How does intensification influence the operational and environmental performance of photo-Fenton processes at acidic and circumneutral pH.

This study evaluates the technical, economical, and environmental impact of sodium persulfate (Na2S2O8) as an enhancing agent in a photo-Fenton process within a solar-pond type reactor (SPR). Photo-Fenton (PF) and photo-Fenton intensified with the addition of persulfate (PFPS) processes decolorize 97% the azo dye direct blue 71 (DB71) and allow producing a highly biodegradable effluent. Intensification with persulfate allowed reducing treatment time in 33% (from 120 to 80 min) and the consumption of chemical auxiliaries needed for pH adjustment. Energy, reagents, and chemical auxiliaries are still and environmental hotspot for PF and PFPS; however, it is worth mentioning that their environmental footprint is lower than that observed for compound parabolic concentrator (CPC)-type reactors. A life-cycle assessment (LCA) confirms that H2O2, NaOH, and energy consumption are the variables with the highest impact from an environmental standpoint. The use of persulfate reduced the relative impact in 1.2 to 12% in 12 of the 18 environmental categories studied using the ReCiPe method. The PFPS process emits 1.23 kg CO2 (CO2-Eqv/m3 treated water). On the other hand, the PF process emits 1.28 kg CO2 (CO2-Eqv/m3 treated water). Process intensification, chemometric techniques, and the use of SPRs minimize the impact of some barriers (reagent and energy consumption, technical complexity of reactors, pressure drops, dirt on the reflecting surfaces, fragility of reactor materials), limiting the application of advanced oxidation systems at an industrial level, and decrease treatment cost as well as potential environmental impacts associated with energy and reagents consumption. Treatment costs for PF processes (US$0.78/m3) and PFPS processes (US$0.63/m3) were 20 times lower than those reported for photo-Fenton processes in CPC-type reactors.

Treatment of synthetic dye baths by Fenton processes: evaluation of their environmental footprint through life cycle assessment.

Inorganic and organic constituents present in textile effluents have a noticeable effect on the performance of Fenton processes. However, studies have been focused on simple wastewater matrices that do not offer enough information to stakeholders to evaluate their real potential in large-scale facilities. Chemical auxiliaries, commonly present in textile wastewaters (NaCl = 30 g/L, Na2CO3 = 5 g/L, and CH3COONa = 1 g/L), affect both the economic and environmental performance of the process because they increase the treatment time (from 0.5 to 24 h) and the consumption of H2SO4 (657%) and NaOH (148%) during conditioning steps. The life cycle assessment (LCA) performed with the IPCC-2013 method revealed that dyeing auxiliaries increase from 1.06 to 3.73 (252%) the emissions of carbon dioxide equivalent (CO2-Eqv/m3). Electricity consumption can be considered an environmental hotspot because it represents 60% of the carbon footprint of the Fenton process. Also, the presence of auxiliaries is critical for the process because it results in the increase of the relative impact (between 50 and 80%) in all environmental categories considered by the ReCiPe-2008 method. Chemical auxiliaries increased the costs of the treatment process in 178% (US$2.22/m3) due to the higher energy consumption and the additional reagent requirements. It is worthwhile mentioning that the technical simplicity of the Fenton process and its low economic and environmental costs turn this process into an attractive alternative for the treatment of textile effluents in emerging economies.