The relevant information about the impacts caused by presence of emerging pollutants in mixtures ... more The relevant information about the impacts caused by presence of emerging pollutants in mixtures on the ecological environment, especially on the more vulnerable compartments such as activated sludge (AS) is relatively limited. This study investigated the effect of ibuprofen (IBU) and triclosan (TCS), alone and in combination to the performance and enzymatic activity of AS bacterial community. The assays were carried out in a pilot AS reactor operating for two-weeks under continuous dosage of pollutants. The microbial activity was tracked by measuring oxygen uptake rate, esterase activity, oxidative stress and antioxidant enzyme activities. It was found that IBU and TCS had no acute toxic effects on reactor biomass concentration. TCS led to significant decrease of COD removal efficiency, which dropped from 90% to 35%. Continuous exposure to IBU, TCS and their mixtures increased the activities of glutathione s-transferase (GST) and esterase as a response to oxidative damage. A high increase in GST activity was associated with non-reversible toxic damage while peaks of esterase activity combined with moderate GST increase were attributed to an adaptive response.
Pharmaceuticals and personal care products (PPCPs) are partially degraded in wastewater treatment... more Pharmaceuticals and personal care products (PPCPs) are partially degraded in wastewater treatment plants (WWTPs), thereby leading to the formation of more toxic metabolites. Bacterial populations in bioreactors operated in WWTPs are sensitive to different toxics such as heavy metals and aromatic compounds, but there is still little information on the effect that pharmaceuticals exert on their metabolism, especially under anaerobic conditions. This work evaluated the effect of selected pharmaceuticals that remain in solution and attached to biosolids on the metabolism of anaerobic biomass. Batch reactors operated in parallel under the pressure of four individual and mixed PPCPs (carbamazepine, ibuprofen, triclosan and sulfametoxazole) allowed us to obtain relevant information on anaerobic digestion performance, toxicological effects and alterations to key enzymes involved in the biodegradation process. Cell viability was quantitatively evaluated using an automatic analysis of confoca...
Nucleotide sequences encoding signal peptides from the precursors of 2-amylase/trypsin inhibitors... more Nucleotide sequences encoding signal peptides from the precursors of 2-amylase/trypsin inhibitors from cereals are homologous to those corresponding to the precursors of thaumatin II and of plastocyanins. Non-synonymous (K A) and synonymous {K %) rates of nucleotide substitutions have been calculated for all possible binary combinations. Extreme variation in A' A^S ratios has been observed; from the 0.167 average found within the plastocyanin family to an average of 1.90 calculated for the inhibitors/thaumatin II transition. A similar calculation has been carried out for the signal peptide sequences of thionins. which are unrelated to those of the a-amylase trypsin inhibitor family. and an average /í A //w s of 0.12 has been obtained. This variation can be largely explained in terms of an empirical index of stability related to amino acid composition and seems to be independent of functional constraints.
Conventional wastewater treatment technologies are costly and energy demanding; such issues are e... more Conventional wastewater treatment technologies are costly and energy demanding; such issues are especially remarkable when small communities have to clean up their pollutants. In response to these requirements, a new variety of nature-based solution, so-called METland®, has been recently develop by using concepts from Microbial Electrochemical Technologies (MET) to outperform classical constructed wetland regarding wastewater treatment. Thus, the current study evaluates two operation modes (aerobic and aerobic–anoxic) of a full-scale METland®, including a Life Cycle Assessment (LCA) conducted under a Net Environmental Balance perspective. Moreover, a combined technical and environmental analysis using a Net Eutrophication Balance (NEuB) focus concluded that the downflow (aerobic) mode achieved the highest removal rates for both organic pollutant and nitrogen, and it was revealed as the most environmentally friendly design. Actually, aerobic configuration outperformed anaero/aero-mix...
