentially be used to minimize the mobility of these material in the subsurface, lowering the potential for human and environmental exposure.<ref>{{Cite journal| vauthors = Ghosh M, Singh SP |date= July 2005|title=A Review on Phytoremediation of Heavy Metals and Utilization of Its Byproducts |journal=Asian Journal on Energy and Environment|volume=6|issue=4|pages=214–231|doi= 10.15666/AEER/0301_001018|s2cid= 15886743|issn=|doi-access=free}}</ref> Heavy metals from these factors are predominantly present in water sources due to runoff where it is uptake by marine fauna and flora.<ref name="Kapahi_2019" />


[[Hexavalent chromium]] (Cr[VI]) and uranium (U[VI]) can be reduced to less mobile and/or less toxic forms (e.g., Cr[III], U[IV]). Similarly, reduction of sulfate to sulfide (sulfidogenesis) can be used to immobilize certain metals (e.g., [[zinc]], [[cadmium]]).
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The mobility of certain metals including chromium (Cr) and uranium (U) varies depending on the oxidation state of the material.<ref>{{Cite book|url=https://enviro.wiki/images/c/c1/USEPA-2007-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_1_Technical_Basis_for_Assessment.pdf|title=Monitored natural attenuation of inorganic contaminants in groundwater, Volume 1 Technical basis for assessment| vauthors = Ford RG, Wilkin RT, Puls RW |publisher=U.S. Environmental Protection Agency, EPA/600/R-07/139|year=2007|oclc=191800707}}</ref> Microorganisms can be used to reduce the toxicity and mobility of chromium by reducing hexavalent chromium, Cr(VI) to trivalent Cr (III).<ref>{{Cite book|url=https://enviro.wiki/images/3/3a/USEPA-2007-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_2.pdf|title=Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Volume 2 - Assessment for Non-Radionulcides Including Arsenic, Cadmium, Chromium, Copper, Lead, Nickel, Nitrate, Perchlorate, and Selenium | vauthors = Ford RG, Wilkin RT, Puls RW |publisher=USEPA|year=2007}}</ref> Uranium can be reduced from the more mobile U(VI) oxidation state to the less mobile U(IV) oxidation state.<ref>{{cite journal | vauthors = Williams KH, Bargar JR, Lloyd JR, Lovley DR | title = Bioremediation of uranium-contaminated groundwater: a systems approach to subsurface biogeochemistry | journal = Current Opinion in Biotechnology | volume = 24 | issue = 3 | pages = 489–97 | date = June 2013 | pmid = 23159488 | doi = 10.1016/j.copbio.2012.10.008 }}</ref><ref>{{Cite book|url=https://enviro.wiki/images/0/05/USEPA-2010-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_3.pdf|title=Monitored natural attenuation of inorganic contaminants in groundwater, Volume 3 Assessment for Radionuclides Including Tritium, Radon, Strontium, Technetium, Uranium, Iodine, Radium, Thorium, Cesium, and Plutonium-Americium | vauthors = Ford RG, Wilkin RT, Puls RW |publisher=U.S. Environmental Protection Agency, EPA/600/R-10/093|year=2007}}</ref> Microorganisms are used in this process because the reduction rate of these metals is often slow unless catalyzed by microbial interactions<ref name="Palmisano_2003">{{Cite book|title=Bioremediation of Metals and Radionuclides : What It Is and How It Works | edition = 2nd | vauthors = Palmisano A, Hazen T |date=2003|publisher=Lawrence Berkeley National Laboratory|oclc=316485842}}</ref> Research is also underway to develop methods to remove metals from water by enhancing the sorption of the metal to cell walls.<ref name="Palmisano_2003" /> This approach has been evaluated for treatment of cadmium,<ref name="source 3">{{cite journal | vauthors = Ansari MI, Malik A | title = Biosorption of nickel and cadmium by metal resistant bacterial isolates from agricultural soil irrigated with industrial wastewater | journal = Bioresource Technology | volume = 98 | issue = 16 | pages = 3149–53 | date = November 2007 | pmid = 17166714 | doi = 10.1016/j.biortech.2006.10.008 }}</ref> chromium,<ref name="Durán_2018">{{cite journal | vauthors = Durán U, Coronado-Apodaca KG, Meza-Escalante ER, Ulloa-Mercado G, Serrano D | title = Two combined mechanisms responsible to hexavalent chromium removal on active anaerobic granular consortium | journal = Chemosphere | volume = 198 | pages = 191–197 | date = May 2018 | pmid = 29421729 | doi = 10.1016/j.chemosphere.2018.01.024 | bibcode = 2018Chmsp.198..191D }}</ref> and lead.<ref name="source 1">{{cite journal | vauthors = Tripathi M, Munot HP, Shouche Y, Meyer JM, Goel R | title = Isolation and functional characterization of siderophore-producing lead- and cadmium-resistant Pseudomonas putida KNP9 | journal = Current Microbiology | volume = 50 | issue = 5 | pages = 233–7 | date = May 2005 | pmid = 15886913 | doi = 10.1007/s00284-004-4459-4 | s2cid = 21061197 }}</ref> Genetically modified bacteria has also been explored for use in sequestration of Arsenic.<ref name = "Yam et al, 2021">{{cite journal | vauthors = Yam HM, Leong S, Qiu X, Zaiden N | title = Bioremediation of Arsenic-contaminated water through application of bioengineered Shewanella oneidensis | journal = Proceedings of the 6th IRC Conference on Science, Engineering and Technology, July 2020, Singapore | volume = 1 | pages = 559–574 | date = May 2021 | doi = 10.1007/978-981-15-9472-4_49 | isbn = 978-981-15-9471-7 | s2cid = 236650675 }}</ref> [[Phytoextraction process]]es concentrate contaminants in the biomass for subsequent removal. Different strains of microalgae showed a range of responses and tolerances as well as the capacity to bioaccumulate heavy metals. Proteins and peptides, as well as various functional groups, are in charge of metal binding. Heavy metal bioremediation and biosorption involve a variety of mechanisms, including extracellular adsorption, reduction, volatilization, complex formation, ion exchange, intracellular accumulation, chelation, and bio-methylation. <ref>Leong, Y. K., & Chang, J. S. (2020). Bioremediation of heavy metals using microalgae: Recent advances and mechanisms. Bioresource Technology, 303, 122886. https://doi.org/10.1016/j.biortech.2020.122886</ref>

