Francisco J. Real

Degradation of carbofuran by using ozone, UV radiation and advanced oxidation processes.

The degradation of carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate), a frequently used carbamate derivative pesticide that is considered a priority pollutant, is carried out in batch reactors by means of single oxidants: ozone, UV radiation and Fentons reagent; and by the advanced oxidation processes (AOPs) constituted by combinations of ozone plus UV radiation, UV radiation plus H(2)O(2), and UV radiation plus Fentons reagent (photo-Fenton system). For all these reactions, the apparent pseudo-first-order rate constants are evaluated in order to compare the efficiency of each process. In addition and by means of a competition kinetic model, the rate constants for the reaction of carbofuran with ozone and with hydroxyl radicals are also determined. The improvement in the decomposition levels of carbofuran reached by the combined processes in relation to the single oxidants, due to the generation of the very reactive hydroxyl radicals, is also established in every process. For the oxidant concentrations applied, the most effective process in removing carbofuran was the photo-Fenton system.

The role of hydroxyl radicals for the decomposition of p-hydroxy phenylacetic acid in aqueous solutions.

The chemical decomposition of p-hydroxyphenylacetic acid, a priority phenolic pollutant present in wastewaters from some agro-industrial plants, is studied by means of a single photochemical process produced by a polychromatic UV radiation and by hydroxyl radicals generated by the combination of UV radiation plus hydrogen peroxide and by the Fentons reagent (hydrogen peroxide plus ferrous salts). Batch experiments were conducted to establish the degradation levels obtained and the quantum yields in the single photodecomposition process. An improvement in the decomposition of the phenolic acid in the combined UV/H2O2 oxidation is observed, due to the generation of OH radicals, and the contribution of the radical reaction to the global process is determined. In the Fentons reagent oxidation, the effects of the operating variables (H2O2 and Fe2+ initial concentrations, pH, type of buffer used) are established and the rate constant for the reaction of p-hydroxyphenylacetic acid with OH radicals is evaluated from a kinetic model, its value being 7.02 x 10(8) M-1 s-1 at 20 degrees C.

Ozonation of pharmaceutical compounds: Rate constants and elimination in various water matrices

The ozonation of four pharmaceuticals (metoprolol, naproxen, amoxicillin, and phenacetin) in ultra-pure (UP) water was studied in the pH range between 2.5 and 9. The experiments allowed the determination of the apparent rate constants for the reactions between ozone and the selected compounds. The values obtained varied depending on the pH, and ranged between 239 and 1.27x10(4)M(-1) s(-1) for metoprolol; 2.62x10(4) and 2.97x10(5)M(-1)s(-1) for naproxen; 2.31x10(3) and 1.21x10(7)M(-1)s(-1) for amoxicillin; and 215 and 1.57x10(3)M(-1)s(-1) for phenacetin. Due to the acidic nature of these substances, the degree of dissociation of each pharmaceutical was determined at every pH of work, and the specific rate constants of the neutral and ionic species formed were evaluated. Additionally, the simultaneous ozonation of the pharmaceuticals in different water matrices was carried out by considering a groundwater, a surface water from a public reservoir, and three secondary effluents from municipal wastewater treatment plants. The influence of the operating conditions (initial ozone dose, nature of pharmaceuticals and type of water) on the pharmaceuticals elimination efficiency was established, and a kinetic model was proposed for the evaluation of the partial contribution to the global oxidation of both, the direct ozonation reaction and the radical pathway.

Kinetics of aqueous chlorination of some pharmaceuticals and their elimination from water matrices

