Use of vinasse and coffee waste as chelating agent of photo-Fenton landfill leachate treatment.

This research studies the use of vinasse (VS) coming from Pisco and caffeic acid (Caa) from solid coffee waste as chelating agents of this process, to carry out a photo-Fenton process using UVc lamps of 254-nm wavelength for 60 min, at the natural pH of the landfill leachate (8.9). Without the chelating agent, there was a removal of UV 254 and COD of 54.2% and 54.7%, respectively, when the photo-Fenton reaction was carried out at pH 3; at pH 6, the removal of UV 254 and COD was 13.1% and 39.2%, respectively, and at pH 8.9, the elimination of UV 254 and COD was 10.8% and 16.1%, respectively. When Caa was used in the landfill leachate (LL) for the photo-catalytic processes carried out at pH 8.9, a removal of 24.1%, 43.0%, and 47.4% of UV 254 was obtained using 5 mg/L, 50 mg/L, and 100 mg/L of Caa. The removal of UV 254 was 27.3%, 30.7%, and 36.3% using 5 mg/L, 50 mg/L, and 100 mg/L of VS, respectively, and the removal of COD was 32.2%, 35.4%, and 39.2% using 5 mg/L, 50 mg/L, and 100 mg/L of VS, respectively. When Caa was used in the LL at pH 8.9, the concentration of total Fe went from 37.5 to 33.2, from 40.2 to 36.8, and from 45.2 to 42.1, using 5 mg/L, 50 mg/L, and 100 mg/L of caffeic acid, respectively. Using VS in the LL at pH 8.9, the concentration of total Fe along the run went from 35.1 to 32.2, from 39.4 to 34.8, and from 42.1 to 40.2, using 5 mg/L, 50 mg/L, and 100 mg/L of VS, respectively. As a result of these processes, it was noted that the use of Caa and VS increases the solubility of Fe at a higher pH.

Improved landfill leachate quality using ozone, UV solar radiation, hydrogen peroxide, persulfate and adsorption processes.

Advanced oxidation processes based on ozonation, UV solar radiation, hydrogen peroxide, and persulfate were tested for the complete treatment of a specific landfill leachate. As a post-treatment of the advanced oxidation process, an additional adsorption process was carried out using a natural zeolite. Application of the UVsolar/O3/H2O2 process required 140 min of irradiation and the consumption of 0.67 g/L H2O2 to eliminate 56% and 17% of colour and chemical oxygen demand (COD), respectively. When adding persulfate to the system (UVsolar/O3/H2O2/S2O8-2), colour and COD were reduced by 29% and 77%, respectively, with a 0.2 g/L concentration of S2O8-2 requiring 250 min of irradiation time. In an experimental run with landfill leachate, adsorption post-treatment with a natural zeolite resulted in 36%, 99%, and 18% total reductions in COD, ammonium, and chloride, respectively. In another experimental run, adsorption with a zeolite was used as a pre-treatment for the advanced oxidation process (UVsolar/O3/H2O2 and UVsolar/O3/H2O2/S2O8-2). The results were similar to those for adsorption post-treatment, with 30%, 90%, and 20% total reductions in COD, ammonium, and chloride, respectively. Despite improvements, some measured parameters of treated landfill leachate still exceeded Chilean regulations for water quality. Furthermore, Lactuca sativa seeds did not germinate after irrigation with 100% treated landfill leachate or dilutions above 3%. Finally, EC50 values were enhanced during treatment, going from 0.002% for raw landfill leachate to 1.179% after the adsorption process.

Mature landfill leachate treatment by coagulation/flocculation combined with Fenton and solar photo-Fenton processes.

