Future Outlook
The above account shows that bioremediation has a promising future with several potential applications to clean up polluted environments and treat wastes. Compared to physical cleanup methods, in situ bioremediation is much less expensive and causes less environmental perturbation. It may alter manufacturing practices, fuel production and composition, the way of individual disposal of waste, the cost of products, and environmental quality. (BSc Microbiology Bioremediation Notes Study Material)
However, employing bioremediation effectively in many applications requires both further R&D and clarification of government policies, particularly in the release of genetically- engineered organisms, a controversial issue, scientifically as well as politically. Most European countries as well as the U.S. and Japan have regulations that ban the deliberate release of genetically engineered microorganisms.
However, it may be possible to use them in contained bioreactors. Most successful applications of bioremediation such as the treatment of the shorelines contaminated by the Exxon Valdez oil spill have relied on indigenous microorganisms and simple environmental modifications such as nutrient applications and aeration. The current and emerging applications of bioremediation are different in Europe and Japan than they are in the U.S.A. Research in the U.S.A. promises to contribute to the development of cost-effective solutions for the bioremediation of contaminated sites. This new biotechnology will enable contaminated soils and waters to be cleaned up for reuse.
In several European countries, existing biological waste treatment technologies are to be extended to new areas for the removal of harmful toxicants from the air and industrial waste streams. If current trends continue, the Netherlands and Germany are likely to become worldwide leaders in the biotreatment of waste by the end of the century. (BSc Microbiology Bioremediation Notes Study Material)
Japanese research could aptly combine a quest for improved global environmental quality with a drive for energy self-sufficiency. Their efforts to reduce global warming, if successful, will have far-reaching effects. Japanese programmes to replace petroleum with biologically produced hydrogen and to replace gasoline-powered automobiles with cars that burn hydrogen would greatly reduce the future buildup of carbon dioxide in the atmosphere. A change to hydrogen fuel produced by microbes would be a major new use of bioremediation for pollution prevention that would revolutionize not only the petrochemical and automotive industries but the worldwide economy.
Phytoremediation – Biotechnology of Cleaning Up the Environment By Plants
The ability of microorganisms to uptake and accumulate heavy metals such as Co, Cd, Zn, Mn, Cu, Pb, Ni, Hg, Ag, etc. is very well known. Different bacteria; fungi (yeasts, dimorphic as well as filamentous) such as species of Saccharomyces, Rhodotorula, Aureobasidium, Ophiostoma, Aspergillus, Rhizopus, and Trichoderma: some algae, and diatoms such as Thalassiosira pseudonana have such an ability and being studied for their biotechnological potential as agents of effluent detoxification.
Among vascular plants, some aquatic weeds such as species of Salvinia, and Lemna. Azolla, Eichhornia; sedges and even tree species are also known to tolerate, uptake, and even accumulate heavy metals and other toxicants in their cells. Besides microorganisms plants are also being studied for their potential for environmental cleanup. (BSc Microbiology Bioremediation Notes Study Material)
Green plants are not only the lungs of nature with the unique ability to purify impure air by photosynthesis releasing oxygen to sustain aerobic life in the biosphere, but it has also been only quite recently demonstrated that they could also be very useful in cleaning up the hazardous waste sites. Vegetation can filter contaminated runoff and may someday be used in the treatment of hazardous industrial and other waste sites.
Though phytoremediation has a long history its industrial application is quite recent. Plants are being tested for their ability to clean up contaminated soil, and even genetically engineered varieties are on the horizon. “The process of recovery of hazardous substances from soil or groundwater contaminated with municipal or industrial wastes etc. by using plants is called phytoremediation.” Some examples of experimental field tests on the removal of toxicants from soil and industrial wastes by using plant systems are given below.
[I] Recovery of heavy metals from the soil
It has already been briefly described earlier under bioremediation that green plants such as specific strains of Indian mustard (Brassica juncea) can accumulate heavy metals when grown in chromium-contaminated soils. Modified strains of this plant have been shown to accumulate up to 40% of their biomass as heavy metals, such as lead and chromium. Researchers in the State of New Jersey in the U.S.A. carried out field trials in 1994 and demonstrated that the plants could be safely grown in chromium-contaminated soil at a site adjacent to Liberty State Park, N. J. A small amount of chromium was taken up by the plants and removed from the soil.
The plants were then harvested and the metal was recovered for recycling or disposal. The use of these Indian mustard plants is being developed by Burt D. Ensley at Phytotech. Corporation, Manmouth Junction, N.J., U.S.A. in collaboration with Ilya Raskin and coworkers at Rutgers University, New Brunswick, N.J., U.S.A. Tests to optimize metal uptake by such modified Brassicas are already in progress at these research centers. It is quite possible that in near future such plant systems could be effectively used for the cleanup of metal-contaminated soils at various sites.
Another such study is being made by Scott Cunningham, a senior researcher at DuPont. He has already undertaken field tests for such studies on plants to remove lead contamination from DuPont facilities. They include manufacturing sites for alkyl lead, Remington lead-based bullets, and lead-based explosives as well as lead paint and lead pipes. According to him lead is “sticky” and difficult to coax into a plant, and “using plants as waste treatment systems is in its infancy”.
