Cesar Pulgarin

Photocatalytical inactivation of E. coli: effect of (continuous–intermittent) light intensity and of (suspended–fixed) TiO2 concentration

A detrimental effect on the survival of bacteria Escherichia coli KI2 was observed after photocatalytic exposure. The reactions have been carried out in a batch photoreactor using mainly titanium dioxide (TiO2) P-25 Degussa as a catalyst. Illumination was produced by a Hanau Suntest lamp. Some parameters, such as light intensity, extend of continuous irradiation, catalyst concentration and temperature have a positive effect on disinfection. Intermittent illumination results in an increase in the time required for E. coli inactivation. No bacterial growth was observed after illumination of a contaminated TiO2 suspension. In contrast, without catalyst, illuminated bacteria recovered its initial concentration after 3 h in the dark. Bacterial inactivation in the absence of catalyst was more affected than that with catalyst when increasing light intensity from 400 to 1000 W/m(2). TiO2 concentrations higher than 1 g/l do not significantly increase the initial inactivation rate for both intensities. However, at 1000W/m(2) a modification of TiO2 concentration ranging between 0.25 and 1.5g/l did not affect the total inactivation time, as with 400 W/m(2). Water turbidity negatively affects the photocatalytic inactivation of bacteria. TiO2 immobilized on Nafion((R)) membranes inactivates E. coli with efficiencies close to those observed for bacterial suspension containing the same concentration of suspended TiO2. For fixed TiO2 on glass, the dose (W min/m(2)) necessary for the total inactivation decreases by increasing the fixed TiO2 amount. Fixed TiO2 P-25 was more active to photocatalytic inactivation when compared with immobilized rutile and anatase. However fixed rutile enhances E. coli inactivation as anatase. The effect of temperature and turbidity were made using wastewater sample

Antibacterial textiles prepared by RF-plasma and vacuum-UV mediated deposition of silver

The bacterial inactivation efficiencies of silver metal and oxides and their combinations on textile fabrics was investigated to evaluate the disinfectant action on airborne bacteria. The inactivation performance was seen to depend on the amount of silver on the textile surface. The preparation of the polyester-polyamide Ag-loaded textiles was carried out by RF-plasma and vacuum-UV (V-UV) surface activation followed by chemical reduction of silver salts. The rate of bacterial inactivation by the silver loaded textile was tested on Escherichia coli K-12 and showed long lasting residual effect. Specular reflectance has been employed to assess the optical properties of the Ag-loaded fabrics. By elemental analysis it was found that levels of Ag loading >0.118% (w/w) for the vacuum-UV samples lead to complete inhibition of bacterial growth. X-ray photoelectron spectroscopy (XPS) shows that for textiles activated by RF or V-UV methods, the silver in the topmost layer increases with increasing concentration of the Ag used in the precursor solution. The exact determination of the oxidation state of the Ag-clusters on the textile is difficult because of the variation of particle size and electrostatic charging of the supported particles. Ag metal was found to be the main component of the Ag-clusters and not Ag2O and AgO as identified by the binding peak energies (BE). By transmission electron spectroscopy (TEM) it was seen that the Ag-clusters were deposited on the two polymer components of the textile fabric but having widely different sizes

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.

Degradation of 32 emergent contaminants by UV and neutral photo-fenton in domestic wastewater effluent previously treated by activated sludge

This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L(-1), and a real global quantity of micropollutants of 29.5 μg L(-1). The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV(254)) alone, dark Fenton (Fe(2+,3+)/H(2)O(2)) and photo-Fenton (Fe(2+,3+)/H(2)O(2)/light). Different irradiation sources were used for the photo-Fenton experiences: UV(254) and simulated sunlight. Iron and H(2)O(2) concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV(254), 50 mg L(-1) of H(2)O(2), with and without adding iron (5 mg L(-1) of Fe(2+) added or 1.48 mg L(-1) of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treatments. As the H(2)O(2) concentration increased (10, 25 and 50 mg L(-1)), best degradations were observed. UV(254), Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal. The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations.

Ultrasonic treatment of water contaminated with ibuprofen

The application of ultrasound (US) waves for remediation of wastewater is an area of increasing interest and promising results. The aim of this paper is to evaluate the influence of several parameters of the US process on the degradation of ibuprofen (IBP), a widely used non-steroidal anti-inflammatory recalcitrant drug found in water. Applied US power, dissolved gas, pH and initial concentration of IBP were the parameters investigated under sonication (300 kHz). Ultrasound increased the degradation of IBP from 30 to 98% in 30 min. Initial rate of IBP degradation was evaluated in the range of 1.35 and 6.1 micromolL(-1)min(-1) for initial concentrations of 2 to 21 mgL(-1) or 9.7 micromolL(-1) to 101 micromolL(-1), respectively. Under air and oxygen the degradation rate of IBP was 4 micromolL(-1)min(-1) being higher than that when argon was used. The most favorable degradation pH was acidic media. Complete removal of IBP was achieved but some dissolved organic carbon (DOC) remained in solution showing that long-lived intermediates were recalcitrant to the US irradiation. However, chemical and biological oxygen demands (COD and BOD(5)) indicated that the process oxidize the ibuprofen compound to biodegradable substances removable in a subsequent biological step.

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.

Relationships between physicochemical properties and photoreactivity of four biorecalcitrant phenylurea herbicides in aqueous TiO2 suspension

Abstract The degradation of metobromuron (MB), isoproturon (IP), chlortoluron (CT), and chlorbromuron (CB) in heterogeneous photocatalytic solution via TiO2 was studied in detail. The influence of parameters such as TiO2 and herbicide concentration has been investigated and the optimal conditions for the abatement of the herbicides were found. The primary degradation of the herbicides was measured by HPLC analysis. A systematic study of their photodegradation has been made to assess structure–photoreactivity relationships. Correlation analysis showed that photoreactivity is associated with the molecular dipolar moment dependent on the differences in electronegativity of the substituents in the aromatic ring of each herbicide. The effect of the molecular charge distribution encoded in the dipolar moment was confirmed calculating electrostatic potential contour maps. It was also found that photoreactivity is inverse to the adsorption capability of these compounds on TiO2. Indeed, as confirmed in this paper, the extent of adsorption is not necessarily decisive in the evolution of the photochemical process and the photocatalytic reactions can occur independently of the degree of adsorption of the herbicides on TiO2.

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

Photo-Fenton treatment of a biorecalcitrant wastewater generated in textile activities: biodegradability of the photo-treated solution

Photo-Fenton process was explored as photochemical pre-treatment to improve the biodegradability of a wastewater coming from a textile industry located in the south of France, which was characterized as very biorecalcitrant by means of Zahn–Wellens biodegradability test. The effect of H2O2, Fe(III) and temperature on the photo-mineralization processes have been studied and the optimal conditions were found. Experiments were made to obtain information concerning the evolution of the biodegradability of the treated effluent after 40 and 70% of photo-mineralization. The photo-treated effluent is not biocompatible and its complete mineralization cannot be performed by biological means. UV–VIS and high-performance liquid chromatography (HPLC) analyses show that aromatic intermediates remain in the effluent after the photo-treatment, which have been identified as the principal reason of the biorecalcitrance.