Paul Péringer

Recent developments in the coupling of photoassisted and aerobic biological processes for the treatment of biorecalcitrant compounds

A general strategy to develop combined photochemical and biological system for biorecalcitrant wastewater treatment is proposed. For the development of this strategy, the following points were taken into account: the biodegradability of initial solutions, the operation mode of the coupled reactor, the chemical and biological characteristics of the phototreated solutions, the evaluation of different photoassisted advanced oxidation processes, the optimal conditions of both photochemical and biological processes, and the efficiency of the coupled reactor. The strategy to couple photochemical and biological processes is illustrated by case studies of four different biorecalcitrant pollutants. Three kinds of combined systems were developed using either photo-Fenton, Fe3+/UV, or TiO2 supported on glass rings for the photocatalytic pretreatment and in all cases immobilized biomass for the biological step. The advantages of the each coupled system are discussed and beneficial effects of such two-step treatments were found. However this strategy is not a universal solution. Chemical, biological, and kinetic studies must be always carried out to ensure that the photochemical pretreatment increase the biocompatibility of the treated wastewater. Some field experiments using solar reactor indicated that a coupled photochemical–biological treatment system at pilot scale is a possible way to achieve the complete mineralization of the biorecalcitrant pollutants.

Effect of Fenton and photo-Fenton reactions on the degradation and biodegradability of 2 and 4-nitrophenols in water treatment

Abstract Photo-Fenton, Fenton and biodegradation reactions have been investigated in detail during the degradation of 2 and 4-nitrophenols. Fenton-type reactions accelerated nitrophenols degradation in comparison with direct photolysis using pyrex flasks (λ > 290 nm). The influence of Fe3+, H2O2, light, temperature, reactant concentration and gas atmosphere was systematically studied. Experimental techniques used involved total organic carbon determination (TOC), high pressure liquid chromatography (HPLC), nuclear magnetic resonance (NMR) and spectroscopy (OD). A solution containing 3.6·10−1M of 2-nitrophenol was degraded in ca. 3 h (30°C) in the dark and in ca. 1 h (30°C) under light where continuous photoproduction of the Fenton reagent is achieved. This study shows that the hydrolxylation of the phenol ring is fast as compared to the slower concomitant decrease in DOC in dark or light processes. Using NMR an explanation is proposed in terms of pathways involving direct oxidation of the nitrophenols under study by hydroxy type radicals. Chemical insight is provided why the photo-Fenton degradation observed for 2-nitrophenol proceeds at about half the rate than his homologue 4-nitrophenol. Biodegradability of 2-nitrophenol was monitored before and after photo-Fenton treatment by biochemical oxygen demand (BOD) and dissolved organic carbon (DOC) and indicated the formation of substances which are non-biodegradable during photo-Fenton pretreatment.

Electrochemical detoxification of a 1,4-benzoquinone solution in wastewater treatment

The electro-oxidn. of 1,4-benzoquinone in water soln. was investigated. The benzoquinone concn., intermediate products, dissolved org. C (DOC), COD, and toxicity of the oxidized soln. was monitored during oxidn. with Ti/IrO2 and Ti/SnO2 anodes (in the following text: IrO2 and SnO2 anodes). It was found that the most important parameter is the nature of the anode. With the IrO2 anode, primary oxidn. was attained, i.e. benzene ring rupture occurred, resulting in an accumulation of carboxylic acids formation as final non-toxic products. With the SnO2 anode, carboxylic acids are formed in a much faster reaction and then oxidized, giving only CO2 as the final product. Detoxification of benzoquinone soln. using both electrodes was detd. in the course of the reaction by the Microtox test, activated sludge respirometric test, and were also predicted using a developed formula. Calcd. av. toxicity, knowing the chem. compn. of the oxidized soln., DOC, and individual EC50 of the components were in agreement with obsd. values. The biodegradability of compds. in the soln. at the end of electrolysis with the IrO2 anode was demonstrated. [on SciFinder (R)]

