SABRE (Source Area in situ BioREmediation) was a collaborative R&D project undertaken by an international, multidisciplinary team which ran between 2004 and 2008. The project comprised laboratory and field-pilot scale development of an accelerated anaerobic bioremediation process for free-phase chlorinated solvent contamination in groundwater. Quantitative performance validation of the SABRE field study, to assess remediation efficiency, entailed detailed monitoring, numerical modelling and statistical analysis. A UK test site contaminated with trichloroethene (TCE) was used to undertake the project, which is supported through the UK DTI Bioremediation LINK programme.
Chlorinated solvents have been used in large quantities by a diverse range of industries (including chemicals production, metalworking, automotive, aerospace, electronics and dry cleaning). They are consequently extremely common contaminants in soil and groundwater.
Chlorinated solvent releases 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.
Bioremediation is the application of biological degradation processes to reduce the amount of contamination present in the subsurface (soil or groundwater) and/or the risks posed by such contamination.
Under anaerobic (oxygen-free) conditions, the process of dehalorespiration undertaken by specific bacteria can result in the complete degradation of many specific chlorinated solvents to innocuous end-products. This biodegradation process can also take place even when chlorinated solvent DNAPL is present.
The SABRE project comprises laboratory and field-pilot scale development of an accelerated anaerobic bioremediation process for DNAPL source areas in soil and groundwater based upon use of dehalorespiring bacteria. Treatment is achieved by the controlled addition of growth substrates to support dehalorespiring bacteria under conditions that ensure the maximum rate of reductive dechlorination. The process offers the potential to be a technically and economically effective in situ remediation option for soil and groundwater contaminated with large amounts of chlorinated solvents.
Dehalorespiration is the deliberate use by certain bacteria of chlorinated solvents and other compounds as their respiratory substrate (terminal electron acceptor) under anaerobic (oxygen-free) conditions. These dehalorespiring bacteria form part of the natural microbial community that can develop in environments where chlorinated solvents are present and conditions suitable for their growth. Dehalorespiration brings about a step-wise removal of chlorine atoms from the chlorinated solvent molecule and can yield a fully dechlorinated product, for example: trichloroethene (TCE) is converted through cis-1,2-dichloroethene (DCE) and vinyl chloride (VC) to ethene.
The objective of Project SABRE was to generate scientifically robust, multiple lines of evidence to enable:
The project ran from October 2004-2008 and involved the following work packages:
Site investigation. To characterise the test area, provide design information for the field-scale process and determine the initial quantity of contamination.
Microbiology. Use of laboratory microcosm and column tests to determine the optimal conditions for the bioremediation process. Application of microbiological and molecular biological techniques for process monitoring.
Test cell design, installation and operation. Design, engineering and installation of two field-pilot scale test areas suitable for technology demonstration and the development of design criteria for future routine technology application. Operation of these in response to data obtained.
Performance assessment. Monitoring of the process by traditional and novel geophysical techniques and evaluation of the data collected.
Flow and process modelling. For process design and the development of tools to aid in interpretation of results and for future technology implementation.
Technical quality management. Ensuring that the data collected are robust and statistically valid. A Scientific Advisory Group was appointed to help guide the project and ensure the highest scientific standards are maintained.