Gustavo Peñuela

Degradation of the antibiotic oxolinic acid by photocatalysis with TiO2 in suspension

In the work presented here, a photocatalytic system using titanium Degussa P-25 in suspension was used to evaluate the degradation of 20mg L(-1) of antibiotic oxolinic acid (OA). The effects of catalyst load (0.2-1.5 g L(-1)) and pH (7.5-11) were evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, low pH values and 1.0 g L(-1) of TiO(2) favoured the efficiency of the process. Under optimal conditions the evolution of the substrate, chemical oxygen demand, dissolved organic carbon, toxicity and antimicrobial activity on Escherichia coli cultures were evaluated. The results indicate that, under optimal conditions, after 30 min, the TiO(2) photocatalytic system is able to eliminate both the substrate and the antimicrobial activity, and to reduce the toxicity of the solution by 60%. However, at the same time, ∼53% of both initial DOC and COD remain in solution. Thus, the photocatalytical system is able to transform the target compound into more oxidized by-products without antimicrobial activity and with a low toxicity. The study of OA by-products using liquid chromatography coupled with mass spectrometry, as well as the evaluation of OA degradation in acetonitrile media as solvent or in the presence of isopropanol and iodide suggest that the reaction is initiated by the photo-Kolbe reaction. Adsorption isotherm experiments in the dark indicated that under pH 7.5, adsorption corresponded to the Langmuir adsorption model, indicating the dependence of the reaction on an initial adsorption step.

Multi-class determination of personal care products and pharmaceuticals in environmental and wastewater samples by ultra-high performance liquid-chromatography-tandem mass spectrometry.

In this work, a multi-class method for the simultaneous determination of 17 emerging contaminants, including pharmaceuticals and personal care products, has been developed. Target analytes were two anti-inflammatories, a lipid regulator agent, two angiotensin II antagonists, two antiepileptic drugs and a diuretic. Among personal care products, four preservatives and five UV filters were included. The method is based on solid-phase extraction (SPE) using Oasis HLB cartridges followed by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Up to three simultaneous transitions per compound were acquired to assure a reliable identification. A detailed study of the extraction process efficiency and matrix effects was carried out in surface water and effluent wastewater. The use of isotope-labeled internal standards (ILIS) was tested to compensate both potential SPE losses during sample extraction and signal suppression/enhancement observed, especially in EWW. Satisfactory correction in all water samples was only ensured when the own analyte ILIS was used. The use of analogues ILIS was a rather useful approach for correction in the majority of the samples tested when analyte ILIS was unavailable. The method was successfully validated in five different surface water (SW) samples and five effluent wastewater (EWW) samples spiked at two concentration levels (0.05 and 0.5 μg/L in SW; 0.1 and 0.5 μg/L in EWW). The developed method was applied to the analysis of 22 samples (SW and EWW) from the Spanish Mediterranean area and 51 reservoir water samples from Colombia. Personal care products were frequently detected, with the highest concentrations corresponding to benzophenone and benzophenone-4 (samples from Spain), and methylparaben (samples from Colombia). Several pharmaceuticals were detected in the Spanish samples, where irbesartan and valsartan - two Angiotensin II antagonists that are not commonly monitored in the aquatic environment - were the compounds most frequently detected.

Discrimination of infectious bacteriophage T4 virus by propidium monoazide real-time PCR

The advent of quantitative PCR has improved the detection of human viral pathogens in the environment. However, a serious limitation of this method may arise from the inability to discriminate between viruses that are infectious and viruses that have been inactivated and do not represent a human health hazard. To assess whether propidium monoazide (PMA) pre-treatment is a good approach to inhibiting DNA amplification from non-infectious viruses, bacteriophage T4 survival was measured using cell culture titration and real-time PCR with and without PMA pre-treatment. Heat (85 degrees C) and proteolysis methods were carried out. After these inactivation treatments, the results indicated that the PMA pre-treatment approach is not appropriate for differentiating infectious viruses. However, when a heat treatment at 110 degrees C was undertaken, PMA pre-treatment did allow differentiation of non-infectious from infectious viruses. In this case, effective binding of PMA to bacteriophage T4 DNA could be taken to indicate capsid damage. Therefore, PMA pre-treatment may be appropriate for assessing effective disinfection treatments and for a more reliable understanding of the factors that contribute to viral inactivation through capsid damage monitoring. The PMA-PCR approach could be useful as a rapid and inexpensive analytical tool for screening and evaluation of the efficacy of disinfectants.

