Chem321:Bioremediation

Bioremediation: Innovations for Sustainable Clean Up Processes

Recent discoveries in ecology and molecular biology have helped set the path for more efficient research in environmental biotechnologies. Bioremediation is a process that uses living organisms to break down environmental contaminates into undisruptive biological waste. When a location becomes polluted with toxic substances and is harmful to humans and the environment; bioremediation processes draw on naturally occurring bacteria, fungi, or plants (microorganisms) to detoxify those substances [5]. It is important to point out that biodegradation differs from bioremediation. Biodegradation is a 100% naturally occurring process in which microorganisms alter and decompose organic molecules eventually generating carbon dioxide and fatty acids. Bioremediation accelerates biodegradation by using in situ and ex situ remediation technologies [5]. The Environmental Protection Agency (EPA) defines bioremediation as “the use of living microbes to transform undesirable and harmful substances into a non-toxic compound, through the husbandry and management of naturally-occurring microbes which degrade target organic pollutants for the purpose of restoring a contaminated environment” [7]. Essentially bioremediation can occur naturally (intrinsic bioremediation) or aided by humans as engineered bioremediation and has provided multiple aids in environmental clean ups. The use of the bioremediation microorganisms have successfully been applied for treating contaminated soils and wastewater in controlled systems, as well as oil spill cleanups in seawater, freshwater, and terrestrial areas [3]. Water, however is a bit more sensitive than soil so it requires different remediation techniques. Oil spills that occur in surface water are easier to clean up than oil spills that contaminate groundwater because it’s harder to see the extent to which you have to cleanup [3]. Microbiologists have been studying bioremediation since the 1940’s. So bioremediation itself is not necessarily a new concept; however, the application of this process to cleanup oil spills and superfund sites is a newly innovative idea that seems to be spreading to other types of environmental contaminations [8].

Microorganisms for Bioremediation: A Win-Win Relationship

Microorganisms have the ability to grow and adapt in extreme conditions all over the world making them a prime specimen for consuming toxic substances. The microbes used in bioremediation processes share a reciprocal relationship with contaminants. Naturally microorganisms obtain their food source from the soil and water in which they live. Contaminants, when present, can serve as a supplementary food source for the microbes. Carbon is needed for microorganisms to grow which is provided by the contaminants. Oxidation-reduction reaction permits microorganisms to obtain energy by splitting chemical bonds and transporting electrons away from contaminants. Toxic substances losing electrons are oxidized and the electron acceptor is reduced. New cells can be produced by microbes using the carbon and the energy produced from the electron transport. Aerobic respiration uses oxygen as the electron acceptor. Some examples of aerobic bacteria (microbes) that work well in bioremediation are Myobacterium, Alcaligenes, Pseudomonas, and Sphingomonas. Hydrocarbons, pesticides, polyaromatic compounds, and alkanes are some examples of the contaminants degraded by aerobic microbes. By products of aerobic respiration include water, carbon dioxide, and an enlarged microorganism populace not nearly as bad as the toxics still left behind in traditional processes. Anaerobic respiration does not use oxygen as an electron acceptor instead iron, carbon dioxide, nitrate, or sulfate is used. Some of the contaminants that can be degraded by anaerobic bacterium are benzoates, toluene, PCB’s, DDT, carbon tetrachloride, ethylbenzene, phenols, and chloroform [3].

In Situ and Ex Situ Bioremediation

In situ bioremediation means that the bioremediation cleanup takes place right at the polluted site so there is no contaminated garbage, water, or dirt that needs to be trucked out to a different location. The most common in situ treatment is bioventing. Bioventing can be used when contamination is deep under surfaces and stimulates indigenous bacteria growth to degrade simple hydrocarbons by providing just the right amount of oxygen needed (low air flow rates). Other in situ bioremediation techniques are biosparging, for groundwater contamination sites, which increases contact between soil and groundwater, and bioaugmentation which involves adding indigenous or non-indigenous microorganisms to a contaminated site. In situ bioremediation techniques are cost efficient and noninvasive, but they have environmental constraints and trouble arises with monitoring these processes. Ex situ bioremediation techniques entail moving contaminated soil from the ground. Examples include: composting, landfarming which contaminated soil is moved and laid out over a previously mixed plot and tilled until contaminants are degraded, and biopiles which combines aspects of composting and landfarming [2].

