Pilot-Scale Destruction of TNT, RDX, and HMX on Contaminated Soils Using Subcritical Water

Subcritical (hot/liquid) water was used in a simple static (nonflowing) vessel to treat two soils from former defense sites which were contaminated with the explosives TNT (12 wt %) or RDX (0.32 wt %) and HMX (0.08 wt %). Laboratory studies demonstrated that significant degradation of RDX began at 100 °C and at 125 °C for TNT and HMX. For highly contaminated soils, the bulk of the undegraded explosives remained in the soil rather than in the water phase. Based on HPLC/UV analysis, intermediate degradation products formed but quickly degraded at <250 °C. Pilot-scale remediations (4−6 kg soil) using 4-L of water at 275 °C for 1 h (with 2-h heat-up time) of real soils resulted in >99.9% destruction of TNT and RDX and ca. 98% destruction of HMX. None of the mutagenic nitroso derivatives of RDX and HMX were formed. “Microtox” acute toxicity tests with Vibrio fischeri showed no significant (compared to background) residual toxicity in either the process wastewaters or leachates from the treated soils.