Improved reductive transformation of iopromide by magnetite containing reduced graphene oxide nanosacks as electron shuttles.

The novel application of magnetite containing reduced graphene oxide nanosacks (MrGO-N) as electron shuttles to improve the reductive degradation of pharmaceutical pollutant, iopromide (IOP), was evaluated. The MrGO-N were synthesized by ultrasonicated nebulization process, and their physicochemical characterization was performed by potentiometric titrations, zeta potential, high resolution transmission electron microscopy (HR-TEM), X-ray diffraction, as well as by Raman and Fourier transform infrared spectroscopies. Results demonstrated the thermal reduction of precursor graphene oxide sheets, the removal of different oxygenated groups, and the successful assembly of magnetite nanoparticles (MNP) in the graphene sacks. Also, reduction experiments revealed 72 % of IOP removal efficiency and up to 2.5-fold faster degradation of this pollutant performed with MrGO-N as redox catalysts in batch assays and with sulfide as electron donor. Chemical transformation pathway of IOP provides evidence of complete dehalogenation and further transformation of aromatic ring substituents. Greater redox-mediating ability of MrGO-N was observed, which was reflected in the catalytic activity of these nanomaterials during the reductive degradation of IOP. Transformation byproducts with simpler chemical structure were identified, which could lead to complete degradation by conventional methodologies in a complementary treatment process. Redox-mediating activity of MrGO-N could potentially be applied in wastewater treatment systems in order to facilitate the biodegradation of priority contaminants.

Novel application of magnetic nano-carbon composite as redox mediator in the reductive biodegradation of iopromide in anaerobic continuous systems.

The redox-mediating capacity of magnetic reduced graphene oxide nanosacks (MNS) to promote the reductive biodegradation of the halogenated pollutant, iopromide (IOP), was tested. Experiments were performed using glucose as electron donor in an upflow anaerobic sludge blanket (UASB) reactor under methanogenic conditions. Higher removal efficiency of IOP in the UASB reactor supplied with MNS as redox mediator was observed as compared with the control reactor lacking MNS. Results showed 82% of IOP removal efficiency under steady state conditions in the UASB reactor enriched with MNS, while the reactor control showed IOP removal efficiency of 51%. The precise microbial transformation pathway of IOP was elucidated by high-performance liquid chromatography coupled to mass spectroscopy (HPLC-MS) analysis. Biotransformation by-products with lower molecular weight than IOP molecule were identified in the reactor supplied with MNS, which were not detected in the reactor control, indicating the contribution of these magnetic nano-carbon composites in the redox conversion of this halogenated pollutant. Reductive reactions of IOP favored by MNS led to complete dehalogenation of the benzene ring and partial rupture of side chains of this pollutant, which is the first step towards its complete biodegradation. Possible reductive mechanisms that took place in the biodegradation of IOP were stated. Finally, the novel and successful application of magnetic graphene composites in a continuous bioreactor to enhance the microbial transformation of IOP was demonstrated.

Biofilm development during the start-up of a sulfate-reducing down-flow fluidized bed reactor at different COD/SO4(2-) ratios and HRT.

In sulfate-reducing reactors, it has been reported that the sulfate removal efficiency increases when the COD/SO4(2-) ratio is increased. The start-up of a down-flow fluidized bed reactor constitutes an important step to establish a microbial community in the biofilm able to survive under the operational bioreactor conditions in order to achieve effective removal of both sulfate and organic matter. In this work the influence of COD/SO4(2-) ratio and HRT in the development of a biofilm during reactor start-up (35 days) was studied. The reactor was inoculated with 1.6 g VSS/L of granular sludge, ground low density polyethylene was used as support material; the feed consisted of mineral medium at pH 5.5 containing 1 g COD/L (acetate:lactate, 70:30) and sodium sulfate. Four experiments were conducted at HRT of 1 or 2 days and COD/SO4(2-) ratio of 0.67 or 2.5. The results obtained indicated that a COD/SO4(2-) ratio of 2.5 and HRT 2 days allowed high sulfate and COD removal (66.1 and 69.8%, respectively), whereas maximum amount of attached biomass (1.9 g SVI/L support) and highest sulfate reducing biofilm activity (10.1 g COD-H2S/g VSS-d) was achieved at HRT of 1 day and at COD/sulfate ratios of 0.67 and 2.5, respectively, which suggests that suspended biomass also played a key role in the performance of the reactors.

