Injection Services

The limitations of conventional ground water cleanup technologies and the hazards of conventional soil treatment methods, along with the high costs of both have spurred investigations into alternative cleanup technologies, including In-Situ Bioremediation.

In-situ Bioremediation uses microorganisms to destroy or immobilize contaminants in place.

Halogenated aliphatic compounds such as trichloroethylene (TCE), tetrachloroethylene (PCE), dichloroethane (DCA) and other chlorinated solvents which, have historically proven to be difficult to bioremediate, can now be biologically treated in a safe cost effective manner.

Chlorinated solvent bioremediation involves the use of microorganisms (bacteria) to biodegrade solvents present in the sub-surface to environmentally acceptable products such as carbon dioxide, chloride and water. Figure 1 illustrates several common biodegradation pathways for a common chlorinated solvent, trichloroethene (TCE). 

Benefit 1- "The technology may be less costly, faster, and safer than conventional cleanup methods."

Benefit 2- "Chlorinated solvent bioremediation is an environmentally-friendly, common-sense approach to site remediation because it destroys chemicals in-place rather than transferring them to other locations (e.g. landfills) or phases (gases in the atmosphere).

Bioremediation is an innovative, cost-effective technology that is ideally suited to long-term passive treatment of these chemicals."
Benefit 3-"Chlorinated solvent bioremediation (intrinsic or enhanced) can be used as either a stand-alone remediation technology or in concert with conventional remediation technologies to destroy solvents present in soil and groundwater."

The most important principle of bioremediation is that microorganisms (mainly bacteria) can be used to destroy hazardous contaminants or transform them to less harmful forms. The microorganisms act against the contaminants only when they have access to a variety of materials—compounds to help them generate energy and nutrients to build more cells. In a few cases the natural conditions at the contaminated site provide all the essential materials in large enough quantities that bioremediation can occur without human intervention—a process called intrinsic bioremediation More often, bioremediation requires the construction of engineered systems to supply microbe-stimulating materials-a process called engineered bioremediation Engineered bioremediation relies on accelerating the desired biodegradation reactions by encouraging the growth of more organisms, as well as by optimizing the environment in which the organisms must carry out the detoxification reactions.

A critical factor in deciding whether bioremediation is the appropriate cleanup remedy for a site is whether the contaminants are susceptible to biodegradation by the organisms at the site (or by organisms that could be successfully added to the site). Although existing microorganisms can detoxify a vast array of contaminants, some compounds are more easily degraded than others. In general, the compounds most easily degraded in the subsurface are petroleum hydrocarbons, but technologies for stimulating the growth of organisms to degrade a wide range of other contaminants are emerging and have been successfully field tested.

The suitability of a site for bioremediation depends not only on the contaminant's biodegradability but also on the site's geological and chemical characteristics. The types of site conditions that favor bioremediation differ for intrinsic and engineered bioremediation For intrinsic bioremediation, the key site characteristics are consistent ground water flow throughout the seasons; the presence of minerals that can prevent pH changes; and high concentrations of either oxygen, nitrate, sulfate, or ferric iron. For engineered bioremediation, the key site characteristics are permeability of the subsurface to fluids, uniformity of the subsurface, and relatively low (less than 10,000 mg/kg solids) residual concentrations of nonaqueous-phase contaminants.

When deciding whether a site is suitable for bioremediation, it is important to realize that no single set of site characteristics will favor bioremediation of all contaminants. For example, certain compounds can only be degraded when oxygen is absent, but destruction of others requires that oxygen be present. In addition, one must consider how the bioremediation system may perform under variable and not perfectly known conditions. A scheme that works optimally under specific conditions but poorly otherwise may be inappropriate for in situ bioremediation.