Development of an ENA based bioremediation technology for a BTEX contaminated aquifer in Berlin-Spandau - Laboratory experiments to the enhanced biodegradation of BTEX compounds with nitrate and scientific support of the field test – Project phase 2
Partner: GICON - Großmann Ingenieur Consult GmbH, Dresden
Funding: Federal Ministry of Education and Research (BMBF)
Duration: July 2008 - March 2012
Contact:
Dr.-Ing. Thomas Fichtner
Project description:
The primary goal of the overall project was to develop a Natural Attenuation-based, cost-effective and feasible in-situ process for the remediation of hydrocarbon-contaminated aquifers at the Vereinigte Molkereizentralen GmbH & Co KG (VMZ) site in Berlin-Spandau. The use of the site as a petroleum tank farm resulted in contamination of the soil and groundwater with the monoaromatic hydrocarbons benzene, toluene, ethylbenzene and xylene (BTEX) as well as the substances 1,2,4 trimethylbenzene, 1,3,5 trimethylbenzene and 1,2,3 trimethylbenzene (TMB). Furthermore, mineral oil hydrocarbons (MKW) and polycyclic aromatic hydrocarbons (PAH) were detected in the pollutant cocktail. In the course of laboratory investigations on the biodegradation of the pollutants, column and batch experiments on the influence of the electron acceptors nitrate and sulfate, temperature and other nutrients on the degradation processes and their kinetics were investigated in more detail.
It was shown that the microorganisms present in the aquifer of the site are able to degrade BTEX and TMB with both nitrate and sulfate after a certain adaptation period. The performance of a column experiment in which autochthonous soil material was used in addition to native site water and the electron acceptor nitrate showed that the use of highly contaminated sediment from the site resulted in delayed or incomplete degradation of BTEX and TMB.
The batch experiments conducted also demonstrated that the enrichment cultures obtained with material from the site were capable of degrading all major contaminants (BTEX, TMB) under strictly anaerobic conditions with nitrate as well as sulfate as electron acceptors. In both the column experiments and the batch experiments, sulfate formation was observed due to the reoxidation of sulfides present in the soil.
In parallel to the laboratory tests, a test field was set up at the site in cooperation with the project partner GICON on the basis of the results obtained during project phase 1 (6/2003 to 12/2006). The aim of the field test was to validate the laboratory results obtained.
Following a tracer test with lithium bromide, eight infiltration levels and 38 control levels were set up, evenly distributed over the upper and lower aquifer. During the test, a continuous nitrate infiltration was carried out via the infiltration levels. The amount of nitrate to be infiltrated was determined by considering the nitrate consuming processes (microbial pollutant degradation of BTEX and TMB and the reoxidation of sulfides) and based on the specified output concentration of 200 mg/l nitrate at the 2nd control level. For process monitoring and effluent control, the control levels constructed across the flow direction were available at a total of 5 control levels. During the process monitoring of the test field operation, a continuous sampling and analysis of the environmentally relevant parameters (BTEX and TMB, PAH, alkylphenols, MKW, ions) as well as an associated evaluation and interpretation of the field data took place.
The distribution of nitrate in the lower aquifer was approximately as previously determined (200 mg/l at the 2nd control level). In the shallow aquifer, the desired nitrate concentrations have not yet been achieved. Based on the data collected during the 600-day test period to date, a decrease in BTEX and TMB and a depletion of nitrate could be detected in the shallow and deep groundwater in the first two control levels downstream of the infiltration level. The proof that this decrease is due to biological processes still had to be provided by an isotope investigation. Furthermore, in areas with sufficient nitrate present, a continuous increase in sulfate concentrations due to the reoxidation of sulfides present in the soil could be demonstrated.