Effect of surfactant and oil additions in the biodegradation of hexane and toluene vapours in batch tests.

The biological treatment of gaseous emissions of hydrophobic volatile organic compounds (VOCs) results in low rates of elimination partially because of the low solubility of VOCs in water. Recently, the use of two-phase partition bioreactors (TPPBs) was proposed to increase the bioavailability and consequently the elimination capacities of this kind of VOC. In the present study, TPPBs operating in a batch feed mode were tested for biodegradation of hexane and toluene vapours with a microbial consortium. The results obtained were compared with single-phase systems (control experiments). The liquid phase used was silicone oil (organic phase) with the surfactant Pluronic F-68. Experiments were named F1 and F2 for one and two phases, respectively, and F(1S) and F(2S) when the surfactant was included. The maximum specific rates (S(rates)) of hydrocarbon consumption for hexane and toluene were 539 and 773 mg(hydrocarbon)/(g(protein) x h), respectively. For both substrates, the systems that showed the highest S(rates) of hydrocarbon consumption were F2 and F(2S). In experiment F(1S) the surfactant Pluronic F-68 increased the solubility of hydrocarbons in the liquid phase, but did not increase the S(rates). The maximum percentages of mineralization were 51% and 72% for hexane and toluene, respectively. The results showed that simultaneous addition of silicone oil and surfactant favours the mineralization, but not the rate ofbiodegradation, of toluene and hexane vapours.

Effect of nitrate on the reduction of Reactive Red 2 by mesophilic anaerobic sludge.

This research aimed to evaluate the effect of nitrate on anaerobic azo dye reduction by using mesophilic bioreactors, in the absence (reactor R2) and in the presence (reactor R1) of redox mediators. The azo dye Reactive Red 2 (RR2) and the redox mediator anthraquinone-2,6-disulphonate (AQDS) were selected as model compounds. The results showed that the bioreactors were efficient on RR2 reduction, in which ethanol showed to be a good electron donor to sustain dye reduction under anaerobic conditions. The redox mediator AQDS increased the rates of reductive decolourisation, but its effect was not so remarkable compared to the previous experiments conducted. Contrary to the raised hypothesis that the nitrate addition could decrease decolourisation rates and catalytic properties of the redox mediators, no effect of nitrate was observed in the bioreactors, suggesting that the presence of nitrate in textile wastewaters will not decrease the capacity of anaerobic reactors supplemented or not with redox mediators to decolourize azo dyes.

Qualitative and quantitative determination of a humic model compound in microbial cultures by cyclic voltammetry.

The humic model compound, anthraquinone-2,6-disulfonate (AQDS), was characterized and measured in microbial cultures by cyclic voltammetry (CV). Under the experimental conditions, the formal reduction potential (E(o')) of the couple AQDS/AHQDS was found to be of -0.520 V vs. SCE (standard calomel electrode) at pH value of 7.0. Control experiments showed that there were no interferences of the culture medium or the microbial consortium on the quantitative determination of the quinone. The linear equation E(o') = -0.294 - 0.032 pH was found, showing that the pH used (7.0-7.8) did not affect significantly the AQDS determination by CV and AHQDS was the predominant hydroquinone formed. A calibration curve was obtained by plotting current response versus AQDS concentration with a linear correlation (r = 0.999) from 0.2 to 10 mM of AQDS. This technique was applied in a denitrifying culture to establish kinetic profiles for AHQDS formation coupled to acetate and p-cresol oxidation. CV results showed that organic matter oxidation by the denitrifying sludge was stoichiometrically associated to AQDS reduction into AHQDS-. CV was shown to be a useful tool for monitoring oxidation/reduction processes of quinones occurring in complex microbial media.

