Mixtures of chelating agents to enhance photo-Fenton process at natural pH: Influence of wastewater matrix on micropollutant removal and bacterial inactivation.

Three organic fertilizers (EDTA (Ethylenedinitrilotetraacetic acid), EDDS (Ethylenediamine-N, N'-disuccinic acid) and DTPA (Diethylene triamine pentaacetic acid)) were tested as Fe-complexes in photo-Fenton process at natural pH for micropollutants (MPs) abatement and simultaneous E.coli inactivation. Less stable Fe-complexes show high iron precipitation, stopping MPs degradation. On the contrary, stable Fe-complexes imply low kinetic rates for MPs removal. To solve these inconveniences, three mixtures of organic fertilizers were also tested, trying to improve the kinetic rates of micropollutants oxidation and overcome iron precipitation. Three different pollutants (propranolol (PROP), acetamiprid (ACMP) and sulfamethoxazole (SMX)) were used as the target compounds. As the iron release is, in part, linked to the hardness of water, two water matrices from two different secondary wastewaters (Membrane Bioreactor (MBR) and Conventional Activated Sludge (CAS)) were tested. The best performance in micropollutant degradation and E.coli inactivation was achieved with the combination of EDDS + EDTA, accomplishing a good equilibrium between iron precipitation and rate of MPs removal. For instance, total removal of propranolol was achieved at 45 min in MBR, while it was only 85.7% in CAS, being an improvement of the process comparing with that obtained using single organic fertilizers. At the end of the treatment, 2.1 log-inactivation for E.coli was reached in CAS. The differences observed between both wastewaters were related to CAS' higher DOC, turbidity, and hardness. Finally, from the physicochemical characterization conducted, including Biochemical Oxygen Demand at 5 days and phytotoxicity, it is possible to highlight the suitability of these treated effluents for its reuse in irrigation, as long as in CAS matrix the final values of E. coli are within the legal limit.

Synergies, radiation and kinetics in photo-Fenton process with UVA-LEDs.

The photo-Fenton process, with UV-A LED (λ = 380-390, 390-400 and 380-400 nm) has demonstrated to be effective in the abatement of a target micropollutant, such as diphenhydramine hydrochloride (DPH). Different concentrations of iron (Fe2+) and H2O2 were tested and monitored, and the best results in DPH removal were obtained for the highest concentrations of both iron (II) and H2O2 (10 mg Fe2+/L - 150 mg H2O2/L). The evolution of iron and peroxide concentration was also monitored. Kinetic studies showed that dark Fenton process prevails at the beginning of the experiment, when Fe2+ concentration is higher. However, after these initial moments, the prevailing process is photo-Fenton and, in addition, wavelength radiation plays an important role. Concerning the effect of radiation, four LEDs (4.2 W total power) were used, emitting radiation in the wavelength range between 380-390 or 390-400 nm. Similar results were obtained in both cases in DPH removal by photo-Fenton (30 min for total elimination). However, a synergistic effect was observed when two LEDs of 380-390 nm and two LEDs of 390-400 nm were used. Total power was the same (4.2 W) in each experimental condition, but the increase in the wavelength range to 20 nm (380-400 nm) produces an increase in the rate of DPH removal, achieving its total elimination at 15 min. This fact, with the use of a simple radiation model, reveals the important role that radiation plays in the photo-Fenton process. Finally, the formed intermediates were determined and some reaction pathways were proposed.

Kinetic study of colored species formation during paracetamol removal from water in a semicontinuous ozonation contactor.

