Applications of Immobilized Soil Bioreactors

Treatment of trichloroethylene (TCE) -contaminated groundwater

Chlorinated aliphatic hydrocarbons, especially trichloroethylene (TCE) are among the most frequently cited groundwater contaminants. Their remediation almost always involves a "pump and treat" approach. Usually these compounds are transferred to activated carbon by an air stripping process or the contaminated water is exposed to ultraviolet light and an oxidizing agent. The first approach does not destroy the compound while the second is expensive. Methanotrophic bacteria especially those producing "soluble" methane monooxgenase (sMMO) have been shown to be highly effective degraders of TCE and related compounds. Until now they could not be used in "pump and treat" processes because they could not be grown to a useful density. The immobilized soil bioreactor (ISBR) has been shown to be at least one order of magnitude more efficient at the mineralization of TCE (on a volumetric basis) when operated under methanotrophic conditions at the laboratory scale (2L). This project aims to develop an economical TCE biomineralization process suitable for use under typical "pump and treat" conditions using a 2 m3 methanotrophic ISBR with gas recycle and associated methanotrophic biofilter.

Treatment of effuents contaminated with nonylphenyl ethoxylates (NPEO)

Alkylphenyl ethoxylates represent one of the largest classes of non-ionic surfactants with nonylphenyl ethoxylates (NPEOs; Fig. 1) being the most widely used commercially. NPEOs vary in ethoxylate chain length where n ranges from 1 to 100 with the most common being n = 6-10. They are used in industrial and institutional cleaning, as emulsifiers in polymers and paints, in the textile and leather industries and in agricultural chemicals. Worldwide, about 600,000 metric tons of NPEOs (mostly branched) are produced yearly. NPEOs are endocrine disrupters causing acute adverse effects, including estrogenic effects, in aquatic organisms.

Nonylphenol ethoxylate

Fig 1. Nonylphenol ethoxylate

Biological treatment of wastewaters has found widespread application due to its effectiveness and low cost. Although these processes are very effective at reducing high levels of biological O2 demand (BOD) and chemical O2 demand (COD), they are often unable to degrade nanomolar concentrations of problem compounds. Many biologically active organic materials such as NPEOs are finding their way into wastewater treatment facilities, passing through, and entering aquatic systems. Although they are at very low concentrations, they can significantly and detrimentally affect biological activity. Although nonbiological approaches such as granular activated carbon or ozone may effectively remove problem compounds from wastewaters, COD is typically high enough to render these approaches impractical. We are developing methodologies that use an immobilized soil bioreactor (ISBR) to treat nanomolar concentrations of such compounds using NPEOs as models. It is also hoped that knowledge gained from this research can be applied to modify existing wastewater treatment processes to efficiently treat such problematic pollutants.

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