Successful pilot injection of nanoscale zero-valent iron for groundwater remediation in Kara Trutnov site in Czech Republic
Remediation company EKORA in collaboration with NANO IRON, producer of zero-valent iron nanoparticles (nZVI), conducted laboratory study and subsequent pilot injection of surface stabilized nanoparticles of elemental iron (product NANOFER 25S) to eliminate groundwater contamination of chlorinated hydrocarbons and hexavalent chromium in KARA Trutnov site in Czech Republic.
Groundwater contamination at the KARA site is caused mainly by obsolete technological practices and irresponsible handling of chlorinated ethylene and chromium compounds during processing of fur in past. The spots of massive contamination beneath the degreasing buildings have already been removed in previous years, using conventional and innovative remediation technologies (pump and treat, venting, vapour extraction, potassium permanganate ISCO). Nevertheless, the site currently still remains several spots above the limit contamination posing serious environmental risks. There is a mixed contamination of hexavalent chromium (Cr6+) and chlorinated hydrocarbons in two spots excluding in-situ chemical oxidation methods, therefore EKORA company has been looking for other efficient and economically acceptable solution. The solution has been found in the innovative reductive technology of nZVI.
The effectiveness of the technology was verified first in a laboratory on total of 100 samples of real ground water, possibly with the addition of soil from the site. Based on the evaluation of laboratory experiments, the pilot application of 200kg of NANOFER 25S was then carried out in cooperation with NANO IRON Company. The aqueous dispersion of nZVI at a target dosing concentration of 2g/L was applied by proportional dosing pump into 2 injection wells ME-6 and ME-24.
The results of pilot test were surprisingly promising! It was observed an immediate decrease in concentrations of hexavalent chromium to the detection limit (<0,005mg/L) and there was no rebound effect during the next 45 days. 100% of hexavalent chromium was removed from the application well and its surroundings, Cr6+ was reduced to significantly less toxic form and strongly bound in the rock environment.
It was also observed a gradual decrease in concentrations of chlorinated hydrocarbons (CHC) in well ME-24 from initial value 4200 μ/L to 1300μ/L (one week after application) and then further to 20μg/L (45 days after application). It was removed 99,55% of CHC sum (up to 100% of PCE, TCE and VC and 99,2% cis-1,2-DCE).
Pilot application of zero-valent iron nanoparticles (NANOFER 25S) for groundwater remediation contaminated by mix of hexavalent chromium and chlorinated hydrocarbons confirmed the results of laboratory experiments and the high efficiency and safety of this method. Based on success of the pilot study, EKORA is now preparing a full scale injection of NANOFER 25S slurry, which will be prepared directly on site by unique dispersion technology provided by NANO IRON.