Search

This article describes the photolytic degradation of malachite green (MG), a cationic triphenylmethane dye used worldwide as a fungicide and antiseptic in the aquaculture industry. Photolysis experiments were performed by direct exposure of a solution of MG in water to natural sunlight. The main transformation products (TPs) generated during the process were identified by liquid chromatography time-of-flight mass spectrometry (LC–TOF-MS) and gas chromatography mass spectrometry (GC–MS). The 28 TPs identified with this strategy indicate that MG undergoes three main reactions, N-demethylation, hydroxylation and cleavage of the conjugated structure forming benzophenone derivatives. These processes involve hydroxyl radical attack on the phenyl ring, the N,N-dimethylamine group and the central carbon atom. The Vibrio fischeri acute toxicity test showed that the solution remains toxic after MG has completely disappeared. This toxicity could be assigned, at least in part, to the formation of 4-(dimethylamine)benzophenone, which has an EC50,30min of 0.061mgl−1, and is considered “very toxic to aquatic organisms” by current EU legislation. [Copyright &y& Elsevier]

Abstract: Pilot plant experiments applying solar titanium dioxide photocatalysis and solar photo-Fenton treatment at different pH and iron concentrations with an initial diclofenac concentration of 50mgL−1 are described. In preliminary experiments absence of hydrolysis and slow photolysis under solar irradiation of diclofenac solutions were observed. Solar photo-Fenton treatment with freshly precipitated iron at pH around 7 showed first order kinetics, the reaction taking place on the surface of the iron precipitate. Simultaneous oxidation, precipitation and re-dissolution processes of diclofenac governed photo-Fenton decomposition kinetics at pH 2.8. The use of different iron concentrations (0.03–0.75mM) showed no influence on the reaction rate in a neutral medium due to reactor geometry. Similar behaviour (no influence of iron concentration) was observed at pH 2.8, due to precipitation problems. A pH of around 4, close to the pK a of diclofenac, showed promising results, partly overcoming both iron and diclofenac precipitation. Solar titanium dioxide photocatalysis with Degussa P-25 followed first order kinetics and no precipitation or adsorption occurred. Decomposition of diclofenac took around 100min under all photo-Fenton treatment conditions employed. Decomposition by titanium dioxide photocatalysis took about 200min. In photo-Fenton treatment, hydrogen peroxide consumption to diclofenac decomposition was about 80–110mM at pH 2.8 and 40mM in the other two treatments (neutral pH and pH=4). [Copyright &y& Elsevier]

Abstract: Aqueous solutions of a mixture of several pesticides (alachlor, atrazine, chlorfenvinphos, diuron and isoproturon), considered PS (priority substances) by the European Commission, and an intermediate product of the pharmaceutical industry (α-methylphenylglycine, MPG) chosen as a model industrial pollutant, have been degraded at pilot-plant scale using ozonation. This study is part of a large research project [CADOX Project, A Coupled Advanced Oxidation-Biological Process for Recycling of Industrial Wastewater Containing Persistent Organic Contaminants, Contract No.: EVK1-CT-2002-00122, European Commission, http://www.psa.es/webeng/projects/cadox/index.html] founded by the European Union that inquires into the potential coupling between chemical and biological oxidations for the removal of toxic or non-biodegradable contaminants from water. The evolution of pollutant concentration, TOC mineralization, generation of inorganic species and consumption of O3 have been followed in order to visualize the chemical treatment effectiveness. Although complete mineralization is hard to accomplish, and large amounts of the oxidant are required to lower the organic content of the solutions, the possibility of ozonation cannot be ruled out if partial degradation is the final goal wanted. In this sense, Zahn–Wellens biodegradability tests of the ozonated MPG solutions have been performed, and the possibility of a further coupling with a secondary biological treatment for complete organic removal is envisaged. [Copyright &y& Elsevier]

