Pedro Letón

Removal of pharmaceuticals and kinetics of mineralization by O3/H2O2 in a biotreated municipal wastewater

The ozonation of an effluent from the secondary clarifier of two Municipal Wastewater Treatment Plants was performed by using alkaline ozone and a combination of ozone and hydrogen peroxide. Alkaline ozonation achieved only a moderate degree of mineralization, essentially concentrated during the first few minutes; but the addition of hydrogen peroxide eventually led to a complete mineralization. The evolution of total organic carbon (TOC) as a measure of the extent of mineralization and the concentration of dissolved ozone were analyzed and linked in a kinetic model whose parameter represented the product of the exposure to hydroxyl radicals and the kinetic constant of indirect ozonation. This rate parameter yielded the highest values during the first part of O(3)/H(2)O(2) runs. The kinetic constant for the decomposition of ozone at the end of the run was also measured and computed for the non-oxidizable water matrix and yielded essentially the same values regardless of whether or not hydrogen peroxide was used. A group of 33 organic compounds, mainly pharmaceuticals and some relevant metabolites present in the wastewater effluents, were evaluated before and after the ozonation process using a liquid chromatography-hybrid triple-quadrupole linear ion trap system (LC-QqLIT-MS). The results demonstrate that the ozonation degrades these compounds with efficiencies of over 99% in most cases, even under low mineralization conditions in alkaline ozonation.

Identification of intermediates and assessment of ecotoxicity in the oxidation products generated during the ozonation of clofibric acid.

The degradation of an aqueous solution of clofibric acid was investigated during catalytic and non-catalytic ozonation. The catalyst, TiO(2), enhanced the production of hydroxyl radicals from ozone and raised the fraction or clofibric acid degraded by hydroxyl radicals. The rate constant for the reaction of clofibric acid and hydroxyl radicals was not affected by the presence of the catalyst. The toxicity of the oxidation products obtained during the reaction was assessed by means of Vibrio fischeri and Daphnia magna tests in order to evaluate the potential formation of toxic by-products. The results showed that the ozonation was enhanced by the presence of TiO(2,) the clofibric acid being removed completely after 15 min at pH 5. The evolution of dissolved organic carbon, specific ultraviolet absorption at 254 nm and the concentration of carboxylic acids monitored the degradation process. The formation of 4-chlorophenol, hydroquinone, 4-chlorocatechol, 2-hydroxyisobutyric acid and three non-aromatic compounds identified as a product of the ring-opening reaction was assessed by exact mass measurements performed by liquid chromatography coupled to time-of-flight mass spectrometry (LC-TOF-MS). The bioassays showed a significant increase in toxicity during the initial stages of ozonation following a toxicity pattern closely related to the formation of ring-opening by-products.

Biodesulfurization of dibenzothiophene by growing cells of Pseudomonas putida CECT 5279 in biphasic media

Several studies have proven that natural or genetically modified bacteria, such as Pseudomonas putida strain, degrade recalcitrant organic sulfur compounds. However, from a practical point of view, the biodesulfurization (BDS) process has to be performed with really high proportions of organic solvents. In this work, the dibenzothiophene (DBT) was selected as recalcitrant model compound, and hexadecane as model organic solvent. It has been observed that P. putida CECT 5279 was able to desulfurize DBT even in the presence of 50% (v/v) of hexadecane. A concentration of 400 ppm of DBT was converted at a specific rate of generation of desulfurized final product, 2-hydroxybiphenyl (HBP), of 2.3 and 1.5 mg HBP L-1 (g DC L-1 h)-1 for 27% and 50% (v/v) of hexadecane, respectively. Finally, the Haldane kinetic model was used to describe the process evolution. The study is relevant as it has been proven that the strain CECT 5279 is a potential biocatalyst for developing an efficient BDS process.

Ozone-Based Technologies in Water and Wastewater Treatment

Ozone is a strong oxidant that can be used in the potabilization of surface or ground water as well as in wastewater treatment to remove microorganisms, inorganic ions and organic pollutants. The oldest use of ozone is as a biocide in drinking water potabilization. The integral ozone exposure required for a given degree of disinfection can be calculated from the deactivation kinetic constant of the microorganism. Ozone removes iron, manganese and arsenic from water by oxidation to an insoluble form that is further separated by filtration. Both processes require ozone in molecular form, but the removal of organic pollutants that are refractory to other treatments can be possible only by exploiting the indirect radical reactions that take place during ozonation. Ozone decomposes in water, especially when hydrogen peroxide is present, to yield the hydroxyl radical, the strongest oxidizer available in water treatment. Models for the ozonation process are required to adjust the ozone dosing to the desired degree of removal of a given pollutant or an aggregate measure of pollution. Mineralization, defined as the removal of organic carbon, has been accomplished in wastewaters from urban and domestic treatment plants. The results show that the logarithmic decrease of TOC as a function of the integral ozone exposure usually presents two zones with different kinetic parameters. Among advanced oxidation processes, a promising alternative currently under development is the use of ozone in combination with solid catalysts. The mechanism of catalytic ozonation is not clear, but in the case of metal oxides, the adsorption of ozone or organic compounds on Lewis acid sites is only possible near the point of zero charge of the surface. Activated carbon seems to behave as an initiator of ozone decomposition, a role that may also occur with other types of catalysts. Some results on the mineralization of water with the drugs naproxen (non-steroidal anti-inflammatory) and carbamazepine (anticonvulsant) are presented using titanium dioxide as catalyst.

