Effects of carrier on the transport and DDT removal performance of nano-zerovalent iron in packed sands

The delivery of nano-zerovalent iron (nZVI) as a remediation agent to targeted areas in soil was studied using different carriers. Among water, surfactant solution, and surfactant foam, the nZVI transport and carrying abilities followed the order of surfactant foam > surfactant solution > water. The nZVI migration was also facilitated by increased soil particle size and high surfactant concentration. Batch experiments probed the remediation of dichlorodiphenyltrichloroethane (DDT)-contaminated sand under different conditions. Compared to surfactant solution, the use of foam as a carrier achieved much higher DDT removal efficiencies for both coarse (foam/solution: 99/69%) and fine (foam/solution: 60/26%) sands. Additionally, the DDT removal efficiency was strongly influenced by surfactant concentration: foams generated using 1 and 5 g L−1 sodium lauryl ether sulfate (SLES) solutions reached the respective efficiencies of 44% and 75% under identical experimental conditions. However, the nature of the surfactant did not significantly affect the total removal efficiency of DDT. Solubilization, increased sweep efficiency, and reduction by nZVI were identified as factors affecting the DDT removal efficiency, and all three of them were involved when foam-nZVI was used as the flushing fluid.