Evaluation of enhancement techniques for the dechlorination of DDT by nanoscale zero-valent iron

Due to its low toxicity and high reactivity, nanoscale zero-valent iron (nZVI) is widely used as a remediation agent. However, nZVI is also prone to rapid aggregation and surface oxidation, which significantly reduces its practical efficacy. Here three enhancement techniques, proposed to overcome these limiting factors, incremental addition, pH adjustment and the application of ultrasonic energy, were systematically evaluated for their ability to increase the remediation efficiency of 1,1,1-Trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) sorbed onto the surface of a soil surrogate. The efficacy of nZVI was also compared to the effectiveness of microscale zero valent iron (μZVI). Of the three enhancement techniques studied, only ultrasonic energy significantly enhanced the effectiveness of nZVI for the degradation of DDT and its primary degradation products due to disaggregation and surface cleaning of nZVI and increased ultrasound induced mixing. While pH had no effect on the degradation efficiency of nZVI, low pH significantly enhanced the effectiveness of μZVI remediation. This was attributed to the sustained low solution pH reducing surface corrosion products, increasing surface area and maintaining a cationic surface for attracting anionic DDT.