Paracetamol aqueous solutions, when ozonized, acquired a strong red coloration depending on the applied ozone dose and the initial pH of the aqueous solution. Then, this color loses intensity and turns to yellow. Color formation is favored when operating at initial pH0 = 12.0 and ozone flow-rate 4.2 mg/min. A mechanism describing color formation was proposed, being the main pathway involved an initial paracetamol hydroxylation to yield 3-hydroxyacetaminophen followed by the formation of 2-amino-5-hydroxyacetofenone. Then, these compounds are degraded to colored oxidation by-products. A model describing color evolution was also proposed, considering first-order kinetics for both color formation and degradation. The corresponding kinetic constant values were determined to be kf = 0.01 (1/min) and kd = 0.03 pH -0.055 (1/min), respectively. A relationship between aromaticity loss and color changes during the reaction has been estimated considering the parameter α=kA/kf, being α = 1.62 pH + 3.5 and the first-order rate constant for aromaticity loss given by kA = 0.0162 pH + 0.035 (1/min).

Exploring ozonation as treatment alternative for methiocarb and formed transformation products abatement.

Despite the high toxicity and resistance to conventional water treatments exhibited by methiocarb (MC), there are no reports regarding the degradation of this priority pesticide by means of alternative purification technologies. In this work, the removal of MC by means of ozonation was studied for the first time, employing a multi-reactor methodology and neutral pH conditions. The second-order rate constants of MC reaction with molecular ozone (O3) and formed hydroxyl radicals (OH·) were determined to be 1.7·106 and 8.2·109 M-1 s-1, respectively. During degradation experiments, direct ozone reaction was observed to effectively remove MC, but not its formed intermediates, whereas OH· could oxidize all species. The major identified TPs were methiocarb sulfoxide (MCX), methiocarb sulfoxide phenol (MCXP) and methiocarb sulfone phenol (MCNP), all of them formed through MC oxidation by O3 or OH· in combination with hydrolysis. A toxicity assessment evidenced a strong dependence on MCX concentration, even at very low values. Despite the OH· capability to degrade MC and its main metabolites, the relative resistance of TPs towards ozone attack enlarged the oxidant dosage (2.5 mg O3/mg DOC) necessary to achieve a relatively low toxicity of the medium. Even though ozonation could be a suitable technique for MC removal from water compartments, strategies aimed to further promote the indirect contribution of hydroxyl radicals during this process should be explored.

Priority pesticides abatement by advanced water technologies: The case of acetamiprid removal by ozonation.

With the aim of exploring treatment alternatives for priority insecticide acetamiprid (ACMP) abatement, the removal of this compound from water by ozonation was studied for the first time, paying special attention to the kinetic, mechanistic and toxicological aspects of the process. The second order rate constants of reactions between ACMP and both molecular ozone (O3) and hydroxyl radicals (OH) were determined to be 0.25M-1s-1 and 2.1·109M-1s-1, respectively. On the basis of kinetic results, the degradation of ACMP during ozonation could be well-explained by the reactivity of this pesticide with OH. HPLC/MS analysis of the ozonated ACMP showed ACMP-N-desmethyl, 6-chloronicotinic acid, N'cyano-N-methyl acetamidine and N'-cyano acetamidine as the major transformation products (TPs), all of them formed through amine α carbon oxidation in combination with hydrolysis. Microtox bioassays revealed an increase in the toxicity of the medium during ACMP ozonation process, followed by a decrease to relatively low values. These changes could be attributed to the synergistic effects between TPs as well as to the presence of toxic intermediate aldehydes. Even though adopting strategies to further promote ozone decomposition to hydroxyl radicals appears to be essential, ozonation can be an effective treatment process for ACMP removal and associated toxicity abatement.

Enhancement of Fenton and photo-Fenton processes at initial circumneutral pH for the degradation of the ß-blocker metoprolol.

