Treatment of a synthetic colored effluent in raceway reactors: The role of operational conditions on the environmental performance of a photo-Fenton process

Abstract

This study assessed the environmental and economic performance of a photo-Fenton process in a raceway reactor at laboratory scale. For the best operational condition (BOC) identified (dye = 55.0 mg/L, H2O2/dye = 0.862 mg/L, Fe2+/dye = 0.184) a carbon footprint (CFP) of 1.335 kg CO2 Eqv/m3 was obtained. Consumption of electrical energy, construction materials, and reagents represent 97.2% (1.298 kg CO2 Eqv/m3) of the CFP. Similarly, ReCiPe-2016 v1.1 evidenced that these activities play an important role on the environmental performance of the process because their relative impact ranged from 96.5% to 99.7% at least in 14 of the 18 categories considered by this method. It should be noted that the CFP is scarcely sensitive to variations in the use of cement, steel, H2O2, and NaOH as a 50.0% increase in their expenditure increases the CFP in 4.4%, 5.0%, 5.9%, and 7.2%, respectively. A 50.0% increment in electricity consumption increased the CFP in 20.7% whereas categories related to acidification, eutrophication, resources depletion, and toxicity-related impacts had significant increments (20.0%–34.0%) in the emissions of substances used for impact characterization. BOC led to the lowest treatment cost (US$0.540/m3) and a CFP between 5- and 10-times lower than that reported for solar tubular reactors. Also, higher proportions of H2O2 (H2O2/dye = 1.200–1.800) and Fe2+ (Fe2+/dye = 0.200–0.300) increased cost in 1.9%–5.6% but reduced the CFP in 1.2%–3.7%. Finally, our results evidenced that it is possible to increase the raceway reactor's capacity by increasing the depth of the reactor without affecting the effluent quality. When the depth of the reaction medium went from 3 cm to 6 cm, the treatment capacity (TC) was increased 102.4%, and a 33.3% diminution in the CFP and of 29.1% in the treatment cost occurred. An increase from 3 cm to 9 cm rose the TC up to 204.4% and reduced the CFP (44.4%) and treatment cost (39.3%).