Correction: Humic-like substances from urban waste as auxiliaries for photo-Fenton treatment: a fluorescence EEM-PARAFAC study.

Correction for 'Humic-like substances from urban waste as auxiliaries for photo-Fenton treatment: a fluorescence EEM-PARAFAC study' by S. García Ballesteros et al., Photochem. Photobiol. Sci., 2017, 16, 38-45.

Humic-like substances from urban waste as auxiliaries for photo-Fenton treatment: a fluorescence EEM-PARAFAC study.

In this work, analysis of excitation-emission-matrices (EEM) has been employed to gain further insight into the characterization of humic like substances (HLS) obtained from urban wastes (soluble bio-organic substances, SBOs). In particular, complexation of these substances with iron and changes along a photo-Fenton process have been studied. Recorded EEMs were decomposed by using parallel factor analysis (PARAFAC). Three fluorescent components were identified by PARAFAC modeling of the entire set of SBO solutions studied. The EEM peak locations (λex/λem) of these components were 310-330 nm/400-420 nm (C1), 340-360 nm/450-500 nm (C2), and 285 nm/335-380 nm (C3). Slight variations of the maximum position of each component with the solution pH were observed. The interaction of SBO with Fe(iii) was characterized by determining the stability constants of the components with Fe(iii) at different pH values, which were in the order of magnitude of the ones reported for humic substances and reached their highest values at pH = 5. Photochemical experiments employing SBO and Fe(iii), with and without H2O2, showed pH-dependent trends for the evolution of the modeled components, which exhibited a strong correlation with the efficiency reported for the photo-Fenton processes in the presence of SBO at different pH values.

A reliable monitoring of the biocompatibility of an effluent along an oxidative pre-treatment by sequential bioassays and chemical analyses.

A new approach to assess biocompatibility of an effluent, based on combination of different bioassays and chemical analyses, has been tested using a mixture of four commercial pesticides treated by a solar photo-Fenton as target effluent. A very fast elimination of the pesticides occurred (all of them were below detection limit at t30W=36 min), but mineralisation was a more time-consuming process, due to the formation of organic intermediates and to the presence of solvents, as shown by GC-MS analysis. Measurements based on activated sludge indicated that detoxification was coincident with the removal of the active ingredients, while more sensitive Vibrio fischeri bacterium showed significant toxicity until the end of the experiment, although the effluent might be compatible with biological processes. Biodegradability of the solutions was enhanced by the photochemical process, to reach BOD5/COD ratios above 0.8. Longer time bioassays, such as the Zahn-Wellens' test, support the applicability of coupling photochemical with activated sludge-based biological processes to deal with these effluents.

Confirming Pseudomonas putida as a reliable bioassay for demonstrating biocompatibility enhancement by solar photo-oxidative processes of a biorecalcitrant effluent.

Experiments based on Vibrio fischeri, activated sludge and Pseudomonas putida have been employed to check variation in the biocompatibility of an aqueous solution of a commercial pesticide, along solar photo-oxidative process (TiO(2) and Fenton reagent). Activated sludge-based experiments have demonstrated a complete detoxification of the solution, although important toxicity is still detected according to the more sensitive V. fischeri assays. In parallel, the biodegradability of organic matter is strongly enhanced, with BOD(5)/COD ratio above 0.8. Bioassays run with P. putida have given similar trends, remarking the convenience of using P. putida culture as a reliable and reproducible method for assessing both toxicity and biodegradability, as a substitute to other more time consuming methods.

A new methodology to assess the performance of AOPs in complex samples: Application to the degradation of phenolic compounds by O3 and O3/UV-A-Vis.

A methodology combining experimental design methodology, liquid chromatography, excitation emission matrixes (EEM) and bioassays has been applied to study the performance of O3 and O3/UVA-vis in the treatment of a mixture of eight phenolic pollutants. An experimental design methodology based on Doehlert matrixes was employed to determine the effect of pH (between 3 and 12), ozone dosage (02-1.0 g/h) and initial concentration of the pollutants (1-6 mg/L each). The following conclusions were obtained: a) acidic pH and low O3 dosage resulted in an inefficient process, b) increasing pH and O3 amount produced an enhancement of the reaction, and c) interaction of basic pH and high amounts of ozone decreased the efficiency of the process. The combination of O3/UVA-vis was able to enhance ozonation in those experimental regions were this reagent was less efficient, namely low pH and low ozone dosages. The application of EEM-PARAFAC showed four components, corresponding to the parent pollutants and three different groups of reaction product and its evolution with time. Bioassys indicated important detoxification (from 100% to less than 30% after 1 min of treatment with initial pollutant concentration of 6 mg/L, pH = 9 and ozone dosage of 0.8 g/h) according to the studied methods (D. magna and P. subcapitata). Also estrogenic activity and dioxin-like behavior were significantly decreased.

Activated sludge respirometry to assess solar detoxification of a metal finishing effluent.