Experimental possibilities, according to Cunningham, include genetically engineering the plants to include genes for enzymes from microbes or animal livers to things that break down molecular bonds. The lead uptake in the field tests conducted by him has not reached an amount that would promise a site cleanup. He hopes to achieve 20 tons of plants per acre with 1 to 3% metal content. He claimed to have got there. But for the time being, the plants are being used “as a guardian, for in situ stabilization, so that the site looks like a field, not a concrete block”. (BSc Microbiology Bioremediation Notes Study Material)
While microorganisms break down the organic bonds, the plants themselves take up the metals through their root system and sequester the contaminants in their cells. Useful plants can be found growing on ore outcroppings or contaminated areas. One variety of plants came from the lot of a convenience store. For instance, a variety of trees, Sebertia acuminate, a native of New Caledonia accumulates an astonishing 20-25% of its body dry weight of a nickel. The plant bleeds a bluish-green latex (sap).
[II] Treatment of municipal wastewater and industrial wastes
Plants as such may not be able to sequester toxic pollutants from wastes. The roots and rhizomes of some plants provide an ideal habitat for the growth of different kinds of microorganisms, chiefly bacteria, and fungi. These microbes are very effective in the remediation of contaminated wastewater and industrial wastes containing chlorides, bromides, sulphates, etc. The microbes remain active even in extreme conditions through frosts and surface freezing and the hot summer, as well as highly extreme pH and anaerobic reducing conditions. Each plant on earth harbours its own microbes around the roots and the microbes are able to adapt themselves to growing roots.
In the U.S.A. suitable species of plants are being grown in artificially designed experimental marsh systems to study the potential of plants in the treatment of wastewater. One such plant’s wastewater system, the newest tourist attraction is the one designed for the treatment of wastewater of Albemarle’s two bromine plants in Magnolia. At Albemarle’s Magnolia South Bromine Facility in Arkansas, tourists do not come to see the chemicals being manufactured but for this wastewater treatment system using marshy plants.
The South unit of the wastewater system is a 54-acre artificial marsh populated by sedge plants such as Scirpus lacustris, maiden cane, and Typha latifolia. Each marsh unit is 2000 feet long, 180 feet wide, and 12 to 18 inches deep with 40,000 plants. A 30-acre stormwater impoundment basin is used for heavy rainfall. The marsh was designed by a former National Aeronautics & Specs Administration (NASA), U.S.A. scientist who treats the facility’s rainwater runoff and noncontact process water.
The marsh does what a mechanical wastewater treatment plant would do, but with a smaller outlay of less than $ 2 million and for lower operating costs. A mechanical system would have required as much electricity as an entire town, whereas the marsh requires only monitoring equipment demanding as much energy as a single hair dryer. (BSc Microbiology Bioremediation Notes Study Material)
Bill Wolverton, former NASA research Head and founder of Wolverton Environmental Services Picayune. Missouri. The U.S.A. designed Albemarle’s two marsh systems. He also helped build a rock reed filter marsh at Degussa’s Theodore, Alaska, U.S.A. plant in the late 1980s. Wolverton, who retired from NASA in 1989 designs plant systems for the treatment of indoor air, municipal wastewater, and industrial waste.
This technology is being used in the biotreatment of waste. Wolverton has also been a consultant to Biosphere 2 earlier in which people were sealed into a closed environment. Phytoremediation is most exciting and challenging in indoor air treatment dealing with problems of sick building syndrome, and in the industrial area. (BSc Microbiology Bioremediation Notes Study Material)
Albemarle’s first marsh at the South plant has been filtering and cleaning rainwater runoff and noncontact process water since 1993. The system was the cheapest alternative for dealing with the increasing demands of the Clean Water Act in the U.S.A. Based on the success of the South plant, a second unit was built at the beginning of 1995 at Albemarle’s Magnolia West Facility This second unit, about one-fourth the size of the first one, started operating in early October 1995. (BSc Microbiology Bioremediation Notes Study Material)
Each of the marsh systems consists of three areas. Runoff and cooling water enter a lagoon, where pH and temperature fluctuations are equalized. The lagoon releases water to two parallel marshes. The stormwater impoundment basin is used for heavy rainfall. The marshes are the heart of the biotreatment process of phytoremediation. The plants, bulrush (Scirpus spp), maiden cane, and cattails (Typha spp), create the environment for the cleanup process, whereas the microorganisms, chiefly bacteria living on roots and rhizomes of these sedges breakdown the contaminants (chlorides, sulphates, bromides, etc) entering the system.
The new marsh is beginning too! establish itself with the natural selection of the most ideal strains of microorganisms to attack the pollutants. It is in the developmental stage at present and its effectiveness is likely to increase with time. The marsh is engineered to act as a natural marsh designed with deep holes and shallow areas. (BSc Microbiology Bioremediation Notes Study Material)
The system can handle daily loads ranging from thousands to several million gallons of water. You cannot design a mechanical system that can fluctuate so much. It can handle a serious accidental spill. If a tank truck spilled on site, the marsh would treat. The only problem with these natural systems is that we don’t have knobs to shut things off. Albemarle intends to set up similar facilities in Baton Rouge, Houston, and Orangeburg, S.C. in the U.S.A., and in Feluy (Belgium) and Thann (France). (BSc Microbiology Bioremediation Notes Study Material)
BSc Microbiology Bioremediation Notes Study Material
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