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The mobility of certain metals including chromium (Cr) and uranium (U) varies depending on the oxidation state of the material.<ref>{{Cite book|url=https://enviro.wiki/images/c/c1/USEPA-2007-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_1_Technical_Basis_for_Assessment.pdf|title=Monitored natural attenuation of inorganic contaminants in groundwater, Volume 1 Technical basis for assessment| vauthors = Ford RG, Wilkin RT, Puls RW |publisher=U.S. Environmental Protection Agency, EPA/600/R-07/139|year=2007|oclc=191800707}}</ref> Microorganisms can be used to lower the toxicity and mobility of chromium by reducing hexavalent chromium, Cr(VI) to trivalent Cr(III).<ref>{{Cite book|url=https://enviro.wiki/images/3/3a/USEPA-2007-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_2.pdf|title=Monitored Natural Attenuation of Inorganic Contaminants in Groundwater, Volume 2 - Assessment for Non-Radionulcides Including Arsenic, Cadmium, Chromium, Copper, Lead, Nickel, Nitrate, Perchlorate, and Selenium | vauthors = Ford RG, Wilkin RT, Puls RW |publisher=USEPA|year=2007}}</ref> Reduction of the more mobile U(VI) species affords the less mobile U(IV) derivatives.<ref>{{cite journal | vauthors = Williams KH, Bargar JR, Lloyd JR, Lovley DR | title = Bioremediation of uranium-contaminated groundwater: a systems approach to subsurface biogeochemistry | journal = Current Opinion in Biotechnology | volume = 24 | issue = 3 | pages = 489–97 | date = June 2013 | pmid = 23159488 | doi = 10.1016/j.copbio.2012.10.008 }}</ref><ref>{{Cite book|url=https://enviro.wiki/images/0/05/USEPA-2010-MNA_of_Inorganic_Contaminants_in_GW%2C_Vol_3.pdf|title=Monitored natural attenuation of inorganic contaminants in groundwater, Volume 3 Assessment for Radionuclides Including Tritium, Radon, Strontium, Technetium, Uranium, Iodine, Radium, Thorium, Cesium, and Plutonium-Americium | vauthors = Ford RG, Wilkin RT, Puls RW |publisher=U.S. Environmental Protection Agency, EPA/600/R-10/093|year=2007}}</ref> Microorganisms are used in this process because the reduction rate of these metals is often slow in the absence of microbial interactions<ref name="Palmisano_2003">{{Cite book|title=Bioremediation of Metals and Radionuclides: What It Is and How It Works | edition = 2nd | vauthors = Palmisano A, Hazen T |date=2003|publisher=Lawrence Berkeley National Laboratory|oclc=316485842}}</ref> Research is also underway to develop methods to remove metals from water by enhancing the sorption of the metal to cell walls.<ref name="Palmisano_2003" /> This approach has been evaluated for treatment of cadmium,<ref name="source 3">{{cite journal | vauthors = Ansari MI, Malik A | title = Biosorption of nickel and cadmium by metal resistant bacterial isolates from agricultural soil irrigated with industrial wastewater | journal = Bioresource Technology | volume = 98 | issue = 16 | pages = 3149–53 | date = November 2007 | pmid = 17166714 | doi = 10.1016/j.biortech.2006.10.008 | bibcode = 2007BiTec..98.3149A }}</ref> chromium,<ref name="Durán_2018">{{cite journal | vauthors = Durán U, Coronado-Apodaca KG, Meza-Escalante ER, Ulloa-Mercado G, Serrano D | title = Two combined mechanisms responsible to hexavalent chromium removal on active anaerobic granular consortium | journal = Chemosphere | volume = 198 | pages = 191–197 | date = May 2018 | pmid = 29421729 | doi = 10.1016/j.chemosphere.2018.01.024 | bibcode = 2018Chmsp.198..191D }}</ref> and lead.<ref name="source 1">{{cite journal | vauthors = Tripathi M, Munot HP, Shouche Y, Meyer JM, Goel R | title = Isolation and functional characterization of siderophore-producing lead- and cadmium-resistant Pseudomonas putida KNP9 | journal = Current Microbiology | volume = 50 | issue = 5 | pages = 233–7 | date = May 2005 | pmid = 15886913 | doi = 10.1007/s00284-004-4459-4 | s2cid = 21061197 }}</ref> Genetically modified bacteria has also been explored for use in sequestration of Arsenic.<ref name = "Yam et al, 2021">{{cite book | vauthors = Yam HM, Leong S, Qiu X, Zaiden N | title = Irc-Set 2020 | chapter = Bioremediation of Arsenic-Contaminated Water Through Application of Bioengineered Shewanella oneidensis | volume = 1 | pages = 559–574 | date = May 2021 | doi = 10.1007/978-981-15-9472-4_49 | isbn = 978-981-15-9471-7 | s2cid = 236650675 }}</ref> [[Phytoextraction process]]es concentrate contaminants in the biomass for subsequent removal.

Metal extractions can in principle be performed in situ or ex situ where in situ is preferred since it is less expensive to excavate the substrate.<ref>{{cite journal | vauthors = Azubuike CC, Chikere CB, Okpokwasili GC | title = Bioremediation techniques-classification based on site of application: principles, advantages, limitations and prospects | journal = World Journal of Microbiology & Biotechnology | volume = 32 | issue = 11 | pages = 180 | date = November 2016 | pmid = 27638318 | pmc = 5026719 | doi = 10.1007/s11274-016-2137-x }}</ref>

Bioremediation is not specific to metals. In 2010 there was a [[Deepwater Horizon oil spill|massive oil spill in the Gulf of Mexico]]. Populations of bacteria and [[archaea]] were used to rejuvenate the coast after the oil spill. These microorganisms over time have developed metabolic networks that can utilize hydrocarbons such as oil and petroleum as a source of carbon and energy.<ref>{{cite journal | vauthors = Fathepure BZ | title = Recent studies in microbial degradation of petroleum hydrocarbons in hypersaline environments | language = English | journal = Frontiers in Microbiology | volume = 5 | pages = 173 | date = 2014-01-01 | pmid = 24795705 | pmc = 4005966 | doi = 10.3389/fmicb.2014.00173 | doi-access = free }}</ref> Microbial bioremediation is a very effective modern technique for restoring natural systems by removing toxins from the environment.


== Pesticides ==
== Pesticides ==
Of the many ways to deal with pesticide contamination, bioremediation promises to be more effective.<ref>{{cite journal | vauthors = Nie J, Sun Y, Zhou Y, Kumar M, Usman M, Li J, Shao J, Wang L, Tsang DC | title = Bioremediation of water containing pesticides by microalgae: Mechanisms, methods, and prospects for future research | journal = The Science of the Total Environment | volume = 707 | pages = 136080 | date = March 2020 | pmid = 31869621 | doi = 10.1016/j.scitotenv.2019.136080 | bibcode = 2020ScTEn.70736080N }}</ref> Many sites around the world are contaminated with agrichemicals. <ref>{{cite journal | vauthors = Alvarez A, Saez JM, Davila Costa JS, Colin VL, Fuentes MS, Cuozzo SA, Benimeli CS, Polti MA, Amoroso MJ | title = Actinobacteria: Current research and perspectives for bioremediation of pesticides and heavy metals | journal = Chemosphere | volume = 166 | pages = 41–62 | date = January 2017 | pmid = 27684437 | doi = 10.1016/j.chemosphere.2016.09.070 | bibcode = 2017Chmsp.166...41A | hdl = 11336/63289 | hdl-access = free }}</ref> These agrichemicals often resist biodegradation, by design.<ref name = "Mohapatra_2022">{{Cite journal | vauthors = Mohapatra D, Rath SK, Mohapatra PK |date=2022-05-02 |title=Soil Fungi for Bioremediation of Pesticide Toxicants: A Perspective |journal=Geomicrobiology Journal |language=en |volume=39 |issue=3–5 |pages=352–372 |doi=10.1080/01490451.2021.2019855 |bibcode=2022GmbJ...39..352M |issn=0149-0451}}</ref><ref>{{cite journal | vauthors = Nie J, Sun Y, Zhou Y, Kumar M, Usman M, Li J, Shao J, Wang L, Tsang DC | title = Bioremediation of water containing pesticides by microalgae: Mechanisms, methods, and prospects for future research | journal = The Science of the Total Environment | volume = 707 | pages = 136080 | date = March 2020 | pmid = 31869621 | doi = 10.1016/j.scitotenv.2019.136080 | bibcode = 2020ScTEn.70736080N }}</ref> Harming all manners of organic life with long term health issues such as cancer, rashes, blindness, paralysis, and mental illness.<ref name = "Mohapatra_2022" /> An example is [[Lindane]] which was a commonly used insecticide in the 20th century. Long time exposure poses a serious threat to humans and the surrounding ecosystem. Lindane reduces the potential of beneficial bacteria in the soil such as nitrogen fixation cyanobacteria. As well as causing central nervous system issues in smaller mammals such as seizures, dizziness, and even death. What makes it so harmful to these organisms is how quickly distributed it gets through the brain and fatty tissues. While Lindane has been mostly limited to specific use, it is still produced and used around the world.<ref>{{cite journal | vauthors = Chaurasia AK, Adhya TK, Apte SK | title = Engineering bacteria for bioremediation of persistent organochlorine pesticide lindane (γ-hexachlorocyclohexane) | journal = Bioresource Technology | volume = 149 | pages = 439–445 | date = December 2013 | pmid = 24135568 | doi = 10.1016/j.biortech.2013.09.084 | bibcode = 2013BiTec.149..439C }}</ref>
Recent technological advancements have exposed the ecology and people to a variety of chemical toxins, particularly ([[pesticides]], [[herbicide]]s, [[insecticide]]s, and [[fungicide]]s). Pesticides are synthetic chemical compounds that are used to manage pests in a variety of settings, including agriculture. Therefore, in integrated pest control systems, pesticides are viewed as efficient, economical, and effective tools (IPMs). Unchecked pesticide use results in their bioaccumulation in food chains, which puts mammals and other non-target animals at serious risk. Additionally, pesticides' direct or indirect effects on organisms other than their intended targets cause an environmental imbalance. Furthermore, pesticide residues persist in plant tissues, soil, air, and even water. These residues are among the most harmful dangers to the ecosystem since they can linger in the environment for a very long period and have [[carcinogenic]] consequences.

