Due to their extensive use as industrial solvents, dry cleaning agents and degreasers, chlorinated solvents are extremely common contaminants in soil and groundwater. Chlorinated solvents released into the sub-surface may result in the presence of free-phase (dense non-aqueous phase liquid; DNAPL) chlorinated solvent contamination, which will persist for decades and act as long-term sources of groundwater contamination. All chloroethenes are either known or suspected carcinogens and therefore their presence in the environment is of major concern. Microbial degradation mechanisms for chlorinated ethenes are often limited in the field by a lack of electron donors and electron acceptors.

The purpose of this STSM is to assess the potential for electrochemical stimulation of TCE biodegradation in a contaminated soil. Specifically it will look at the enhancement affects of hydrogen and Fe(III), compounds which may be generated by electrochemical processes. Two soil cores (from a depth of 1.5m to 6m) were taken anaerobically from a TCE contaminated site in the UK using a sonic drilling technique. Each core consisted of three 1.5 m length filled plastic liners, with a 15cm diameter. From the same site, 60 litres of groundwater were taken anaerobically from 6 bore holes. The initial stage of this work was to establish the extent of contamination throughout the soil core profiles. The cores were therefore analysed for TCE and metabolite concentrations using Gas Chromatography. Samples were also analysed for chloride and sulphate concentrations using Ion Chromatography. The ground water was tested for O2, pH, chlorinated solvents, sulphate and chloride.

The in-depth chemical analysis of the soil cores showed that complete dechlorination from TCE to ethene had occurred in parts of the profile. This indicates that dechlorinating organisms are present in the soil. However, dechlorination of the contaminants is likely to be limited by the availability of electron donors. In order to assess the enhancement effects of hydrogen and Fe(III), soil samples from the most contaminated parts of the cores were homogenised and used for the set up of flow column experiments and microcosms. Groundwater sampled from a borehole in between the two soil cores was also used for these experiments. Three microcosms containing sediment and groundwater were amended with acetate, iron and iron plus acetate. Three microcosms containing only groundwater were amended with acetate, iron and hydrogen. It is hypothesized that in the microcosms and flow columns with hydrogen and acetate added, dechlorination will be greatly enhanced. Weekly sampling of the microcosms and flow columns will take place to assess biodegradation rates. In addition, soil samples will be investigated for the presence of specific dechlorinating microorganisms and for overall shifts in the microbial community using molecular techniques.

Acknowledgment: The authors gratefully acknowledge financial support by the COST office, AIF Otto von Guericke, EPSRC, BUCKINGHAM Group Contracting and IPM-Net.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/8234 must be provided.

1. High-energy micro-environments in biotechnology: year 2006 update
2. Dechlorination activity and microbial population dynamics after exposure to an electric field
3. Application of ultrasonically produced nano zerovalent iron for the degradation of chloroethenes