The antimicrobial polypeptide ε-poly(L-lysine) (ε-PL) was electrostatically incorporated to poly(... more The antimicrobial polypeptide ε-poly(L-lysine) (ε-PL) was electrostatically incorporated to poly(acr yli acid) (PAA)/poly(vinyl alcohol) (PVA) electrospun nanofib ers. ε-PL loading and distribution was assessed by infrar ed spectra, ζ-potential measurements and the primary amino react ive dye fluorescamine. Functionalized fibers with 4 85 ± 140 nm diameter, could be loaded with 0.57-0.74 g ε-PL (g dressing) -1 that released at a constant rate of 5.4 ± 2.8 mg ε-PL (g dressing day) . Such a dressings resulted in two orders of magnit ude lower bacterial colonization than nonfunctionalized PAA-PVA after 14 days of incubation. Bacterial impairment was attributed to the damage of cell membranes and the formation of intracellular reacti ve oxygen species. ε-PL functionalized nanofibers did not display cytotoxicity to human corneal epithelial cells, HCE pC, in 24 h MTT assays. However, the viability of r apidly growing tumoral HeLa cells decreased > 50 % under the same conditions. The pr...
The ozonation of an effluent from the secondary clarifier of two Municipal Wastewater Treatment P... more 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 nonoxidizable 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.
Ahstroct-A simple model for flow behavior and liquid mixing in bubble columns containing Newtonia... more Ahstroct-A simple model for flow behavior and liquid mixing in bubble columns containing Newtonian (water and salt solutions) and non-Newtonian (CMC at different concentrations) liquids was developed. Based on an energy balance which takes into account the energy losses at the gas-liquid interface, and on the Baird and Rice relation for axial dispersion, the model predicts experimental data of gas holdup, liquid velocities profiles and liquid axial dispersion coefficient with satisfactory accuracy in a wide range of column sizes, fluid systems and experimental conditions. Model predictions were compared with recommended correlations for different types of fluids and a good agreement was found. Therefore, the present model may be a more general tool for fluid dynamic and mixing description of bubble columns.
A simple model based on an energy balance which takes into account the friction losses at the gas... more A simple model based on an energy balance which takes into account the friction losses at the gas-liquid interface and the slip velocity of single bubble is used to simulate the gas holdup in bubble columns containing Newtonian and non-Newtonian liquids which circulate in both laminar and turbulent flows. Experimental data available from the literature for bubble columns up to
Abstract Removal of a mixture of 13 pharmaceutical compounds was investigated in this work in a h... more Abstract Removal of a mixture of 13 pharmaceutical compounds was investigated in this work in a horizontal subsurface flow electroconductive filter. Biofilter was constructed using electroconductive carbon with capacity for allowing the electron flow between microbial communities at different redox environments; under a configuration called snorkel. Stable operation was observed during 200 days, with medium values for COD and N-NH4 removal of 92 ± 3% and 70 ± 10%, respectively under different organic loading rates. Most of the pharmaceuticals tested were removed above 90% (seven compounds) at HRT of 1 day while 65% were removed at HRT as low as 0.5 days. These results were corroborated by analysing the detoxification efficiency of the biofilter using microcrustaceans and a green alga as bioreporters. Results revealed that effluents were detoxified in 80% for HRT of 0.5 days. Electroconductive biofilter was proved as a promising technology for the elimination of emerging pollutant from wastewater with minimum operational requirements.
The aim of this work was to immobilize antimicrobial peptides onto a fibrous scaffold to create f... more The aim of this work was to immobilize antimicrobial peptides onto a fibrous scaffold to create functional wound dressings.
&NA; The antimicrobial polypeptide &egr;‐poly(L‐lysine) (&egr;‐PL) was electrostatica... more &NA; The antimicrobial polypeptide &egr;‐poly(L‐lysine) (&egr;‐PL) was electrostatically incorporated to poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) electrospun nanofibers. &egr;‐PL loading and distribution was assessed by infrared spectra, &zgr;‐potential measurements and the primary amino reactive dye fluorescamine. Functionalized fibers with 485 ± 140 nm diameter, could be loaded with 0.57–0.74 g &egr;‐PL (g dressing)−1 that released at a constant rate of 5.4 ± 2.8 mg &egr;‐PL (g dressing day)−1. Such a dressings resulted in two orders of magnitude lower bacterial colonization than non‐functionalized PAA‐PVA after 14 days of incubation. Bacterial impairment was attributed to the damage of cell membranes and the formation of intracellular reactive oxygen species. &egr;‐PL functionalized nanofibers did not display cytotoxicity to human corneal epithelial cells, HCEpC, in 24 h MTT assays. However, the viability of rapidly growing tumoral HeLa cells decreased >50% under the same conditions. The prepared biocompatible nanofibrous dressings with durable antibacterial activity show potential application as wound dressings and other biomedical uses.