Previous Contamination Site Techniques

Conventional techniques to clean up contaminated areas have not proven to be effective because they are not based on completely eliminating the pollution but just moving contaminated soil from one place to another, and capping off or closing off sites. These methods don’t actually solve the issue though because they not only fail to terminate the contaminated materials they create risks during excavation, handling, and transporting the hazardous materials. It is becoming harder and more expensive to find new landfill sites which continue to leach pollutants into the ground. Capping and containing contaminations is a very short term solution which requires monitoring and maintenance of the isolation barriers set up costing money and perhaps liabilities. Some generally more effective technologies used include high-temperature incineration, air stripping, carbon absorption, and chemical decompositions like base-catalyzed dechlorination, advanced oxidations, UV oxidation, and UV photolysis. These technologies can actually reduce contaminants. Although there are still many drawbacks to these solutions because they are technologically complex, have a very large cost even for small applications, and aren’t always publicly accepted. Careless incineration in particular can increase exposure to nearby residents and workers, and don’t always eradicate certain pollutants[3].

Advantages to Bioremediation

Bioremediation harnesses the ability to destroy a large range of toxic contaminants. Compounds that are legally deemed hazardous can be altered to completely safe substances. The potential health and safety liabilities associated with landfill, superfund, incineration, and cap/containing strategies don’t exist with bioremediation. Bioremediation doesn’t just transfer toxics from one environmental medium to another like incineration from landfills to the air it can remove contaminates completely. Bioremediation is a relatively cheap process compared to other hazardous waste cleanup technologies because it does not require a lot of equipment and labor. The public seems to be generally accepting of bioremediation because it is essentially a natural process what is left behind is just water, carbon dioxide, and cell biomass. Bioremediation is also frequently done in situ (on-site) so there is no transportation of hazardous waste from one location to another which burns fossil fuels, further disturbs multiple environments, and creates more chances for accidents that could be detrimental to human health [8].

Disadvantages to Bioremediation

Contamination sites with complex mixtures of contaminants that are unevenly dispersed require more research to develop and engineer bioremediation technologies suitable for those sites. Not all compounds are able to be completely degraded so bioremediation is restricted to removing contaminants that are biodegradable. Regulations on acceptable performance standards for bioremediation are not yet established this makes evaluation of end “clean” substances very difficult. There are many site factors for bioremediation that need to be regulated in order for successful degradation because biological processes tend to be very specific. These site factors include optimal soil moisture, soil pH, oxygen content, nutrient content, temperature, the type of soil, content of heavy metals, and extent of toxicity of contaminants. Time is a big factor in bioremediation and it can sometimes take up to several years to fully clean up a site depending on the volume and depth of a polluted area, the extent of harmful chemicals present, type of soil of medium, and whether the process is above ground or underground [7].

Bacterium That Eats a Cancer Causing Chemical

Shaily Mahendra, an assistant professor of civil and environmental engineering at UCLA, is researching a specific bacterium to use in bioremediation of contaminated drinking water. Some of the emerging water contaminants include: perfluorinated compounds found in firefighting foam, non-stick cookware and other scratch resistant coatings, nanomaterials found in titanium dioxide in sunscreen, and nanotubes in electronics. In another two or three decades Mahendra believes these contaminates will be found everywhere, and we are still unaware of the full extent these microtoxins will have on us or the environment. 1,4 Dioxane is a common industrial chemical found in a variety of applications like paper manufacturing, solvents, textiles, and is also found in personal care products like cosmetics, baby shampoo, lotions, etc. A very large number of people are being exposed to this common groundwater contaminate which is known to cause cancer. 1,4 Dioxane is also infinitely soluble in water making it easy to impact a large number of people within a short period of time. The bacterium being researched by Mahendra and her colleagues is Pseudonocardia dioxanivorans which effectively degrades the 1,4 dioxane. They have been able to sequence the entire DNA genome of Pseudonocardia dioxanivorans. This means they can utilize the information the DNA sequence holds to put this bacterium to use in field application of bioremediation. The research team at UCLA uses genomics based tools to find out the DNA sequences, gene chips or messenger RNA Transcriptomics, proteomics to understand the protein profile when it’s working. This helps understand the metabolic pathways and how it can be utilized to get rid of 1,4 dioxane to improve our health and our environments’ health. This research team monitors dioxane during bioremediation using stable isotopes. They are able to validate if bioremediation is occurring or if the dioxine is simply being removed through other environmental processes by looking for signatures, which differ for every compound, during their tests [4].

