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) ves sel to treat two soils from former defense sites which were contaminated wi th the explosives TNT (12 wt%) or RDX (0.32 wt%) and HMX(0.08 wt%). Laborat ory studies demonstrated that significant degradation of RDX began at 100 d egrees C and at 125 degrees C for TNT and HMX. For highly contaminated soil s, the bulk of the undegraded explosives remained in the soil rather than i n the water phase. Based on HPLC/UV analysis, intermediate degradation prod ucts formed but quickly degraded at <250 degrees C. Pilot-scale remediation s (4-6 kg soil) using 4-L of water at 275 degrees C for 1 h (with 2-h heat- up time) of real soils resulted in >99.9% destruction of TNT a nd RDX and c a. 98% destruction of HMX. None of the mutagenic nitroso derivatives of RDX and HMX were formed. "Microtox" ac ute toxicity tests with Vibrio fischeri showed no significant (compared to background) residual toxicity in either the process wastewaters or leachates from the treated soils.