Inhibition of the respiration of activated sludge has been tested as a convenient method to estimate toxicity of aqueous solutions containing copper and cyanide, such as metal finishing effluents; according to this method, an EC50 of 0.5 mg/l was determined for CN(-) and 3.0 mg/l for copper. Solar detoxification of cyanide-containing solutions was studied using TiO2, but this process was unfavourable because of the inhibitory role that plays the copper ions present in real effluents on the oxidation of cyanide. On the other hand, the oxidative effect of hydrogen peroxide was greatly enhanced by Cu2+ and solar irradiation, as complete elimination of free and complexed cyanide could be accomplished, together with precipitation of copper, in experiments carried out at pilot plant scale with real metal finishing effluents. Under these conditions, total detoxification was achieved according to respirometric measurements although some remaining toxicity was determined by more sensitive Vibrio fischeri luminescent assay.

Direct detection of the triphenylpyrylium-derived short-lived intermediates in the photocatalyzed degradation of acetaminophen, acetamiprid, caffeine and carbamazepine.

Advanced oxidation processes are useful methodologies to accomplish abatement of contaminants; however, elucidation of the reaction mechanisms is hampered by the difficult detection of the short-lived primary key species involved in the photocatalytic processes. Nevertheless, herein the combined use of an organic photocatalyst such as triphenylpyrylium (TPP+) and photophysical techniques based on emission and absorption spectroscopy allowed monitoring the photocatalyst-derived short-lived intermediates. This methodology has been applied to the photocatalyzed degradation of different pollutants, such as acetaminophen, acetamiprid, caffeine and carbamazepine. First, photocatalytic degradation of a mixture of the pollutants showed that acetaminophen was the most easily photodegraded, followed by carbamazepine and caffeine, being the abatement of acetamiprid almost negligible. This process was accompanied by mineralization, as demonstrated by trapping of carbon dioxide using barium hydroxide. Then, emission spectroscopy measurements (steady-state and time-resolved fluorescence) allowed demonstrating quenching of the singlet excited state of TPP+. Laser flash photolysis experiments with absorption detection showed that oxidation of contaminants is accompanied by TPP+ reduction, with formation of a pyranyl radical (TPP), that constituted a fingerprint of the redox nature of the occurring process. The relative amounts of TPP detected was also correlated with the efficiency of the photodegradation process.

Direct detection of the triphenylpyrylium-derived short-lived intermediates in the photocatalyzed degradation of acetaminophen, acetamiprid, caffeine and carbamazepine.

Advanced oxidation processes are useful methodologies to accomplish abatement of contaminants; however, elucidation of the reaction mechanisms is hampered by the difficult detection of the short-lived primary key species involved in the photocatalytic processes. Nevertheless, herein the combined use of an organic photocatalyst such as triphenylpyrylium (TPP+) and photophysical techniques based on emission and absorption spectroscopy allowed monitoring the photocatalyst-derived short-lived intermediates. This methodology has been applied to the photocatalyzed degradation of different pollutants, such as acetaminophen, acetamiprid, caffeine and carbamazepine. First, photocatalytic degradation of a mixture of the pollutants showed that acetaminophen was the most easily photodegraded, followed by carbamazepine and caffeine, being the abatement of acetamiprid almost negligible. This process was accompanied by mineralization, as demonstrated by trapping of carbon dioxide using barium hydroxide. Then, emission spectroscopy measurements (steady-state and time-resolved fluorescence) allowed demonstrating quenching of the singlet excited state of TPP+. Laser flash photolysis experiments with absorption detection showed that oxidation of contaminants is accompanied by TPP+ reduction, with formation of a pyranyl radical (TPP), that constituted a fingerprint of the redox nature of the occurring process. The relative amounts of TPP detected was also correlated with the efficiency of the photodegradation process.

Increased biodegradability of Ultracid in aqueous solutions with solar TiO2 photocatalysis.

A study of solar TiO(2) photocatalytic degradation of the insecticide Ultracidtrade mark, a commercial formulation containing methidathion as the active ingredient, is described. Total elimination of methidathion can be achieved in less than 2h of irradiation, although longer solar exposures are needed for complete mineralisation of the solution (7-8h). Activated sludge respirometry shows that when methidathion is eliminated, the solution is detoxified, so further irradiation does not seem necessary. A Zahn-Wellens test also indicates improved biodegradability of the treated sample after abatement of the active ingredient. Finally, analysis of the ions formed indicates that the thiophosphate moiety of the molecule is preferentially attacked in the early stages of the reaction, while the thiadiazole ring is more sluggish to the effect of TiO(2)-photocatalysis.

Detoxification and/or increase of the biodegradability of aqueous solutions of dimethoate by means of solar photocatalysis.

