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.     

Assessment of photo-Fenton and biological treatment coupling for Diuron and Linuron removal from water

The coupling of photo-Fenton (chemical) and biological treatments has been used for the removal of Diuron and Linuron herbicides from water. The chemical reaction was employed as a pre-treatment step for the conversion of the toxic and non-biodegradable herbicides into biodegradable intermediates that were subsequently removed by means of a biological sequencing batch reactor (SBR). Multivariate experimental design was used to select four photo-Fenton reagent dose combinations for the coupling experiments. Concentrations of hydrogen peroxide between 10 and 250 mg L(-1), and iron (II) concentrations between 2 and 20 mg L(-1) have been tested. 15.9 mg L(-1) of Fe(II) and 202 mg L(-1) of H(2)O(2) were needed to convert initial toxic and non-biodegradable herbicides into suitable intermediates for a subsequent biological treatment. Detrimental effects due to the excess of reactants were detected. Chemical oxygen demand (COD), average oxidation state (AOS), total organic carbon (TOC) and hydrogen peroxide concentration are the parameters used to trace the experiments course. Also, toxicity (EC(50)(15)) and biodegradability (BOD(5)/COD) tests were carried out at the end of each chemical oxidation. Complete disappearance of the herbicides from water was observed after the chemical treatment, while 3,4-dichloroaniline and 3,4-dichlorophenyl isocyanate were identified as the main by-products of the degradation process. Complete TOC removal was achieved after biological treatment in a SBR using a hydraulic retention time (HRT) of 2 days.     

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.     

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.     

Ozone and photocatalytic processes to remove the antibiotic sulfamethoxazole from water

In this study, water containing the pharmaceutical compound sulfamethoxazole (SMT) was subjected to the various treatments of different oxidation processes involving ozonation, and photolysis and catalysis under different experimental conditions. Removal rates of SMT and total organic carbon (TOC), from experiments of simple UVA radiation, ozonation (O(3)), catalytic ozonation (O(3)/TiO(2)), ozone photolysis (O(3)/UVA), photocatalytic oxidation (O(2)/TiO(2)/UVA) and photocatalytic ozonation (O(3)/UVA/TiO(2)), have been compared. Photocatalytic ozonation leads to the highest SMT removal rate (pH 7 in buffered systems, complete removal is achieved in less than 5min) and total organic carbon (in unbuffered systems, with initial pH=4, 93% TOC removal is reached). Also, lowest ozone consumption per TOC removed and toxicity was achieved with the O(3)/UVA/TiO(2) process. Direct ozone and free radical reactions were found to be the principal mechanisms for SMT and TOC removal, respectively. In photocatalytic ozonation, with buffered (pH 7) aqueous solutions phosphates (buffering salts) and accumulation of bicarbonate scavengers inhibit the reactions completely on the TiO(2) surface. As a consequence, TOC removal diminishes. In all cases, hydrogen peroxide plays a key role in TOC mineralization. According to the results obtained in this work the use of photocatalytic ozonation is recommended to achieve a high mineralization degree of water containing SMT type compounds.     

Characterization of the degradation performance of the sulfamethazine antibiotic by photo-Fenton process

The present study provides results describing the degradation performance of the Sulfamethazine (SMT) antibiotic via photo-Fenton treatment. Experiments were carried out using 1 L solution samples of SMT (50 mg L⁻¹) under different conditions. HPLC results reveal that both Fenton and photo-Fenton reactions were able to completely remove SMT antibiotic from the studied samples in less than 2 min treatment. Half-life times and kinetic parameters (assuming a pseudo-first-order kinetics at reaction initial stage, far from the equilibrium) for SMT degradation were determined and discussed. Hence, appropriate Fenton reagent loads are given to attain different targets proposed. TOC and HPLC data also revealed the presence of reaction intermediates; thus toxicity assays were performed regarding bacterial growth rate. The toxicity of an SMT solution was shown to increase during its degradation by means of photo-Fenton reactions.     

