The Author is the President of Common Sense Solutions, LLC and founder of the Common Sense Environmental Fund. A Registered Environmental Professional (REM), Dr. Popino has more than 25 years of experience in the environmental field - as a Park Ranger for the U.S. National Parks Service and as an Environmental Regulator for the U.S. Coast Guard and the U.S. Environmental Protection Agency.
Microbe bioremediation is the application of biological treatment to the cleanup of hazardous contaminants in soil and surface or subsurface waters. In the many forms of bioremediation, microorganisms are utilized and managed through the control of environmental factors to reduce environmental pollution. Normally microbe bioremediation treats organic contaminants.
Most microbe bioremediation processes take advantage of indigenous microorganisms, although some rely on the introduction of bacterial or fungal strains. Currently, work is being conducted on genetically engineered microbes as well as the possibilities of algae for use in bioremediation.
Bacterial digestion is the process of bacteria-consuming organic matter. The bacteria feed on the contamination, deriving nutrition for growth and reproduction. Undergoing complex chemical reactions, the waste is metabolized into the final metabolic waste products, water and carbon dioxide. This provides the bacteria with the energy they need to live. The result of this natural process is that wastes are used up completely or converted into an innocuous product such as water and carbon dioxide.
A bacterium is a single cell life form. Each individual cell is a separate, unique organism. Bacteria often grow into colonies but each cell remains an independent life. Bacteria reproduce by a process called cell division. A mature bacterium reproduces by dividing into two "daughter cells," each cell identical to the other and the parent bacteria. Under ideal conditions, bacteria can reproduce rapidly, producing a new generation every 20 to 30 minutes. Thousands of different species of bacteria exist everywhere in our world, and most of them carry on bacterial digestion in some way. However, some of them are found only in a specific environment, require specialized types of food, or have unique niches.
Following the reproduction process, the number of individual bacteria doubles with each generation. The population explodes as the number of microorganisms increases Logarithmically. At some point, the food source will be depleted, or some other change in the environment will cause the population to decrease. These changes could be pH, temperature, or oxygen content of the environment.
The objective of a microbe bioremediation program is to immobilize or to transform them to chemical products no longer hazardous to human health and the environment. For certain cases in which contaminants pose no significant risk to sensitive receptors (e.g., water supply wells, surface water bodies), intrinsic bioremediation may be an appropriate strategy. For other cases in which receptors are at risk, an enhanced (engineered) bioremediation strategy may be necessary. Enhanced bioremediation can be performed in-situ (e.g., biosparging; bioventing, hydrogen peroxide/inorganic nutrient amendment) or ex-situ (e.g., land farming, biopiles), depending on a variety of site-specific factors and the constraints imposed by site usage. In many instances, biostimulation activities may be limited to electron acceptor (e.g., molecular oxygen, nitrate, etc.) amendment, however, in other cases inorganic nutrient amendment or pH adjustment may be required. Typically, indigenous microbes are capable of effecting transformation because they are acclimated to the contaminant as well as their microniche; however, research is currently underway at a number of facilities using exogenous, specialized microbes or genetically engineered microbes to optimize bioremediation.
Microbe Bioremediation has proven to be an important remediation technology because it:
Bioremediation of unconsolidated materials, bedrock, groundwater, and other media contaminated with synthetic organic/inorganic compounds is an emerging technology that can cost-effectively treat many sites. Bioremediation is defined by the American Academy of Microbiology as "the use of living organisms to reduce or eliminate environmental hazards resulting from accumulations of toxic chemicals and other hazardous wastes" (Gibson and Sayler, 1992). The technology is approved by the United States Environmental Protection Agency, Environment Canada, and other regulatory agencies worldwide.
Intrinsic (passive) bioremediation of many synthetic organic compounds is carried out by indigenous microorganisms, principally heterotrophic bacteria, that transform contaminants to intermediate products or innocuous end products.
In many cases, contaminants such as petroleum hydrocarbons serve as sources of organic carbon and electron donors (assimilation). In other metabolic processes, contaminants such as trichloroethylene may serve as electron acceptors (reductive dehalogenation), or may be transformed by fortuitous co-metabolic processes that offer no added benefit to microbes from the reactions (co-oxidation). These processes occur within a wide range of hydrogeologic settings, biogeochemical interactions, microorganisms, and contaminants.
A successful, cost-effective microbe bioremediation program is dependent on hydrogeologic conditions, the contaminant, microbial ecology, and other spatial/temporal factors that vary widely. Biotreatability studies are necessary components of the program so that remedial design data are collected cost-effectively. Biotreatability studies are performed to evaluate whether site conditions are conducive for bioremediation.
Microbe bioremediation programs that address these factors will have the greatest likelihood of success and will conserve limited financial resources. Properly executed, microbe bioremediation can cost-effectively and expeditiously destroy or immobilize contaminants in a manner that fosters regulatory compliance and is protective of human health and the environment.
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