Field investigation for enhanced in-situ removal of nitrate from groundwater stimulated by the combined injection of acetate and nano zero-valent iron

Abstract

This study evaluated, at the field-scale, the feasibility of tandem acetate and nano zero-valent iron (nZVI) injection for the removal of NO3- from groundwater through both abiotic and biotic processes. The field pilot consisted of a dual-well system comprising an injection-withdrawal well pair, whose performance was assessed under various injection strategies differing in reagent(s) type, dosage, and injection pulse frequency. Results demonstrated that the combined amendment of acetate and nZVI achieved satisfactory NO3- removals (64 %), with most of the removed NO3- being converted to N2(g). The inclusion of nZVI permitted achieving similar removal efficiencies with less frequent acetate injections, highlighting the synergistic effect of applying both reagents together. NO3- removal was primarily attributed -though not necessarily limited- to heterotrophic denitrification, as confirmed by isotopes analysis. However, several operational challenges were identified. First, excessive reagents dosing led to severe clogging of the injection well. Second, the complex hydraulics of the aquifer, complicated by fluctuating abstraction rates in the pumping well, made it difficult to predict NO3- removal percentages in treated groundwater. Third, high groundwater velocities and the resulting short residence times within the reactive zone constrained NO3- removal efficiency. Overall, these findings underscore the importance of thoroughly characterizing the site hydrogeology to design a precise injection strategy that ensures effective and sustainable remediation while minimizing undesirable side-effects.

Abstract corregit This study was funded by the European Community under the LIFE program (LIFE18 ENV/ES/000335). Support was also received from the Catalan AGAUR Agency through the Research Groups Support Programme (2021-SGR-GRC-00596) and from the AEI through the María de Maeztu Programme (CEX2023-001300-M/10.13039/501100011033).

Postprint (published version)