Remediation of RDX-Contaminated Water Using Alkaline Hydrolysis

The objective of this study was to assess the effectiveness of alkaline hydrolysis as an alternative ex situ technology for remediating groundwater contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Treatment in both batch reactor and continuous stirred tank reactor (CSTR) was investigated. RDX reactivity was strongly dependent on the reaction pH investigated (11–13). The batch system achieved pseudo-first-order RDX reaction rates in the range of $(0.8–27.7)\times {10}^{-3}{\min }^{-1}$ , corresponding to half-life periods of $17.9\text{to}0.5\mathrm{h}$ , respectively. In the CSTR system operated at the initial RDX concentration of $4.5\times {10}^{-3}\mathrm{mM}$ , 99% RDX removal was achieved with the hydraulic retention time of $2\text{days}$ and the reaction pH of 11.9. Formate and nitrite were produced as the major hydrolysates in the CSTR system, indicating a simultaneous reaction mechanism involving RDX ring cleavage and elimination of the ring nitrogen. The net $\mathrm{O}{\mathrm{H}}^{-}$ demand used only for RDX removal in the CSTR was found to be 1.5, 390, and $130\mathrm{M}$ $\mathrm{O}{\mathrm{H}}^{-}∕\mathrm{M}$ ${\mathrm{RDX}}_{\text{removed}}$ at pH values of 11.9, 11.5, and 11.0, respectively. A conceptual cost analysis indicated that the expense of alkaline treatment may be comparable to the expense of granular activated carbon treatment for long treatment periods ( $30\text{years}$ or more), due to the potentially lower annual operational cost of alkali treatment.