<ref>Alengebawy, A., Abdelkhalek, S. T., Qureshi, S. R., & Wang, M. Q. (2021). Heavy Metals and Pesticides Toxicity in Agricultural Soil and Plants: Ecological Risks and Human Health Implications. Toxics, 9(3), 42. https://doi.org/10.3390/toxics9030042</ref>
[[Actinomycetota|Actinobacteria]] has been a promising candidate ''in situ'' technique specifically for removing pesticides. When certain strains of Actinobacteria have been grouped together, their efficiency in degrading pesticides has enhanced. As well as being a reusable technique that strengthens through further use by limiting the migration space of these cells to target specific areas and not fully consume their cleansing abilities. Despite encouraging results, Actinobacteria has only been used in controlled lab settings and will need further development in finding the cost effectiveness and scalability of use.<ref>{{cite journal | vauthors = Alvarez A, Saez JM, Davila Costa JS, Colin VL, Fuentes MS, Cuozzo SA, Benimeli CS, Polti MA, Amoroso MJ | title = Actinobacteria: Current research and perspectives for bioremediation of pesticides and heavy metals | journal = Chemosphere | volume = 166 | pages = 41–62 | date = January 2017 | pmid = 27684437 | doi = 10.1016/j.chemosphere.2016.09.070 | bibcode = 2017Chmsp.166...41A | hdl = 11336/63289 | hdl-access = free }}</ref>


== Limitations of bioremediation ==
== Limitations of bioremediation ==
Bioremediation can be used to completely mineralize organic pollutants, to partially transform the pollutants, or alter their mobility. [[Heavy metals]] and [[Agricultural pollution#Radioactive elements|radionuclides]] are elements that cannot be biodegraded, but can be bio-transformed to less mobile forms.<ref name="Disadv-Comprehensive">{{cite journal| vauthors = Juwarkar AA, Singh SK, Mudhoo A |year=2010|title=A comprehensive overview of elements in bioremediation|journal=Reviews in Environmental Science and Bio/Technology|volume=9|issue=3|pages=215–88 |doi=10.1007/s11157-010-9215-6|s2cid=85268562}}</ref><ref name="Disadv-Factors">{{cite journal |doi=10.1016/S0960-8524(99)00144-3 |title=Factors limiting bioremediation technologies |journal=Bioresource Technology |volume=74 |pages=63–7 |year=2000 | vauthors = Boopathy R |s2cid=1027603 }}</ref><ref name="Disadv-EncTox">{{cite book|title=Encyclopedia of toxicology| vauthors = Wexler P |date=2014|publisher=Academic Press Inc|isbn=9780123864543|edition=3rd|location=San Diego, Ca|page=489}}</ref> In some cases, microbes do not fully mineralize the pollutant, potentially producing a more toxic compound.<ref name="Disadv-EncTox" /> For example, under anaerobic conditions, the [[Reductive dechlorination|reductive dehalogenation]] of [[Trichloroethylene|TCE]] may produce [[Dichloroethene|dichloroethylene]] (DCE) and [[vinyl chloride]] (VC), which are suspected or known [[carcinogen]]s.<ref name="Disadv-Comprehensive" /> However, the microorganism ''[[Dehalococcoides]]'' can further reduce DCE and VC to the non-toxic product ethene.<ref>{{cite journal | vauthors = Maymó-Gatell X, Chien Y, Gossett JM, Zinder SH | title = Isolation of a bacterium that reductively dechlorinates tetrachloroethene to ethene | journal = Science | volume = 276 | issue = 5318 | pages = 1568–71 | date = June 1997 | pmid = 9171062 | doi = 10.1126/science.276.5318.1568 }}</ref> The molecular pathways for bioremediation are of considerable interest.<ref name="Disadv-Comprehensive" /> In addition, knowing these pathways will help develop new technologies that can deal with sites that have uneven distributions of a mixture of contaminants.<ref name="Disadv-Overview">{{cite journal| vauthors = Vidali M |year=2001|title=Bioremediation. An overview|url=https://www.iupac.org/publications/pac/pdf/2001/pdf/7307x1163.pdf|journal=Pure and Applied Chemistry|volume=73|issue=7|pages=1163–72|doi=10.1351/pac200173071163|s2cid=18507182}}</ref>
Bioremediation can be used to mineralize organic pollutants, to partially transform the pollutants, or alter their mobility. [[Heavy metals]] and [[Agricultural pollution#Radioactive elements|radionuclides]] generally cannot be biodegraded, but can be bio-transformed to less mobile forms.<ref name="Disadv-Comprehensive">{{cite journal| vauthors = Juwarkar AA, Singh SK, Mudhoo A |year=2010|title=A comprehensive overview of elements in bioremediation|journal=Reviews in Environmental Science and Bio/Technology|volume=9|issue=3|pages=215–88 |doi=10.1007/s11157-010-9215-6|bibcode=2010RESBT...9..215J |s2cid=85268562}}</ref><ref name="Disadv-Factors">{{cite journal |doi=10.1016/S0960-8524(99)00144-3 |title=Factors limiting bioremediation technologies |journal=Bioresource Technology |volume=74 |pages=63–7 |year=2000 | vauthors = Boopathy R |issue=1 |bibcode=2000BiTec..74...63B |s2cid=1027603 }}</ref><ref name="Disadv-EncTox">{{cite book|title=Encyclopedia of toxicology| vauthors = Wexler P |date=2014|publisher=Academic Press Inc|isbn=978-0-12-386454-3|edition=3rd|location=San Diego, Ca|page=489}}</ref> In some cases, microbes do not fully mineralize the pollutant, potentially producing a more toxic compound.<ref name="Disadv-EncTox" /> For example, under anaerobic conditions, the [[Reductive dechlorination|reductive dehalogenation]] of [[Trichloroethylene|TCE]] may produce [[Dichloroethene|dichloroethylene]] (DCE) and [[vinyl chloride]] (VC), which are suspected or known [[carcinogen]]s.<ref name="Disadv-Comprehensive" /> However, the microorganism ''[[Dehalococcoides]]'' can further reduce DCE and VC to the non-toxic product ethene.<ref>{{cite journal | vauthors = Maymó-Gatell X, Chien Y, Gossett JM, Zinder SH | title = Isolation of a bacterium that reductively dechlorinates tetrachloroethene to ethene | journal = Science | volume = 276 | issue = 5318 | pages = 1568–71 | date = June 1997 | pmid = 9171062 | doi = 10.1126/science.276.5318.1568 }}</ref> The molecular pathways for bioremediation are of considerable interest.<ref name="Disadv-Comprehensive" /> In addition, knowing these pathways will help develop new technologies that can deal with sites that have uneven distributions of a mixture of contaminants.<ref name="Disadv-Overview">{{cite journal| vauthors = Vidali M |year=2001|title=Bioremediation. An overview|url=https://www.iupac.org/publications/pac/pdf/2001/pdf/7307x1163.pdf|journal=Pure and Applied Chemistry|volume=73|issue=7|pages=1163–72|doi=10.1351/pac200173071163|s2cid=18507182}}</ref>