Amino-terminated PAMAM dendrimers were grafted onto poly(acrylic acid)/poly(vinyl alcohol) electr... more Amino-terminated PAMAM dendrimers were grafted onto poly(acrylic acid)/poly(vinyl alcohol) electrospun fibres to create a host–guest architecture for the controlled delivery of the antioxidant thymol.
The Science of the total environment, Jan 31, 2017
This work reports the preparation of composite electrospun membranes combining antimicrobial acti... more This work reports the preparation of composite electrospun membranes combining antimicrobial action with the capacity of retaining low-molecular weight non-polar pollutants. The membranes were electrospun blends of polyvinyl alcohol (PVA) and poly(acrylic acid) (PAA) stabilized using heat curing. The membranes were functionalized by grafting amino-terminated poly(amidoamine) (PAMAM) G3 dendrimers. The antimicrobial effect was assessed using strains of Escherichia coli and Staphylococcus aureus by tracking their capacity to form new colonies and their metabolic impairment upon contact with membranes. The antimicrobial activity was particularly high to the gram-positive bacterium S. aureus with a 3-log reduction in their capacity to colonize dendrimer-functionalized membranes with respect to neat PVA/PAA fibers. The effect to gram-positive bacteria was attributed to the interaction of dendrimers with the negatively charged bacterial membranes and resulted in membranes essentially free...
The growing use of pharmaceutical and personal care products increases their concentrations in th... more 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 ± 13 mg L −1 and 0.32 ± 0.07 mg L −1 for ibuprofen and triclosan respectively using 125 mg L −1 activated sludge. For the inhibition of enzymatic activity values were 633 ± 63 mg L −1 for ibuprofen and 1.94 ± 0.32 mg L −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.
Electrospun nanofibers were prepared from blends of poly(acrylic acid) (PAA) and poly(vinyl alcoh... more 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.
The relevant information about the impacts caused by presence of emerging pollutants in mixtures ... more The relevant information about the impacts caused by presence of emerging pollutants in mixtures on the ecological environment, especially on the more vulnerable compartments such as activated sludge (AS) is relatively limited. This study investigated the effect of ibuprofen (IBU) and triclosan (TCS), alone and in combination to the performance and enzymatic activity of AS bacterial community. The assays were carried out in a pilot AS reactor operating for two-weeks under continuous dosage of pollutants. The microbial activity was tracked by measuring oxygen uptake rate, esterase activity, oxidative stress and antioxidant enzyme activities. It was found that IBU and TCS had no acute toxic effects on reactor biomass concentration. TCS led to significant decrease of COD removal efficiency, which dropped from 90% to 35%. Continuous exposure to IBU, TCS and their mixtures increased the activities of glutathione s-transferase (GST) and esterase as a response to oxidative damage. A high increase in GST activity was associated with non-reversible toxic damage while peaks of esterase activity combined with moderate GST increase were attributed to an adaptive response.
Pharmaceuticals and personal care products (PPCPs) are partially degraded in wastewater treatment... more Pharmaceuticals and personal care products (PPCPs) are partially degraded in wastewater treatment plants (WWTPs), thereby leading to the formation of more toxic metabolites. Bacterial populations in bioreactors operated in WWTPs are sensitive to different toxics such as heavy metals and aromatic compounds, but there is still little information on the effect that pharmaceuticals exert on their metabolism, especially under anaerobic conditions. This work evaluated the effect of selected pharmaceuticals that remain in solution and attached to biosolids on the metabolism of anaerobic biomass. Batch reactors operated in parallel under the pressure of four individual and mixed PPCPs (carbamazepine, ibuprofen, triclosan and sulfametoxazole) allowed us to obtain relevant information on anaerobic digestion performance, toxicological effects and alterations to key enzymes involved in the biodegradation process. Cell viability was quantitatively evaluated using an automatic analysis of confoca...