Effect of pesticide concentration on the degradation process by combined solar photo-Fenton and biological treatment

The influence of pesticide concentration, expressed as dissolved organic carbon (DOC), on combined solar photo-Fenton and biological oxidation treatment was studied using wastewater containing a mixture of five commercial pesticides, Vydate, Metomur, Couraze, Ditumur and Scala. Two initial DOC concentrations, 200 mg L⁻¹ and 500 mg L⁻¹ were assayed. Variation in biodegradability with photocatalytic treatment intensity was tested using Pseudomonas putida. Thus the mineralisation required for combining with biodegradation of intermediates by activated sludge was 33% and 55% at 200 mg L⁻¹ and 500 mg L⁻¹, respectively. Biotreatment was carried out in a stirred tank in sequencing batch reactor (SBR) mode. As revealed by the biodegradation kinetics, intermediates generated at the higher pesticide concentration caused lower carbon removal rates in spite of the longer photo-Fenton treatment time applied. One strategy for treating water with high concentrations of pesticides and overcoming the low biodegradability of photo-Fenton intermediates is to mix it with a biodegradable carbon source before biological oxidation. This combination of photo-Fenton and acclimatized activated sludge in several SBR cycles led to complete biodegradation of a concentrated pesticide solution of 500 mg L⁻¹ DOC in 5 h with a carbon removal efficiency of 90%.     

Mineralization enhancement of a recalcitrant pharmaceutical pollutant in water by advanced oxidation hybrid processes

Degradation of the biorecalcitrant pharmaceutical micropollutant ibuprofen (IBP) was carried out by means of several advanced oxidation hybrid configurations. TiO₂ photocatalysis, photo-Fenton and sonolysis - all of them under solar simulated illumination - were tested in the hybrid systems: sonophoto-Fenton (FS), sonophotocatalysis (TS) and TiO₂/Fe²⁺/sonolysis (TFS). In the case of the sonophoto-Fenton process, the IBP degradation (95%) and mineralization (60%) were attained with photo-Fenton (FH). The presence of ultrasonic irradiation slightly improves the iron catalytic activity. On the other hand, total removal of IBP and elimination of more than 50% of dissolved organic carbon (DOC) were observed by photocatalysis with TiO₂ in the presence of ultrasound irradiation (TS). In contrast only 26% of mineralization was observed by photocatalysis with H₂O₂ (TH) in the absence of ultrasound irradiation. Additional results showed that, in the TFS system, 92% of DOC removal and complete degradation of IBP were obtained within 240 min of treatment. The advanced oxidation hybrid systems seems to be a promising alternative for full elimination/mineralization for the recalcitrant micro-contaminant IBP.     

Heterogenous photocatalytic degradation kinetics and detoxification of an urban wastewater treatment plant effluent contaminated with pharmaceuticals

Degradation kinetics and mineralization of an urban wastewater treatment plant effluent contaminated with a mixture of pharmaceutical compounds composed of amoxicillin (10 mg L⁻¹), carbamazepine (5 mg L⁻¹) and diclofenac (2.5 mg L⁻¹) by TiO₂ photocatalysis were investigated. The photocatalytic effect was investigated using both spiked distilled water and actual wastewater solutions. The process efficiency was evaluated through UV absorbance and TOC measurements. A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Lepidium sativum) was performed to evaluate the potential toxicity of the oxidation intermediates. A pseudo-first order kinetic model was found to fit well the experimental data. The mineralization rate (TOC) of the wastewater contaminated with the pharmaceuticals was found to be really slow (t_1/2 = 86.6 min) compared to that of the same pharmaceuticals spiked in distilled water (t_1/2 = 46.5 min). The results from the toxicity tests of single pharmaceuticals, their mixture and the wastewater matrix spiked with the pharmaceuticals displayed a general accordance between the responses of the freshwater aquatic species (P. subscapitata > D. magna). In general the photocatalytic treatment did not completely reduce the toxicity under the investigated conditions (maximum catalyst loading and irradiation time 0.8 g TiO₂ L⁻¹ and 120 min respectively).     

