Microcontaminant removal by solar photo-Fenton at natural pH run with sequential and continuous iron additions I. Carra a,b , S. Malato b,c , M. Jiménez c , M.I. Maldonado b,c , J.A. Sánchez Pérez a,b,⇑ a Department of Chemical Engineering, University of Almería, 04120 Almería, Spain b CIESOL, Joint Centre of the University of Almería-CIEMAT, 04120 Almería, Spain c Plataforma Solar de Almería (CIEMAT), 04200 Tabernas, Almería, Spain highlights  Continuous and sequential iron dosage allowed micropollutants removal at natural pH.  Bicarbonates were detrimental to the process efficiency when using iron additions.  Iron addition mode affects reaction time and efficacy.  Continuous addition allows a better distribution of iron in the photo- reactor.  Acetamiprid, thiabendazole and imazalil degradation could be achieved in 15 min. graphical abstract transceiver pH, T Recycling tank Radiometer Pilotplant Input/output card Recycling pump Iron pump Process scheme Exponentially decreasing iron dosage t (min) 0 5 10 15 C/C 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Fe, H 2 O 2 (mg/L) 0 20 40 60 80 pesticides Fe H2O2 article info Article history: Received 27 June 2013 Received in revised form 2 September 2013 Accepted 3 September 2013 Available online 12 September 2013 Keywords: Micropollutants Iron additions Pesticides pH Bicarbonates photo-Fenton abstract This paper deals with iron dosage used to remove micropollutants in short reaction times with solar photo-Fenton at natural pH. The impact of bicarbonates on the process operated with iron additions was also considered. Different sequential and continuous dosage modes were studied at pilot plant scale to remove a pollutant mixture formed by acetamiprid, thiabendazole and imazalil at a concentration of 100 lg/L each and with hydrogen peroxide excess. Both operating modes proved successful in rapid pol- lutant degradation. Nevertheless, iron distribution in the system, which is a consequence of the dosage mode, is critical to both efficiency and degradation time and it was different for each dosage mode. Spe- cifically, the iron sequence of 20  4 (20 mg/L Fe added four times every mixing time) removed acetam- iprid in 20 min, which is the least reactive pollutant. Meanwhile, iron added continuously as an exponentially decreasing function allowed the shortest reaction time – 15 min for removal below the limit of detection. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Water scarcity and the pollution found in it have prompted re- search directed at water reuse treatments in recent years [1]. At the same time, the development of highly sensitive analytical tech- niques has allowed accurate pollutant detection in urban and industrial wastewaters. Pesticides, drugs, endocrine disruptors and other common substances such as caffeine or nicotine can be easily detected in water effluents [2,3]. They are the so-called ‘‘micropollutants’’ due to the low concentrations in which they are found (nanograms or micrograms per liter). Among pesticides, acetamiprid (ACTM), thiabendazole (TBZ) and imazalil (IMZ) are common biocides used in citrus crops [4–6]. Treatments of a different nature are being studied as alterna- tives to remove these substances from surface water. Along with physical processes such as ultrafiltration [7] or activated carbon 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2013.09.029 ⇑ Corresponding author at: Department of Chemical Engineering, University of Almería, 04120 Almería, Spain. Tel.: +34 950015314; fax: +34 950015484. E-mail address: jsanchez@ual.es (J.A. Sánchez Pérez). Chemical Engineering Journal 235 (2014) 132–140 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej