1.1.07 SAFIRA joint research project – remediation research using the Bitterfeld site as a model

Coal mining and chemical industry have heavily contaminated the soil and groundwater in the Bitterfeld area. Experiences from the last 20 years indicate that hydraulic soil and groundwater remediationRemediation process based on the mechanical properties of fluids. is often ineffective – particularly on large abandoned waste sites if the source of the contamination either cannot be precisely located or is very difficult to remove. The remediation research in regionally contaminated aquifers (SAFIRA) research project therefore used the sample model site at Bitterfeld-Wolfen to develop new technologies and methods for in-situ remediation of groundwater contaminated with complex pollutant compounds.

The Bitterfeld-Wolfen area is still suffering the effects of abandoned waste. The ground beneath the former industrial and landfill sites is polluted, the groundwater heavily contaminated in places with organic compounds, primarily chlorinated hydrocarbons (CHC), over an area of around 25 square kilometres. In Bitterfeld this contamination reaches a depth of 30 to 40 metres and affects an estimated 250 million cubic metres of groundwater. Conventional remediation procedures demand mainly protracted and expensive pump and treat measures. However, for such widespread contamination and such a complex mix of pollutants, in-situ cleaning is an appealing approach as it does not involve digging up and moving the soil.

Active and passive methods

In-situ remediation methods are divided into active technologies (e.g. soil gas suction) and passive methods, the latter requiring little or no energy feed during the remediation process. The most developed passive version is reaction walls. While this method is already successfully applied to simple combinations of pollutants, development is still needed to handle complex mixtures.

The SAFIRA research project investigated the hydro-geological and geochemical framework conditions for cost-effective in-situ procedures and tested these at the Bitterfeld site. Researchers at the UFZ centre for environmental research at Leipzig-Halle and the universities of Dresden, Halle, Kiel, Leipzig and Tübingen were able to use areas formerly home to the Bitterfeld chemical industry to develop and test the suitability of technologies for passive decontamination in a real-life situation.

The main objectives of the project were:

• Development and gradual implementation of efficient passive water treatment technologies for organic pollutant mixtures from the lab stage to a pilot phase.
• Technical-economic optimisation of the new technologies plus their combination.
• Demonstration of their long-term stability under field conditions.
• In addition, the actual operating costs and the environmental law and planning aspects of in-situ reaction zones were to be evaluated.

Pilot facility for various procedures

At the heart of this project is a pilot facility installed in Bitterfeld’s groundwater, 23 metres below the surface of the site. The scientists used this to investigate seven procedures that had been successfully tested in the lab and in small-scale field trials:

• AdsorptionThe accumulation of gaseous or liquid substances on the surface of a solid. and microbial degradation of pollutants with activated carbonCollective name for a group of artificially produced, highly porous carbons with a sponge-like structure. This pure material is characterised by its large specific surface area (up to 300 m2/g). Activated carbon is manufactured from peat, wood, lignite, black coal or nutshells. The materials are first carbonised, during which tiny pores are created. Activated carbon adsorbs organic substances from water and the air and is thus able to clean contaminated water or polluted air.
• Zeolite-supported palladium (PD) catalysts◄
• Oxidation all-metal catalysts◄
• Oxygen-reducing combination reactors◄
• Membrane-supported palladium (PD) catalysts◄
• Adsorption with activated carbon
• AnaerobicAbsence of oxygen (O2). Also used in the context of organisms that do not require oxygen to live, or to describe chemical reactions that occur in the absence of oxygen. microbial degradation

Transferring these procedures to a larger pilot scale proved problematic in some cases. Although the microorganisms at the site are in a position to break down chlorobenzeneAromatic organic compound used, among other things, as a thinner in the paint industry, a degreasing agent in the textile and metal industry and as an extracting agent. under anaerobic conditions, the rates of degradation were insufficient in practice so procedures for adding oxygen also had to be developed. The scientists also ascertained that although palladium catalysts were suitable for quick reduction dechlorinationProcedure in which chlorine is removed from chemicals in the absence of oxygen. This process is important for the remediation of groundwater contamination, for example. they needed better protection in groundwater containing sulphates against the products used for the microbiological reduction of sulphate such as hydrogen sulphide. Conventional adsorbents (such as activated carbonCollective name for a group of artificially produced, highly porous carbons with a sponge-like structure. This pure material is characterised by its large specific surface area (up to 300 m2/g). Activated carbon is manufactured from peat, wood, lignite, black coal or nutshells. The materials are first carbonised, during which tiny pores are created. Activated carbon adsorbs organic substances from water and the air and is thus able to clean contaminated water or polluted air.) help to remove pollutants. The operating life of treatment walls can be significantly extended through microbiological colonisation. The project also showed that oxidation catalytic procedures can also be used to treat complex pollutant mixtures. Methods for reactivating the surfaces of the catalysts is an area where optimisation was required.

Implementation in specific remediation concepts

In additional investigations, the project partners adapted their research to the extremely diverse composition of pollution at each site, in particular the many different substances and the high concentrations of individual substances at Bitterfeld. The new projects focused on three areas promising huge benefits for future remediation concepts at Bitterfeld-Wolfen:

• Innovative remediation technologies (catalysisChemical reaction in which a suitable substance is employed as a catalyst (accelerator), usually with the aim if increasing the reaction speed.)
• Coupled systems (hydrochemistry/microbiology)
• Spatial effect (digital area model, visualisation, models)

Within innovative remediation technologies, the project team developed a new method that uses vacuum strips through a hollow-fibre membrane to convert pollutants from the liquid phaseA phase is a spatial area in which the physical parameters and chemical composition of the relevant matter are homogeneous. to the gaseous phase, which enables a highly efficient level of destruction through catalysis. This technology deals with a broad range of contaminants in high concentrations. Once the procedure had been successfully used in a pilot scheme, it was developed further at various locations. The focus of this development was on removing and destroying crucial substances from a procedural perspective. A new form of technology will now make it much easier to treat the specific contaminated groundwater in the Bitterfeld-Wolfen region. It was tested in a pilot scheme that included a procedural stage for strippingRemoval of water-based substances through the injection of air/gas. The dissolved substances are transferred to the gaseous phase and consequently removed from the water. out pollutants with hollow-fibre membrane modules and devices for applying innovative procedural steps for removing the sulphur from the stripped-out gases (UFZ patent). The facility aims to demonstrate alternatives for complex groundwater contamination where there has previously been no economically viable cleaning concept. The “treatment train” approach was followed to achieve a sufficient overall cleaning performance, in other words the intelligent interlinking of modular standard and/or innovative individual processes.

Another focus was on the combination of different microbiological degradation paths in corresponding conditioned aerobicState involving the presence of oxygen (O2). Also used in the context of organisms that require oxygen to live, or to describe chemical reactions that require the presence of oxygen. /anaerobic zones permitting the successive degradation of certain pollutants or groups of pollutants. The third area of focus looked at the creation of a digital database for Bitterfeld, which included a geological structure model, a description of regional groundwater qualities at various periods and remediation scenarios based on land usage.

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1.1.08 Direct oxygen injection

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1.1.06 Treatment walls combating TCE