Photochemical versus coupled photochemical-biological flow system for the treatment of two biorecalcitrant herbicides: metobromuron and isoproturon

Reference LBE-ARTICLE-2000-005doi:10.1016/S0926-3373(00)00151-XView record in Web of Science Record created on 2005-03-02, modified on 2016-08-08

Electrochemical degradation of p-substituted phenols of industrial interest on Pt electrodes. Attempt of a structure-reactivity relationship assessment

The electrochemical oxidation of p-substituted phenols, with both electron donor (OH- and NH2-) and electron withdrawing groups (NO2-, COOH-, and halogens), on Pt anodes using sodium sulfate as support electrolyte has been studied. It was found that, except for p-halogen phenols, compounds with electron donor substituents are easier to remove and their initial rates of degradation are correlated to the octanol-water partitioning coefficient (log Poct) and the Hammetts constant. Degradation of all of our starting compounds produced the same intermediates, therefore, a general pathway of reaction is proposed. Additionally, the influence of pH, temperature, electrolyte concentration and current density on the initial and total degradation of p-chlorophenol was also investigated.

Degradation/decoloration of concentrated solutions of Orange II. Kinetics and quantum yield for sunlight induced reactions via Fenton type reagents

Abstract Light and thermal processes involving Fenton reagent are shown to be effective in the mineralization/decoloration of concentrated Orange II solutions. Light activation accelerates the observed degradation and the UV component of natural sunlight is sufficient to promote the reaction leading to the azo-dye abatement. The degradation involves dark and light steps. Kinetic information on these steps is reported. The results obtained in this study suggests that the thermodynamic potential for the redox couple in a Fenton-like reagent is not the most important factor controlling ther degradation of this dye. A quantum yield of 0.10 was observed for Orange II disappearance. Decoloration of a 2.9 mM dye solution (450 mg Cl−1) is achieved in less than 2 h via photo-Fenton reactions and mineralization is completed to 95% in less than 8 h. A turnover number of 4.7 was estimated for light induced processes in the model system used. Cyanuric acid added to the Fenton system suggests that besides the OH radicals, highly stable Fe-complexes in combination with H2O2 are active in the abatement of this azo-dye. Near surface radical formation is shown to be important during the observed photocatalysis. No activation energy was detected during the mineralization suggesting a radical mechanism for this reaction. The quantum yields observed as a function of wavelength during Orange II disappearance corresponds in experimental error to the point-by-point addition of the absorbance of the Fe3+ and H2O2 solutions used in the photolysis.

Degradation of a biorecalcitrant dye precursor present in industrial wastewaters by a new integrated iron(III) photoassisted-biological treatment

This study focuses on the mineralization of 5-amino-6-methyl-2-benzimidazolone (AMBI), an important precursor in the industrial production of dyes, through an integrated Fe(III) photoassisted–biological system without addition of other electron acceptor than O2. The iron photoassisted process produces a biocompatible solution, removing 100% of the initial biorecalcitrant compound and 40% of the Dissolved Organic Carbon (DOC), and then the complete mineralization was achieved in the biological treatment. The transformation of AMBI photoinduced by only Fe(III) is mainly attributed to three simultaneous process: direct photolysis of the [Fe3+–AMBI] complex, the attack of the complex by √OH radicals generated by the photolysis of Fe(OH)2+, and by the attack of supplementary √OH radicals generated by the Fenton and photo-Fenton like reactions, which are induced by the H2O2 that have been formed “in situ”. The following topics are also studied in this paper: (a) the UV-Vis spectroscopic characterization of Fe(III), AMBI, and its mixture in aqueous solution, (b) the involvement of √OH radicals and oxygen in the photodegradation of AMBI, (c) the comparison between O2 and H2O2 as electron acceptors in the iron photoassisted pretreatment, and their performances as a pretreatment step in the coupled photochemical biological reactor. Some field experiments under direct solar radiation were carried out using a compound parabolic collector (CPC) erected at the Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland. The obtained results indicate that a coupled solar–biological treatment system at pilot scale is a possible way to achieve the complete mineralization of biorecalcitrant pollutants.