Nucleotide sequences encoding signal peptides from the precursors of 2-amylase/trypsin inhibitors... more Nucleotide sequences encoding signal peptides from the precursors of 2-amylase/trypsin inhibitors from cereals are homologous to those corresponding to the precursors of thaumatin II and of plastocyanins. Non-synonymous (K A) and synonymous {K %) rates of nucleotide substitutions have been calculated for all possible binary combinations. Extreme variation in A' A^S ratios has been observed; from the 0.167 average found within the plastocyanin family to an average of 1.90 calculated for the inhibitors/thaumatin II transition. A similar calculation has been carried out for the signal peptide sequences of thionins. which are unrelated to those of the a-amylase trypsin inhibitor family. and an average /í A //w s of 0.12 has been obtained. This variation can be largely explained in terms of an empirical index of stability related to amino acid composition and seems to be independent of functional constraints.
Conventional wastewater treatment technologies are costly and energy demanding; such issues are e... more Conventional wastewater treatment technologies are costly and energy demanding; such issues are especially remarkable when small communities have to clean up their pollutants. In response to these requirements, a new variety of nature-based solution, so-called METland®, has been recently develop by using concepts from Microbial Electrochemical Technologies (MET) to outperform classical constructed wetland regarding wastewater treatment. Thus, the current study evaluates two operation modes (aerobic and aerobic–anoxic) of a full-scale METland®, including a Life Cycle Assessment (LCA) conducted under a Net Environmental Balance perspective. Moreover, a combined technical and environmental analysis using a Net Eutrophication Balance (NEuB) focus concluded that the downflow (aerobic) mode achieved the highest removal rates for both organic pollutant and nitrogen, and it was revealed as the most environmentally friendly design. Actually, aerobic configuration outperformed anaero/aero-mix...
The antimicrobial polypeptide ε-poly(L-lysine) (ε-PL) was electrostatically incorporated to poly(... more The antimicrobial polypeptide ε-poly(L-lysine) (ε-PL) was electrostatically incorporated to poly(acr yli acid) (PAA)/poly(vinyl alcohol) (PVA) electrospun nanofib ers. ε-PL loading and distribution was assessed by infrar ed spectra, ζ-potential measurements and the primary amino react ive dye fluorescamine. Functionalized fibers with 4 85 ± 140 nm diameter, could be loaded with 0.57-0.74 g ε-PL (g dressing) -1 that released at a constant rate of 5.4 ± 2.8 mg ε-PL (g dressing day) . Such a dressings resulted in two orders of magnit ude lower bacterial colonization than nonfunctionalized PAA-PVA after 14 days of incubation. Bacterial impairment was attributed to the damage of cell membranes and the formation of intracellular reacti ve oxygen species. ε-PL functionalized nanofibers did not display cytotoxicity to human corneal epithelial cells, HCE pC, in 24 h MTT assays. However, the viability of r apidly growing tumoral HeLa cells decreased > 50 % under the same conditions. The pr...
The ozonation of an effluent from the secondary clarifier of two Municipal Wastewater Treatment P... more 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 nonoxidizable 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.
Ahstroct-A simple model for flow behavior and liquid mixing in bubble columns containing Newtonia... more Ahstroct-A simple model for flow behavior and liquid mixing in bubble columns containing Newtonian (water and salt solutions) and non-Newtonian (CMC at different concentrations) liquids was developed. Based on an energy balance which takes into account the energy losses at the gas-liquid interface, and on the Baird and Rice relation for axial dispersion, the model predicts experimental data of gas holdup, liquid velocities profiles and liquid axial dispersion coefficient with satisfactory accuracy in a wide range of column sizes, fluid systems and experimental conditions. Model predictions were compared with recommended correlations for different types of fluids and a good agreement was found. Therefore, the present model may be a more general tool for fluid dynamic and mixing description of bubble columns.