Biodegradation requires microbial population with the metabolic capacity to degrade the pollutant.<ref name="Disadv-Overview" /><ref name="Disadv-Factors" /> The biological processes used by these microbes are highly specific, therefore, many environmental factors must be taken into account and regulated as well.<ref name="Disadv-Overview" /><ref name="Disadv-Comprehensive" /> It can be difficult to extrapolate the results from the small-scale test studies into big field operations.<ref name="Disadv-Overview" /> In many cases, bioremediation takes more time than other alternatives such as [[Landfill|land filling]] and [[incineration]].<ref name="Disadv-Overview" /><ref name="Disadv-Comprehensive" /> Another example is bioventing, which is inexpensive to bioremediate contaminated sites, however, this process is extensive and can take a few years to decontaminate a site.<ref name="Sharma_2019">{{Cite journal| vauthors = Sharma J |date=2019|title=Advantages and Limitations of In Situ Methods of Bioremediation|url=https://rabm.scholasticahq.com/article/10941-advantages-and-limitations-of-in-situ-methods-of-bioremediation|journal=Recent Adv Biol Med|language=en|volume=5|issue=2019|pages=10941|doi=10.18639/RABM.2019.955923|doi-access=free}}</ref>>
Biodegradation requires microbial population with the metabolic capacity to degrade the pollutant.<ref name="Disadv-Overview" /><ref name="Disadv-Factors" /> The biological processes used by these microbes are highly specific, therefore, many environmental factors must be taken into account and regulated as well.<ref name="Disadv-Overview" /><ref name="Disadv-Comprehensive" /> It can be difficult to extrapolate the results from the small-scale test studies into big field operations.<ref name="Disadv-Overview" /> In many cases, bioremediation takes more time than other alternatives such as [[Landfill|land filling]] and [[incineration]].<ref name="Disadv-Overview" /><ref name="Disadv-Comprehensive" /> Another example is bioventing, which is inexpensive to bioremediate contaminated sites, however, this process is extensive and can take a few years to decontaminate a site.<ref name="Sharma_2019">{{Cite journal|vauthors=Sharma J|date=2019|title=Advantages and Limitations of In Situ Methods of Bioremediation|journal=Recent Adv Biol Med|language=en|volume=5|issue=2019|page=10941|doi=10.18639/RABM.2019.955923|doi-broken-date=November 1, 2024 |doi-access=free}}</ref>>


Another major drawback is finding the right species to perform bioremediation. In order to prevent the introduction and spreading of an invasive species to the ecosystem, an indigenous species is needed. As well as a species plentiful enough to clean the whole site without exhausting the population. Finally the species should be resilient enough to withstand the environmental conditions.<ref>{{cite journal | vauthors = Nie J, Sun Y, Zhou Y, Kumar M, Usman M, Li J, Shao J, Wang L, Tsang DC | title = Bioremediation of water containing pesticides by microalgae: Mechanisms, methods, and prospects for future research | journal = The Science of the Total Environment | volume = 707 | pages = 136080 | date = March 2020 | pmid = 31869621 | doi = 10.1016/j.scitotenv.2019.136080 | bibcode = 2020ScTEn.70736080N }}</ref> These specific criteria may make it difficult to perform bioremediation on a contaminated site.
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In agricultural industries, the use of [[pesticide]]s is a top factor in direct soil contamination and runoff water contamination. The limitation or remediation of pesticides is the low bioavailability.<ref name="Odukkathil_2013">{{Cite journal| vauthors = Odukkathil G, Vasudevan N |date=2013|title=Toxicity and bioremediation of pesticides in agricultural soil |journal=Reviews in Environmental Science and Bio/Technology|language=en|volume=12|issue=4|pages=421–444|doi=10.1007/s11157-013-9320-4|s2cid=85173331|issn=1569-1705}}</ref> Altering the pH and temperature of the contaminated soil is a resolution to increase bioavailability which, in turn, increased degradation of harmful compounds.<ref name="Odukkathil_2013" />

⚫
In agricultural industries, the use of [[pesticide]]s is a top factor in direct [[soil contamination]] and runoff water contamination. The limitation or remediation of pesticides is the low bioavailability.<ref name="Odukkathil_2013">{{Cite journal| vauthors = Odukkathil G, Vasudevan N |date=2013|title=Toxicity and bioremediation of pesticides in agricultural soil |journal=Reviews in Environmental Science and Bio/Technology|language=en|volume=12|issue=4|pages=421–444|doi=10.1007/s11157-013-9320-4|bibcode=2013RESBT..12..421O |s2cid=85173331|issn=1569-1705}}</ref> Altering the pH and temperature of the contaminated soil is a resolution to increase bioavailability which, in turn, increased degradation of harmful compounds.<ref name="Odukkathil_2013" />


