Field Demonstration Of Successful Bioaugmentation To Achieve Dechlorination Of Tetrachloroethene To Ethene

Army Forces University-ESPE

Life Sciences Department

Career of Biotechnology Engineering

Environmental Biotechnology

Field demonstration of successful bioaugmentation to achieve dechlorination of tetrachloroethene to ethene

David W. Major *; Michaye L. McMaster*; Evan E. Cox*; Elizabeth A .Edwards°; Sandra M .Dworatzek°; Edwin R. Hendrickson´; Mark G. Starr´; Jo Ann Payne´ and Lois W. Buonamici´.

*Geosyntec consultants, Inc; 130 Research Lane, Suite2 , Guelph, Ontario, N1G 5G3 Canada.

°Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario, M5S 3E5 Canada.

´E.I. DuPont de Nemours & Company, Inc; Central Research and Development, P.O.Box 6101, Glasgow 300, Newark, Delaware 19714-6101.

ABSTRACT

The chlorinated ethenes are a concern around the world because they can be carcinogenic and cause an impact in public health and in the environment.

Over the last years, bioremediation techniques were developed to promote the fast and efficient reduction of these compounds.

In this document the bioaugmentation was probed to be a successful biological treatment by the addition of nutrients and bacterial cultures with the predominance of Dehalococcoides.

But we can see that not only the Dehalococcoides are capable to degrade chlorinated compounds and we can use various biological methods to assess the presence or absence of the bacteria that we inoculated in the contaminated area.

INTRODUCTION

With the development of the different industries, mainly at the beginning of the twentieth century, a large amount of chlorinated compounds such as the tetrachloroethene (PCE) and other chlorinated aliphatic hydrocarbons were produced and applied in a wide range of fields (agriculture, industry, domestic applications, etc). (3)

Specifically, the chlorinated ethenes are a problem as a result of their common use like solvents and cleaning agents in the industry. The unknown of the health and environment effects of this compounds, in addition with an absence of regulatory laws led to groundwater and soil contamination with highest concentrations of PCE and trichloroethene. (3,9)

The principal problem with the PCE and TCE is that they are considered as a concern in the public healht in parts because of the potentially carcinogenic development in humans. (3)

The approaches to remediate contaminated zones with chlorinated solvents were developed approximately 30 years ago until now. There are some technologies that were studied , all of this find to convert the chlorinated compounds into non toxic compounds like ethene by in situ techniques that include: extraction with surfactants, thermal treatments, chemical oxidation and biological degradation. (10)

Biological treatments like bioaugmentation and biostimulation are very attractive due to the relative low costs and the conversion and destruction of the pollutants by the addition of electron donors or foreign bacterias (of the genus Dehalococcoides), in this case to promote the reductive dechlorination of PCE where the PCE is the electron acceptor and a chlorine atom is replaced with a hydrogen atom. (10,12)

The efforts to design a efficient treatment to remediate the contamination with PCE are high and many people have been studying different ways to characterize degrading bacterias, isolate enzymes , etc.

One technique consists in the transformation of E.Coli by the isolation of the gene pceC that comes from Clostridium bifermentans DH1. In the process; the enzyme was isolated, purified and sequenced, then the gene that encodes the protein capable to degradate chlorinated compounds was cloned and inserted into the E.Coli to transform this microorganism into a dechlorinating bacteria. (6)

Another technique is the using of an upflow anaerobic sludge blanket (UASB) to do a continuous dechlorination of PCE with a previous inoculation of anaerobic sludge, in this case the contaminated groundwater with PCE is dechlorinated by. the Dehalococcoides-like species presente in the sludge and depending in the increase of the hydraulic retention time (HRT) the efficiency might be between 51% to 87%. (9)

An interesting technologie is the combination of anaerobic microbial community (MB) and zero-valent metals such as Zinc (Zn) an Iron (Fe). Assays with this technique suggest that the removing of PCE can be high: 99% with Fe-MB and 84.8% with Zn-MB. (4)

METODOLOGY

For the study, a dechlorination culture (designed as KB-1) was used for the bioaugmentation. This culture was maintained at anaerobic conditions with a routinely fed with TCE in amounts of 300uM and methanol (1.5 mM), the culture was monitored to prevent a probable contamination with pathogens.

The microcosm was conducted in a sterile glass bottles of 250mL filled with 60g of soil and 150mL of groundwater, and various treatments were evaluated: Sterile control, intrinsic control, lactate-amended, methanol amended, and bioaugmented.

The pilot test area had extraction wells and monitoring wells in a closed loop recirculation system where in a first phase the electron donors (methanol and acetate) had been added to amend the conditions (biostimulation) prior to promote and assure the optimal conditions before the second phase (bioaugmentation) with the addition of the Kb1 culture.

Analytical procedures were used to evaluate the concentration of the PCE and derivatives like TCE, cis 1-2 dichloroethene (cis12DCE), VC, and ethene.; Gas chromatography(GC) and flame ionization detector for the microcosm study and the using of EPA Method 8260, GC and Inductively coupled plasma atomic emission spectroscopy (ICP-AES) for the pilot test area.

For the molecular analysis to detect the presence of Dehalococcoides in the pilot test area a PCR amplification of DNA (previously extracted from the groundwater and soil samples)

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