Improvement of the biodegradability of diatrizoate by electroreduction of its amido groups

Abstract

The occurrence of iodine X-ray contrast media (ICM) in the environment is a global concern since they can be transformed into toxic compounds during water disinfection process. Among the different approaches that have been tested to degrade them, electroreduction offers the advantages to be selective, targeting in a cost-effective way the functional groups responsible for ICM biorecalcitrance and allowing the recovery of iodide ions. We have previously shown that total deiodination of diatrizoate, a highly biorecalcitrant ICM, did not lead to a significant enhancement of its biodegradability. In this work, the electroreduction of amido groups of diatrizoate was attempted to further improve its biodegradability. Electrolyses of diatrizoate and its deiodinated derivative, were investigated in neutral and acidic medium. A total deiodination of diatrizoate was rapidly achieved in both media along with a slower reduction of the amido groups, as shown by LC-MS/MS analysis of by-products. The biodegradability of the solutions was estimated by the evaluation of the BOD5/COD ratio. Results show that it was improved after the electroreduction performed in acidic medium. This result was confirmed by a biological treatment on activated sludge over a 21 days period, leading to mineralization yields of 46% and 68% for diatrizoate and 3,5-diacetamidobenzoic acid, respectively, after the electroreduction process.