Dehalogenation of diatrizoate using nanoscale zero-valent iron: impacts of various parameters and assessment of aerobic biological post-treatment

Abstract

This study investigated the feasibility of nanoscale zero-valent iron (nZVI) for reductive dehalogenation of iodinated contrast medium diatrizoate (DTA). The impacts of various parameters, including nZVI dosage, DTA concentration, solution pH, aging time of nZVI, the presence of natural organic matter, and the type of competitive anions, on the dehalogenation of DTA as well as the formation of its reductive product 5-diacetamidobenzoate (DABA) using nZVI were evaluated. Furthermore, an aerobic biological post-treatment was conducted to study the biodegradability of reductive products of DTA dehalogenation using nZVI. The results showed that dosing with 0.5 g L⁻¹ nZVI particles resulted in a rapid decrease in DTA concentration and a corresponding rise of the concentrations of DABA and I⁻. DTA dehalogenation in terms of its removal and DABA formation was enhanced with the increase in nZVI dosage but deteriorated when increasing solution pH. nZVI aging time had a negative impact on DTA dehalogenation. Natural organic matter at much low level could improve DTA dehalogenation, while had a negative influence at high concentrations. Contrary to sulfate, the presence of nitrate and phosphate strongly inhibited DTA removal using nZVI. The results also showed that the reductive product DABA could be degraded by aerobic biological post-treatment, suggesting DTA dehalogenation with nZVI may be a vital procedure for its biodegradability improvement and consequently complete removal.