Apparent rate constants for the reactions of four selected pharmaceutical compounds (metoprolol, naproxen, amoxicillin, and phenacetin) with chlorine in ultra-pure (UP) water were determined as a function of the pH. It was found that amoxicillin (in the whole pH range 3-12), and naproxen (in the low pH range 2-4) presented high reaction rates, while naproxen (in the pH range 5-9), and phenacetin and metoprolol (in the pH range 2.5-12 for phenacetin, and 3-10 for metoprolol) followed intermediate and slow reaction rates. A mechanism is proposed for the chlorination reaction, which allowed the evaluation of the intrinsic rate constants for the elementary reactions of the ionized and un-ionized species of each selected pharmaceutical with chlorine. An excellent agreement is obtained between experimental and calculated rate constants by this mechanism.The elimination of these substances in several waters (a groundwater, a surface water from a public reservoir, and two effluents from municipal wastewater treatment plants) was also investigated at neutral pH. The efficiency of the chlorination process with respect to the pharmaceuticals elimination and the formation THMs was also established. It is generally observed that the increasing presence of organic and inorganic matter in the water matrices demand more oxidant agent (chlorine), and therefore, less chlorine is available for the oxidation of these compounds. Finally, half-life times and oxidant exposures (CT) required for the removal of 99% of the four pharmaceuticals are also evaluated. These parameters are useful for the establishment of safety chlorine doses in oxidation or disinfection stages of pharmaceuticals in treatment plants.

Membrane filtration technologies applied to municipal secondary effluents for potential reuse.

Four UF membranes (denoted GH, GK, PT and PW with MWCO of 1000, 2000, 5000 and 20,000Da, respectively) and four NF membranes (denoted DL, CK, DK and HL, with an approximate MWCO of 150-300Da in all cases) were used for the filtration of an effluent generated in a municipal wastewater plant after a secondary treatment. The influence of the most important operating variables (nature and MWCO of the membranes, transmembrane pressure, tangential velocity, and temperature) on the permeate flux was widely discussed, and the resistances to the permeate flux were determined following the resistances in series model. Rejection coefficients for parameters that measure the global pollutant content of the effluent (chemical oxygen demand, total organic carbon, absorbance at 254nm, turbidity, total nitrogen and total phosphorus) were also evaluated, and the results revealed that both UF and NF are feasible options for the treatment of this effluent, yielding a permeate stream that can be reused in several applications. Finally, 28 pharmaceutical compounds were initially detected in this effluent, and their respective rejection coefficients were determined, with eliminations higher than 75% in the case of NF with the HL membrane. Therefore, it is concluded that NF is an excellent option for the removal of toxic pharmaceuticals in municipal wastewaters.

Kinetics of photodegradation and ozonation of pentachlorophenol

The oxidation of 2,3,4,5,6-pentachlorophenol (PCP) has been carried out by a photodecomposition process using a polychromatic UV irradiation, and by an ozonation process. In the photodegradation process, the pH accelerated the decomposition rate and the approximate first-order rate constants were evaluated, with values between 0.16+/-0.005 min(-1) at pH=3 and 0.26+/-0.007 min(-1) at pH=9. A more rigorous kinetic study led to the determination of the quantum yields of the reaction, with values of 200+/-7x10(-3) mol/Eins for pH=3 and 22+/-1.1x10(-3) mol/Eins for pH=9. In the ozonation process, the rate constants for the reaction between ozone and PCP were determined by means of a competition kinetics, with values in the range from 0.67x10(5) to 314x10(5) l/mols. The specific rate constants for the un-dissociated and dissociated forms of PCP were also calculated. Finally, in both processes, the intermediate reaction products were identified, the most important being tetrachlorocatechol, tetrachlorohydroquinone and tetra-p-chlorobenzoquinone. Free chloride ion released, which was favored at high pHs, was also followed in both processes.

Photolysis of model emerging contaminants in ultra-pure water: kinetics, by-products formation and degradation pathways.

The photolysis of five frequent emerging contaminants (Benzotriazole, Chlorophene, N,N-diethyl-m-toluamide or DEET, Methylindole, and Nortriptyline HCl) was investigated in ultrapure water under monochromatic ultraviolet radiation at 254 nm and by a combination of UV and hydrogen peroxide. The results revealed that the photolysis rates followed first-order kinetics, with rate constant values depending on the nature of the specific compound, the pH, and the presence or absence of the scavenger tert-butanol. Quantum yields were also determined and values in the range of 53.8 × 10⁻³ - 9.4 × 10⁻³ mol E⁻¹ for Benzotriazole, 525 × 10⁻³ - 469 × 10⁻³ mol E⁻¹ for Chlorophene, 2.8 × 10⁻³ - 0.9 × 10⁻³ mol E⁻¹ for DEET, 108 × 10⁻³ - 165 × 10⁻³ mol E⁻¹ for Methylindole, and 13.8 × 10⁻³ - 15.0 × 10⁻³ mol E⁻¹ for Nortriptyline were obtained. The study also found that the UV/H₂O₂ process enhanced the oxidation rate in comparison to direct photolysis. High-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS) technique was applied to the concentrations evaluation and further identification of the parent compounds and their by-products, which allowed the proposal of the degradation pathways for each compound. Finally, in order to assess the aquatic toxicity in the photodegradation of these compounds, the Vibrio fischeri acute toxicity test was used, and the results indicated an initial increase of this parameter in all cases, followed by a decrease in the specific case of Benzotriazole, DEET, Methylindole, and Chlorophene.