This work reports the treatment of a mature landfill leachate through the application of chemical-based treatment processes in order to achieve the discharge legal limits into natural water courses. Firstly, the effect of coagulation/flocculation with different chemicals was studied, evaluating the role of different initial pH and chemicals concentration. Afterwards, the efficiency of two different advanced oxidation processes for leachate remediation was assessed. Fenton and solar photo-Fenton processes were applied alone and in combination with a coagulation/flocculation pre-treatment. This physicochemical conditioning step, with 2 g L(-1) of FeCl3 · 6H2O at pH 5, allowed removing 63% of COD, 80% of turbidity and 74% of total polyphenols. Combining the coagulation/flocculation pre-treatment with Fenton reagent, it was possible to reach 89% of COD removal in 96 h. Moreover, coagulation/flocculation combined with solar photo-Fenton revealed higher DOC (75%) reductions than single solar photo-Fenton (54%). In the combined treatment (coagulation/flocculation and solar photo-Fenton), it was reached a DOC reduction of 50% after the chemical oxidation, with 110 kJ L(-1) of accumulated UV energy and a H2O2 consumption of 116 mM. Toxicity and biodegradability assays were performed to evaluate possible variations along the oxidation processes. After the combined treatment, the leachate under study presented non-toxicity but biodegradability increased.

Fosetyl-Al photo-Fenton degradation and its endogenous catalyst inhibition.

Interferences from many sources can affect photo-Fenton reaction performance. Among them, catalyst inhibition can be caused by the complexation and/or precipitation of iron species by the organic matter and salts present in the reaction media. This is the case of the oxidation of effluents containing organophosphorous fosetyl-Al. The degradation of this fungicide generates phosphate anions that scavenge iron and hinder Fe(II) availability. Experimental design was applied to artificially enlighten photo-Fenton reaction, in order to evaluate fosetyl-Al degradation. The performed experiments suggested how iron inhibition takes place. The monitoring of photo-Fenton reaction over a mixture of fosetyl-Al with other two pesticides also showed the interferences caused by the presence of the fungicide on other species degradation. Solar empowered photo-Fenton was also essayed for comparison purposes. Artificial and solar light photo-Fenton reactions were revealed as effective treatments for the elimination of tested fungicide. However, the phosphate ions generated during fosetyl oxidation decreased iron availability, what hampered organic matter degradation.

Solar photocatalytic treatment of landfill leachate using a solid mineral by-product as a catalyst.

The treatment of municipal solid waste landfill leachate in a pilot plant made up of solar compound parabolic collectors, using a solid industrial titanium by-product (WTiO(2)) containing TiO(2) and Fe(III) as a photocatalyst, was investigated. In the study evidence was found showing that the degradation performed with WTiO(2) was mainly due to the Fe provided by this by-product, instead of TiO(2). However, although TiO(2) had very little effect by itself, a synergistic effect was observed between Fe and TiO(2). The application of WTiO(2), which produced coupled photo-Fenton and heterogeneous catalysis reactions, achieved a surprisingly high depuration level (86% of COD removal), higher than that reached by photo-Fenton using commercial FeSO(4) (43%) in the same conditions. After the oxidation process the biodegradability and toxicity of the landfill leachate were studied. The results showed that the leachate biodegradability was substantially increased, at least in the first stages of the process, and again that WTiO(2) was more efficient than FeSO(4) in terms of increasing biodegradability.

Tertiary treatment of pulp mill wastewater by solar photo-Fenton.

This work reports on pulp mill wastewater (PMW) tertiary treatment by Fenton (Fe(2+)/H(2)O(2)) and solar photo-Fenton (Fe(2+)/H(2)O(2)/UV) processes in a pilot plant based on compound parabolic collectors (CPCs). Solar photo-Fenton reaction is much more efficient than the respective dark reaction under identical experimental conditions. It leads to DOC mineralisation, COD and total polyphenols (TP) removal higher than 90%. The solar photo-Fenton experiment with 5mg Fe L(-1) reaches 90% of DOC mineralisation with 31kJ L(-1) of UV energy and 50mM of H(2)O(2). The initial non-biodegradability of PMW, as shown by respirometry assays and BOD(5)/COD ratio, can be changed after a solar photo-Fenton treatment. Experiments with 20 and 50mg Fe L(-1) revealed that solar photo-Fenton can reach the same DOC degradation (90%), however, consuming less H(2)O(2) and time. Diluting the initial organic load to 50% also diminishes the dosage of H(2)O(2) and the necessary reaction time to achieve high DOC removals. Accordingly, solar photo-Fenton can be considered an alternative or complementary process to improve the performance of a biologic treatment and, subsequently, achieve legal limits on discharge into natural waters.

