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.     

Degradation of fifteen emerging contaminants at μg L 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 μg L⁻¹, was found to depend on the presence of CO₃²⁻ and HCO₃⁻ (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 H₂O₂ concentration used. Toxicity tests with Vibrio fisheri showed that degradation of the compounds in real effluent wastewater led to toxicity increase.     

Decontamination industrial pharmaceutical wastewater by combining solar photo-Fenton and biological treatment

Characterization and treatment of a real pharmaceutical wastewater containing 775 mg dissolved organic carbon per liter by a solar photo-Fenton/biotreatment were studied. There were also many inorganic compounds present in the matrix. The most important chemical in this wastewater was nalidixic acid (45 mg/L), an antibiotic pertaining to the quinolone group. A Zahn-Wellens test demonstrated that the real bulk organic content of the wastewater was biodegradable, but only after long biomass adaptation; however, the nalidixic acid concentration remained constant, showing that it cannot be biodegraded. An alternative is chemical oxidation (photo-Fenton process) first to enhance biodegradability, followed by a biological treatment (Immobilized Biomass Reactor - IBR). In this case, two studies of photo-Fenton treatment of the real wastewater were performed, one with an excess of H₂O₂ (kinetic study) and another with controlled H₂O₂ dosing (biodegradability and toxicity studies). In the kinetic study, nalidixic acid completely disappeared after 190 min. In the other experiment with controlled H₂O₂, nalidixic acid degradation was complete at 66 mM of H₂O₂ consumed. Biodegradability and toxicity bioassays showed that photo-Fenton should be performed until total degradation of nalidixic acid before coupling a biological treatment. Analysis of the average oxidation state (AOS) demonstrated the formation of more oxidized intermediates. With this information, the photo-Fenton treatment time (190 min) and H₂O₂ dose (66 mM) necessary for adequate biodegradability of the wastewater could be determined. An IBR operated in batch mode was able to reduce the remaining DOC to less than 35 mg/L. Ammonium consumption and NO₃⁻ generation demonstrated that nitrification was also attained in the IBR. Overall DOC degradation efficiency of the combined photo-Fenton and biological treatment was over 95%, of which 33% correspond to the solar photochemical process and 62% to the biological treatment.     

Oxidation of two organophosphorous insecticides by the photo-assisted Fenton reaction

The photocatalytic degradation of two selected insecticides (dimethoate and methyl parathion) has been studied using the photo-assisted Fenton reaction. The degradation kinetics were studied under different conditions such as iron's and oxidant's concentration, temperature and inorganic ions. The degradation rates proved to be strongly influenced by these parameters. The replacement of hydrogen peroxide with peroxydisulfate was also tested in a photo-Fenton-like reaction. This system achieved high degradation rates of the selected compounds. Intermediate products formed during photocatalytic treatment were identified by means of solid-phase extraction (SPE) coupled to gas chromatography-mass spectroscopy techniques (GC-MS). Eight possible by-products were identified for parathion methyl and three for dimethoate formed through mainly oxidation and dealkylation reactions. Mineralization studies showed also that the photo-Fenton and the photo-Fenton-like systems are able to achieve mineralization of the insecticides. However, complete detoxification is achieved only in the presence of the photo-Fenton reagent.     

Decolorization of dark brown colored coffee effluent by solar photo-Fenton reaction: effect of solar light dose on decolorization kinetics

The decolorization of dark brown colored coffee effluent by solar photo-Fenton process has been studied. Effects of accumulated solar light energy and dosage of Fenton reagents (iron and hydrogen peroxide) on the color removal have been examined. With increasing Fe dosage the rate of the decolorization increased but the enhancement was not pronounced beyond 10 mg L⁻¹. Although addition of H₂O₂ increased the decolorization rate up to around 1000 mg L⁻¹ of H₂O₂, further addition of H₂O₂ could not enhance the color removal. At excess dosages of Fenton reagents, the color removal was not improved due to their scavenging of hydroxyl radicals. It was found that the pseudo-first order decolorization kinetic constant based on the accumulated solar energy is a sole parameter unifying solar photo-Fenton decolorization processes under the different weather conditions. The kinetic constant can be readily used to calculate the amount of solar energy required to achieve a certain degree of color removal. The mineralization was rather slower as compared with the decolorization. The decolorization capability with solar irradiation was found to be comparable to UV light irradiation. The present results suggest that abundant solar energy driving decolorization of coffee effluent by photo-Fenton reaction is highly efficient.     