Beneficial effects of homogeneous photo-Fenton pretreatment upon the biodegradation of anthraquinone sulfonate in waste water treatment

Homogeneous photo-oxidation of anthraquinone-2-sulfonic acid sodium salt (ASS) with H2O2 and Fe3+ was investigated. The continuous photoproduction of Fenton reagent can be achieved in this way. The behaviour of Fe3+ was similar to Fe2+ under the same experimental conditions and the photoactivity was favourably influenced in the presence of oxygen. The photo-Fenton reactions greatly accelerated ASS degradation in comparison with direct photolysis using Pyrex flasks (λ > 290 nm). The influence of Fe3+, Cu2+, H2O2 concentration, pH, temperature and gas atmosphere was systematically studied. A solution containing ASS 3·10−3 M was degraded up to ca. 90% under light (AM 1) at 60°C in 3 h and in ca. 5 h at 35°C. Complete oxidation was achieved after 15 h. About 90% of the total organic carbon was degraded to carbon dioxide when dearomatization was completed. Photo-Fenton systems could be used for initial treatment of waste waters containing ASS to obtain aliphatic and oxidized compounds susceptible to being more easily degraded in biological waste water treatment plants. Reaction products were characterized by total organic carbon (TOC); nuclear magnetic resonance (NMR); gas chromatography (GC) and spectroscopy (OD).

Electrochemical treatment of industrial wastewater containing 5-amino-6-methyl-2-benzimidazolone: toward an electrochemical–biological coupling

We studied the electrochemical oxidation, on Pt anodes, of industrial wastewaters containing 5-amino-6-methyl-2-benzimidazolone (AMBI). Electrolysis of this non-biodegradable effluent produces simultaneous oxidation of AMBI and chloride ions. Highly oxidative chlorine intermediate species further boost the degradation of AMBI. Solution temperature, pH and current density affect little the degradation of AMBI. At our best conditions, AMBI was 100% degraded in 45 min. However, because the reaction intermediates exhibited high toxicity and non-biodegradability, the electrolysis had to continue for 3 more hours in order to obtain a biocompatible solution. Then, complete mineralization of the outputs from the electrolytic cells was readily achieved in a fixed bed biological reactor.

Chemical (photo-activated) coupled biological homogeneous degradation of p-nitro-o-toluene-sulfonic acid in a flow reactor

This study presents the combined photochemical (Fenton) and biological flow reactor degradation of p-nitrotoluene-ortho-sulfonic acid (p-NTS). p-NTS is a compound whose degradation is not possible by waste water bacteria. From this point of view it is considered as a non-biodegradable intermediate found in the manufacture of dyes, surfuctants and brighteners. By way of HPLC technique it is shown that the photochemical pretreatment of p-NTS induces dearomatization due to -OH radical attack. A concomitant 20–25% decrease in the initial carbon content during the photochemical pretreatment was observed along the abatement of the aromaticity. This study shows that the intermediates produced in the pretreatment stage are biodegradable. After pretreatment a minimum residual H2O2 (< 0.2 mg l−1) was attained. This level of oxidant did not interfere with the subsequent biological degradation. The influence of the reaction parameters such as: input concentration of p-NTS, rate of H2O2 addition, reactor flow rate, TOC reduction rate and BOD5/COD as a function of the time of photochemical pretreatment are reported. At a flow rate of 0.18 l h−1 (5.5. h residence time) a photochemical degradation efficiency of 75%, a biological degradation efficiency of 52% and an overall degradation efficiency for the coupled process of 88% was observed. The disappearance of p-NTS in the photochemical reactor, the growth and degradation of the benzoquinone like aromatic intermediate followed by the appearance short chain aliphatic compounds are reported as a function of pretreatment time. The increase in BOD/TOC as function of pretreatment time has been correlated to the p-NTS and aliphatic recalcitrants existing in the solution. The biological degradation was observed to be strongly dependent on the flow used and on the pollutant loading of the solution. These were the two main parameters affecting the degradation in the bioreactor.