Florence Fourcade

Relevance of an electrochemical process prior to a biological treatment for the removal of an organophosphorous pesticide, phosmet.

The aim of this study was to examine the feasibility of coupling an electrochemical pre-treatment with a biological step in order to degrade phosmet, an organophosphorous pesticide. Preliminary biodegradation experiments showed that the target molecule was not assimilated by activated sludge. The pre-treatment consisted of potentiostatic electrolysis (-1.3 V/SCE) in a flow cell. After only one pass (1 mL min(-1)), cyclic voltammetry with a vitreous carbon electrode showed a total phosmet reduction in neutral medium confirmed by thin layer chromatography, which also highlighted the presence of several by-products. H NMR spectra of the main by-product showed the absence of the aromatic ring, only the phosphorus part of phosmet has been identified and phosmet-oxon, a very toxic derivative, was not formed. Lower toxicity and higher biodegradability characterized the electrolyzed solution, EC(50) value increased from 7% to 58% and BOD(5) value increased from 4 to 9 mg O(2) L(-1) after electrolysis leading to an increase of the BOD(5) on COD ratio from 0.19 to 0.42 (limit of biodegradability, 0.4). These encouraging results were confirmed during activated sludge culture since an almost total mineralization of the electrolyzed solution was recorded (97%), confirming the feasibility of the proposed coupled process.

Photocatalytic degradation of bezacryl yellow in batch reactors – feasibility of the combination of photocatalysis and a biological treatment

A combined process coupling photocatalysis and a biological treatment was investigated for the removal of Bezacryl yellow (BZY), an industrial-use textile dye. Photocatalytic degradation experiments of BZY were carried out in two stirred reactors, operating in batch mode with internal or external irradiation. Two photocatalysts (TiO2P25 and TiO2PC500) were tested and the dye degradation was studied for different initial pollutant concentrations (10–117 mg L−1). A comparative study showed that the photocatalytic degradation led to the highest degradation and mineralization yields in a stirred reactor with internal irradiation in the presence of the P25 catalyst. Regardless of the photocatalyst, discoloration yields up to 99% were obtained for 10 and 20 mg L−1 dye concentrations in the reactor with internal irradiation. Moreover, the first-order kinetic and Langmuir–Hinshelwood models were examined by using the nonlinear method for different initial concentrations and showed that the two models lead to completely different predicted kinetics suggesting that they were completely different.According to the BOD5/ Chemical oxygen demand (COD) ratio, the non-treated solution (20 mg L−1 of BZY) was estimated as non-biodegradable. After photocatalytic pretreatment of bezacryl solution containing 20 mg/L of initial dye, the biodegradability test showed a BOD5/COD ratio of 0.5, which is above the limit of biodegradability (0.4). These results were promising regarding the feasibility of combining photocatalysis and biological mineralization for the removal of BZY.

Indirect electroreduction as pretreatment to enhance biodegradability of metronidazole.

The removal of metronidazole, a biorecalcitrant antibiotic, by coupling an electrochemical reduction with a biological treatment was examined. Electroreduction was performed in a home-made flow cell at -1.2V/SCE on graphite felt. After only one pass through the cell, analysis of the electrolyzed solution showed a total degradation of metronidazole. The biodegradability estimated from the BOD5/COD ratio increased from 0.07 to 0.2, namely below the value usually considered as the limit of biodegradability (0.4). In order to improve these results, indirect electrolysis of metronidazole was performed with a titanium complex known to reduce selectively nitro compounds into amine. The catalytic activity of the titanium complex towards electroreduction of metronidazole was shown by cyclic voltammetry analyses. Indirect electrolysis led to an improvement of the biodegradability from 0.07 to 0.42. To confirm the interest of indirect electroreduction to improve the electrochemical pretreatment, biological treatment was then carried out on activated sludge after direct and indirect electrolyses; different parameters were followed during the culture such as pH, TOC and metronidazole concentration. Both electrochemical processes led to a more efficient biodegradation of metronidazole compared with the single biological treatment, leading to an overall mineralization yield for the coupling process of 85%.