A simple model based on an energy balance which takes into account the friction losses at the gas... more A simple model based on an energy balance which takes into account the friction losses at the gas-liquid interface and the slip velocity of single bubble is used to simulate the gas holdup in bubble columns containing Newtonian and non-Newtonian liquids which circulate in both laminar and turbulent flows. Experimental data available from the literature for bubble columns up to
Abstract Removal of a mixture of 13 pharmaceutical compounds was investigated in this work in a h... more Abstract Removal of a mixture of 13 pharmaceutical compounds was investigated in this work in a horizontal subsurface flow electroconductive filter. Biofilter was constructed using electroconductive carbon with capacity for allowing the electron flow between microbial communities at different redox environments; under a configuration called snorkel. Stable operation was observed during 200 days, with medium values for COD and N-NH4 removal of 92 ± 3% and 70 ± 10%, respectively under different organic loading rates. Most of the pharmaceuticals tested were removed above 90% (seven compounds) at HRT of 1 day while 65% were removed at HRT as low as 0.5 days. These results were corroborated by analysing the detoxification efficiency of the biofilter using microcrustaceans and a green alga as bioreporters. Results revealed that effluents were detoxified in 80% for HRT of 0.5 days. Electroconductive biofilter was proved as a promising technology for the elimination of emerging pollutant from wastewater with minimum operational requirements.
The aim of this work was to immobilize antimicrobial peptides onto a fibrous scaffold to create f... more The aim of this work was to immobilize antimicrobial peptides onto a fibrous scaffold to create functional wound dressings.
&NA; The antimicrobial polypeptide &egr;‐poly(L‐lysine) (&egr;‐PL) was electrostatica... more &NA; The antimicrobial polypeptide &egr;‐poly(L‐lysine) (&egr;‐PL) was electrostatically incorporated to poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) electrospun nanofibers. &egr;‐PL loading and distribution was assessed by infrared spectra, &zgr;‐potential measurements and the primary amino reactive dye fluorescamine. Functionalized fibers with 485 ± 140 nm diameter, could be loaded with 0.57–0.74 g &egr;‐PL (g dressing)−1 that released at a constant rate of 5.4 ± 2.8 mg &egr;‐PL (g dressing day)−1. Such a dressings resulted in two orders of magnitude lower bacterial colonization than non‐functionalized PAA‐PVA after 14 days of incubation. Bacterial impairment was attributed to the damage of cell membranes and the formation of intracellular reactive oxygen species. &egr;‐PL functionalized nanofibers did not display cytotoxicity to human corneal epithelial cells, HCEpC, in 24 h MTT assays. However, the viability of rapidly growing tumoral HeLa cells decreased >50% under the same conditions. The prepared biocompatible nanofibrous dressings with durable antibacterial activity show potential application as wound dressings and other biomedical uses.
Amino-terminated PAMAM dendrimers were grafted onto poly(acrylic acid)/poly(vinyl alcohol) electr... more Amino-terminated PAMAM dendrimers were grafted onto poly(acrylic acid)/poly(vinyl alcohol) electrospun fibres to create a host–guest architecture for the controlled delivery of the antioxidant thymol.
The Science of the total environment, Jan 31, 2017
This work reports the preparation of composite electrospun membranes combining antimicrobial acti... more This work reports the preparation of composite electrospun membranes combining antimicrobial action with the capacity of retaining low-molecular weight non-polar pollutants. The membranes were electrospun blends of polyvinyl alcohol (PVA) and poly(acrylic acid) (PAA) stabilized using heat curing. The membranes were functionalized by grafting amino-terminated poly(amidoamine) (PAMAM) G3 dendrimers. The antimicrobial effect was assessed using strains of Escherichia coli and Staphylococcus aureus by tracking their capacity to form new colonies and their metabolic impairment upon contact with membranes. The antimicrobial activity was particularly high to the gram-positive bacterium S. aureus with a 3-log reduction in their capacity to colonize dendrimer-functionalized membranes with respect to neat PVA/PAA fibers. The effect to gram-positive bacteria was attributed to the interaction of dendrimers with the negatively charged bacterial membranes and resulted in membranes essentially free...
The growing use of pharmaceutical and personal care products increases their concentrations in th... more 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 ± 13 mg L −1 and 0.32 ± 0.07 mg L −1 for ibuprofen and triclosan respectively using 125 mg L −1 activated sludge. For the inhibition of enzymatic activity values were 633 ± 63 mg L −1 for ibuprofen and 1.94 ± 0.32 mg L −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.
Electrospun nanofibers were prepared from blends of poly(acrylic acid) (PAA) and poly(vinyl alcoh... more 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.
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Papers by Pedro Letón