Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Enhancing solar disinfection of water in PET bottles by optimized in-situ formation of iron oxide flms. From heterogeneous to homogeneous action modes with H 2 O 2 vs. O 2 – Part 1: Iron salts as oxide precursors Sakine Shekoohiyan a,b , Sami Rtimi b , Gholamreza Moussavi a , Stefanos Giannakis b, ⁎ , Cesar Pulgarin b, ⁎ a Department of Environmental Health Engineering, Tarbiat Modares University, Jalal Ale Ahmad Highway, Tehran, Iran b School of Basic Sciences (SB), Institute of Chemical Science and Engineering (ISIC), Group of Advanced Oxidation Processes (GPAO), École Polytechnique Fédérale de Lausanne (EPFL), Station 6, CH-1015 Lausanne, Switzerland HIGHLIGHTS • Solar disinfection in PET bottles was enhanced deposing iron by homo- geneous precursor. • The optimization parameters in- dicated a simple, fast and durable re- actor for SODIS. • Semiconductor action and ppb levels of iron leaching enhanced disinfec- tion. • Photo-Fenton process was efectively yielded with H 2 O 2 addition. • The process can be efective in slightly acidic natural waters, without re- growth. GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Solar disinfection (SODIS) Semiconductor Photo-Fenton Bacterial inactivation Iron flms ABSTRACT Solar disinfection (SODIS) is a WHO-accepted intervention method for improving water sources in developing countries. Despite its efectiveness, the limitations of long exposure and bacterial regrowth risk demand further improvement of the practice. In this work, we have generated an iron oxide flm on the inner surface of PET bottles used in SODIS, to generate further pathways of solar-mediated inactivation, namely a semiconductor mode of action and controlled iron leaching in the system, which both have demonstrated bactericidal capacity. More specifcally, in this Part 1, the deposition process using Fe salts has been scrutinized, assessing the use of various homogeneous Fe precursors (FeCl 3 , FeSO 4 and Fe 2 (SO 4 ) 3 ), amounts of iron (0.5–20 g/L) and deposition time (1–8 h) to fnd the delicate balance among deposition layer thickness and light penetration. At the optimal conditions (4 h deposition, 1 g/L FeCl 3 ) SODIS was enhanced, reducing 60% the exposure time; a simple washing step brought a further reduction (70%), while eliminating regrowth in volumes from 330 up to 1500 mL reactors. A robust process and reactor was attained, able to reuse its precursor solution almost 10 times and the reactor in 5 consecutive tests, without the need for re-deposition. The modifcation also proved to be an invaluable iron source to fuel the photo-Fenton process, when H 2 O 2 as an electron acceptor was added to the system. The improvement induced by the heterogeneous photo-Fenton process was around 80% compared to the SODIS/ H 2 O 2 process in plain PET bottles and exceeded 85% when compared to SODIS, while being durable to the high https://doi.org/10.1016/j.cej.2018.09.219 Received 24 July 2018; Received in revised form 26 September 2018; Accepted 29 September 2018 ⁎ Corresponding authors. E-mail addresses: Stefanos.Giannakis@epf.ch (S. Giannakis), Cesar.Pulgarin@epf.ch (C. Pulgarin). Chemical Engineering Journal 358 (2019) 211–224 Available online 03 October 2018 1385-8947/ © 2018 Elsevier B.V. All rights reserved. T