Removal of phenyl-urea herbicides in ultrapure water by ultrafiltration and nanofiltration processes.

Membrane filtration of four phenyl-urea herbicides (linuron, diuron, chlortoluron, and isoproturon) dissolved in ultrapure water was studied in a laboratory cross-flow device in batch concentration mode (with recycling of the retentate stream). Three UF (MWCO of 20 000, 5000 and 2000Da) and three NF (MWCO of 150-300Da) membranes were used. The influence of the main operating conditions (transmembrane pressure, tangential velocity, temperature, pH, and MWCO of the membranes) on the steady-state permeate fluxes and the retention factors of the phenyl-ureas was evaluated. The herbicide mass adsorbed onto the membranes was also determined, and the contribution of the fouling resistance to the total resistance to permeate flux was much lower than the inherent resistance of the clean membranes.

Oxidation of MCPA and 2,4-d by UV Radiation, Ozone, and the Combinations UV/H2O2 and O3/H2O2

Abstract The phenoxyalkyl acid derivative herbicides MCPA (4-chloro 2-methylphenoxyacetic acid) and 2,4-d (2,4-dichlorophenoxyacetic acid) were oxidized in ultrapure water by means of a monochromatic UV irradiation and by ozone, as well as by the combinations UV/H2O2 and O3/H2O2. In the direct photolysis of MCPA, the quantum yield at 20°C was directly evaluated and a value of 0.150 mol Eins−1 was obtained in the pH range 5–9, while a lower value of 0.41 × 10−2 mol Eins−1 was determined at pH = 3. Similarly, for 2,4-d a value of 0.81 × 10−2 mol Eins−1 was deduced, independent of the pH of work. The influence of the additional presence of hydrogen peroxide was established in the combined process UV/H2O2, and the specific contribution of the radical pathway to the global photo-degradation was evaluated. The oxidation by ozone and by the combination O3/H2O2 was also studied, with the determination of the rate constants for the reactions of both herbicides with ozone and hydroxyl radicals at 20°C. These rate constants for the direct reactions with ozone were 47.7 and 21.9 M−1 s−1 for MCPA and 2,4-d respectively, while the found values for the rate constants corresponding to the radical reactions were 6.6 × 109 and 5.1 × 109 M−1 s−1.

Removal of phenolic compounds in water by ultrafiltration membrane treatments

The ultrafiltration (UF) of aqueous solutions containing mixtures of three phenolic compounds (gallic acid, acetovanillone, and esculetin) was studied in a tangential UF laboratory system. These substances were selected as model pollutants present in the tannic fraction of the cork processing wastewaters. The two membranes used were a polyethersulfone membrane (Biomax5KTM) and a regenerated cellulose membrane (Ultracel5KTM), both with a molecular weight cut-off (MWCO) of 5000 Da. Previous experiments for the characterization of the membranes led to values for the water hydraulic permeability of 70.3 and 18.1 L/h · m2 · bar for the Biomax5K and Ultracel5K membranes, respectively. During the UF experiments, the permeate flow rate remained almost constant with processing time and the evolution of the pollutants concentrations varied depending on the nature of the membranes and the substances. The influence of the main operating variables (tansmembrane pressure and feed flow rate) on the permeate flux was established, and values for the apparent and intrinsic rejection coefficients were evaluated. Cork processing wastewater UF experiments were also conducted under similar operating conditions to those applied to the ultrapure water solutions. Removals of chemical oxygen demand, aromatic and tannic contents, and color were determined in these experiments, and the elimination of the three model compounds in the wastewater was also followed, with the evaluation of their apparent rejection coefficients.