Elimination of HCH and their transformation products from drain water by a permeable reactive barrier (PRB) on a metallic iron basis (zero-valent iron, ZVI).
Metallic iron-based PRB is a well-known option for groundwater remediation from chlorinated pollutants (e.g. chlorinated ethylenes). PRB work also for HCH isomers, which quickly transform into chlorobenzenes, that are further dechlorinated to benzene.
For HCH sites with missing infrastructure, ZVI-based PRB is a good option of a passive treatment system of contaminated drain water. PRB´s are designed as porous pools filled with macroscopic ZVI or cast-iron chips.
As a consequence of ZVI surface gradual deactivation by corrosion and reduced minerals precipitation, the overall efficiency of PRB is dropping over time. Depending on the environmental limits set for the effluent, the replacement of the ZVI bed is necessary after some period of PRB operation. Alternatively, one of the related ZVI applications from in situ groundwater treatment area can be used as additional PRB reactivation step. E.g., injections of ZVI in nanoparticle suspension form (nZVI) enlarge PRB filling operation time.
ZVI based PRB is a key element of Wetland+ technology, that comprises 4 modules lined up into a passive flow cascade:
Aeration/sedimentation - PRB - anaerobic biosorption module aerobic wetland.
Wetland+ technology is taylor-designed for HCH dump sites with HCH containing mine water or drain water with further perspective towards other chlorinated pesticides. Wetland+ installations are intended to be operated in passive-flow mode.
Wetland+ is a working tool of Lifepopwat project.
Resources needed
The key issue in using PRB or Wetland+ technology is to find a reliable supplier of ZVI chips in the required quality, quantity, and delivery dates. This is valid for initial PRB filling as well as for PRB refilling after the reductive strength drops.
Evidence of success
A full-scale ZVI-based PRB was installed as a part of Wetland+ technology prototype on demonstration site Hájek, Czech Republic, within LIFEPOPWAT project (2020-2023). The prototype was put into trial operation in November 2021 and its immediate efficiency of HCH elimination reached 96. ZVI reactivity towards HCH is described widely in scientific literature (see e.g. S. Wacławek et al., „Chemical oxidation and reduction of hexachlorocyclohexanes: A review", Water Research, 162, 302–319, 2019.)
Difficulties encountered
Today, difficulties insufficient quality and quantity of ZVI supply can be faced. Also, highly mineralized water can cause quick pores clogging. Laboratory testing phase and small-scale field test phase should be done prior the full-scale installation to enumerate the speed of clogging processes.
Potential for learning or transfer
The potential of transfer is wide, it is actually defined by the number of HCH sites with the need of drain or ground water treatment. Within “HCH in EU” project the sites inventory was done that concludes 299 HCH sites are present with 54 of them being of high risk. PRB or Wetland+ installations are suitable for off-grid and engineering infrastructure-missing sites. They are intended to be placed as measures preventing spreading of HCH leachates into ecosystems prior a solution for HCH source elimination is found. Many remediation companies and universities are able to provide consultancy and services related to PRB design and construction.