To run the photo-Fenton process at circumneutral pH as a tertiary wastewater treatment, the use of chelating agents, such as ethylenediamine disuccinic acid (EDDS), has been proposed. For the design and optimization of photocatalytic reactors, the concept of volumetric rate of photon absorption (VRPA) is very useful, since it combines the effects of light absorption and reactor geometry. This research is focused on the study of the effect of VRPA of the Fe 3+ -EDDS complex on the kinetics of micropollutant removal by solar photo-Fenton at neutral pH. To this end, experiments were carried out at different values of VRPA, from 383 to 1933 µE m −3 s −1 , using the pesticide acetamiprid (ACTM) as a model pollutant at an initial concentration of 100 µg L −1 . Despite instability of the complex with light, high removal percentages were achieved for short reaction times with 0.1 mM Fe 3+ -EDDS. Due to the higher absorptivity of the complexed iron, the process became photosaturated at higher values of VRPA than those reported at pH 2.8 for Fe 3+ allowing to work under photolimitation conditions at shorter optical path lengths than at acidic pH. The higher absorptivity of the complexed iron at neutral pH than Fe 3+ at pH 2.8 allowed to work under photolimitation conditions at shorter optical path lengths because the process became photosaturated at higher values of VRPA. Nonetheless, a 50% increase in the treatment capacity was achieved by increasing the liquid depth by three times. As far as the authors know, this is the first work that quantitatively describes the effect of the radiation and the optical path length on micropollutant removal with Fe 3+ -EDDS. [ABSTRACT FROM AUTHOR]

Abstract: The solar light photocatalytic degradation of ethidium bromide (EtBr) in aqueous suspensions has been analyzed over titania-based catalysts. A nanosized titania and an iron-doped TiO2 (with ≈2wt.% of iron content), synthesized within reverse microemulsions, were compared with a commercial Degussa P-25 titania. Structural and/or light handling properties of a different nature arise upon doping the titania with iron. These include favoring a titania crystal phase transformation from anatase to rutile and lowering the band gap energy. Almost total degradation of EtBr upon solar light assisted photodestruction and with significant total organic carbon (TOC) removal can be achieved over the three studied catalysts although the highest mineralization activity is achieved over the P25 titania sample. The results evidence that heterogeneous photocatalysis can be a promising advanced oxidation process to treat diluted EtBr residues typically generated in biomedical and biomolecular laboratories. [Copyright &y& Elsevier]

Abstract: A coupled solar photocatalytic-biological pilot plant system has been employed to enhance the biodegradability and complete mineralization of a biorecalcitrant industrial compound, α-methylphenylglycine, dissolved in distilled water and simulated seawater at 500mgL−1. The pollutant was completely degraded by a solar photo-Fenton treatment in a 75-L pilot plant made up of four compound parabolic collector (CPC) units. The catalyst concentration employed was 2 and 20mgL−1 of Fe2+ and the H2O2 concentration was kept in the range of 200–500mgL−1. A Zahn–Wellens (Z–W) test applied to photo-treated samples demonstrated that intermediates produced within a short time of starting the photo-Fenton process were biodegradable. Consequently, the photocatalytic and biological processes were combined. Biodegradable compounds generated during the preliminary oxidative process were biologically mineralized in a 170-L aerobic immobilised biomass reactor (IBR), filled with 90–95L propylene Pall® Ring supports colonized by activated sludge. Almost total mineralization (90% overall total organic carbon removed) was attained in the combined treatment system (for both distilled and seawater experiments). Moreover, nitrification and denitrification phenomena were also observed. [Copyright &y& Elsevier]

Abstract: The technical feasibility and performance of photocatalytic degradation of six water-soluble pesticides (cymoxanil, methomyl, oxamyl, dimethoate, pyrimethanil and telone) have been studied at pilot-plant scale in two well-defined systems which are of special interest because natural solar UV light can be used: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. TiO2 photocatalysis tests were performed in a 35L solar pilot plant with three Compound Parabolic Collectors (CPCs) under natural illumination and a 75L solar pilot plant with four CPC units was used for homogeneous photocatalysis tests. The initial pesticide concentration studied was 50mgL−1 and the catalyst concentrations employed were 200mgL−1 of TiO2 and 20mgL−1 of iron. Both toxicity (Vibrio fischeri, Biofix®) and biodegradability (Zahn–Wellens test) of the initial pesticide solutions were also measured. Total disappearance of the parent compounds and nearly complete mineralization were attained with all pesticides tested. Treatment time, hydrogen peroxide consumption and release of heteroatoms are discussed. [Copyright &y& Elsevier]