6533b85afe1ef96bd12b8b82

RESEARCH PRODUCT

Controlled treatment of a high velocity anisotropic aquifer model contaminated by hexachlorocyclohexanes

Julien MaireNicolas Fatin-rougeFabien LaurentIheb BouzidMathias Broquaire

subject

010504 meteorology & atmospheric sciencesWater flowHealth Toxicology and MutagenesisInorganic chemistryKineticsAlkalinityAlkalinityAquifer010501 environmental sciencesToxicology01 natural sciencesPermeabilityRheologyReductive dechlorinationmedicine[CHIM]Chemical SciencesGroundwaterXanthan gum0105 earth and related environmental sciencesgeographygeography.geographical_feature_categoryChemistryPolysaccharides BacterialAquifer remediationGeneral MedicinePollution6. Clean waterPermeability (electromagnetism)AnisotropyRheologyGelsHexachlorocyclohexaneXanthan gummedicine.drug

description

International audience; Xanthan gels were assessed to control the reductive dechlorination of hexachlorocyclohexanes (HCHs) and trichlorobenzenes (TCBs) in a strong permeability contrast and high velocity sedimentary aquifer. An alkaline degradation was selected because of the low cost of NaOH and Ca(OH)2. The rheology of alkaline xanthan gels and their ability to deliver alkalinity homogeneously, while maintaining the latter, were studied. Whereas the xanthan gels behaved like non-Newtonian shear-thinning fluids, alkalinity and Ca(OH)2 microparticles had detrimental effects, yet, the latter decreased with the shear-rate. Breakthrough curves for the NaOH and Ca(OH)2 in xanthan solutions, carried out in the lowest permeability soil (9.9 μm2), demonstrated the excellent transmission of alkalinity, while moderate pressure gradients were applied. Injection velocities ranging from 1.8 to 3.8 m h−1 are anticipated in the field, given the permeability range from 9.9 to 848.7 μm2. Despite a permeability contrast of 8.7 in an anisotropic aquifer model, the NaOH and the Ca(OH)2 both in xanthan gels spread only 5- and 7-times faster in the higher permeability zone, demonstrating that the delivery was enhanced. Moreover, the alkaline gels which were injected into a high permeability layer under lateral water flow, showed a persistent blocking effect and longevity (timescale of weeks), in contrast to the alkaline solution in absence of xanthan. Kinetics of alkaline dechlorination carried out on the historically contaminated soil, using the Ca(OH)2 suspension in xanthan solution, showed that HCHs were converted in TCBs by dehydrodechlorination, whereas the latter were then degraded by reductive hydrogenolysis. Degradation kinetics were achieved within 30 h for the major and most reactive fraction of HCHs.

https://doi.org/10.1016/j.envpol.2020.115678