Degradation of fifteen emerging contaminants at microg L(-1) initial concentrations by mild solar photo-Fenton in MWTP effluents.

The degradation of 15 emerging contaminants (ECs) at low concentrations in simulated and real effluent of municipal wastewater treatment plant with photo-Fenton at unchanged pH and Fe=5 mg L(-1) in a pilot-scale solar CPC reactor was studied. The degradation of those 15 compounds (Acetaminophen, Antipyrine, Atrazine, Caffeine, Carbamazepine, Diclofenac, Flumequine, Hydroxybiphenyl, Ibuprofen, Isoproturon, Ketorolac, Ofloxacin, Progesterone, Sulfamethoxazole and Triclosan), each with an initial concentration of 100 microg L(-1), was found to depend on the presence of CO(3)(2-) and HCO(3)(-) (hydroxyl radicals scavengers) and on the type of water (simulated water, simulated effluent wastewater and real effluent wastewater), but is relatively independent of pH, the type of acid used for release of hydroxyl radicals scavengers and the initial H(2)O(2) concentration used. Toxicity tests with Vibrio fisheri showed that degradation of the compounds in real effluent wastewater led to toxicity increase.

Solar photochemical treatment of winery wastewater in a CPC reactor.

Degradation of simulated winery wastewater was studied in a pilot-scale compound parabolic collector (CPC) solar reactor. Total organic carbon (TOC) reduction by heterogeneous photocatalysis (TiO(2)) and homogeneous photocatalysis with photo-Fenton was observed. The influence of TiO(2) concentration (200 or 500 mg/L) and also of combining TiO(2) with H(2)O(2) or Na(2)S(2)O(8) on heterogeneous photocatalysis was evaluated. Heterogeneous photocatalysis with TiO(2), TiO(2)/H(2)O(2) and TiO(2)/S(2)O(8)(2-) is revealed to be inefficient in removing TOC, originating TOC degradation of 10%, 11% and 25%, respectively, at best. However, photo-Fenton experiments led to 46% TOC degradation in simulated wastewater prepared with diluted wine (WV) and 93% in wastewater prepared with diluted grape juice (WG), and if ethanol is previously eliminated from mixed wine and grape juice wastewater (WW) by air stripping, it removes 96% of TOC. Furthermore, toxicity decreases during the photo-Fenton reaction very significantly from 48% to 28%. At the same time, total polyphenols decrease 92%, improving wastewater biodegradability.

Solar treatment of cork boiling and bleaching wastewaters in a pilot plant.

This paper reports on cork boiling and bleaching wastewaters treatment by solar photocatalytic processes, TiO(2)/UV and Fe(2+)/H(2)O(2)/UV (TiO(2)-only for bleaching wastewater), in a pilot plant with compound parabolic collectors. The photo-Fenton reaction (k=0.12L/kJ(UV), r(0)=59.4 mg/kJ(UV)) is much more efficient that TiO(2) photocatalysis and TiO(2)+S(2)O(8)(2-) (k=0.0024 L/kJ(UV), r(0)=1.36 mg/kJ(UV)), leading to 94% mineralization of the bleaching wastewater after 31.5 kJ(UV)/L, consuming 77.1mM of H(2)O(2) (3.0 mmol/kJ(UV)) and using 20 mg/L of iron. For the cork boiling wastewater, after a slow initial reaction rate, the DOC degradation curve shows a first-order kinetics behaviour (k=0.015 L/kJ(UV), r(0)=20.8 mg/kJ(UV)) until 173 kJ(UV)/L ( approximately 300 mgC/L). According to the average oxidation state (AOS), toxicity profiles, respirometry and kinetic results obtained in two solar CPCs plants, the optimal energy dose estimated for phototreatment to reach a biodegradable effluent is 15 kJ(UV)/L and 114 kJ(UV)/L, consuming 33 mM and 151 mM of H(2)OT:/PGN/ELSEVIER/WR/web/00007490/(2), achieving almost 49% and 48% mineralization of the wastewaters, respectively for the cork bleaching and boiling wastewaters.