Continuous ozonation treatment of ofloxacin: transformation products, water matrix effect and aquatic toxicity.

The continuous ozonation of the antibiotic ofloxacin (OFX) has been performed using a synthetic water matrix and in a sewage treatment plant (STP) effluent. The aim was to study the effect of the water matrix on the ozonation with particular emphasis on the aquatic toxicity of treated water. OFX was completely removed in both water matrices, although the amount of ozone consumed for its depletion was strongly matrix-dependent. The extent of mineralization was limited and a number of intermediate transformation products (TPs) appeared, twelve of which could be identified. OFX reaction pathway includes the degradation of piperazinyl and quinolone moieties. The further oxidation of TPs gave rise to the formation and accumulation of carboxylic acids, aldehydes, nitrogen-containing organic compounds and inorganic ions. Aquatic toxicity of treated mixtures was assessed using four standard species: the bacteria Vibrio fischeri and Pseudomonas putida as target organisms and the algae Pseudokirchneriella subcapitata and the protozoan Tetrahymena thermophila as non-target organisms. OFX was toxic for the bacteria and the microalgae at the spiked concentration in untreated water. However, the continuous ozonation at the upper operational limit removed its toxic effects. T. thermophila was not affected by OFX, but was sensitive to STP effluent.

Prediction of gas hold-up and liquid velocity in airlift reactors using two-phase flow friction coefficients

The overall friction coefficient (K f ) of airlift reactors was estimated using equivalent lengths (L eq ) and friction factors (f). The friction factor was calculated taking into account the riser liquid velocity profile corresponding to the two-phase flow and using classical one-phase equations. A previously described model was used to obtain simultaneously both gas hold-up and liquid circulation velocity. The model simulates experimental data obtained in a wide range of configurations of internal (2 and 30 dm 3 volume) and external (from 8 to 600 dm 3 volume) airlift reactors with Newtonian (water and alcohol solutions) and non-Newtonian (carboxymethylcellulose (CMC) solutions) systems. Comparison with other models from the literature yielded similar results.

Description of by-product inhibiton effects on biodesulfurization of dibenzothiophene in biphasic media

As several authors have reported previously, the Biodesulfurization of hydrodesulfurization recalcitrants, such as dibenzothiophene, is not yet commercially viable because mass transfer limitations and feedback inhibition effects are produced during the conversion. This work has been focused to investigate the inhibition process in aqueous and oil-water systems with two different aerobic biocatalysts types, Rhodococcus erythropolis IGTS8 and Pseudomonas putida CECT 5279. The results obtained have proven that global DBT desulfurization process using CECT 5279 was not clearly deactivated due to final product accumulation, under the experimental conditions assayed. Consistently, the desulfurization pattern has been described with the Michaelis-Menten equation, determining the kinetic parameters. On other hand, the assays have shown that important mass transfer limitations produced the decrease of the yields obtained with this Gram− strain in biphasic media. With strain IGTS8 it was observed lower mass transfer problems, but contrary the reaction was severely affected by the final product accumulation, in both aqueous and biphasic systems. Therefore it has been proposed an enzymatic kinetic model with competitive inhibition to describe the BDS evolution pattern when this Gram+ strain was used.

Antimicrobial activity of poly(vinyl alcohol)-poly(acrylic acid) electrospun nanofibers

Electrospun nanofibers were prepared from blends of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA). The fibers were stabilized by heat curing at 140°C via anhydride and ketone formation and crosslinking esterification. The antimicrobial effect was assessed using strains of Escherichia coli and Staphylococcus aureus by tracking their capacity to form colonies and their metabolic impairment upon contact with PAA/PVA membranes. Membranes containing >35wt.% PAA displayed significant antibacterial activity, which was particularly high for the gram-positive S. aureus. All membranes were negatively charged, with surface ζ-potential in the (-34.5)-(-45.6)mV range, but the electrostatic interaction with the negatively charged cells was not the reason for the antimicrobial effect. Neither pH reduction nor the passing of non-crosslinked polymers to the solution affected microbial growth. The antibacterial activity was attributed to the chelation of the divalent cations stabilizing the outer cell membrane. The effect on gram-positive bacteria was attributed to the destabilization of the peptidoglycan layer. The sequestration of divalent cations was demonstrated with experiments in which calcium and a chelating agent were added to the cultures in contact with membranes. The damage to bacterial cells was tracked by measuring their surface charge and the evolution of intracellular calcium during the early stages after contact with PAA/PVA membranes.