The compound [[acrylonitrile]] is commonly produced in industrial setting but adversely contaminates soils. Microorganisms containing nitrile hydratases (NHase) degraded harmful acrylonitrile compounds into non-polluting substances.<ref>{{cite journal | vauthors = Supreetha K, Rao SN, Srividya D, Anil HS, Kiran S | title = Advances in cloning, structural and bioremediation aspects of nitrile hydratases | journal = Molecular Biology Reports | volume = 46 | issue = 4 | pages = 4661–4673 | date = August 2019 | pmid = 31201677 | doi = 10.1007/s11033-019-04811-w | s2cid = 189819253 }}</ref>
The compound [[acrylonitrile]] is commonly produced in industrial setting but adversely contaminates soils. Microorganisms containing nitrile hydratases (NHase) degraded harmful acrylonitrile compounds into non-polluting substances.<ref>{{cite journal | vauthors = Supreetha K, Rao SN, Srividya D, Anil HS, Kiran S | title = Advances in cloning, structural and bioremediation aspects of nitrile hydratases | journal = Molecular Biology Reports | volume = 46 | issue = 4 | pages = 4661–4673 | date = August 2019 | pmid = 31201677 | doi = 10.1007/s11033-019-04811-w | s2cid = 189819253 }}</ref>
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== Genetic engineering ==
== Genetic engineering ==
The use of [[genetic engineering]] to create organisms specifically designed for bioremediation is under preliminary research.<ref name=pmid15040178>{{cite journal | vauthors = Lovley DR | title = Cleaning up with genomics: applying molecular biology to bioremediation | journal = Nature Reviews. Microbiology | volume = 1 | issue = 1 | pages = 35–44 | date = October 2003 | pmid = 15040178 | doi = 10.1038/nrmicro731 | s2cid = 40604152 }}</ref> Two category of genes can be inserted in the organism: degradative genes which encode proteins required for the degradation of pollutants, and reporter genes that are able to monitor pollution levels.<ref name="Menn et al 2001">{{cite book |doi=10.1002/9783527620999.ch21m |chapter=Genetically Engineered Microorganisms and Bioremediation |title=Biotechnology Set |pages=441–63 |year=2001 | vauthors = Menn FM, Easter JP, Sayler GS |isbn=978-3-527-62099-9 }}</ref> Numerous members of ''[[Pseudomonas]]'' have also been modified with the lux gene, but for the detection of the polyaromatic hydrocarbon naphthalene. A field test for the release of the modified organism has been successful on a moderately large scale.<ref>{{cite journal |doi=10.1021/es9908319 |title=Controlled Field Release of a Bioluminescent Genetically Engineered Microorganism for Bioremediation Process Monitoring and Control |journal=Environmental Science & Technology |volume=34 |issue=5 |pages=846–53 |year=2000 | vauthors = Ripp S, Nivens DE, Ahn Y, Werner C, Jarrell J, Easter JP, Cox CD, Burlage RS, Sayler GS | display-authors = 6 |bibcode=2000EnST...34..846R }}</ref>
The use of [[genetic engineering]] to create organisms specifically designed for bioremediation is under preliminary research.<ref name=pmid15040178>{{cite journal | vauthors = Lovley DR | title = Cleaning up with genomics: applying molecular biology to bioremediation | journal = Nature Reviews. Microbiology | volume = 1 | issue = 1 | pages = 35–44 | date = October 2003 | pmid = 15040178 | doi = 10.1038/nrmicro731 | s2cid = 40604152 }}</ref> Two category of genes can be inserted in the organism: degradative genes, which encode proteins required for the degradation of pollutants, and reporter genes, which encode proteins able to monitor pollution levels.<ref name="Menn et al 2001">{{cite book |doi=10.1002/9783527620999.ch21m |chapter=Genetically Engineered Microorganisms and Bioremediation |title=Biotechnology Set |pages=441–63 |year=2001 | vauthors = Menn FM, Easter JP, Sayler GS |isbn=978-3-527-62099-9 }}</ref> Numerous members of ''[[Pseudomonas]]'' have been modified with the ''lux'' gene for the detection of the polyaromatic hydrocarbon naphthalene. A field test for the release of the modified organism has been successful on a moderately large scale.<ref>{{cite journal |doi=10.1021/es9908319 |title=Controlled Field Release of a Bioluminescent Genetically Engineered Microorganism for Bioremediation Process Monitoring and Control |journal=Environmental Science & Technology |volume=34 |issue=5 |pages=846–53 |year=2000 | vauthors = Ripp S, Nivens DE, Ahn Y, Werner C, Jarrell J, Easter JP, Cox CD, Burlage RS, Sayler GS |bibcode=2000EnST...34..846R }}</ref>


There are concerns surrounding release and containment of genetically modified organisms into the environment due to the potential of horizontal gene transfer.<ref name=Davison2005>{{cite journal | vauthors = Davison J | title = Risk mitigation of genetically modified bacteria and plants designed for bioremediation | journal = Journal of Industrial Microbiology & Biotechnology | volume = 32 | issue = 11–12 | pages = 639–50 | date = December 2005 | pmid = 15973534 | doi = 10.1007/s10295-005-0242-1 | s2cid = 7986980 }}</ref> Genetically modified organisms are classified and controlled under the [[Toxic Substances Control Act of 1976]] under [[United States Environmental Protection Agency]].<ref>{{cite journal | vauthors = Sayler GS, Ripp S | title = Field applications of genetically engineered microorganisms for bioremediation processes | journal = Current Opinion in Biotechnology | volume = 11 | issue = 3 | pages = 286–9 | date = June 2000 | pmid = 10851144 | doi = 10.1016/S0958-1669(00)00097-5 }}</ref> Measures have been created to address these concerns. Organisms can be modified such that they can only survive and grow under specific sets of environmental conditions.<ref name=Davison2005/> In addition, the tracking of modified organisms can be made easier with the insertion of [[bioluminescence]] genes for visual identification.<ref name="Irvine">{{cite book | vauthors = Shanker R, Purohit HJ, Khanna P |year=1998 |chapter=Bioremediation for Hazardous Waste Management: The Indian Scenario |pages=81–96 |chapter-url={{Google books|oLNtgk_VKXsC|page=81|plainurl=yes}} | veditors = Irvine RL, Sikdar SK |title=Bioremediation Technologies: Principles and Practice |isbn=978-1-56676-561-9 }}</ref>
There are concerns surrounding release and containment of genetically modified organisms into the environment due to the potential of horizontal gene transfer.<ref name=Davison2005>{{cite journal | vauthors = Davison J | title = Risk mitigation of genetically modified bacteria and plants designed for bioremediation | journal = Journal of Industrial Microbiology & Biotechnology | volume = 32 | issue = 11–12 | pages = 639–50 | date = December 2005 | pmid = 15973534 | doi = 10.1007/s10295-005-0242-1 | s2cid = 7986980 }}</ref> Genetically modified organisms are classified and controlled under the [[Toxic Substances Control Act of 1976]] under [[United States Environmental Protection Agency]].<ref>{{cite journal | vauthors = Sayler GS, Ripp S | title = Field applications of genetically engineered microorganisms for bioremediation processes | journal = Current Opinion in Biotechnology | volume = 11 | issue = 3 | pages = 286–9 | date = June 2000 | pmid = 10851144 | doi = 10.1016/S0958-1669(00)00097-5 }}</ref> Measures have been created to address these concerns. Organisms can be modified such that they can only survive and grow under specific sets of environmental conditions.<ref name=Davison2005/> In addition, the tracking of modified organisms can be made easier with the insertion of [[bioluminescence]] genes for visual identification.<ref name="Irvine">{{cite book | vauthors = Shanker R, Purohit HJ, Khanna P |year=1998 |chapter=Bioremediation for Hazardous Waste Management: The Indian Scenario |pages=81–96 |chapter-url={{Google books|oLNtgk_VKXsC|page=81|plainurl=yes}} | veditors = Irvine RL, Sikdar SK |title=Bioremediation Technologies: Principles and Practice |isbn=978-1-56676-561-9 }}</ref>


Genetically modified organisms have been created to [[Oil spill#Cleanup and recovery|treat oil spills]] and break down certain [[plastic]]s (PET).<ref>{{cite web | vauthors = Bojar D | date = 7 May 2018 | url = https://phys.org/news/2018-05-circular-bioeconomy-synthetic-biology.html | title = Building a circular economy with synthetic biology | work = Phys.org }}</ref>
Genetically modified organisms have been created to [[Oil spill#Cleanup and recovery|treat oil spills]] and break down certain [[plastic]]s (PET).<ref>{{cite web | vauthors = Bojar D | date = May 7, 2018 | url = https://phys.org/news/2018-05-circular-bioeconomy-synthetic-biology.html | title = Building a circular economy with synthetic biology | work = Phys.org }}</ref>

== Additive manufacturing ==
[[Additive manufacturing]] technologies such as [[3D bioprinting|bioprinting]] offer distinctive benefits that can be leveraged in bioremediation to develop structures with characteristics tailored to biological systems and environmental cleanup needs, and even though the adoption of this technology in bioremediation is in its early stages, the area is seeing massive growth.<ref name=":0">{{cite journal | vauthors = Finny AS | title = 3D bioprinting in bioremediation: a comprehensive review of principles, applications, and future directions | journal = PeerJ | volume = 12 | pages = e16897 | date = February 8, 2024 | pmid = 38344299 | pmc = 10859081 | doi = 10.7717/peerj.16897 | s2cid = 267586847 | doi-access = free }}</ref>


