Many water-stressed cities are considering the capture and recharge of urban stormwater as a means of replenishing depleted groundwater aquifers. This practice raises concerns about the potential for contaminating water supplies with trace organic contaminants. During the recharge process, captured stormwater is percolated through gravel or sand prior to entering the aquifer. The addition of manganese-oxides to this material could provide an inexpensive means of removing contamination during the recharge process; however, manganese oxide-coated sands exhibit decreases in reactivity through surface reaction when they are deployed for long periods. To restore the reactivity of passivated Mn-oxide coated sands chemical oxidants can be used to convert Mn2+ back into Mn3+ and Mn4+ oxides. To assess the potential for using this approach, four oxidants (i.e., HOCl, HOBr, KMnO4, and H2O2) were evaluated. Results indicate that HOCl and HOBr added in a pH 6 buffer regenerate failed Mn-oxide coated sand, producing a surface that is just as reactive as the virgin material initially deployed. KMnO4 and H2O2 restored some of the oxidative capacity of Mn-oxide coated sands but there were no conditions under which they completely reversed the passivation. Despite the loss of some Mn-oxide coating density on the media, media regenerated with HOCl exhibited a similar longevity to the virgin media under conditions encountered in stormwater infiltration systems. Chemical regenerants increased the average oxidation state of the Mn, and X-ray photoelectron spectroscopy reveals that the regenerants greatly diminish the extensive carbon content associated with the failed Mn-oxides. The regeneration technique provides a feasible means of in situ regeneration of manganese oxides without the need to excavate and replace the material.

Chemical regeneration of Mn-oxide coated sand for oxidation of organic stormwater contaminants

255th National Meeting (2018)

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