Alkaline hydrolysis of TNT and TNT in soil followed by thermal treatment of the hydrolysates

Lab-scale experiments were conducted on the alkaline hydrolysis of TNT and a mixture of TNT and soil followed by thermal treatment of the hydrolysates. Four hours of alkaline hydrolysis (T=80°C, initial pH of 14) resulted in complete deactivation of TNT and partial mineralization (10% TIC, 90% DOC). Additionally, more than one nitrogroup of the TNT-molecule was split off and appeared as nitrite with very little ammonium in the dark-brown hydrolysate. Ultrafiltration experiments showed that roughly 50% of the DOC in the 80°C-hydrolysates belonged either to molecules of molecular mass between 3 and 30 kDa or >30 kDa. Similar results were observed with the TNT/soil-mixture. During thermal treatment at TTT ≈ 200°C solids were formed, which contributed 50–70% to the DOC removal in this step. At temperatures up to TTT=350°C the DOC removal increased to 85%, the high molecular mass compounds were broken down to smaller molecules and nitrite was completely removed from the hydrolysates. Thus, the alkaline hydrolysis of pure TNT was shown to be a safe deactivation process without detonation and with negligible gas production. The overall results suggest that alkaline hydrolysis followed by thermal and biological post treatment of the hydrolysates might be an efficient technology for the remediation of highly TNT-contaminated soils.