Potentials of high-temperature anaerobic treatment and redox mediators for the reductive decolorization of azo dyes from textile wastewaters.

The discharge of dye-colored wastewaters in surface water represents a serious environmental problem because it may decrease the water transparency, therefore having an effect on photosynthesis, and a public health concern because dyes and their reducing products are carcinogenic. In recent years, big achievements have been made in the use of anaerobic granular sludge not only on colored wastewaters but also on the detoxification of other xenobiotics compounds. This paper compiles some important findings related to the potentials of high-temperature anaerobic treatment and redox mediators on the reductive decolorization of azo dyes from textile wastewaters.

The role of sulphate reduction on the reductive S decolorization of the azo dye reactive orange 14.

The aim of this study was to investigate the impact of a broad range of sulphate concentrations (0-10g SO4(-2) L(-1)) on the reduction of an azo dye (reactive orange 14 (RO14)) by an anaerobic sludge. An increase in the sulphate concentration generally stimulated the reduction of RO14 by sludge incubations supplemented with glucose, acetate or propionate as electron donor. Sulphate and azo dye reductions took place simultaneously in all incubations. However, there was a decrease on the rate of decolorization when sulphate was supplied at 10g SO4(-2) L(-1). Abiotic incubations at different sulphide concentrations (0-2.5 g sulphide L(-1)) promoted very poor reduction of RO14. However, addition of riboflavin (20 microM), as a redox mediator, accelerated the reduction of RO14 up to 44-fold compared to a control lacking the catalyst. Our results indicate that sulphate-reduction may significantly contribute to the reduction of azo dyes both by biological mechanisms and by abiotic reductions implicating sulphide as an electron donor. The contribution of abiotic decolorization by sulphide, however, was only significant when a proper redox mediator was included. Our results also revealed that sulphate-reduction can out-compete with azo reduction at high sulphate concentrations leading to a poor decolorising performance when no sufficient reducing capacity is available.

Catalytic effects of different redox mediators on the reductive decolorization of azo dyes.

The catalytic effects of redox mediators, with distinct standard redox potentials (E'0), were evaluated on the first-order rate constant of decolorization (Kd) of recalcitrant azo dyes by an anaerobic granular sludge. The dyes studied included mono-azo (Reactive Orange 14, RO14), di-azo (Direct Blue 53, DB53), and tri-azo (Direct Blue 71, DB71) compounds. Toxicity and auto-catalytic aspects seemed to play a role in determining the rate of decolorization. Addition of riboflavin, anthraquinone-2,6-disulphonate (AQDS) or lawsone as a redox mediator, increased the Kd value for all dyes studied, although their impact varied in every case. Kd values were increased from 1.1-fold up to 3.8-fold depending on the redox mediator applied. Moreover, catalysts with moderately similar E'0 value caused distinct stimulation on the rate of decolorization. These results should be considered for selecting the proper redox mediator to be applied during the anaerobic treatment of textile wastewaters and effluents containing electron-withdrawing pollutants, such as nitro-aromatic and polychlorinated compounds.

Thermophilic treatment by anaerobic granular sludge as an effective approach to accelerate the electron transfer and improve the reductive decolorization of azo dyes in bioreactors.

The effects of temperature, hydraulic retention time (HRT), and the redox mediator, anthraquinone-2,6-disulfonate (AQDS), on electron transfer and subsequent reductive decolorization of dyes from textile wastewater was assessed in mesophilic and thermophilic anaerobic bioreactors. The results clearly show that compared to mesophilic anaerobic treatment, thermophilic treatment at 55 degrees C is an effective approach for increasing the electron transfer capacity in bioreactors, and thus improving the decolorization rates. At an HRT of 2.5 h and in the absence of AQDS, the color removal was 5.3-fold higher at 55 degrees C compared to 30 degrees C. Furthermore, similar decolorizations were found at 55 degrees C between the AQDS-free and AQDS-supplemented reactors, whereas a significant difference (up to 3.6-fold) on dye reduction occurred at 30 degrees C.