The need for acidification in the Fenton and photo-Fenton process is often outlined as one of its major drawbacks, thus in this work the acidification of the Metoprolol (MET) is avoided by the addition of resorcinol (RES), which is used to simulate model organic matter. The experiments were carried out at natural pH (6.2) with different Fe(2+) (1, 2.5, 5, and 10 mg/L) and H2O2 (25, 50, 125 and 150 mg/L) concentrations. The performance of MET and RES degradation was assessed along the reaction time. Working with the highest concentrations (5 and 10 mg/L of ferrous iron and 125 and 150 mg/L of H2O2) more than 90% of MET and RES removals were reached within 50 and 20 min of treatment, respectively, by Fenton process. However a low mineralization was achieved in both cases, likely, due to by-products accumulation. Regarding to photo-Fenton process, within 3 min with the highest iron and hydrogen peroxide concentrations, a complete MET degradation was obtained and 95% of RES conversion was achieved. Parameters such Total Organic Carbon, Chemical Oxygen Demand, and AOS were measured. Intermediates were identified and MET degradation path was proposed in the presence of resorcinol. Finally, a comparison between Fenton and photo-Fenton processes at acid pH and at initial circumneutral pH was discussed. The positive effect of RES on Fenton and photo-Fenton systems has been confirmed, allowing the work at circumneutral pH.

Oestrogenicity assessment of s-triazines by-products during ozonation.

The triazines are a group of herbicides with a wide range of uses. Atrazine is, in fact, one of the most used agricultural pesticides in the world. The terbuthylazine is applied as a substitute of atrazine in some countries of Europe since 2004, when the European Union announced a ban of atrazine because of ubiquitous water contamination. In this study, both atrazine and terbuthylazine were degraded by the ozone process to estimate the efficiency on pesticide removal in water, the intermediates formed and their potential oestrogenic activity using the yeast oestrogen screen (YES) test. Both pesticides were rapidly eliminated from the medium during ozonation (applied ozone dose 0.083 and 0.02 mmol O3 L(-1), respectively). The results show that both compounds generated similar by-products from ozone degradation. Moreover, significant oestrogenic activity was detected for both atrazine and terbuthylazine intermediates, during the first minutes of ozonation. The YES assay used in this study proved to be a sensitive tool in assessing trace amounts of oestrogenic chemicals, which can represent critical issues influencing the experimental results in environmental applications.

Advanced UV/H2O2 oxidation of deca-bromo diphenyl ether in sediments.

Removal of BDE-209 from contaminated sediments by UV/H2O2 treatment was investigated under different reaction conditions (different UV irradiance and H2O2 concentrations). After 10h of UV/H2O2 treatment, 90% of BDE-209 was removed with a half-life time (t1/2) of 3.5h and a kinetic constant (k) of 0.22 h(-1). Possible formation of OH-PBDEs and debrominated polybromodiphenyl ethers was investigated by GC-MS and LC-MS/MS. None of the abovementioned BDE-209 by-products was found after 2.5, 5.5 and 10h of UV/H2O2 treatment. Toxicity experiments carried out with zebrafish embryos exposed to the sediment before and after the UV/H2O2 treatment did not show any morphological or behavioural alterations, suggesting that no putative debrominated or oxidation products were originated by the treatment in concentrations high enough to elicit significant toxic effects in zebrafish embryos.

Reverse osmosis concentrate treatment by chemical oxidation and moving bed biofilm processes.

In the present work, four oxidation techniques were investigated (O3, O3/UV, H2O2/O3, O3/H2O2/UV) to pre-treat reverse osmosis (RO) concentrate before treatment in a moving-bed biofilm reactor (MBBR) system. Without previous oxidation, the MBBR was able to remove a small fraction of the chemical oxygen demand (COD) (5-20%) and dissolved organic carbon (DOC) (2-15%). When the concentrate was previously submitted to oxidation, DOC removal efficiencies in the MBBR increased to 40-55%. All the tested oxidation techniques improved concentrate biodegradability. The concentrate treated by the combined process (oxidation and MBBR) presented residual DOC and COD in the ranges of 6-12 and 25-41 mg L(-1), respectively. Nitrification of the RO concentrate, pre-treated by oxidation, was observed in the MBBR. Ammonium removal was comprised between 54 and 79%. The results indicate that the MBBR was effective for the treatment of the RO concentrate, previously submitted to oxidation, generating water with an improved quality.

Pharmaceuticals and organic pollution mitigation in reclamation osmosis brines by UV/H2O2 and ozone.