Hybrid photocatalysis/membrane treatment for surface waters containing low concentrations of natural organic matters

Since the mid-1990s, numerous studies on the treatment of drinking water by photocatalysis have been reported. Once optimised, the photocatalytic process can completely degrade numerous natural and artificial organic compounds. In this study, a hybrid photocatalysis/membrane process was used as a polishing treatment of surface water containing a small concentration of natural organic matters (i.e. total organic carbon (TOC) concentration of around 3mg/L) which may be difficult to remove using conventional filtration or coagulation. An optimum pH of 4.5 and a TiO(2) concentration of 0.1g/L were found to lead to the highest removal efficiencies. The relative effect of the individual processes featuring in the hybrid system (UV radiation, TiO(2) adsorption and membrane filtration) was also assessed for different pH values. The membrane separation process was accounted to remove around 18% of the initial TOC concentration, while TiO(2) adsorption alone was generally responsible for less than 5% of TOC removal during the 120 min of the experiments. However, when the natural water was only radiated by UV light, up to 70% of TOC was removed. A synergetic effect was observed when the three processes (TiO(2), UV and membrane) were used together. Comparison of removal efficiencies obtained during real and model (International Humic Substance Society) waters treatment by photocatalysis is also presented, revealing the importance of the nature of the feed in this type of treatment.     

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 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.     

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 t_30W = 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.     

Degradation of the antibiotic amoxicillin by photo-Fenton process--chemical and toxicological assessment

The influence of iron species on amoxicillin (AMX) degradation, intermediate products generated and toxicity during the photo-Fenton process using a solar simulator were evaluated in this work. The AMX degradation was favored in the presence of the potassium ferrioxalate complex (FeOx) when compared to FeSO₄. Total oxidation of AMX in the presence of FeOx was obtained after 5 min, while 15 min were necessary using FeSO₄. The results obtained with Daphnia magna biossays showed that the toxicity decreased from 65 to 5% after 90 min of irradiation in the presence of FeSO₄. However, it increased again to a maximum of 100% after 150 min, what indicates the generation of more toxic intermediates than AMX, reaching 45% after 240 min. However, using FeOx, the inhibition of mobility varied between 100 and 70% during treatment, probably due to the presence of oxalate, which is toxic to the neonates. After 240 min, between 73 and 81% TOC removal was observed. Different pathways of AMX degradation were suggested including the opening of the four-membered β-lactamic ring and further oxidations of the methyl group to aldehyde and/or hydroxylation of the benzoic ring, generating other intermediates after bound cleavage between different atoms and further oxidation to carboxylates such acetate, oxalate and propionate, besides the generation of nitrate and ammonium.     

Combined toxicity effects of MTBE and pesticides measured with Vibrio fischeri and Daphnia magna bioassays

Methyl-tert-butyl ether (MTBE), a fuel oxygenate that is added to gasoline, commonly contaminates aquatic systems, many of which are already contaminated with pesticides. The toxic effects (EC(50) value) of several pure pesticides (Diuron, Linuron, Dichlofluanid, Sea nine, Irgarol and tributyltin (TBT)) were measured and compared with the EC(50) value of the pesticide mixed with MTBE, using the Vibrio fischeri and Daphnia magna acute toxicity assays. The interaction between chemicals was evaluated in terms of the effects of mixing on the EC(50) value (i.e. the concentration (mg/L) of a compound or mixture that is required to produce a 50% change in a toxic response parameter) and the time required to generate the toxic response. Presence of MTBE enhanced the EC(50) value of several pesticides (Diuron, Dichlofluanid, TBT and Linuron) and/or the toxic response manifested more rapidly than with pure pesticides. Toxicity enhancements were quite substantial in many cases. For example, the presence of MTBE increased the toxicity of Diuron by more than 50% when tested with the V. fischeri assay (5, 15 and 30 min exposure). Also, the toxic response manifested itself within 5 min whereas without the MTBE the same response arose in 30 min. Presence of MTBE increased the toxicity of Dichlofluanid by 30% when measured with the D. magna assay. Toxicities of only two pesticides (Sea nine and Irgarol) were not raised by the presence of MTBE.     

