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Deltares | R&D Highlights 2015
Anaerobic degradation of
organic pollutants in soil
and groundwater
The contamination of soil and groundwater with organic pollutants is a serious problem worldwide. Biodegradation is the most important process involved in the removal and mineralisation of these contaminants. Oxygen (O2) is usually not available in groundwater in the Netherlands, and anaerobic microorganisms perform biodegradation. Deltares developed new microbiological, biochemical and molecular analyses to detect anaerobic biodegradation in soil and groundwater. These analyses are used in numerical models to predict the transport and degradation of organic pollutants in the subsurface. In addition, we are developing new concepts to enhance the anaerobic degradation of these compounds at polluted sites.
Groundwater contaminants often originate from crude oil: petroleum diesel, gasoline and tar, for example. These complex mixtures contain hundreds of types of organic molecules. Petroleum diesel mainly consists of alkane molecules with C8–C21 carbon chain length. Aromatic compounds such as benzene, toluene, ethylbenzene and xylenes (BTEX) are major components of gasoline. High concentrations of polycyclic aromatic hydrocarbons (PAH) are found in tar. Chlorinated solvents such as chloro-ethenes, -ethanes and -methanes form another category of groundwater pollution caused by the dry cleaning, metals and chemical industries. The transition to a bio-based economy may result in the introduction of new organic chemicals in our environment such as the gasoline additive ethyl tert-butylether (EtBE) and biodiesel.
In many cases it is not possible to determine the degradation of organic pollutants by simply measuring changes in concentrations in groundwater. We therefore use degradation intermediates and end products, and the enrichment of stable
carbon and hydrogen isotopes in organic pollutants, as additional biodegradation indicators. The conditions in soil and groundwater determine whether, how fast, and how the complete degradation of organic contaminants can occur. In the absence of O2, the availability of alternative electron acceptors such as nitrate, iron-oxides and sulphate is important for the biodegradation of alkanes, BTEX and PAH. The measurement of these electron acceptors in soil and groundwater allows us to assess whether conditions are favourable for the biodegradation of these organic contaminants. If not, we can inject electron acceptors such as nitrate and nutrients into groundwater to enhance the activity of anaerobic microorganisms that degrade alkanes, BTEX and PAH. By contrast, the anaerobic microorganisms that degrade chlorinated solvents are usually inhibited by electron acceptors. These microbes can be stimulated by introducing an electron donor substrate such as organic acids or molasses to the groundwater.
Deltares uses laboratory tests in microcosms, bioreactors and soil columns to determine the optimal conditions for the biodegradation of different organic pollutants, and to identify the microorganisms involved. By designing specific DNA analyses, we can quantify these microorganisms and reveal degradation processes in the laboratory and in the field. Current research at Deltares focuses on the opportunities to augment contaminated groundwater with active laboratory cultures to enhance the anaerobic degradation of chlorinated solvents, benzene, PAH and biofuels.
With the development of these innovative monitoring and remediation methods, Deltares is helping public bodies and industry to significantly reduce remediation time and costs.
Further reading:
Van der Zaan et al. (2012) Anaerobic benzene degradation under denitrifying conditions: Peptococcaceae as dominant benzene degraders and evidence for a syntrophic process. Environmental Microbiology 14(5),1171-1181
jan.gerritse@deltares.nl T +31(0)6 3007 3547
Ecosystems and Environmental Quality