== See also ==
== See also ==
Line 108: Line 111:
* [[Mycoremediation]]
* [[Mycoremediation]]
* [[Mycorrhizal bioremediation]]
* [[Mycorrhizal bioremediation]]
* [[Pleurotus]]
* [[Phytoremediation]]
* [[Phytoremediation]]
* ''[[Pseudomonas putida]]'' (used for degrading oil)
* ''[[Pseudomonas putida]]'' (used for degrading oil)
Line 119: Line 123:
* [https://web.archive.org/web/20100914030753/http://www.mobot.org/jwcross/phytoremediation/ Phytoremediation, hosted by the Missouri Botanical Garden]
* [https://web.archive.org/web/20100914030753/http://www.mobot.org/jwcross/phytoremediation/ Phytoremediation, hosted by the Missouri Botanical Garden]
* [https://atlasofscience.org/to-remediate-or-to-not-remediate/#more-17692 To remediate or to not remediate?]
* [https://atlasofscience.org/to-remediate-or-to-not-remediate/#more-17692 To remediate or to not remediate?]
*Anaerobic [http://enviro.wiki/index.php?title=Bioremediation_-_Anaerobic Bioremediation]
* Anaerobic [http://enviro.wiki/index.php?title=Bioremediation_-_Anaerobic Bioremediation]


{{Clear}}
{{Clear}}

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Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi in mycoremediation, and plants in phytoremediation), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluents etc., in natural or artificial settings.[1] The natural ability of organisms to adsorb, accumulate, and degrade common and emerging pollutants has attracted the use of biological resources in treatment of contaminated environment.[1] In comparison to conventional physicochemical treatment methods bioremediation may offer advantages as it aims to be sustainable, eco-friendly, cheap, and scalable.[1]

Most bioremediation is inadvertent, involving native organisms. Research on bioremediation is heavily focused on stimulating the process by inoculation of a polluted site with organisms or supplying nutrients to promote their growth. Environmental remediation is an alternative to bioremediation.[2]

While organic pollutants are susceptible to biodegradation, heavy metals cannot be degraded, but rather oxidized or reduced. Typical bioremediations involves oxidations.[3][4] Oxidations enhance the water-solubility of organic compounds and their susceptibility to further degradation by further oxidation and hydrolysis. Ultimately biodegradation converts hydrocarbons to carbon dioxide and water.[5] For heavy metals, bioremediation offers few solutions. Metal-containing pollutant can be removed, at least partially, with varying bioremediation techniques.[6] The main challenge to bioremediations is rate: the processes are slow.[7]

Bioremediation techniques can be classified as (i) in situ techniques, which treat polluted sites directly, vs (ii) ex situ techniques which are applied to excavated materials.[8] In both these approaches, additional nutrients, vitamins, minerals, and pH buffers are added to enhance the growth and metabolism of the microorganisms. In some cases, specialized microbial cultures are added (biostimulation). Some examples of bioremediation related technologies are phytoremediation, bioventing, bioattenuation, biosparging, composting (biopiles and windrows), and landfarming. Other remediation techniques include thermal desorption, vitrification, air stripping, bioleaching, rhizofiltration, and soil washing. Biological treatment, bioremediation, is a similar approach used to treat wastes including wastewater, industrial waste and solid waste. The end goal of bioremediation is to remove harmful compounds to improve soil and water quality.[9]

In situ techniques

[edit]
Visual representation showing in-situ bioremediation. This process involves the addition of oxygen, nutrients, or microbes into contaminated soil to remove toxic pollutants.[9] Contamination includes buried waste and underground pipe leakage that infiltrate ground water systems.[10] The addition of oxygen removes the pollutants by producing carbon dioxide and water.[6]

Bioventing

[edit]

Bioventing is a process that increases the oxygen or air flow into the unsaturated zone of the soil, this in turn increases the rate of natural in situ degradation of the targeted hydrocarbon contaminant.[11] Bioventing, an aerobic bioremediation, is the most common form of oxidative bioremediation process where oxygen is provided as the electron acceptor for oxidation of petroleum, polyaromatic hydrocarbons (PAHs), phenols, and other reduced pollutants. Oxygen is generally the preferred electron acceptor because of the higher energy yield and because oxygen is required for some enzyme systems to initiate the degradation process.[7] Microorganisms can degrade a wide variety of hydrocarbons, including components of gasoline, kerosene, diesel, and jet fuel. Under ideal aerobic conditions, the biodegradation rates of the low- to moderate-weight aliphatic, alicyclic, and aromatic compounds can be very high. As molecular weight of the compound increases, the resistance to biodegradation increases simultaneously.[7] This results in higher contaminated volatile compounds due to their high molecular weight and an increased difficulty to remove from the environment.

Most bioremediation processes involve oxidation-reduction reactions where either an electron acceptor (commonly oxygen) is added to stimulate oxidation of a reduced pollutant (e.g. hydrocarbons) or an electron donor (commonly an organic substrate) is added to reduce oxidized pollutants (nitrate, perchlorate, oxidized metals, chlorinated solvents, explosives and propellants).[5] In both these approaches, additional nutrients, vitamins, minerals, and pH buffers may be added to optimize conditions for the microorganisms. In some cases, specialized microbial cultures are added (bioaugmentation) to further enhance biodegradation.

Approaches for oxygen addition below the water table include recirculating aerated water through the treatment zone, addition of pure oxygen or peroxides, and air sparging.[12] Recirculation systems typically consist of a combination of injection wells or galleries and one or more recovery wells where the extracted groundwater is treated, oxygenated, amended with nutrients and re-injected.[13] However, the amount of oxygen that can be provided by this method is limited by the low solubility of oxygen in water (8 to 10 mg/L for water in equilibrium with air at typical temperatures). Greater amounts of oxygen can be provided by contacting the water with pure oxygen or addition of hydrogen peroxide (H2O2) to the water. In some cases, slurries of solid calcium or magnesium peroxide are injected under pressure through soil borings. These solid peroxides react with water releasing H2O2 which then decomposes releasing oxygen. Air sparging involves the injection of air under pressure below the water table. The air injection pressure must be great enough to overcome the hydrostatic pressure of the water and resistance to air flow through the soil.[12][13]

Biostimulation

[edit]
An example of biostimulation at the Snake River Plain Aquifer in Idaho. This process involves the addition of whey powder to promote the utilization of naturally present bacteria. Whey powder acts as a substrate to aid in the growth of bacteria.[14] At this site, microorganisms break down the carcinogenic compound trichloroethylene (TCE), which is a process seen in previous studies.[14]

Bioremediation can be carried out by bacteria that are naturally present. In biostimulation, the population of these helpful bacteria can be increased by adding nutrients.[6][15]

Bacteria can in principle be used to degrade hydrocarbons.[16][17] Specific to marine oil spills, nitrogen and phosphorus have been key nutrients in biodegradation.[18] The bioremediation of hydrocarbons suffers from low rates.