Degradation of a four-pesticide mixture by combined photo-Fenton and biological oxidation

Complete degradation of a pesticide mixture by a combination of a photo-Fenton pretreatment and an activated-sludge batch reactor is demonstrated. Four commercial pesticides, Laition, Metasystox, Sevnol and Ultracid were chosen for this experiment. The active ingredients are, respectively, dimethoate, oxydemeton-methyl, carbaryl and methidathion. The original pesticide concentration was 200 mg L⁻¹. Biotreatment began after 31% photocatalytic mineralization, which after 5 h in a 6-L stirred batch-mode tank reactor with non-acclimated activated sludge, leaves the photo-Fenton effluent completely degraded. This biotreatment time is shorter than commonly found in municipal wastewater treatment plants (∼8-10 h). Therefore, the combined process is effective for rapid pesticide degradation in wastewater with complete removal of parent compounds and the associated DOC concentration. Nonetheless, assessment of this technology should take into account higher pesticide concentrations and how this factor affects both the photocatalytic and the biological oxidation.     

Oxidation of chlorfenvinphos in ultrapure and natural waters by ozonation and photochemical processes

The chemical oxidation of the organophosphorus insecticide chlorfenvinphos, a priority pollutant in aquatic environments, has been conducted in ultrapure water, by means of single degradation agents (ozone and UV radiation), and by the Advanced Oxidation Processes constituted by combinations of these oxidants (O(3)/H(2)O(2) and UV/H(2)O(2)). The influence of the operating variables was discussed, and the degradation rates were evaluated by determining the rate constants for the reactions with ozone ( [Formula: see text] =3.7+/-0.2 L mol(-1)s(-1)) and OH radicals (k(OH)=(3.2+/-0.2)x10(9) L mol(-1)s(-1)), as well as the quantum yield for the photodegradation (around 0.1 mol E(-1), depending on the pH). Additionally, the ozonation of chlorfenvinphos in a natural water system (a surface water from a reservoir) was studied. The influence of the operating conditions on the insecticide removal efficiency was established, and the R(ct) parameter was evaluated. A kinetic model was proposed for the prediction of the elimination rate of chlorfenvinphos in the ozonation process and the results obtained reveal a good agreement between experimental results and predicted values.     

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, TiO₂/UV and Fe²⁺/H₂O₂/UV (TiO₂-only for bleaching wastewater), in a pilot plant with compound parabolic collectors. The photo-Fenton reaction (k = 0.12 L/kJ_UV, r₀ = 59.4 mg/kJ_UV) is much more efficient that TiO₂ photocatalysis and TiO₂ + S₂O₈²⁻ (k = 0.0024 L/kJ_UV, r₀ = 1.36 mg/kJ_UV), leading to 94% mineralization of the bleaching wastewater after 31.5 kJ_UV/L, consuming 77.1 mM of H₂O₂ (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, r₀ = 20.8 mg/kJ_UV) until 173 kJ_UV/L (≈300 mg C/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 H₂OT:/PGN/ELSEVIER/WR/web/00007490/₂, achieving almost 49% and 48% mineralization of the wastewaters, respectively for the cork bleaching and boiling wastewaters.     

Life cycle assessment of a coupled solar photocatalytic-biological process for wastewater treatment

A comparative life cycle assessment (LCA) of two solar-driven advanced oxidation processes, namely heterogeneous semiconductor photocatalysis and homogeneous photo-Fenton, both coupled to biological treatment, is carried out in order to identify the environmentally preferable alternative to treat industrial wastewaters containing non-biodegradable priority hazardous substances. The study is based on solar pilot plant tests using alpha-methyl-phenylglycine as a target substance. The LCA study is based on the experimental results obtained, along with data from an industrial-scale plant. The system under study includes production of the plant infrastructure, chemicals, electricity, transport of all these materials to the plant site, management of the spent catalyst by transport and landfilling, as well as treatment of the biodegradable effluent obtained in a conventional municipal wastewater treatment plant, and excess sludge treatment by incineration. Nine environmental impact categories are included in the LCA: global warming, ozone depletion, human toxicity, freshwater aquatic toxicity, photochemical ozone formation, acidification, eutrophication, energy consumption, and land use. The experimental results obtained in the pilot plant show that solar photo-Fenton is able to obtain a biodegradable effluent much faster than solar heterogeneous photocatalysis, implying that the latter would require a much larger solar collector area in an industrial application. The results of the LCA show that, an industrial wastewater treatment plant based on heterogeneous photocatalysis involves a higher environmental impact than the photo-Fenton alternative, which displays impact scores 80-90% lower in most impact categories assessed. These results are mainly due to the larger size of the solar collector field needed by the plant.     

