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

Abstract

This study evaluates the technical, economical, and environmental impact of sodium persulfate (NaSO) 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 HO, 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 CO (CO-Eqv/m treated water). On the other hand, the PF process emits 1.28 kg CO (CO-Eqv/m 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/m) and PFPS processes (US$0.63/m) were 20 times lower than those reported for photo-Fenton processes in CPC-type reactors.

Enhanced Degradation of Phenol by a Fenton-Like System (Fe/EDTA/H2O2) at Circumneutral pH

“…Many studies have been devoted to applying modifications in order to circumvent the drawbacks associated with conventional Fenton and Fenton-like processes. Among many others, use of different sources of oxyradicals, photo irradiation, ultrasound, and electrochemical methods have been tested for their intensified performance [16][17][18][19]. In this sense, addition of chelating agents in the reaction system could prevent precipitation of iron in the solution at higher pH (6.0-7.0) by forming stable chelates with iron ions and promoting its availability for hydroxyl radical generation from peroxide in a wider pH range [13].…”

Catalytic Oxidation Process for the Degradation of Synthetic Dyes: An Overview

“…During our research on the catalytic decomposition of H 2 O 2 using Pd or Pt-coated tubular reactors, we found that the catalytic conversion of H 2 O 2 to hydroxyl radicals increased with increasing pH using oxidized Pd-coated tubular reactors at room temperature [191,222]. The optimized range of pH was described as 6–9.…”

“…It is reported in many research papers that an increase in operational temperature could be beneficial for both the oxidation rate and the extent of the catalytic decomposition of synthetic dyes [218,222], whereas very limited research has been conducted to evaluate the influence of experimental temperature conditions on the performance of the catalyst for the decomposition of synthetic dyes. Mostly, Fenton-based methods have been carried out at room temperature [223].…”