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.     

Photodecomposition of bisphenol A on nanometer-sized TiO2 thin film and the associated biological toxicity to zebrafish (Danio rerio) during and after photocatalysis

We investigated the relationship between the TiO2 photocatalytic decomposition of bisphenol A and biological toxicity to zebrafish (Danio rerio). TiO2 particles, which prepared using a solvothermal method, were applied to produce a nanometer-sized TiO2 thin film. An alcoholic solution containing the TiO2 particles and an inorganic binder was directly coated on the UV-lamp substrate. It was equipped in a photoreactor that was manufactured in our laboratory. The attachment of the thin TiO2 film to the UV-lamp substrate resulted in a stable and transparent coating. The TiO2 particles on the thin film were approximately 20-30 nm in size, and the resulting film thickness was approximately 200 nm after a single coat. The bisphenol A, which was eluted from epoxy resin in a drinking water tank, was completely degraded by the TiO2 photocatalysis. We initially detected approximately 7.8 ng/ml of bisphenol A in the epoxy-resin tank, but its concentration was undetectable after a 48-h photocatalytic reaction over TiO2. We observed a decreased survival rate in zebrafish that were reared in water exposed to the leaching process of the epoxy resin. After the photocatalysis, however, no toxic effects on the hatching rates or morphogenesis of the zebrafish were observed. In summary, toxicity during the TiO2 photocatalysis was observed; however, toxicity was no longer observed once the bisphenol A was completely decomposed by the TiO2 photocatalysis. On the basis of these experimental observations, we suggest that TiO2 photocatalysis can be adopted as a treatment method to purify an epoxy-resin tank.     

Mineralisation of coloured aqueous solutions by ozonation in the presence of activated carbon

The degradation of organic matter in coloured solutions of different classes of dyes by ozonation in the presence of activated carbon is investigated. The kinetics of the decolourisation and mineralisation of three different dyes solutions (CI Acid Blue 113, CI Reactive Red 241 and CI Basic Red 14) were studied in a laboratory scale reactor by three different processes: adsorption on activated carbon, oxidation with ozone and ozonation in the presence of activated carbon. The mineralisation of the solutions was followed by measuring the total organic carbon (TOC). Under the experimental conditions used in this work, activated carbon was not capable of completely removing the colour of the solutions in reasonable time. On the other hand, ozonation quickly decolourised all the solutions, but satisfactory removal of TOC was never achieved by this process. The combination of activated carbon with ozone enhanced the decolourisation of the solutions and especially the mineralisation of the organic matter. Activated carbon acts both as an adsorbent and as a catalyst in the reaction of ozonation. The surface chemistry of the activated carbon is an important parameter; it was observed that basic samples improve TOC removal. The main conclusions of this work were validated by treating a real textile effluent collected after the conventional biological treatment.     

An innovative ultrasound, Fe and TiO2 photoassisted process for bisphenol a mineralization

This paper explores the degradation of a model pollutant, bisphenol A, by an advanced oxidation process that combines sonolysis, Fe²⁺, and TiO₂ in a photoassisted process. Experiments were done under saturated oxygen conditions. The effect of different Fe²⁺ (0.56 and 5.6 mg/L) and TiO₂ (10 and 50 mg/L) concentrations was investigated on both the elimination and mineralization of the pollutant. A pronounced synergistic effect that led to the complete and rapid elimination of dissolved organic carbon (DOC) was observed even at low catalyst loadings. In this system, almost a complete removal of DOC (93%) was observed after 4 h using 10 and 5.6 mg/L of TiO₂ and Fe²⁺, respectively, whereas at the same time, only 5, 6, and 22% of DOC was removed by an individual process alone (TiO₂ photocatalysis, ultrasound, and photo-Fenton, respectively). In this system, ultrasound has the principal role of eliminating the initial substrate and providing hydrogen peroxide for the photocatalytic systems, while photo-Fenton and TiO₂ photocatalysis are mainly responsible for the transformation of the intermediates in CO₂ and H₂O. The role of H₂O₂ generated from the sonochemical process is also discussed.