Bioremediation Technologies

While bioremediation may appear to be a radical new approach to treating hazardous wastes, it is actually nothing new at all. Nature makes wide use of microscopic bacteria and fungi to break down organic materials into energy, carbon dioxide, methane, and water. Sewage treatment plant operators have for many decades harnessed microbes to remove and digest the organic matter in their waste streams. Likewise, composting of organic waste, leaves and grass clippings utilizing native microbes is neither new nor sophisticated. What is new about bioremediation is its commercial application to hazardous waste sites, which only dates to the mid-1980s.

Bioremediation technologies that will be discussed below in detail include biostimulation, which involves adding nutrients and/or oxygen to augment the actions of microbes already present at a contaminated site; and bioaugmentation, in which specially selected or genetically engineered strains of microbes are introduced to a site. Also falling within the scope of bioremediation are closely related methods such as fungal remediation and phytoremediation, which involves the use of plants.

Bioremediation is usually done on site, minimizing site disruption and eliminating transportation costs and associated liabilities. Waste is largely converted into harmless compounds such as carbon dioxide, methane, and water. The biological systems used are often less expensive, especially if the site is simple and natural degrading microbes are present. Finally, bioremediation may be linked with other remediation methods into a comprehensive treatment system.

Types of Treatment

Biostimulation

As much as 70% of bioremediation is classified as "biostimulation." This "classic" approach to bioremediation amounts to the controlled delivery of oxygen and nutrients, such as nitrogen and phosphorous, into soil or groundwater. Manipulation of other environmental factors such as pH, temperature, and site permeability is usually also involved. This approach stimulates growth of the native microbial population, which is always present, even at the most severely contaminated sites, albeit in insufficient quantity to promote significant degradation. Biostimulation is usually effective when the contamination is simple and straightforward, as it very often is in the case of petroleum hydrocarbons.

Bioaugmentation

Bioaugmentation, the addition of external microorganisms to a site with contaminated soil and/or groundwater, can sometimes show dramatically improved results where biostimulation alone has proven inadequate or ineffective. Sources of microbes can include other sites with similar contamination, bacterial blends based on results from many sites, selectively adapted organisms capable of surviving under more difficult conditions, or genetically engineered microbes incorporating the most recent developments in recombinant DNA biotechnology.

A recent case dramatizes the c apability of bioaugmentation done with proper regard for the contaminant mix. Soil contaminated with slop (waste) oil from a petrochemical operation was found to contain over 240 different hydrocarbon compounds. A mixed bacterial culture was introduced to the site, resulting in 70% degradation, versus only 40% under biostimulation. The differential is accounted for by a dramatically higher microorganism count under bioaugmentation. .