Bioremediation can involve the action of microbial consortium. Within the consortium, the product of one species could be the substrate for another species.[19]

Anaerobic bioremediation can in principle be employed to treat a range of oxidized contaminants including chlorinated ethylenes (PCE, TCE, DCE, VC), chlorinated ethanes (TCA, DCA), chloromethanes (CT, CF), chlorinated cyclic hydrocarbons, various energetics (e.g., perchlorate,[20] RDX, TNT), and nitrate.[6] This process involves the addition of an electron donor to: 1) deplete background electron acceptors including oxygen, nitrate, oxidized iron and manganese and sulfate; and 2) stimulate the biological and/or chemical reduction of the oxidized pollutants. The choice of substrate and the method of injection depend on the contaminant type and distribution in the aquifer, hydrogeology, and remediation objectives. Substrate can be added using conventional well installations, by direct-push technology, or by excavation and backfill such as permeable reactive barriers (PRB) or biowalls.[21] Slow-release products composed of edible oils or solid substrates tend to stay in place for an extended treatment period. Soluble substrates or soluble fermentation products of slow-release substrates can potentially migrate via advection and diffusion, providing broader but shorter-lived treatment zones. The added organic substrates are first fermented to hydrogen (H2) and volatile fatty acids (VFAs). The VFAs, including acetate, lactate, propionate and butyrate, provide carbon and energy for bacterial metabolism.[6][5]

Bioattenuation

[edit]

During bioattenuation, biodegradation occurs naturally with the addition of nutrients or bacteria. The indigenous microbes present will determine the metabolic activity and act as a natural attenuation.[22] While there is no anthropogenic involvement in bioattenuation, the contaminated site must still be monitored.[22]

Biosparging

[edit]

Biosparging is the process of groundwater remediation as oxygen, and possible nutrients, is injected. When oxygen is injected, indigenous bacteria are stimulated to increase rate of degradation.[23] However, biosparging focuses on saturated contaminated zones, specifically related to ground water remediation.[24]

UNICEF, power producers, bulk water suppliers, and local governments are early adopters of low cost bioremediation, such as aerobic bacteria tablets which are simply dropped into water.[25]

Ex situ techniques

[edit]

Biopiles

[edit]

Biopiles, similar to bioventing, are used to remove petroleum pollutants by introducing aerobic hydrocarbons to contaminated soils. However, the soil is excavated and piled with an aeration system. This aeration system enhances microbial activity by introducing oxygen under positive pressure or removes oxygen under negative pressure.[26]

Windrows

[edit]
The former Shell Haven Refinery in Standford-le-Hope which underwent bioremediation to minimize the oil contaminated site. Bioremediation techniques, such as windrows, were used to promote oxygen transfer.[27] The refinery has excavated approximately 115,000 m3 of contaminated soil.[27]

Windrow systems are similar to compost techniques where soil is periodically turned in order to enhance aeration.[28] This periodic turning also allows contaminants present in the soil to be uniformly distributed which accelerates the process of bioremediation.[29]

Landfarming

[edit]
Main article: Landfarming

Landfarming, or land treatment, is a method commonly used for sludge spills. This method disperses contaminated soil and aerates the soil by cyclically rotating.[30] This process is an above land application and contaminated soils are required to be shallow in order for microbial activity to be stimulated. However, if the contamination is deeper than 5 feet, then the soil is required to be excavated to above ground.[13] While it is an ex situ technique, it can also be considered an in situ technique as Landfarming can be performed at the site of contamination.[31]

In situ vs. Ex situ

[edit]

Ex situ techniques are often more expensive because of excavation and transportation costs to the treatment facility, while in situ techniques are performed at the site of contamination so they only have installation costs. While there is less cost there is also less of an ability to determine the scale and spread of the pollutant. The pollutant ultimately determines which bioremediation method to use. The depth and spread of the pollutantare other important factors.[32]

Heavy metals

[edit]

Heavy metals are introduced into the environment by both anthropogenic activities and natural factors.[6] Anthropogenic activities include industrial emissions, electronic waste, and mining. Natural factors include mineral weathering, soil erosion, and forest fires.[6] Heavy metals including cadmium, chromium, lead and uranium are unlike organic compounds and cannot be biodegraded. However, bioremediation processes can potentially be used to minimize the mobility of these material in the subsurface, lowering the potential for human and environmental exposure.[33] Heavy metals from these factors are predominantly present in water sources due to runoff where it is uptake by marine fauna and flora.[6]

Hexavalent chromium (Cr[VI]) and uranium (U[VI]) can be reduced to less mobile and/or less toxic forms (e.g., Cr[III], U[IV]). Similarly, reduction of sulfate to sulfide (sulfidogenesis) can be used to immobilize certain metals (e.g., zinc, cadmium).

The mobility of certain metals including chromium (Cr) and uranium (U) varies depending on the oxidation state of the material.[34] Microorganisms can be used to lower the toxicity and mobility of chromium by reducing hexavalent chromium, Cr(VI) to trivalent Cr(III).[35] Reduction of the more mobile U(VI) species affords the less mobile U(IV) derivatives.[36][37] Microorganisms are used in this process because the reduction rate of these metals is often slow in the absence of microbial interactions[38] Research is also underway to develop methods to remove metals from water by enhancing the sorption of the metal to cell walls.[38] This approach has been evaluated for treatment of cadmium,[39] chromium,[40] and lead.[41] Genetically modified bacteria has also been explored for use in sequestration of Arsenic.[42] Phytoextraction processes concentrate contaminants in the biomass for subsequent removal.

Metal extractions can in principle be performed in situ or ex situ where in situ is preferred since it is less expensive to excavate the substrate.[43]

Bioremediation is not specific to metals. In 2010 there was a massive oil spill in the Gulf of Mexico. Populations of bacteria and archaea were used to rejuvenate the coast after the oil spill. These microorganisms over time have developed metabolic networks that can utilize hydrocarbons such as oil and petroleum as a source of carbon and energy.[44] Microbial bioremediation is a very effective modern technique for restoring natural systems by removing toxins from the environment.

Pesticides

[edit]

Of the many ways to deal with pesticide contamination, bioremediation promises to be more effective.[45] Many sites around the world are contaminated with agrichemicals. [46] These agrichemicals often resist biodegradation, by design.[47][48] Harming all manners of organic life with long term health issues such as cancer, rashes, blindness, paralysis, and mental illness.[47] An example is Lindane which was a commonly used insecticide in the 20th century. Long time exposure poses a serious threat to humans and the surrounding ecosystem. Lindane reduces the potential of beneficial bacteria in the soil such as nitrogen fixation cyanobacteria. As well as causing central nervous system issues in smaller mammals such as seizures, dizziness, and even death. What makes it so harmful to these organisms is how quickly distributed it gets through the brain and fatty tissues. While Lindane has been mostly limited to specific use, it is still produced and used around the world.[49]

Actinobacteria has been a promising candidate in situ technique specifically for removing pesticides. When certain strains of Actinobacteria have been grouped together, their efficiency in degrading pesticides has enhanced. As well as being a reusable technique that strengthens through further use by limiting the migration space of these cells to target specific areas and not fully consume their cleansing abilities. Despite encouraging results, Actinobacteria has only been used in controlled lab settings and will need further development in finding the cost effectiveness and scalability of use.[50]

Limitations of bioremediation

[edit]

Bioremediation can be used to mineralize organic pollutants, to partially transform the pollutants, or alter their mobility. Heavy metals and radionuclides generally cannot be biodegraded, but can be bio-transformed to less mobile forms.[51][52][53] In some cases, microbes do not fully mineralize the pollutant, potentially producing a more toxic compound.[53] For example, under anaerobic conditions, the reductive dehalogenation of TCE may produce dichloroethylene (DCE) and vinyl chloride (VC), which are suspected or known carcinogens.[51] However, the microorganism Dehalococcoides can further reduce DCE and VC to the non-toxic product ethene.[54] The molecular pathways for bioremediation are of considerable interest.[51] In addition, knowing these pathways will help develop new technologies that can deal with sites that have uneven distributions of a mixture of contaminants.[23]

Biodegradation requires microbial population with the metabolic capacity to degrade the pollutant.[23][52] The biological processes used by these microbes are highly specific, therefore, many environmental factors must be taken into account and regulated as well.[23][51] It can be difficult to extrapolate the results from the small-scale test studies into big field operations.[23] In many cases, bioremediation takes more time than other alternatives such as land filling and incineration.[23][51] Another example is bioventing, which is inexpensive to bioremediate contaminated sites, however, this process is extensive and can take a few years to decontaminate a site.[55]>

Another major drawback is finding the right species to perform bioremediation. In order to prevent the introduction and spreading of an invasive species to the ecosystem, an indigenous species is needed. As well as a species plentiful enough to clean the whole site without exhausting the population. Finally the species should be resilient enough to withstand the environmental conditions.[56] These specific criteria may make it difficult to perform bioremediation on a contaminated site.