Different methods have been used to measure changes in biodegradability/toxicity of aqueous solutions of the pesticide Laition (a commercial formula of methidathion) when it is treated by means of TiO(2) photocatalysis: short time biological oxygen demand (BOD(st)) was used to determine the instantaneous biodegradability of the sample; BOD(5) was also chosen to determine biodegradability, employing in this case the manometric method; the BOD(5)/COD ratio was also calculated. Finally, the Zahn-Wellens test was employed to evaluate the long-term biodegradation of the effluents. The inhibition of the respiration of activated sludge in the presence of toxic pollutants was used to test the toxicity of the treated sample. An alternative method based on the decrease of BOD(5) of a very biodegradable mixture (glucose+glutamic acid) upon addition of the toxic solution was also employed. Similar trends were obtained with all methods and allowed us to distinguish between two periods: At the beginning of the reaction, there is a decrease in the concentration of dimethoate to reach complete abatement of this pesticide; this produces a nearly complete detoxification of the solution and a very significant increase of biodegradability (BOD(5)/COD ratio reached values close to 0.5 and important increase of BOD(5) and BOD(st) were observed). Beyond this point, slow mineralization is detected, but further improvement of the biodegradability cannot be achieved.

Treatment and reuse of textile wastewaters by mild solar photo-Fenton in the presence of humic-like substances.

In this paper, the possibility of reusing textile effluents for new dyeing baths has been investigated. For this purpose, different trichromies using Direct Red 80, Direct Blue 106, and Direct Yellow 98 on cotton have been used. Effluents have been treated by means of a photo-Fenton process at pH 5. Addition of humic-like substances isolated form urban wastes is necessary in order to prevent iron deactivation because of the formation of non-active iron hydroxides. Laboratory-scale experiments carried out with synthetic effluents show that comparable results were obtained when using as solvent water treated by photo-Fenton with SBO and fresh deionized water. Experiments were scaled up to pilot plant illuminated under sunlight, using in this case a real textile effluent. Decoloration of the effluent could be achieved after moderate irradiation and cotton dyed with this water presented similar characteristics as when deionized water was used.

Use of ozone and/or UV in the treatment of effluents from board paper industry.

The aim of this work has been to study the viability of ozone and/or UV in the treatment of cardboard industry effluents. Several model compounds have been chosen for the experiments: guaicol, eugenol, glucose, acetate and butyrate. Significant differences in the ozonisation rates are observed between phenolic products coming from lignin (eugenol and guaiacol) and aliphatic compounds. Reactions fit in all cases a pseudo-first order kinetics and are influenced by the pH of the solution. Real effluents have also been tested, and the COD decrease has been found to depend on the fatty acids/phenols ratio. Finally, respirometric studies have shown an increase in the BODst in effluents subjected to a mild oxidation, while under stronger conditions a BODst decrease is observed.

Abatement of the major contaminants present in olive oil industry wastewaters by different oxidation methods: ozone and/or UV radiation versus solar light.

Four different cinnamic acids (caffeic acid, ferulic acid, p-coumaric acid and cinnamic acid) present in olive oil wastewaters, were treated with advanced oxidation methods: ozone and/or UV radiation. Basic and acid media were tested. Differences between all four acids were found, both in the reaction times and the intermediates formed. Based on a careful study of these intermediates and the variation of their concentrations all along the reaction time, a general mechanism for the degradative oxidation of cinnamic acids is proposed. These results are compared with those obtained with solar light, using a pyrylium salt as a catalyst.

Effect of organic species on the solar detoxification of water polluted with pesticides.

The effect of organic species on a solar-driven photo-Fenton treatment of a mixture of pesticides (methyl-oxydemethon, methidathion, carbaryl and dimethoate) has been studied in this paper. Triethoxyisododecyl alcohol, acetophenone and ethylenediaminetetraacetic acid (EDTA) have been used as examples of surfactants, solvents and complexing agents, respectively. An inhibitory effect on mineralization as well as on the elimination of the pesticides was observed in the case of the aliphatic surfactants, most probably due to the competition between the pesticides and the added organic matter for reaction with the relatively unselective hydroxyl radical. A methodology combining chemical analyses and bioassays was tested in order to explore the applicability of coupling a photo-Fenton process with a biological treatment in the presence of the surfactant. Despite the complexity of the mixture under study, a reliable monitoring of the process was accomplished; the biocompatibility of the mixture was enhanced and the optimal irradiation intensity was achieved just after complete removal of the pesticides.

Effect of inorganic ions on the solar detoxification of water polluted with pesticides.

The effect of eleven inorganic ions (Cl(-), NO(3)(-), SO(4)(2-); PO(4)(3-), Na(+); NH(4)(+), Ca(2+), Mg(2+), Zn(2+), Cu(2+) and Al(3+)) on the photo-Fenton elimination of pesticides has been investigated. Phosphate and chloride have been demonstrated to have an inhibitory role; on the other hand, the reaction was accelerated in the presence of Cu(2+), most probably due to a copper-driven Fenton-like process. The solar photo-Fenton treatment of a mixture of four commercial pesticides was studied at pilot plant scale in the presence of chlorides. Samples with coincident dissolved organic carbon (DOC) showed similar chemical composition, which resulted in a comparable biocompatibility, however longer irradiation periods were needed to reach the desired mineralization when Cl(-) was present. It was demonstrated that the chemical process was able to improve significantly the biocompatibility of the effluent, as shown by the inhibition of respiration of activated sludge, BOD/COD ratio and Zahn-Wellens test.