Application of the photo-Fenton process to the treatment of wastewaters contaminated with diesel

The application of the photo-Fenton process for the treatment of wastewaters contaminated with diesel oil was investigated. This particular process has been widely studied for the photochemical degradation of highly toxic organic pollutants. Experiments were performed according to a factorial experimental design at two levels and two variables: H(2)O(2) concentration (5-200 mM) and Fe(2+) concentration (0.01-1 mM). Experimental results demonstrated that the photo-Fenton process is technically feasible for the treatment of wastewaters containing diesel oil constituents, with total mineralization. A combination of factorial experimental design and gradient descent techniques was employed to optimize the amount of the Fenton reagents, resulting in Fe(2+) (0.1 mM) and H(2)O(2) (50 mM). These optimized levels did not exceed the limit for disposal of ferrous ions (0.27 mM) proposed at the local environmental legislation.     

Effect of initial solution pH on the degradation of Orange II using clay-based Fe nanocomposites as heterogeneous photo-Fenton catalyst

Effect of initial solution pH on the discoloration and mineralization of 0.2 mM Orange II by using two clay-based Fe nanocomposites (Fe-B (Fe supported on bentonite clay) and Fe-Lap-RD (Fe supported on laponite clay)) as catalysts was studied in detail. It was found that the initial solution pH not only influences the photo-catalytic activity of Fe-B and Fe-Lap-RD but also the Fe leaching from the two catalysts. Both catalysts show the best photo-catalytic activity at an initial solution pH of 3.0, and the activity of the catalysts decreases as the initial solution pH increases. At optimal conditions, 100% discoloration and mineralization of 0.2 mM Orange II are achieved in 60 and 120 min reaction in the presence of 10 mM H2O2, 1.0 g/L Fe-B, and 1 x 8 W UVC at initial solution pH of 3.0. 100% discoloration and 90% mineralization of 0.2 mM Orange II are achieved when Fe-Lap-RD is used as catalyst under the same conditions. Both catalysts also display a reasonable good photo-catalytic activity and negligible Fe leaching at an initial solution pH of 6.6 that is very close to neutral pH. This characteristic makes it possible for the Fe-B and Fe-Lap-RD to have a long-term stability. It also becomes feasible for the photo-Fenton process to treat the original wastewater without the need to pre-adjust the solution pH.     

Degradation of sulfamethoxazole in water by solar photo-Fenton. Chemical and toxicological evaluation

In this work, the photocatalytic degradation of the antibiotic sulfamethoxazole (SMX) by solar photo-Fenton at pilot plant scale was evaluated in distilled water (DW) and in seawater (SW). Degradation and mineralization of SMX were strongly hindered in SW compared to DW. The influence of H₂O₂ and iron concentration on the efficiency of the photocatalytic process was evaluated. An increase in iron concentration from 2.6 to 10.4 mg L⁻¹ showed only a slight improvement in SMX degradation and mineralization. However, an increase in H₂O₂ concentration up to 120 mg L⁻¹ during photo-Fenton in DW decreased SMX solution toxicity from 85% to 20%, according to results of Daphnia magna bioassays. The same behaviour was not observed after photo-Fenton treatment in SW. Despite 45% mineralization in SW, toxicity increased from 16% to 86% as shown by Vibrio fischeri bioassays, which suggests that the intermediates generated in SW are different from those in DW. A SMX degradation pathway during the photo-Fenton treatment in DW is proposed.     