Toxicological interactions of ibuprofen and triclosan on biological activity of activated sludge

The growing use of pharmaceutical and personal care products increases their concentrations in the wastewater entering treatment plants and their levels into biological reactors. The most extended biological wastewater treatment is the activated sludge process. The toxicity of ibuprofen and triclosan, individually and combined, was studied by tracking the biological activity of the activated sludge measuring oxygen uptake rate and the inhibition of the esterase activity. Short-term exposure produced significant inhibition in oxygen uptake, with lower damage to enzymatic activity. Median effect values for oxygen uptake inhibition were 64±13mgL-1 and 0.32±0.07mgL-1 for ibuprofen and triclosan respectively using 125mgL-1 activated sludge. For the inhibition of enzymatic activity values were 633±63mgL-1 for ibuprofen and 1.94±0.32mgL-1 for triclosan. Results indicated that oxygen uptake, related to primary activity of microorganisms, was more strongly affected than the enzymatic activity associated to energy consumption. Toxicity interactions were determined using the Combination Index-isobologram method. Results showed antagonism at lower values of affected population, after which the mixtures tended to additivity and synergism. For the case of enzymatic activity, the antagonism was less marked and the additivity range was higher.

Determination of PASHs by various analytical techniques based on gas chromatography-mass spectrometry Application to a biodesulfurization process

Polycyclic aromatic sulphur heterocyclic (PASH) compounds, such as dibenzothiophene (DBT) and alkylated derivatives are used as model compounds in biodesulfurization processes. The development of these processes is focused on the reduction of the concentration of sulphur in gasoline and gas-oil [D.J. Monticello, Curr. Opin. Biotechnol. 11 (2000) 540], in order to meet European Union and United States directives. The evaluation of biodesulfurization processes requires the development of adequate analytical techniques, allowing the identification of any transformation products generated. The identification of intermediates and final products permits the evaluation of the degradation process. In this work, seven sulfurated compounds and one non-sulfurated compound have been selected to develop an extraction method and to compare the sensitivity and identification capabilities of three different gas chromatography ionization modes. The selected compounds are: dibenzothiophene (DBT), 4-methyl-dibenzothiophene (4-m-DBT), 4,6-dimethyl-dibenzothiophene (4,6-dm-DBT) and 4,6 diethyl-dibenzothiophene (4,6 de-DBT), all of which can be used as model compounds in biodesulfurization processes; as well as dibenzothiophene sulfoxide (DBTO(2)), dibenzothiophene sulfone (DBTO) and 2-(2-hydroxybiphenyl)-benzenesulfinate (HBPS), which are intermediate products in biodesulfurization processes of DBT [ A. Alcon, V.E. Santos, A.B. Martín, P. Yustos, F. García-Ochoa, Biochem. Eng. J. 26 (2005) 168]. Furthermore, a non-sulfurated compound, 2-hydroxybiphenyl (2-HBP), has also been selected as it is the final product in the biodesulfurization process of DBT [A. Alcon, V.E. Santos, A.B. Martín, P. Yustos, F. García-Ochoa. Biochem. Eng. J. 26 (2005) 168]. Since, typically, biodesulfurization reactions take place in a biphasic medium, two extraction methods have been developed: a liquid-liquid extraction method for the watery phase and a solid phase extraction method for the organic phase. Recoveries of the selected compound in both media were studied. They were in the range of 80-100% for the watery and in the range of 40-60% for the organic phase, respectively. Gas chromatography coupled to mass spectrometry (GC-MS) has been employed for the identification of these selected compounds. Three different ionization modes were applied: conventional electron impact (EI); positive chemical ionization (PCI), using methane as the reagent gas; and a recently developed ionization mode known as hybrid chemical ionization (HCI), using perfluorotri-n-butylamine as the reagent gas. Limits of detection and identification capabilities have been compared between the three analytical techniques. The sensitivity of the three analytical techniques was studied and LOD between 0.05 and 1, between 0.09 and 2 and between 0.001 and 0.043 were achieved for PCI, EI and HCI, respectively. The developed method was applied in samples from a biodesulfurization process. The biodesulfurization reactions were conducted in resting cell operation mode, using Erlenmeyer flasks or an agitated tank bioreactor. The microorganism employed was Pseudomonas putida CECT 5279. The reaction was performed under controlled air flow, stirring and temperature conditions.