Solar photocatalysis of a recalcitrant coloured effluent from a wastewater treatment plant.

A photocatalytic study of a coloured effluent from a wastewater treatment plant was carried out in a pilot plant using compound parabolic collectors (CPC) in order to find out the best conditions for colour removal, since the discharge limit for this parameter is not achieved after conventional wastewater treatment. The interaction between ultraviolet natural radiation and TiO(2) strongly enhanced the colour degradation rate. Different TiO(2) concentrations were tested and the optimum concentration achieved was 200 mg L(-1). The use of peroxydisulfate (S(2)O(8)(2-)) as an additional electron scavenger gave a noticeable effect on colour and dissolved organic carbon (DOC) removal due to the formation of additional powerful oxidant species (OH and SO(4) (-)). However, hydrogen peroxide (H(2)O(2)) as additional oxidant was more efficient on colour degradation than S(2)O(8)(2-). The amount of energy necessary for the same colour removal (C/C(0) < 0.1) was 6, 14 and 80 kJ(UV) L(-1), respectively, for the following systems using sunlight: 200 mg L(-1) TiO(2) + 5 mM H(2)O(2), 200 mg L(-1) TiO(2) + 2 mM S(2)O(8)(2-) and 200 mg L(-1) TiO(2). The first-order kinetic constants (0.487, 0.207 and 0.053 L kJ(-1)) and initial degradation rates (32.1, 10.0 and 2.2 mg kJ(-1)) showed the same behaviour.

Degradation pathways of the commercial reactive azo dye Procion Red H-E7B under solar-assisted photo-Fenton reaction.

Reactive azo dye Procion Red H-E7B solutions have been submitted to solar-assisted photo-Fenton degradation. The solution color quickly disappears, indicating a fast degradation of the azo group. Nevertheless, complete DOC removal was not accomplished, in accordance with the presence of resistant triazine rings at the end of the reaction. The intermediates generated along the reaction time have been identified and quantified. LC-(ESI)-TOF-MS analysis allowed the detection of 18 aromatic compounds of different size and complexity. Some of them shared the same accurate mass, and consequently, the same empirical formula, but appeared at different chromatographic retention times, evidencing their different molecular structures. Heteroatom oxidation products like NH4+, NO3-, Cl-, and SO4(2-) have also been quantified and explanations of their release are proposed. Short chain carboxylic acids are also detected at long reaction times, as a previous step to complete dye mineralization. A link between the disappearance of the largest intermediate products and the increase of the solutions biodegradability has been established. Finally, taking into account all the findings of the present study and previous related works, the evolution from the original dye to the final products (triazine and CO2) is proposed in a general reaction scheme.

Evaluating Microtox as a tool for biodegradability assessment of partially treated solutions of pesticides using Fe3+ and TiO2 solar photo-assisted processes.

To shorten phototreatment time is of major concern for the cost and energy benefits of the xenobiotics degradation performed by photocatalytic processes. Using photo-Fenton and TiO(2) phototreatments, partially photodegraded solutions of 6 separate pesticides (alachlor, atrazine, chlorfenvinphos, diuron, isoproturon and pentachlorophenol) were tested for biocompatibility, which was evaluated according to the Zahn-Wellens procedure. This study investigated if Microtox could be considered as a suitable global indicator capable of giving information on the evolution of biocompatibility of the water solution contaminated with organic pollutants during the phototreatment in order to promote biotreatment. The obtained results demonstrated that biodegradability increased significantly after short photo-Fenton treatment times for alachlor, diuron and pentachlorophenol. Uncertain results were obtained with atrazine and isoproturon. Microtox acute toxicity testing was shown to correctly represent dynamics and efficiency of phototreatment.

Coupling solar photo-Fenton and biotreatment at industrial scale: main results of a demonstration plant.