Reductive decolourisation of azo dyes by mesophilic and thermophilic methanogenic consortia.

The contribution of acidogenic bacteria and methanogenic archaea on the reductive decolourisation of azo dyes was assessed in anaerobic granular sludge. Acidogenic bacteria appeared to play an important role in the decolourising processes when glucose was provided as an electron donor; whereas methanogenic archaea showed a minor role when this substrate was supplemented in excess. In the presence of the methanogenic substrates acetate, methanol, hydrogen and formate, methane production became important only after colour was totally removed from the batch assays. This retardation in methane production may be due to either a toxic effect imposed by the azo dyes or to the competitive behaviour of azo dyes to the methanogenic consortia for the available reducing equivalents.

Concurrence of Anaerobic Ammonium Oxidation and Organotrophic Denitrification in Presence of p-Cresol.

This study was carried out to evaluate the capacity of anaerobic granular sludge for oxidizing ammonium and p-cresol with nitrate as terminal electron acceptor. Kinetics for the anaerobic oxidation of ammonium and p-cresol is described in this paper. The phenolic compound was very efficiently consumed, achieving 65 % of mineralization. Ammonium and nitrate were also consumed at 83 and 92 %, respectively, being the main product N2. Anaerobic ammonium oxidation was promoted owing to accumulation of nitrite, and it allowed the synergy of anaerobic ammonium oxidation and organotrophic denitrification for the simultaneous removal of ammonium, nitrate, and p-cresol. A carbonaceous intermediate partially identified was transiently accumulated, and it transitorily truncated the respiratory process of denitrification. These experimental results might be considered for defining strategies in order to remove nitrate, ammonium, and phenolic compounds from wastewaters.

Nitrogen removal from wastewaters at low C/N ratios with ammonium and acetate as electron donors.

A denitrifying upflow anaerobic sludge blanket (UASB) reactor was operated at different nitrate loading rates at a C/N ratio of 1.2, with acetate as an electron donor. This resulted in an increase in the accumulation of nitrite. After this, the UASB reactor was supplemented with 100 mg NH4+-Nl(-1) d(-1), while acetate was gradually limited in the medium. This prevented nitrite accumulation at a C/N ratio of 0.6 due to an enhanced nitrite reduction rate achieved in the reactor. An increasing amount of ammonium was consumed when the C/N ratio was lowered in the medium. This suggested that ammonium was used as an alternative electron donor during denitrification, which is supported by nitrogen balances. Nitrite was shown to be toxic for the nitrogen removal process at 200-400 mg NO2--N(l(-1) when the C/N ratio was decreased to 0.4 leading to formation of ammonium. The present study showed that addition of ammonium as an alternative electron donor for denitrification achieved a nitrogen removal process with negligible accumulation of undesirable intermediates.

Enhanced decolourisation of acid orange 7 in a continuous UASB reactor with quinones as redox mediators.

The reductive biotransformation of acid orange 7 (AO7) was explored in a lab-scale upflow anaerobic sludge blanket (UASB) reactor at low hydraulic residence times (HRT). A colour removal of 85% was achieved when the reactor was operated at a HRT of 6 hours, but decreased up to 70% when the HRT was lowered to 2 hours. Addition of the quinone model compound, anthraquinone 2,6-disulfonate (AQDS), as redox mediator, allowed for a considerably higher decolourising efficiency (> 90% at all the HRT evaluated). The results indicate that the use of catalytic concentrations of AQDS (AQDS/AO7 molar ratio about 0.01) can accelerate decolourising processes achieving satisfying extent of decolourisation.