One significant disadvantage of using reverse osmosis (RO) for reclamation purposes is the need to dispose of the RO retentates. These retentates contain a high concentration of micropollutants, effluent organic matter (EfOM) and other inorganic constituents, which are recalcitrant to biological treatment and may impact the environment. The occurrence of 11 pharmaceuticals (concentrations ranging from 0.2 to 1.6 µg L(-1)) and their mitigation in RO retentates by a UV/H2O2 process and ozonation was studied using a wide range of oxidant dosages. Eleven pharmaceuticals were identified at. Initial observed kinetic constants (kobs) were calculated for the different pharmaceuticals. Other typical wastewater parameters were also monitored during the UV/H2O2 and ozonation reactions. The range for kobs was found to be 0.8-12.8L mmol O3(-1) and 9.7-29.9 L mmol H2O2(-1) for the ozonation and UV/H2O2 process, respectively. For ozonation, Atenolol, Carbamazepine, Codeine, Trimethoprim and Diclofenac showed the lowest initial kobs (in the order mentioned). Atenolol and Carbamazepine appeared as the most ozone resistant pharmaceuticals, exhibiting the lowest percentage of elimination at low ozone doses. On the other hand, despite the non-selectivity of HO, differences in the initial kobs were also observed during the UV/H2O2 process. Trimethoprim, Paroxetine and Sulfamethoxazole exhibited the lowest initial kobs values (in the order mentioned). Trimethoprim and Paroxetine also exhibited the lowest percentage removal when low H2O2 doses were assayed. The compounds that were identified as problematic during ozonation were more efficiently removed by the UV/H2O2 process. UV/H2O2 generally appeared to be a more efficient technology for removing pharmaceuticals from RO brines compared to ozonation.

Evaluation of copper slag to catalyze advanced oxidation processes for the removal of phenol in water.

The aim of this work was to evaluate the use of copper slag to catalyze phenol degradation in water by advanced oxidation processes (AOPs). Copper slag was tested in combination with H(2)O(2) (slag/H(2)O(2)) and H(2)O(2)/UV (slag/H(2)O(2)/UV). The studied methods promoted the complete photocatalytic degradation of phenol. Besides, they were able to reduce about 50% the TOC content in the samples. Slag/H(2)O(2)/UV and slag/H(2)O(2) treatments have favored biodegradability increment along the reaction time. Nevertheless, the irradiated method achieved higher values of the biodegradability indicator (BOD(5)/TOC). The toxicity assessment indicated the formation of more toxic compounds in both treatments. However, the control of the reaction time would minimize the environmental impact of the effluents.

Degradation of 32 emergent contaminants by UV and neutral photo-fenton in domestic wastewater effluent previously treated by activated sludge.

This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L(-1), and a real global quantity of micropollutants of 29.5 µg L(-1). The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV(254)) alone, dark Fenton (Fe(2+,3+)/H(2)O(2)) and photo-Fenton (Fe(2+,3+)/H(2)O(2)/light). Different irradiation sources were used for the photo-Fenton experiences: UV(254) and simulated sunlight. Iron and H(2)O(2) concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV(254), 50 mg L(-1) of H(2)O(2), with and without adding iron (5 mg L(-1) of Fe(2+) added or 1.48 mg L(-1) of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treatments. As the H(2)O(2) concentration increased (10, 25 and 50 mg L(-1)), best degradations were observed. UV(254), Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal. The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations.

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. TiO(2) photocatalysis, photo-Fenton and sonolysis - all of them under solar simulated illumination - were tested in the hybrid systems: sonophoto-Fenton (FS), sonophotocatalysis (TS) and TiO(2)/Fe(2+)/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 TiO(2) in the presence of ultrasound irradiation (TS). In contrast only 26% of mineralization was observed by photocatalysis with H(2)O(2) (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.

Application of solar advanced oxidation processes to the degradation of the antibiotic sulfamethoxazole.