UV light assisted decolorization of dark brown colored coffee effluent by photo-Fenton reaction

The photochemical decolorization of coffee effluent has been examined by photo-Fenton (UV/Fe²⁺/H₂O₂) process. Effects of UV light intensity, initial coffee concentration, iron dose and H₂O₂ dose on the color removal of model coffee effluent have been investigated. The rate of decolorization increased with decreasing initial coffee effluent concentration. It was found that the Fe ion dose and UV light intensity enhanced the decolorization rate. The decolorization process of coffee effluent could be divided into three established phases. At the beginning of the photo-Fenton process, the instantaneous and significant increase in color of the solution was found (Phase-I). In the subsequent phase (Phase-II), the decolorization rate was initially fast and subsequently decreased. In Phase-III, the rate was accelerated and then the complete decolorization of model coffee effluent was achieved. In order to elucidate the mechanisms of coffee effluent color removal process, the concentration changes in Fe³⁺ and Fe²⁺ besides H₂O₂ were measured during the course of the photo-Fenton process. The rate-determining step in Phase-II was the photo-Fenton reaction or photoreduction of Fe³⁺. On the other hand, the decolorization process in Phase-III was highly affected by Fenton reaction or decomposition of H₂O₂ with Fe²⁺. About 93% mineralization of 250 mg L⁻¹ model coffee effluent was achieved after 250 min. A comparative study for TiO₂, ZnO and photo-Fenton oxidation processes has been also carried out and the photo-Fenton process was found to be the most effective for color removal of coffee effluent.     

Fe(III) homogeneous photocatalysis for the removal of 1,2-dichlorobenzene in aqueous solution by means UV lamp and solar light

Chlorinated hydrocarbons are widely used in chemical industries as solvents and intermediates for pesticides and dyes manufacture. Their presence was documented in rivers, groundwaters and seawaters.

In this work, the oxidation of 1,2-dichlorobenzene in aqueous solutions by means of Fe(III) homogeneous photocatalysis under UV lamp and sunlight irradiations is studied. The results show that the best working conditions are found for pH=3.0 and initial [Fe(III)] concentration equal to 1.0×10⁻⁴ mol L⁻¹ although the investigated system can be utilized even at pH close to 4.0 but with slower abatement kinetics.

Some dicholoroderivatives, such as 2,3-dichlorophenol, 3,4-dichlorophenol and 2-chlorophenol, are identified as oxidation intermediates. The values of the kinetic constant for the photochemical reoxidation of Fe(II) to Fe(III) are evaluated by a mathematical model in the range 1.58–3.78 L mol⁻¹ s⁻¹ and 0.69–0.78 L mol⁻¹ s⁻¹ for the systems irradiated by UV lamp and sunlight, respectively.     

A simple simulation of the degradation of natural organic matter in homogeneous and heterogeneous advanced oxidation processes

The degradation of natural organic matter (NOM) in homogeneous and heterogeneous advanced oxidation processes (AOP) was simulated using a simple underlying physical model. By treating the NOM molecules as linear chains and allowing them to be cleaved at any point selected at random, it is possible to reproduce well the results for homogeneous AOP experiments.To simulate a heterogeneous process, a bias was introduced (in the form of different weights for different chain lengths) according to literature data on the adsorption of NOM onto TiO₂ nanoparticle agglomerates. After introduction of the (adsorption) bias, the simulation closely followed the degradation sequence observed in heterogeneous photocatalysis with TiO₂ suspensions.Thus, the experimental results for homogeneous AOP may well be explained by a random breakdown of the NOM molecules; that is, we find no evidence for a selective degradation of the large molecular size material. However, a selectivity is present in the heterogeneous system due to the differential adsorption of NOM onto the reactive surface.     