Solar photocatalitycal treatment of carbofuran at lab and pilot scale: effect of classical parameters, evaluation of the toxicity and analysis of organic by-products.

In this work the TiO(2) solar-photocatalytical degradation of the pesticide carbofuran (CBF) in water, at lab and pilot scale, was studied. At lab scale the evaluation of CBF concentration (14-282 μmol L(-1)) showed that the system followed a Langmuir-Hinshelwood kinetics type. TiO(2) concentration (0.05-2 g L(-1)) and initial pH (3-9) were also evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, initial pH 7.60 and 1.43 g L(-1) of TiO(2) favoured the efficiency of the process. Under optimal conditions the evolution of substrate, chemical oxygen demand, dissolved organic carbon, toxicity and organics by-products were evaluated. In the pilot scale tests, using direct sunlight, 55 mg L(-1) of CBF in a commercial formulation was eliminated after 420 min; while after 900 min of treatment 80% of toxicity (1/E(50) on Vibrium Fischeri), 80% of chemical oxygen demand and 60% of dissolved organic carbon were removed. The analysis and evolution of five CBF by-products, as well the evaluation of the treatment in the presence of isopropanol or using acetonitrile as a solvent suggest that the degradation is mainly carried out by OH radical attack. Finally, a schema depicting the main degradation pathway is proposed.

Monitoring the removal of nitrogen by applying a nitrification-denitrification process in a Sequencing Batch Reactor (SBR).

In this study the evaluation of nitrogen removal in wastewater from a meat products processing company was performed, using a Sequencing Batch Reactor (SBR) at pilot scale. The phases of the SBR operation were: filling, reaction (aeration and intermittent anoxia), sedimentation and discharge. In each of these phases analyses of ammonium (NH(4)(+)), nitrite (NO(2)(-)), nitrate (NO(3)(-)), pH and dissolved oxygen (DO) were carried out to monitor the process of nitrification-denitrification. The results showed that stage IV had the best performance (2.49 g COD(F)/Ld and 1.02 g NH(4)(+)-N/Ld) with a NH(4)(+)-N removal of 71%. The transformation of much of the NH(4)(+)-N to gaseous nitrogen was confirmed, with the concentration of NO(2)(-)-N and NO(3)(-)-N increasing during the reaction phase but decreasing in the effluent due to its transformation to gaseous nitrogen.

Experimental design approach applied to the elimination of crystal violet in water by electrocoagulation with Fe or Al electrodes.

An experimental design methodology was applied to evaluate the decolourization of crystal violet (CV) dye by electrocoagulation using iron or aluminium electrodes. The effects and interactions of four parameters, initial pH (3-9), current density (6-28 A m(-2)), substrate concentration (50-200 mg L(-1)) and supporting electrolyte concentration (284-1420 mg L(-1) of Na(2)SO(4)), were optimized and evaluated. Although the results using iron anodes were better than for aluminium, the effects and interactions of the studied parameters were quite similar. With a confidence level of 95%, initial pH and supporting electrolyte concentration showed limited effects on the removal rate of CV, whereas current density, pollutant concentration and the interaction of both were significant. Reduced models taking into account significant variables and interactions between variables have shown good correlations with the experimental results. Under optimal conditions, almost complete removal of CV and chemical oxygen demand were obtained after electrocoagulation for 5 and 30 min, using iron and aluminium electrodes, respectively. These results indicate that electrocoagulation with iron anodes is a rapid, economical and effective alternative to the complete removal of CV in waters. Evolutions of pH and residual iron or aluminium concentrations in solution are also discussed.

