Solar photoelectro-Fenton treatment of a mixture of parabens spiked into secondary treated wastewater effluent at low input current

Abstract

Aqueous mixtures of methyl, ethyl and propyl paraben (MeP, EtP and PrP) prepared in real urban wastewater with low conductivity were treated by solar photoelectro-Fenton (SPEF) process at low input current (j = 10 mA cm -2 ) using a pre-pilot plant with an electrochemical reactor equipped with an air-diffusion cathode to electrogenerate H2O2 and a boron-doped diamond (BDD) or RuO2-based anode. Comparative trials in simulated water matrices with or without Cl − in the absence of natural organic matter (NOM) always led to a slower decay of parabens concentration and total organic carbon (TOC). This was mainly due to the superior regeneration of Fe 2+ from photoreduction of Fe(III) complexes formed with NOM in real wastewater compared to that from Fe(OH) 2+ . In all matrices, a catalyst concentration as low as 0.20 mM Fe 2+ was enough to ensure the production of • OH in the bulk from Fenton's reaction. SPEF with BDD yielded a complete removal of parabens in 180 min and 66% mineralization at 240 min. This gave rise to the greatest mineralization current efficiencies reported so far, up to 1000%, with a low energy consumption of 84 kWh (kg TOC) -1 . The synergy between homogeneous and heterogeneous catalysis, which allowed the efficient dosage of • OH and M( • OH) at low j, with simultaneous action of high UV power from sunlight justified such a good performance. Analogous apparent rate constants were determined for MeP, EtP and PrP. Slower decays were found with RuO2-based anode due to its lower oxidation power. As a result, the MCE was 425% as maximum, but a lower energy consumption of 52 kWh (kg TOC) -1 was needed. Since the role of active chlorine was of minor importance, the formation of toxic, refractory chloroderivatives was minimized. All byproducts were transformed into malic, formic and oxalic acids prior to total mineralization.

A Boron‐Doped Diamond Anode for the Electrochemical Removal of Parabens in Low‐Conductive Solution: From a Conventional Flow Cell to a Solid Polymer Electrolyte System

“…This means a relevant increase of energy consumptions, with more than 60 kWh m −3 to remove 90 % of initial COD (inset Figure ), while for the SPE‐based system were sufficient 16.25 kWh m −3 . This can be also attributed to the parabens chain (methyl, ethyl and propyl) and to more complex intermediates that required a longer time to be completely oxidized, as reported in literature …”

“…In fact, a bigger size molecule (PrPa>EtPa>MePa) leads to a removal decrease caused by a slower diffusion as reported also by Steter et al. . Nevertheless, the time required for parabens removal with SPE‐system remains lower than those required by CONV‐system to reach the same performance.…”

“…The apparent rate constants gradually increased, from 0.014 min −1 to 0.027 min −1 for CONV‐system and from 0.020 min −1 to 0.036 min −1 for SPE‐system, confirming that MePa oxidation is limited by mass transfer transport for both the systems. Values obtained in this work are in accordance with other works dealing with EAOPs for removal of parabens, confirming that SPE‐system does not hinder the oxidation of organic matter.…”

Heterogeneous catalytic degradation of methylparaben using persulfate activated by natural magnetite; optimization and modeling by response surface methodology

“…In contrast to SO 4 •− radicals, hydroxyl radicals are non‐selective and can react with the aromatic ring in the aqueous solution via either hydrogen abstraction route or addition reaction . The observed by‐products can be further degraded into lower‐molecular‐weight molecules such as oxalic, malic and formic acids and finally mineralized to H 2 O and CO 2 through continuous attack of SO 4 •− and • OH radicals …”

“…69 The observed by-products can be further degraded into lower-molecular-weight molecules such as oxalic, malic and formic acids and finally mineralized to H 2 O and CO 2 through continuous attack of SO 4 •− and • OH radicals. 31,54,70 Reusability, mineralization and stability degree studies In this study, the reusability of the magnetite and its capability for mineralization of MeP in the SPS/NM-SCM system were evaluated for five successive cycles under optimized conditions. It should be pointed out that both the degradation and mineralization of organic pollutants by SO 4 •− systems are favored under acidic conditions.…”