Bacterial inactivation with iron citrate complex: A new source of dissolved iron in solar photo-Fenton process at near-neutral and alkaline pH

• First application of Fe–citrate-based photo-Fenton process for E. coli inactivation.
• Photo-Fenton process was efficient for E. coli inactivation at neutral and alkaline pH.
• The order of efficiency of the photo-Fenton process was Fe–citrate > FeSO4 > goethite.
• ROS involved in homogeneous and heterogeneous photo-Fenton process are identified.

This study reports the first application of Fe–citrate-based photo-Fenton chemistry for the inactivation of Escherichia coli. Promising results of bacterial inactivation at near-neutral and alkaline pH conditions were obtained, while using low iron concentration (Fe–citrate concentration: 0.6 mg/L, relative to the Fe content) and avoiding precipitation of ferric hydroxides. The effects of the solution pH and Fe–citrate complex concentration on E. coli inactivation during the photo-Fenton reaction were investigated. The efficiency of the homogeneous photo-Fenton process using Fe–citrate complex as a source of iron strongly improved bacterial inactivation as compared with the heterogeneous photo-Fenton treatment (FeSO4 and goethite as sources of iron) at near-neutral pH. The bacterial inactivation rate increased in the order of goethite < FeSO4 < Fe–citrate, which agreed well with the trend for the HO radical formation, monitored by ESR. Encouraging results were also obtained while applying this treatment for bacterial inactivation in natural water samples from Lake Geneva (Switzerland) at pH 8.5, since no bacterial reactivation and/or growth were observed after photo-Fenton treatment. This type of application is promising, considering the simplicity of the installations and procedures, the ability to use the Sun as the light source, and the safety of all of the chemicals in this system.

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