Relationship between anode material, supporting electrolyte and current density during electrochemical degradation of organic compounds in water

Taking crystal violet (CV) dye as pollutant model, the electrode, electrolyte and current density (i) relationship for electro-degrading organic molecules is discussed. Boron-doped diamond (BDD) or Iridium dioxide (IrO2) used as anode materials were tested with Na2SO4 or NaCl as electrolytes. CV degradation and generated oxidants showed that degradation pathways and efficiency are strongly linked to the current density-electrode-electrolyte interaction. With BDD, the degradation pathway depends on i: If ii(lim), generated oxidants play a major role in the CV elimination. When IrO2 was used, CV removal was not dependent on i, but on the electrolyte. Pollutant degradation in Na2SO4 on IrO2 seems to occur via IrO3; however, in the presence of NaCl, degradation was dependent on the chlorinated oxidative species generated. In terms of efficiency, the Na2SO4 electrolyte showed better results than NaCl when BDD anodes were employed. On the contrary, NaCl was superior when combined with IrO2. Thus, the IrO2/Cl(-) and BDD/SO4(2-) systems were better at removing the pollutant, being the former the most effective. On the other hand, pollutant degradation with the BDD/SO4(2-) and IrO2/Cl(-) systems is favored at low and high current densities, respectively.

Discrimination of viable Acanthamoeba castellani trophozoites and cysts by propidium monoazide real-time polymerase chain reaction.

ABSTRACT. Even though the advent of quantitative polymerase chain reaction (PCR) has improved the detection of pathogen microorganisms in most of areas of microbiology, a serious limitation of this method may arise from the inability to discriminate between viable and nonviable pathogens. To overcome it, the use of real‐time PCR and selective nucleic acid intercalating dyes like propidium monoazide (PMA) have been effectively evaluated for different microorganisms. To assess whether PMA pretreatment can inhibit PCR amplification of nonviable amoeba DNA, Acanthamoeba castellani survival was measured using cell culture and real‐time PCR with and without PMA pretreatment. Autoclave and contact lens disinfecting solutions were used to inactivate amoebae. After these inactivation treatments, the results indicated that the PMA pretreatment approach is appropriate for differentiating viable A. castellani, both trophozoites and cysts. Therefore, the PMA‐PCR approach could be useful as a rapid and sensitive analytical tool for monitoring treatment and disease control, assessing effective disinfection treatments, and for a more reliable understanding of the factors that contribute to the interaction amoeba–pathogenic bacteria.

CHARACTERIZATION OF DEPOSITS FORMED IN A WATER DISTRIBUTION SYSTEM

The development of unwanted deposits in any water distribution system is unavoidable under standard conditions. Knowing the composition of such deposits will help to establish the causes of deposit formation and consequently to be able to keep water quality as high as possible. This paper presents the results of an extensive study of deposits found in a water distribution system of a tropical city. Characterization of materials collected across the system was made by infrared spectroscopy (IR), X ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Analysis of the samples taken at several sites of the system reveals the presence of three predominant deposits: a brown coloured deposit, tubercles and white deposits. Aluminosilicates and humic acids were found to be main constituents in brown deposits. Tubercles were mostly mixtures of magnetite, goethite and in some cases lepidocrocite. White deposits were formed by calcite, aluminosilicates and quartz. Organic matter as volatile solids were 14.0 ± 5.0% for brown deposits and 11.2 ± 2.0% for tubercles.

Behaviour of molecular weight distribution for the liquid fraction of pig slurry treated by anaerobic digestion

Pig slurry was treated in an upflow anaerobic sludge blanket (UASB) reactor. To maintain a stable operation, the organic loading rate (OLR) applied to the system was increased stepwise by decreasing the dilution ratio of the pig slurry. Finally, during the last operational stage, no dilution was applied to the influent. The reactor maintained a soluble chemical oxygen demand (CODs) removal efficiency of 82% when OLRs lower than 1.73 g CODs l−1 d−1 were applied, although its efficiency fell to 55% when operated at 2.48 g CODs l−1 d−1. System performance was not affected by the presence of free ammonia (concentrations up to 375 mg NH3 l−1). The distribution of the different molecular weight fractions changed significantly during anaerobic digestion. Proteins contained in the fractions higher than 10,000 Daltons are less degraded than those belonging to the lower fractions. An important percentage of both COD and BOD5 in the effluent were observed in the lowest fraction, probably caused by the presence of volatile fatty acids (VFA).