This work deals with the treatment of highly concentrated sulfamethoxazole (SMX) solutions by some advanced oxidation processes (AOPs) that have not been studied until now. The antibiotic has been subjected to oxidation by photolysis, UV/H(2)O(2) and photo-Fenton using both artificial light and sunlight as radiation sources depending on the installation scale. SMX, total organic carbon (TOC) and chemical oxygen demand (COD), as well as the generation of NH(4)(+), NO(3)(-) and SO(4)(2-), were followed. SMX photolytic degradation efficiency followed the ranking: 254 nm lamps > sunlight > black-light blue (BLB) lamps (negligible for the latter). The highest eliminations were obtained by means of UV/H(2)O(2) reaction in a lab-scale reactor (254 nm lamps) with an initial H(2)O(2) concentration of 200 mg L(-1): DeltaTOC = 62.3%; DeltaCOD = 79.1% (more than 6 h). Similar removals were achieved with a lab-scale photo-Fenton reactor (BLB lamps) but using 400 mg L(-1) of oxidant (94 min). The use of solar light appeared to be an interesting option since satisfactory results were obtained in the solar-based photo-Fenton experiments compared to the lab-scale ones, and also since a significant improvement with respect to the solar photolysis was achieved when performing the UV/H(2)O(2) reaction with sunlight. Finally, some of the resultant effluents from different reactions were subjected to a short-term biodegradability test in order to estimate their quality from a biological point of view.

Combination of photo-Fenton and biological SBBR processes for sulfamethoxazole remediation.

A combined strategy of a photo-Fenton pretreatment followed by a Sequencing Batch Biofilm Reactor (SBBR) was evaluated for total C and N removal from a synthetic wastewater containing 200 mg L(-1) of the antibiotic Sulfamethoxazole (SMX). Photo-Fenton reaction was performed with two different H2O2 concentrations (300 and 400 mg L(-1)) and 10 mg L(-1) of Fe2+. The pre-treated effluents with the antibiotic intermediates as sole carbon source, together with a nutrients solution, were used as feed for the biological reactor. The SBBR was operated under aerobic conditions to mineralize the organic carbon and the hydraulic retention time (HRT) was optimized down to 8 hours. Then, an anoxic denitrification stage of 24 hours of HRT was added right after the aerobic stage of the same duration in order to remove the NO3(-) generated along the chemical-biological treatment. TOC, COD and SMX concentrations together with O2 uptake rate (OUR) profiles were monitored in purpose of assessing the performance of the system. NO3(-), NH4+ and total N concentrations were analyzed to find out the fate of N contained in the initial SMX molecule. A start up strategy resulted in the correct formation of a biofilm over the volcanic support. The total TOC removals achieved with the combination of the chemical and the biological processes were 75.7 and 87.7% for the low and the high H2O2 concentration pretreatments respectively. Practically all N present in the SMX solution was eliminated in the SBBR when the aerobic-anoxic strategy was used.

Ultrasonic treatment of water contaminated with ibuprofen.

The application of ultrasound (US) waves for remediation of wastewater is an area of increasing interest and promising results. The aim of this paper is to evaluate the influence of several parameters of the US process on the degradation of ibuprofen (IBP), a widely used non-steroidal anti-inflammatory recalcitrant drug found in water. Applied US power, dissolved gas, pH and initial concentration of IBP were the parameters investigated under sonication (300 kHz). Ultrasound increased the degradation of IBP from 30 to 98% in 30 min. Initial rate of IBP degradation was evaluated in the range of 1.35 and 6.1 micromolL(-1)min(-1) for initial concentrations of 2 to 21 mgL(-1) or 9.7 micromolL(-1) to 101 micromolL(-1), respectively. Under air and oxygen the degradation rate of IBP was 4 micromolL(-1)min(-1) being higher than that when argon was used. The most favorable degradation pH was acidic media. Complete removal of IBP was achieved but some dissolved organic carbon (DOC) remained in solution showing that long-lived intermediates were recalcitrant to the US irradiation. However, chemical and biological oxygen demands (COD and BOD(5)) indicated that the process oxidize the ibuprofen compound to biodegradable substances removable in a subsequent biological step.