Integrated Process for Degradation of Amitrole in Wastewaters: Photocatalysis/Biodegradation

Preliminary studies highlight the positive effect of coupling photocatalysis and biological processes for the treatment of biorecalcitrant compounds. Before biological treatment, photocatalysis can be used as a pre-treatment process to increase pesticide biodegradability. Kinetics of amitrole biodegradation during cultures of Pseudomonas fluorescens was examined to ensure that the target compound was biorecalcitrant; its inhibitory effect justified a pre-oxidation. The biodegradation of cyanuric acid, one of the by-products resulting from photocatalyis of amitrole was confirmed. Pseudomonas fluorescens could metabolize this compound as a nitrogen source when a supplementary carbon source was added. The addition of supplementary carbon and nitrogen sources favoured growth and accordingly cyanuric acid degradation. Degradation yields (with TiO2 coated on cellulose fibers, 25 g.m-2) in the range 47% to 55% were obtained after 50h of irradiation for solutions of amitrole in the range concentrations between 70 to 6000 ppm. Between 10% and 34% of amitrole was mineralized to carbon dioxide. The production of ammonium and nitrate ions was negligible. An inhibition of TiO2 active sites was assumed to account for the weak mineralization. Identification of some of the intermediate by-products by LC-MS/MS shows negligible quantity of cyanuric acid. This work demonstrates that the hybrid process photocatalysis/bioremediation is a cost-effective promising solution for the treatment of wastewater containing biorecalcitrant compounds.

Removal of a mixture tetracycline-tylosin from water based on anodic oxidation on a glassy carbon electrode coupled to activated sludge

The purpose of this study was first to examine the electrochemical oxidation of two antibiotics, tetracycline (TC) and tylosin (Tylo), considered separately or in mixture, on a glassy carbon electrode in aqueous solutions; and then to assess the relevance of such electrochemical process as a pre-treatment prior to a biological treatment (activated sludge) for the removal of these antibiotics. The influence of the working potential and the initial concentration of TC and Tylo on the electrochemical pre-treatment process was also investigated. It was noticed that antibiotics degradation was favoured at high potential (2.4 V/ saturated calomel electrode (SCE)), achieving total degradation after 50 min for TC and 40 min for Tylo for 50 mg L−1 initial concentration, with a higher mineralization efficiency in the case of TC. The biological oxygen demand in 5 days (BOD5)/Chemical oxygen demand (COD) ratio increased substantially, from 0.033 to 0.39 and from 0.038 to 0.50 for TC and Tylo, respectively. Regarding the mixture (TC and Tylo), the mineralization yield increased from 10.6% to 30.0% within 60 min of reaction time when the potential increased from 1.5 to 2.4 V/SCE and the BOD5/COD ratio increased substantially from 0.010 initially to 0.29 after 6 h of electrochemical pre-treatment. A biological treatment was, therefore, performed aerobically during 30 days, leading to an overall decrease of 72% of the dissolved organic carbon by means of the combined process.

Substrate and metabolite diffusion within model medium for soft cheese in relation to growth of Penicillium camembertii

Penicillium camembertii was cultivated on a jellified peptone—lactate based medium to simulate the composition of Camembert cheese. Diffusional limitations due to substrate consumption were not involved in the linear growth recorded during culture, while nitrogen (peptone) limitation accounted for growth cessation. Examination of gradients confirmed that medium neutralization was the consequence of lactate consumption and ammonium production. The diffusion of the lactate assimilated from the core to the rind and that of the ammonium produced from the rind to the core was described by means of a diffusion/reaction model involving a partial linking of consumption or production to growth. The model matched experimental data throughout growth.

Integration of photocatalysis and biological treatment for azo dye removal--application to AR183.

The feasibility of coupling photocatalysis with biological treatment to treat effluents containing azo dyes was examined in this work. With this aim, the degradation of Acid Red 183 was investigated. The very low biodegradability of AR183 was confirmed beforehand by measuring the biological oxygen demand (BOD5). Photocatalysis experiments were carried out in a closed‐loop step photoreactor. The reactor walls were covered by TiO2 catalyst coated on non‐woven paper, and the effluent flowed over the photocatalyst as a thin falling film. The removal of the dye was 82.7% after 4 h, and a quasi‐complete decolorization (98.5%) was obtained for 10 h of irradiation (initial concentration 100 mg L−1). The decrease in concentration followed pseudo‐first‐order kinetics, with a constant k of 0.47 h−1. Mineralization and oxidation yields were 80% and 75%, respectively, after 10 h of pretreatment. Therefore, even if target compound oxidation occurs (COD removal), indicating a modification to the chemical structure, the concomitant high mineralization was not in favour of subsequent microbial growth. The BOD5 measurement confirmed the non‐biodegradability of the irradiated solution, which remained toxic since the EC50 decreased from 35 to 3 mg L−1. The proposed integrated process appeared, therefore, to be not relevant for the treatment of AR183. However, this result should be confirmed for other azo dyes.