Chloramination of organophosphorus pesticides found in drinking water sources

The degradation of commonly detected organophosphorus (OP) pesticides, in drinking water sources, was investigated under simulated chloramination conditions. Due to monochloramine autodecomposition, it is difficult to observe the direct reaction of monochloramine with each OP pesticide. Therefore, a model was developed to examine the reaction of monochloramine (NH₂Cl) and dichloramine (NHCl₂) with chlorpyrifos (CP), diazinon (DZ), and malathion (MA). Monochloramine was found not to be very reactive with each OP pesticides, . While, dichloramine (NHCl₂) was found to be 2 orders of magnitude more reactive with each of the OP pesticides than monochloramine, , which is still three orders of magnitude less than the hypochlorous acid reaction rate coefficient with each OP pesticide. For each pesticide, the reactivity of the three chlorinated oxidants was then found to correlate with half-wave potentials (E_1/2) of each oxidant. With reaction rate coefficients for the three chlorinated oxidations as well as neutral and alkaline hydrolysis rate coefficients for the pesticides, the model was used to determine the dominant reaction pathways as a function of pH. At pH 6.5, OP pesticide transformation was mostly due to the reaction of hypochlorous acid and dichloramine. Above pH 8, alkaline hydrolysis or the direct reaction with monochloramine was the primary degradation pathway responsible for the transformation of OP pesticides. This demonstrates the ability of models to be used as tools to elucidate degradation pathways and parameterize critical reaction parameters when used with select yet comprehensive data sets.     

Solar regeneration of powdered activated carbon impregnated with visible-light responsive photocatalyst: factors affecting performances and predictive model

This study demonstrated a green technique to regenerate spent powdered activated carbon (AC) using solar photocatalysis. The AC was impregnated with a photocatalyst photoexcitable under visible-light irradiation to yield a solar regenerable composite, namely nitrogen-doped titanium dioxide (N-TiO₂/AC). This composite exhibited bifunctional adsorptive-photocatalytic characteristics. Contaminants of emerging environmental concern, i.e. bisphenol-A (BPA), sulfamethazine (SMZ) and clofibric acid (CFA) which exhibited varying affinities for AC were chosen as target pollutants. The adsorption of BPA and SMZ by the N-TiO₂/AC was significantly higher than that of CFA. The performance of solar photocatalytic regeneration (SPR) of the spent N-TiO₂/AC composite generally increased with light intensity, N-TiO₂ loading and temperature. The regeneration efficiency (RE) for CFA-loaded spent composite was the highest compared to the other pollutant-loaded spent composites, achieving 77% within 8 h of solar irradiation (765 W m⁻²). The rate-limiting process was pollutant desorption from the interior AC sorption sites. A kinetic model was developed to predict the transient concentration of the sorbate remaining in the spent composite during SPR. Comparison studies using solvent extraction technique indicated a different order of RE for the three pollutants, attributable to their varying solubilities in the aqueous and organic solvents.     

Photolytic and photocatalytic decomposition of aqueous ciprofloxacin: Transformation products and residual antibacterial activity

Previous work demonstrates that widely used fluoroquinolone antibacterial agents, including ciprofloxacin, are degraded by means of aqueous ultraviolet photolytic and titanium dioxide (TiO₂) photocatalytic (using both ultraviolet-A (UVA) and visible light (Vis) irradiation) treatment processes. In this study, we investigate the effects of photolytic and photocatalytic treatment processes on the antibacterial activity of ciprofloxacin solutions under controlled laboratory conditions. In agreement with earlier work, rates of ciprofloxacin degradation under comparable solution conditions (100 μM ciprofloxacin, 0 or 0.5 g/L TiO₂, pH 6, 25 °C) follow the trend UVA-TiO₂ > Vis-TiO₂ > UVA. Release of ammonia and fluoride ions is observed and a range of organic products have been identified with liquid chromatography-tandem mass spectrometry. However, the identified organic products all appear to retain the core quinolone structure, raising concerns about residual antibacterial potency of the treated solutions. Quantitative microbiological assays with a reference Escherichia coli strain indicate that the antimicrobial potency of ciprofloxacin solutions track closely with the undegraded ciprofloxacin concentration during photolytic or photocatalytic reactions. Quantitative analysis shows that for each mole of ciprofloxacin degraded, the antibacterial potency of irradiated solutions decreases by approximately one “mole” of activity relative to that of the untreated ciprofloxacin solution. This in turn indicates that the ciprofloxacin photo(cata)lytic transformation products retain negligible antibacterial activity relative to the parent compound. The energy demands for achieving one order of magnitude reduction in antibacterial activity within the experimental system are estimated to be 175 J/cm² (UVA-only), 29 J/cm² (Vis-TiO₂), and 20 J/cm² (UVA-TiO₂), which indicates that the UVA-TiO₂ photocatalysis is the most energy efficient process for achieving ciprofloxacin inactivation under laboratory conditions.