Alachlor dechlorination prior to an electro-Fenton process: Influence on the biodegradability of the treated solution

Abstract

This study investigates alachlor herbicide removal by electro-Fenton (EF) process with and without a previous dechlorination step by electro-reduction (ER-EF). The objective is to evaluate the relevance of dechlorination before electro-Fenton according to the biodegradability evolution and the energy consumption. The influence of the applied current, the ferrous ions concentration and the air flow rate on the production of hydrogen peroxide and on the general behavior of alachlor removal by EF oxidation was studied and optimized EF conditions were chosen. Scavenger tests were performed to determine the contribution of hydroxyl radicals (•OH), superoxide radicals (•O2 -) and sulfate radicals ( • SO4 -) during alachlor degradation. Some intermediate products formed during degradation by EF of alachlor and of the electroreduced solution were identified and the evolution of small organic acids was examined. Possible pathways of alachlor degradation and of deschloroalachlor, the mean byproduct from ER, were proposed on the basis of the EF reaction. EF treatment significantly improved the biodegradability of electrolyzed solutions with BOD5/COD ratio increasing from 0 to 0.4 after 0.5 h oxidation and can be further enhanced by the application of ER prior to EF, leading to a maximum value for the BOD5/COD ratio of 0.7 that can be due to the absence of chloroacetic acid found during the EF treatment. The energy consumption of the different electrochemical processes was also evaluated.

Electrochemical Processes Coupled to a Biological Treatment for the Removal of Iodinated X-ray Contrast Media Compounds

“…However, refractory organic carbon (around 42%) still remained even after 21 days of activated sludge culture. The amido groups on the side chain of the benzene ring may be responsible of the persistence of the by-products, as previously observed with other pollutants (Lou et al, 2020).…”

“…After the electrochemical treatment of diatrizoate, the biodegradability was evaluated considering the BOD 5 /COD ratio. Indeed, a solution is considered as biodegradable when this ratio is higher than 0.4 (Lou et al, 2020 ). After electroreduction, the BOD 5 /COD ratio was enhanced from 0.16 ± 0.02 to 0.48 ± 0.11 ( Figure 9 ), which was just above the threshold level of biodegradability.…”

“…Among them, electroreduction reaction can be considered as a green technique to treat pollutants since the addition of a chemical reducing agent is not required. It is also known as an economic and effective method due to its high selectivity for dehalogenation of organic halide pollutants (Fontmorin et al, 2014a ; He et al, 2016 , 2017 , 2018 ; Verlato et al, 2016 ; Lou et al, 2019 , 2020 ), allowing the recovery of iodide ions. Thus, the reductive deiodination of ICM has been applied for the removal of iopamidol with the aim to form controlled intermediates (Yan et al, 2018 ).…”

Metallic nanoparticles for electrocatalytic reduction of halogenated organic compounds: A review

“…Among them, photocatalytic oxidation [3], Fenton oxidation [4], sonoelectrochemical treatments [5] and electrooxidation [6,7] have been throughly studied in the past, showing promising results for the degradation of POPs in both synthetic and real effluents. Despite the very strong oxidative power of hydroxyl radicals (E 0 (•OH/H 2 O) = 2.80 V vs SHE [8]), the complete mineralization of the effluent can be challenging to achieve due to the formation of more resistant by-products, therefore significantly increasing the time and cost of treatment [9]. In order to limit the cost of these technologies and make them more energy-efficient, AOPs and more generally physicochemical processes can be coupled with more classical biological processes [9,10].…”

“…Despite the very strong oxidative power of hydroxyl radicals (E 0 (•OH/H 2 O) = 2.80 V vs SHE [8]), the complete mineralization of the effluent can be challenging to achieve due to the formation of more resistant by-products, therefore significantly increasing the time and cost of treatment [9]. In order to limit the cost of these technologies and make them more energy-efficient, AOPs and more generally physicochemical processes can be coupled with more classical biological processes [9,10]. Depending on the nature of the effluent (load in chemical oxygen demand, toxicity, etc.…”