Evaluation of remediation processes for explosive-contaminated soils: kinetics and Microtox((R)) bioassay

Abstract

BACKGROUNDSoils and sediments near military sites where training regularly occurs are vulnerable to contamination from toxic nitro explosives such as 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). In order to clean up the explosive-contaminated soils, several options have been investigated and evaluated as ex situ remediation processes, including alkaline hydrolysis, subcritical water degradation, zero-valent iron (Fe(0)) reduction, and Fe(0)-assisted Fenton oxidation. The kinetics of the remediation processes were evaluated and the toxicity of treated solutions determined using the Microtox((R)) bioassay. RESULTSKinetically, using four remediation methods, explosives were rapidly degraded in contaminated soils. Under optimal conditions, more than 99% of explosives were destroyed. However, the Microtox((R)) bioassay showed that after degradation of explosives by alkaline hydrolysis, treated solutions did not show any decrease in toxicity, suggesting that hydrolytic products may still be toxic. Similarly, the Fe(0) reduction process did not significantly aid removal of toxicity due to the toxicity of reduction products. In contrast, subcritical water degradation and Fe(0)-assisted Fenton oxidation markedly reduced the toxicity of explosives. When a toxic metal (e.g. Pb in shooting ranges) co-existed with explosives, toxicity still remained after complete degradation of the explosives by subcritical water degradation or Fe(0)-assisted Fenton oxidation, indicating that additional treatment may be needed. CONCLUSIONSResults suggest that, besides removal/degradation of toxic explosives, reduction of toxicity after treatment should be evaluated to select a practical option to remediate explosive-contaminated soils. (c) 2015 Society of Chemical Industry