This paper reports on the combined solar photo-Fenton/biological treatment of an industrial effluent (initial total organic carbon, TOC, around 500mgL(-1)) containing a non-biodegradable organic substance (alpha-methylphenylglycine at 500mgL(-1)), focusing on pilot plant tests performed for design of an industrial plant, the design itself and the plant layout. Pilot plant tests have demonstrated that biodegradability enhancement is closely related to disappearance of the parent compound, for which a certain illumination time and hydrogen peroxide consumption are required, working at pH 2.8 and adding Fe(2+)=20mgL(-1). Based on pilot plant results, an industrial plant with 100m(2) of CPC collectors for a 250L/h treatment capacity has been designed. The solar system discharges the wastewater (WW) pre-treated by photo-Fenton into a biotreatment based on an immobilized biomass reactor. First, results of the industrial plant are also presented, demonstrating that it is able to treat up to 500Lh(-1) at an average solar ultraviolet radiation of 22.9Wm(-2), under the same conditions (pH, hydrogen peroxide consumption) tested in the pilot plant.

Photocatalytic properties of nano-structured TiO2-carbon films obtained by means of electrophoretic deposition.

Recent studies have shown that the light-absorption and photocatalytic efficiencies of TiO2 can be improved by coupling TiO2 nano-particles with nonmetallic dopants, such as carbon. In this paper, we describe the electrophoretic preparation of a novel TiO2-carbon nano-composite photocatalyst on a glass indium thin oxide (ITO) substrate. The objective is to take better advantage of the (e-/h+) pair generated by photoexcitation of semiconducting TiO2 particles. The transfer of electrons (e-) into adjacent carbon nano-particles promotes reduction of oxygen to produce hydrogen peroxide (H2O2) which, in the presence of iron ions, can subsequently form hydroxyl radicals (*OH) via the Fenton reaction. At the same time, *OH is formed from water by the (h+) holes in the TiO2. Thus, the *OH oxidant is produced by two routes. The efficiency of this photolytic-Fenton process was tested with a model organic compound, Orange-II (OG-II) azo dye, which is employed in the textile industry.

In situ electrochemical and photo-electrochemical generation of the fenton reagent: a potentially important new water treatment technology.

In this work, the design and construction of an annular tube reactor for the electrochemical and photo-electrochemical in situ generation of H2O2 are described. By cathodic reduction of dissolved oxygen and the coupled oxidation of water at a UV-illuminated nanocrystalline-TiO2 semiconductor anode, it was found that the electrochemically generated H2O2 can be employed to readily oxidize the model compound Direct Yellow-52 in dilute acidic solution at high rates in the presence of small quantities of dissolved iron(II). Although, the model organic compound is chemically stable under UV radiation, its electrochemical oxidation rate increases substantially when the semiconductor anode is illuminated as compared to the same processes carried out in the dark.

Enhancing biodegradability of priority substances (pesticides) by solar photo-Fenton.

In this paper, we present the photo-Fenton treatment in a solar pilot-plant scale of several EU priority hazardous substances (Alachlor, Atrazine, Chlorfenvinphos, Diuron and Isoproturon) dissolved in water. The results have been evaluated not only from the point of view of contaminant disappearance and mineralisation, but also of toxicity reduction and enhancement of biodegradability. Degradation was monitored by total organic carbon, pesticide concentration by HPLC-UV, inorganics released by ion chromatography, and biodegradability by the Zahn-Wellens (Z-W) test. The total volume of the solar photoreactor, composed of compound parabolic collectors with a total area of 4.16m2, was between 70 and 82 L. The treatment was shown to be effective, mineralising all of the pesticides tested, both alone and in mixtures. In order to find out the conditions for biocompatibility using the photo-Fenton reaction as a pre-treatment step, wastewater inoculated with unacclimated municipal sludge containing pesticides after certain degradation time was evaluated by the Z-W test. Biodegradability was enhanced (70% considered biodegradable) by the photo-Fenton treatment after 12-25min. It may be concluded that the photo-Fenton treatment consistently enhances biodegradability of wastewater containing pesticides.