Benefits and limitations of using Fe(III)-EDDS for the treatment of highly contaminated water at near-neutral pH

• Use of Fe(III)-EDDS complex as a source of iron for photo-Fenton at neutral pH.
• Photolysis of Fe(III)-EDDS generates radical species other than HO that can act in the presence of carbonates.
• Radical generation by Fe(III)-EDDS photolysis dependent on aeration but not on the presence of H2O2.
• Decreased degradation performance at elevated temperatures.
• Classical photo-Fenton at acidic pH remains more robust for treating high contaminant concentrations.

This study evaluates the use of the Fe(III)-EDDS complexing agent as an alternative to conventional acidic pH photo-Fenton for the treatment of the pesticide imidacloprid in natural water. The main objective is to estimate whether Fe(III)-EDDS is a viable alternative when treating waters containing high concentrations of contaminants. To this end, the mode of action of Fe(III)-EDDS is examined in the presence of carbonates, at different aeration conditions and at different temperatures. The role of HO2/O2− radical species and some aspects of the Fe(III)-EDDS complexation mechanism are discussed. Degradation kinetics and toxicities of generated intermediates are compared between Fe(III)-EDDS and conventional photo-Fenton treatment. An overview of the benefits and limitations of the process is presented.