Photo-Fenton processes in raceway reactors: Technical, economic, and environmental implications during treatment of colored wastewaters

Photo-Fenton processes in CPC (compound parabolic concentrators)-type solar reactors have received great attention because of their extraordinary performance during the treatment of a wide range of recalcitrant pollutants. Unfortunately, less effort has been spent on evaluating the technical and operational feasibility of more simple and low-cost solar reactors. In this study, we evidenced the technical, economic, and environmental feasibility of a raceway reactor to treat acid orange 52 dye (AO52), by means of a photo-Fenton process. The raceway reactor presents decolorization efficiencies (97%), chemical oxygen demand reduction (COD = 55%), and organic carbon removal (35%) similar to those obtained by compound parabolic collectors. After 1 h of reaction (25 kJ/L of accumulated energy), the treatment allows generating a highly biodegradable (BOD5/COD > 0.5) effluent using 15% of the theoretically required hydrogen peroxide (0.65 mg H2O2/mg AO52) to mineralize the dye. Phytotoxicity assays confirmed the quality of the effluent because photo-treatment led to an increase in the germination index in Cucumis sativus (from 102% to 104%), Solanum lycopersicum (from 37% to 60%), Allium cepa (from 40% to 80%), and Capsicum annuum (from 40% to 90%). During the photo-treatment, an increase of the accumulated energy, from 17 to 32 kJ/L, did not affect decolorization efficiency or the biodegradability of the effluent (BOD5/COD = 0.55-0.69). The lack of solar radiation caused a slight reduction in decolorization efficiency (similar to 1%) and led to a less biodegradable effluent (BOD5/COD = 0.35); these results suggest that the discharge of the effluent to conventional wastewater plants may affect their robustness. The economic study indicates that it is feasible to biocompatibilize the AO52 dye through a photo-Fenton process in a raceway -type reactor at a low cost (US$1.0/m(3)). Finally, the life cycle impact assessment reveals that electricity and H2O2 consumption can be considered the main environmental hotspots of the process because they have, in terms of relative impact, a contribution greater than 70% in 14 of the 18 environmental categories considered. Photo-Fenton processes in raceway reactors offer key advantages such as low installation and operating cost, robustness, and a lower environmental footprint (0.762 kg CO2-Eqv/m(3) wastewater). Therefore, raceway reactors could become an attractive option for small and medium scale textile mills in low-income economies. (C) 2018 Elsevier Ltd. All rights reserved.