In agricultural industries, the use of pesticides is a top factor in direct soil contamination and runoff water contamination. The limitation or remediation of pesticides is the low bioavailability.[57] Altering the pH and temperature of the contaminated soil is a resolution to increase bioavailability which, in turn, increased degradation of harmful compounds.[57]

The compound acrylonitrile is commonly produced in industrial setting but adversely contaminates soils. Microorganisms containing nitrile hydratases (NHase) degraded harmful acrylonitrile compounds into non-polluting substances.[58]

Since the experience with harmful contaminants are limited, laboratory practices are required to evaluate effectiveness, treatment designs, and estimate treatment times.[55] Bioremediation processes may take several months to several years depending on the size of the contaminated area.[59]

Genetic engineering

[edit]

The use of genetic engineering to create organisms specifically designed for bioremediation is under preliminary research.[60] Two category of genes can be inserted in the organism: degradative genes, which encode proteins required for the degradation of pollutants, and reporter genes, which encode proteins able to monitor pollution levels.[61] Numerous members of Pseudomonas have been modified with the lux gene for the detection of the polyaromatic hydrocarbon naphthalene. A field test for the release of the modified organism has been successful on a moderately large scale.[62]

There are concerns surrounding release and containment of genetically modified organisms into the environment due to the potential of horizontal gene transfer.[63] Genetically modified organisms are classified and controlled under the Toxic Substances Control Act of 1976 under United States Environmental Protection Agency.[64] Measures have been created to address these concerns. Organisms can be modified such that they can only survive and grow under specific sets of environmental conditions.[63] In addition, the tracking of modified organisms can be made easier with the insertion of bioluminescence genes for visual identification.[65]

Genetically modified organisms have been created to treat oil spills and break down certain plastics (PET).[66]

Additive manufacturing

[edit]

Additive manufacturing technologies such as bioprinting offer distinctive benefits that can be leveraged in bioremediation to develop structures with characteristics tailored to biological systems and environmental cleanup needs, and even though the adoption of this technology in bioremediation is in its early stages, the area is seeing massive growth.[67]

See also

[edit]

References

[edit]
  1. ^ a b c Yuvraj (2022). "Microalgal Bioremediation: A Clean and Sustainable Approach for Controlling Environmental Pollution". Innovations in Environmental Biotechnology. Vol. 1. Singapore: Springer Singapore. pp. 305–318. doi:10.1007/978-981-16-4445-0_13. ISBN 978-981-16-4445-0.
  2. ^ "Green Remediation Best Management Practices: Sites with Leaking Underground Storage Tank Systems. EPA 542-F-11-008" (PDF). EPA. June 2011.
  3. ^ Duran N, Esposito E (2022). "Potential Applications of Oxidative Enzymes and Phenoloxidase-like Compounds in Wastewater and Soil Treatment: A Review". Applied Catalysis B: Environmental. 1 (2): 305–318. doi:10.1016/S0926-3373(00)00168-5.
  4. ^ Singh N, Kumar A, Sharma B (2019). "Role of Fungal Enzymes for Bioremediation of Hazardous Chemicals". Recent Advancement in White Biotechnology Through Fungi. Fungal Biology. Vol. 3. Cham: Springer International Publishing. pp. 237–256. doi:10.1007/978-3-030-25506-0_9. ISBN 978-3-030-25506-0. S2CID 210291135.
  5. ^ a b c Introduction to In Situ Bioremediation of Groundwater (PDF). US Environmental Protection Agency. 2013. p. 30.
  6. ^ a b c d e f g h Kapahi M, Sachdeva S (December 2019). "Bioremediation Options for Heavy Metal Pollution". Journal of Health and Pollution. 9 (24): 191203. doi:10.5696/2156-9614-9.24.191203. PMC 6905138. PMID 31893164.
  7. ^ a b c Mirza Hasanuzzaman, Majeti Narasimha Vara Prasad (2020). Handbook of Bioremediation. Academic Press. doi:10.1016/C2018-0-05109-9. ISBN 978-0-12-819382-2. S2CID 127409446.
  8. ^ Kensa VM (2011). "Bioremediation - An Overview". I Control Pollution. 27 (2): 161–168. ISSN 0970-2083.
  9. ^ a b Canak S, Berezljev L, Borojevic K, Asotic J, Ketin S (2019). "Bioremediation and "green chemistry"". Fresenius Environmental Bulletin. 28 (4): 3056–3064.
  10. ^ Jørgensen KS (2007). "In Situ Bioremediation". Advances in Applied Microbiology. 61. Academic Press: 285–305. doi:10.1016/S0065-2164(06)61008-3. ISBN 978-0-12-002663-0. PMID 17448793.
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  16. ^ Lee DW, Lee H, Lee AH, Kwon BO, Khim JS, Yim UH, et al. (March 2018). "Microbial community composition and PAHs removal potential of indigenous bacteria in oil contaminated sediment of Taean coast, Korea". Environmental Pollution. 234: 503–512. Bibcode:2018EPoll.234..503L. doi:10.1016/j.envpol.2017.11.097. PMID 29216488.
  17. ^ Chen Q, Bao B, Li Y, Liu M, Zhu B, Mu J, et al. (2020). "Effects of marine oil pollution on microbial diversity in coastal waters and stimulating indigenous microorganism bioremediation with nutrients". Regional Studies in Marine Science. 39: 101395. Bibcode:2020RSMS...3901395C. doi:10.1016/j.rsma.2020.101395. ISSN 2352-4855. S2CID 225285497.
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  20. ^ Coates JD, Jackson WA (2008). "Principles of Perchlorate Treatment". In Stroo H, Ward CH (eds.). In Situ Bioremediation of Perchlorate in Groundwater. SERDP/ESTCP Environmental Remediation Technology. New York: Springer. pp. 29–53. doi:10.1007/978-0-387-84921-8_3. ISBN 978-0-387-84921-8.
  21. ^ Gavaskar A, Gupta N, Sass B, Janosy R, Hicks J (March 2000). "Design guidance for application of permeable reactive barriers for groundwater remediation". Columbus OH: Battelle.
  22. ^ a b Ying GG (2018). "Chapter 14 - Remediation and Mitigation Strategies". Integrated Analytical Approaches for Pesticide Management. Academic Press. pp. 207–217. doi:10.1016/b978-0-12-816155-5.00014-2. ISBN 978-0-12-816155-5.
  23. ^ a b c d e f Vidali M (2001). "Bioremediation. An overview" (PDF). Pure and Applied Chemistry. 73 (7): 1163–72. doi:10.1351/pac200173071163. S2CID 18507182.
  24. ^ Johnson PC, Johnson RL, Bruce CL, Leeson A (2001). "Advances in In Situ Air Sparging/Biosparging". Bioremediation Journal. 5 (4): 251–266. Bibcode:2001BiorJ...5..251J. doi:10.1080/20018891079311. ISSN 1088-9868. S2CID 131393543.
  25. ^ "Ageing infrastructure gets bio boost". CAXTON. June 2022.
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