Coupled photochemical-biological system to treat biorecalcitrant wastewater.

The aim of the present work is to study a coupled system to treat biorecalcitrant wastewaters. The combination consists of an advanced oxidation process (AOP) named photo-Fenton (Ph-F), which is a photochemical treatment and a sequencing batch biofilter reactor (SBBR). The synthetic wastewater used to optimise this process is a solution of 200 ppm of 4-chlorophenol (4-CP). The first part of the work is the study of the biodegradability enhancement achieved by the photochemical process, measured as the ratio between the biochemical oxygen demand (BOD5) and the chemical oxygen demand (COD). The second step is the start-up and optimisation of the biological process. The results showed that it is necessary to severely treat the toxic solution (with 500 ppm of [H2O2]0) in order to achieve more than 90% of TOC removal in the whole process. The photochemical and biological treatments lasted 50 minutes and 24 hours, respectively.

Approach to TiO2-light interaction in heterogeneous photocatalysis.

Photocatalysis can be a useful tool in the treatment of some recalcitrant and toxic pollutants. In fact, it is being applied today in several industrial processes. However some problems arise in the modelling of photocatalytic systems, most of them related to the radiation field. In this work, some methods are presented which can be powerful tools in the evaluation of the radiation absorbed by the photocatalyst, which is the energy really useful in promoting the photocatalytic process. All these methods are based on actinometric procedures carried out in different experimental conditions and using different photoreactors.

Degradation of 2,4-dichlorophenol by combining photo-assisted Fenton reaction and biological treatment.

The photo-Fenton reaction effect on the biodegradability improvement of 100 mg/L solution of 2,4-dichlorophenol (DCP) has been investigated. Biochemical oxygen demand (BOD) at 5 and 21 days, BODn/ chemical oxygen demand (COD) and BODn/total organic carbon (TOC) ratios, average oxidation state, and inhibition on activated sludge were monitored. For 50 mg/L hydrogen peroxide and 10 mg/L iron(II) initial concentrations and 40 minutes of reaction time in the photo-Fenton process, the biodegradability of the pretreated solution, measured as BOD5/COD ratio, was improved from 0 for the original DCP solution up to 0.18 (BOD21/COD = 0.24). At that point, all DCP was eliminated from the solution. To study the effect of the pretreatment step, the biological oxidation of pretreated solutions was tested in two semicontinuous stirred tank reactors, one operated with activated sludge and one with biomass acclimated to phenol. Results showed that more than 80% TOC removal could be obtained by codigestion of the pretreated solution with municipal wastewater. Total organic carbon removals of approximately 60% were also obtained when the sole carbon source for the aerobic reactors was the pretreated solution. The hydraulic retention times used in the bioreactors were of the same order of magnitude as those used at domestic wastewater treatment plants (i.e., between 12 and 24 hours). Kinetic studies based on pseudo-first-order kinetics have also been carried out. Constants were found to be in range 0.67 to 1.7 L x g total volatiles suspended solids(-1) x h(-1).

Combining photo-Fenton process with biological sequencing batch reactor for 2,4-dichlorophenol degradation.

The effect of the photo-Fenton process on biodegradability enhancement of 100 mg x L(-1) aqueous 2,4-dichlorophenol (2,4-DCP) solution has been investigated. An initial concentration of 65 mg x L(-1) H2O2 and 10 mg x L(-1) Fe (II) during 35 minutes of irradiation time was sufficient for total 2,4-DCP removal. At these working conditions, biodegradability, measured as BODS/COD ratio, was increased from 0 for the original solution up to 0.15. Biological oxidation of photo-Fenton pre-treated solutions was performed in a sequencing batch reactor (SBR). After 32 days of start-up, the reactor was fed with different pre-treated solutions and cycle duration was reduced progressively. TOC removal efficiencies in the SBR went from 30 up to 70%.