Use of abiotic oxidative-reductive technologies for remediation of munition contaminated soil in a bioslurry reactor

The possibility to clean-up TNT contaminated soil, 400 mg TNT kg-1, surrounding Nebraska Ordnance Plant's (US), below the USEPA goal of 17.2 mg TNT kg-1 using Fenton oxidation (Fe2+ + H2O2), Fe0 reduction, combined Fe0/H2O2 and CaO2 was explored at pilot scale. Treatments were performed in a 60 l airlift reactor, which was a prototype of larger commercial unit. All the treatments reduced TNT soil concentration below the required clean-up goal and in shorter time with respect to bench scale. Using 2% (w/w) Fe0, TNT soil concentration reduced below the required standard just within 4 h. No significant TNT destruction improvement was observed when 2% Fe0 (w/w soil) was combined with four sequential additions of 0.25% H2O2. Laboratory experiments with 14C-TNT indicated that most of the 14C, approximately 80%, was unextractable residue. A time greater than 24 h was required either with Fenton reagent, 8 x (80 mg Fe2+ L-1 + 0.125% H2O2) or 0.2% (w/w) CaO2. The optimal performance of Fenton reagent was obtained when the reagent was added in eight increments rather than in a single or double dose and less cumulative amount of H2O2 (0.75%) was required with respect to bench scale (1%).