Bioremediation Research Discovers Vaccine

Dr. Richard Sayre, an Ohio State University Sea Grant researcher set out 10 years ago to study engineered algae for bioremediation techniques. He found Chlamydomonas reinhardtii, unicellular algae found abundantly around the world could be genetically changed to degrade hazardous heavy metals trapped in sediments. He has worked to decontaminate waters in the Great Lakes by improving the algae’s binding abilities. Dr. Sayre and his colleague believed since the Chlamydomonas absorbed the heavy metals so well it was worth researching if these microalgae could be used to make a vaccine that could protect fish from Hematopoietic Necrosis Virus (IHNV) which is a virus that kills 30% of the United States trout population. Attaching the correct antigen to the outside of the Chlamydomonas cell an immune response to the IHNV disease can be triggered when the algae is fed to the trout. Dr. Sayre is utilizing a combinatorial phage display library to monitor peptides that attach to antibodies in infected fish. The contending antigens hold optimism to be used in future vaccine testing. Overfishing and pollution of waterways has caused the global depletion of fisheries. This major issue could worsen if the few fish left are dying from diseases. Often experimental research on one particular technology reveals an answer for another innovation as this article points out. Since many biological processes interrelate with one another implementing bioremediation as a standard cleanup procedure may help provide insight to improve other pressing environmental issues [1].

How Can You Evaluate Bioremediation?

In order to determine if a bioremediation project is actually functioning requires evidence that the contaminant has decreased due to implementation of microorganisms (often bacterium). There are other natural processes that may influence a contaminant like changes due to abiotic reactions, getting stuck to soil solids; it may have migrated off site, or volatilization occurred. To properly evaluate whether or not biodegradation is truly taking place soil or water samples can be taken on site to a laboratory that can determine is the contaminant is decreasing. Lab results can also show if the microorganisms used can degrade contaminants under similar conditions as at the site [3].

The Future for Bioremediation

The mass amounts of municipal, industrial, and agricultural wastes that are produced each day contribute to the ever-increasing need for more sustainable pollution treatment options. The most frequently used current options to toxic clean ups are either too expensive, are impractical, or don’t alleviate toxic substances but simply move them. These inefficient processes waste money, and jeopardize human and environmental health basically a recipe for an unsustainable nightmare. Bioremediation processes, although not perfect, can serve as a viable means to reduce the impacts of pollution and toxic substances. Bioremediation is cost effective, safe, cheap, clean, and overall much more environmentally sustainable than conventional contamination “cleaning” processes. As far back as 2001 the EPA stated that bioremediation had clean up many contaminated sites and was being used at more than 50 Superfund sites in the United States [6]. Bioremediation technologies are used in a multitude of applications like oil spill cleanup, contaminated groundwater and water surfaces, contaminated soils, Superfund site cleanup, agricultural waste contamination cleanup, treating liquids/slurries from reactors, treating toxic air emissions, bioremediation of pesticides, bioabsorption/removal of heavy metals, and most likely there are more bioremediation projects being researched.

References

1.Banicki, Jentes, J. (2001). An Alga a Day Keeps the Doctor Away: Engineered Algae as a New Means to Vaccinate Fish. NOAA’s Office of Oceanic and Atmospheric Research. Retrieved from http://www.oar.noaa.gov/spotlite/archive/spot_fishvaccine.html

2.Federal Remediation Technologies Reference. In Situ Bioremediation Treatment. Retrieved from http://www.frtr.gov/matrix2/section4/4-2.html

3.Juwarkar, A. A., Singh, S. K., & Mudhoo, A. (2010). A comprehensive overview of elements in bioremediation. Reviews In Environmental Science & Biotechnology, 9(3), 215-288.doi:10.1007/s11157-010-9215-6

4.Mahendra, S. (2011, August 7). Shaily Mahendra: Bioremediation [Video File]. Retrieved from http://poptech.org/popcasts/shaily_mahendra_bioremediation

5.Pandey, B. B., & Fulekar, M. H. (2012). Bioremediation technology: A new horizon for environmental clean-up. Biology & Medicine, 4(1), 51-59.

6.U.S. Environmental Protection Agency. (2001). A Citizens Guide to Bioremediation. Retrieved from http://www.epa.gov/tio/download/citizens/bioremediation.pdf

7.U.S. Environmental Protection Agency. NRT Fact Sheet. Bioremediation in Oil Spill Response. Retrieved from http://www.epa.gov/osweroe1/docs/oil/edu/biofact.pdf

8.U.S. Environmental Protection Agency. (2001). Use of Bioremediation at Superfund Sites. Retrieved from http://www.epa.gov/tio/download/remed/542r01019.pdf