1.1.06 Application of treatment walls – combating high TCE concentrations

Iron granulate reaction walls have proven their cleaning effectiveness in several field studies to date. However, the effect of modified pH values on the long-term stability of the reactive material was still unclear. Scientists from the use of permeable treatment walls (RUBIN) programme used the site of a former barracks in Berlin to test a corresponding pilot facility on the groundwater there, which was highly contaminated with trichloroethyleneAliphatic, chlorinated organic compound. One of the most commonly used cleaning and degreasing agents. It also serves as an extracting agent for natural fat, resin, oil and wax. The substance belongs to the group of volatile chlorinated hydrocarbons (->VCHC) and is classified as a category 1 carcinogen and germ cell mutagen. (TCE). The result was overwhelming: the iron granulate was also highly efficient and economical in the long term and it was possible to remove all the TCE.

There are 11,000 known abandoned waste sites in Germany, all representing a significant risk to the groundwater. Quick remediation, e.g. through excavation or pumping out the polluted groundwater, has proven technically unfeasible or disproportionately expensive in many cases. This is especially true when the pollutants are organic substances such as volatile halogenated hydrocarbons (VHHC) or tar oils, and when this pollution takes the form of a separate flow phaseA phase is a spatial area in which the physical parameters and chemical composition of the relevant matter are homogeneous. under the ground. As such, technologies aiming to secure the contaminant plumes being emitted from the sources of contamination are increasingly gaining favour. One example of such technology is permeable treatment walls. Development of this technology began in North America and it has since been funded in Germany via the BMBF’s RUBIN R&D project (see project 1.1.03).

Testing long-term stability

A modular pilot facility was set up in 2001 on the site of a former Soviet barracks in Bernau (approximately 30 km north-east of Berlin) to treat the groundwater there, which was highly contaminated with trichloroethyleneAliphatic, chlorinated organic compound. One of the most commonly used cleaning and degreasing agents. It also serves as an extracting agent for natural fat, resin, oil and wax. The substance belongs to the group of volatile chlorinated hydrocarbons (->VCHC) and is classified as a category 1 carcinogen and germ cell mutagen. (TCE). The main aim of the project was to test the durability and degradation performance of an iron granulate treatment wall under quasi in-situ conditions. The procedure utilised the reduction potential of metallic iron coming into contact with water and halogenated hydrocarbons. The corrosion reaction of the iron served to dehalogenateDehalogenation is the removal of halogens (especially chlorine) from organic compounds. In a narrower sense, the term refers to the removal of halogens from ►volatile halogenated hydrocarbons (VHHC). Volatile halogenated hydrocarbons (VHHC) with up to three chlorine atoms can be dehalogenated through microbial activity. the partially carcinogenic substances. However, the oxygen reduction process increased the pH value, which triggered a string of secondary reactions restricting the long-term stability of the reactive material.

Project aims achieved

The scientists began by erecting a funnel-shaped barrier around the source of the contamination. This barrier borders the reactor, which is placed beneath the natural groundwater table and thus permits passive horizontal permeation. The reactor comprises 18 individual cylindrical modules measuring 2.8 metres in diameter and around 2.2 metres high; each module can be considered to be a standalone reactor. By coupling several modules in series or in parallel, it is possible to control flow lengths and thus the amount of time the water remains in the reactor according to requirements. The research project operated the modules in series.

The most important aims of the project were achieved in full:

• Efficient elimination of the high TCE concentrations remaining stable in the long term.
• Manageable volume flows and pollutant concentration/ quantity over a long flow course in the iron reactor.
• Access to the reactive material to enable countermeasures to be taken against any unforeseen negative influences.

The grey cast iron granulate used as the reaction material achieved a cleaning performance of over 99.5%. It is both a highly efficient and economically beneficial prospect for field-scale projects where pollution concentrations are at least 25 milligrams per litre, as found at the Bernau site. Follow-up cleaning of the slightly contaminated reactor outlet with water 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. has proven to be highly effective over the three and a half years the reactor has been in operation and the most economic measure for remediation available. Running over several years, the research project saw a total of 450 kilograms of TCE removed from 15,000 cubic metres of water overall, and the treated groundwater cleaned up to the TCE detection limit.

Ready for practical application

The results of the research project have been implemented in site remediation since February 2007. The “east VCHC plume” is being cleaned using the iron granulate treatment wall. The requirements for this were:

• Upgrade/retrofit of the equipment. The iron granulate from 10 reactor modules had to be removed, mechanically processed and reinstalled.
• Installation of new piping plus measuring and control technology as a pump system to and from the reactor modules.
• Implementation of six pumping wells plus the necessary pumping technology.

As the cleaning performance of the reaction wall is insufficient for the cDCE degradation productThe formula stands for cis-1,2-dichloro-ethene. It is created by the degradation of ► tetrachloroethylene (PCE) and ►trichloroethylene (TCE). Both substances are examples of volatile chlorinated hydrocarbons (►VCHC)., follow-up cleaning with water activated carbon is also required.

The contaminated groundwater is pumped at a speed of 2.4 cubic metres an hour from six wells. Ten parallel modules are used to clean the water contaminated with volatile chlorinated hydrocarbonsOrganic compounds in which up to four hydrogen atoms are replaced with chlorine atoms. VCHCs were commonly used as solvents and cleaning agents well into the 1980s and primarily evaporated into the atmosphere. Due to their longevity, VCHCs are still ubiquitous in the atmosphere today. In the past, large volumes of these substances found their way into the subsoil due to carelessness, improper handling, sedimentation or accidents.◄(VCHC, predominantly TCE). The treated water then flows through the followup cleaning system and is then fed back into the soil. The equipment is operated and monitored centrally.

The scientists have already modified the equipment several times during operation in order to optimise performance. The water now flows up through the modules in the A section. A mixture of iron and filter sand was placed in the feed area of the B section modules and a gas drainage system made from perforated polyethylene tubes has been installed.

In the last three and a half years, the cleaning installation at the Bernau site has removed approximately 3,200 kilograms of VCHC from around 55,000 cubic metres of groundwater underground. It has removed virtually all the TCE from this location, part of which was not fully dechlorinated but converted to cDCE instead.

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1.1.07 SAFIRA joint research project

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1.1.05 Funnel and gate