Comparative Degradation of Alachlor Using Photocatalysis and Photo-Fenton Margarita Hincapié Pérez & Lina Patricia Vega & Henry Zúñiga-Benítez & Gustavo A. Peñuela Received: 18 July 2018 /Accepted: 26 September 2018 # Springer Nature Switzerland AG 2018 Abstract A comparative study about the degradation of alachlor in aqueous solutions under different photocata- lytic systems, including TiO 2 , TiO 2 /H 2 O 2 , and TiO 2 / Na 2 S 2 O 8 heterogeneous photocatalysis, Fe 2+ /H 2 O 2 , Fe 3+ /H 2 O 2 , and UV radiation, was carried out. In this way, times for alachlor total removal and mineralization followed the order photo-Fenton < photocatalysis with persulfate < photo-Fenton-like < photocatalysis with hydrogen peroxide < photocatalysis with TiO 2 . Ferric chloride was used as ferric ion source under Fenton- like reactions. Oxidation with Fe 2+ /H 2 O 2 was faster than treatment with Fe 3+ /H 2 O 2 , but under UV irradiation, degradation rates were similar, indicating that FeCl 3 could be a good source of ferric ions for alachlor degra- dation. Reduction of the sample toxicity was much faster in the photo-Fenton process than in TiO 2 process (50% mortality reduction in 180 min compared to around 400 min—Daphnia Pullex assays). In addition, evaluation of the nitrogen and chloride contained in the treated samples confirmed a 100% conversion of the N and Cl content in the pollutant molecule. Finally, some of the degradation by-products for pollutant removal using TiO 2 photocatalysis were identified. Keywords Advanced oxidation processes . Alachlor . Pesticides . Photocatalysis . Photo-Fenton . Wastewater treatment 1 Introduction Alachlor, 2-chloro-2,6-diethyl-N-(methoxymethyl) ac- etanilide (ALC), is a herbicide used to control grasses and broadleaf weeds in crops such as corn, soybeans, and sorghum. In the USA, it is of the most widely used herbicides. However, currently, alachlor is included in the list of priority substances in European Union Water Framework Directive 2000/60/EC, because it is consid- ered a carcinogen category 3 (Directive 2000/7/EC, 2000). In this way, the Environmental Protection Agen- cy (EPA) has set as target for maximum contaminant level goal (MCLG) in water for human consumption at zero and a maximum contaminant level (MCL) value of 0.002 mg L -1 (EPA 2009). Alachlor has been found in groundwater above the maximum concentration limit (MCL) of 0.002 mg L -1 (EPA 2009; Ritter 1990). It has a half-life in soil of 70 days and 30 days in water. More than ten transfor- mation products of its degradation have been found in groundwater, in concentrations ranging from 4 to 570 ng L - 1 , exceeding the parent compound Water Air Soil Pollut (2018) 229:346 https://doi.org/10.1007/s11270-018-3996-6 M. H. Pérez Departamento de Ingeniería Ambiental, Facultad de Ingeniería, Universidad de Medellín, Carrera 87 No 30-65, Medellín, Colombia L. P. Vega : H. Zúñiga-Benítez : G. A. Peñuela Grupo GDCON, Facultad de Ingeniería, Sede de Investigación Universitaria (SIU), Universidad de Antioquia UdeA, Calle 70 No 52-21, Medellín, Colombia H. Zúñiga-Benítez (*) Departamento de Ingeniería Química, Facultad de Ingeniería, Universidad de Antioquia UdeA, Calle 70 No 52-21, Medellín, Colombia e-mail: henry.zuniga@udea.edu.co