Are iron chelates suitable to perform photo-Fenton at neutral pH for secondary effluent treatment?

ABSTRACT

There have been concerns about which iron chelate is most suitable for application in the photo-Fenton process as well as the fate of these chelates after application. In this study, five chelating agents, i.e. citric acid (CA), oxalic acid (OA), ethylenediamine disuccinic acid (EDDS), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), representing the most used iron chelates were assessed for suitability of application in homogeneous photo-Fenton-like process at pH of 7. The efficiency of the iron chelates were assessed in the disinfection of secondary effluent. The results for the disinfection and bacteria regrowth followed the order EDTA>OA>NTA>CA>OA. All the iron chelates were observed to have increased the COD of the effluent with EDDS having the highest COD contribution. The ability of the chelates to remove aromaticity was measured by the UV254 measurement. The efficiency of the chelates to remove aromaticity decreased in the order CA>EDDS>NTA>CA>OA. To determine the fate of the chelates, toxicity tests were conducted on the chelates before and after irradiation and the results revealed a decrease in toxicity after photoirradiation, implying the chelates were degraded and the products/intermediates produced were of less toxicity as compared to the parent compounds.