Removal of herbicidal ionic liquids by electrochemical advanced oxidation processes combined with biological treatment

ABSTRACT Recently a new group of ionic liquids (ILs) with herbicidal properties has been proposed for use in agriculture. Owing to the design of specific physicochemical properties, this group, referred to as herbicidal ionic liquids (HILs), allows for reducing herbicide field doses. Several ILs comprising phenoxy herbicides as anions and quaternary ammonium cations have been synthesized and tested under greenhouse and field conditions. However, since they are to be introduced into the environment, appropriate treatment technologies should be developed in order to ensure their proper removal and avoid possible contamination. In this study, didecyldimethylammonium (4-chloro-2-methylphenoxy) acetate was selected as a model HIL to evaluate the efficiency of a hybrid treatment method. Electrochemical oxidation or electro-Fenton was considered as a pretreatment step, whereas biodegradation was selected as the secondary treatment method. Both processes were carried out in current mode, at 10 mA with carbon felt as working electrode. The efficiency of degradation, oxidation and mineralization was evaluated after 6 h. Both processes decreased the total organic carbon and chemical oxygen demand (COD) values and increased the biochemical oxygen demand (BOD5) on the COD ratio to a value close to 0.4, showing that the electrolyzed solutions can be considered as ‘readily biodegradable.’

Direct and indirect electrochemical reduction prior to a biological treatment for dimetridazole removal

Two different electrochemical reduction processes for the removal of dimetridazole, a nitroimidazole-based antibiotic, were examined in this work. A direct electrochemical reduction was first carried out in a home-made flow cell in acidic medium at potentials chosen to minimize the formation of amino derivatives and then the formation of azo dimer. Analysis of the electrolyzed solution showed a total degradation of dimetridazole and the BOD5/COD ratio increased from 0.13 to 0.24. An indirect electrochemical reduction in the presence of titanocene dichloride ((C5H5)2TiCl2), which is used to reduce selectively nitro compounds, was then investigated to favour the formation of amino compounds over hydroxylamines and then to prevent the formation of azo and azoxy dimers. UPLC-MS/MS analyses showed a higher selectivity towards the formation of the amino compound for indirect electrolyses performed at pH 2. To confirm the effectiveness of the electrochemical reduction, a biological treatment involving activated sludge was then carried out after direct and indirect electrolyses at different pH. The enhancement of the biodegradability was clearly shown since mineralization yields of all electrolyzed solutions increased significantly.

Reactive oxygen and iron species monitoring to investigate the electro-Fenton performances. Impact of the electrochemical process on the biodegradability of metronidazole and its by-products

In this study, the monitoring of reactive oxygen species and the regeneration of the ferrous ions catalyst were performed during electro-Fenton (EF) process to highlight the influence of operating parameters. The removal of metronidazole (MTZ) was implemented in an electrochemical mono-compartment batch reactor under various ranges of current densities, initial MTZ and ferrous ions concentrations, and pH values. It was found that under 0.07 mA cm-2, 0.1 mM of ferrous ions and pH = 3, the efficiency of 100 mg L-1 MTZ degradation and mineralization were 100% within 20 min and 40% within 135 min of electrolysis, respectively. The highest hydrogen peroxide and hydroxyl radical concentrations, 1.4 mM and 2.28 mM respectively, were obtained at 60 min electrolysis at 0.07 mA cm-2. Improvement of the biodegradability was reached from 60 min of electrolysis with a BOD5/COD ratio above 0.4, which was reinforced by a respirometric study, that supports the feasibility of coupling electro-Fenton and biological treatment for the metronidazole removal.