Enrichment and immobilization of quinone-respiring bacteria in anaerobic granular sludge.

The capacity of an anaerobic granular sludge for serving as an immobilizing mechanism for quinone-respiring bacteria was evaluated. The inoculum was continuously fed with a basal medium containing the humic model compound, anthraquinone-2,6-disulfonate (AQDS), as a terminal electron acceptor. Complete reduction of AQDS was achieved by the granular sludge for a prolonged period in an anaerobic bioreactor provided with a mixture of volatile fatty acids as a substrate. Phylogenetic analysis revealed the enrichment and immobilization of AQDS-respiring bacteria appearing as dominant organisms in the microbial population of the AQDS-supplemented reactor, compared to a reactor control operated under methanogenic conditions. The consistent quinone-reducing capacity observed in the consortium indicates that it is feasible to apply quinone-reducing microorganisms in continuous bioreactors and this ability can potentially be important in wastewaters rich in humic substances. The quinone reducing activity could also be applied to accelerate the conversion of xenobiotics susceptible to reductive biotransformations such as azo dyes and polychlorinated compounds in continuous bioreactors.

[Polycythemia in newborn infants. II. Umbilical cord and capillary hematocrits]. / Policitemia en el recién nacido. II. Hematócritos del cordón y capilares.

Actual values for capillary hematocrits at 24 and 48 hours of life, through a hospital sample, representative of our population, were obtained; results were 58 +/- 7% (X +/- 1 DS) for both. These results were correlated to the initial hematocrit (50 +/- 5%), with had been reported in the first part of the series. The relationship between capillary hematocrits and the initial one, was very good, and between the capillary ones, was oven better. This relationship persisted after distributing the sample in four groups: Apgar, crying (if it presented before or after clamping) and the features of amniotic fluid. This demonstrates that capillary hematocrits, are as reliable as venous, central and peripheral hematocrit (in this case, from umbilical chord blood), contrary to what has been previously reported in literature. The presence of chord loop or circular, was analyzed also, when it was possible.

Simultaneous oxidation of ammonium and p-cresol linked to nitrite reduction by denitrifying sludge.

The metabolic capability of denitrifying sludge to oxidize ammonium and p-cresol was evaluated in batch cultures. Ammonium oxidation was studied in presence of nitrite and/or p-cresol by 55 h. At 50 mg/L NH4+-N and 76 mg/L NO2--N, the substrates were consumed at 100% and 95%, respectively, being N2 the product. At 50 mg/L NH4+-N and 133 mg/L NO2--N, the consumption efficiencies decreased to 96% and 70%, respectively. The increase in nitrite concentration affected the ammonium oxidation rate. Nonetheless, the N2 production rate did not change. In organotrophic denitrification, the p-cresol oxidation rate was slower than ammonium oxidation. In litho-organotrophic cultures, the p-cresol and ammonium oxidation rates were affected at 133 mg/L NO2--N. Nonetheless, at 76 mg/L NO2--N the denitrifying sludge oxidized ammonium and p-cresol, but at different rate. Finally, this is the first work reporting the simultaneous oxidation of ammonium and p-cresol with the production of N2 from denitrifying sludge.

Thermal modification of activated carbon surface chemistry improves its capacity as redox mediator for azo dye reduction.

The surface chemistry of a commercial AC (AC(0)) was selectively modified, without changing significantly its textural properties, by chemical oxidation with HNO(3) (AC(HNO3)) and O(2) (AC(O2)), and thermal treatments under H(2) (AC(H2)) or N(2) (AC(N2)) flow. The effect of modified AC on anaerobic chemical dye reduction was assayed with sulphide at different pH values 5, 7 and 9. Four dyes were tested: Acid Orange 7, Reactive Red 2, Mordant Yellow 10 and Direct Blue 71. Batch experiments with low amounts of AC (0.1 g L(-1)) demonstrated an increase of the first-order reduction rate constants, up to 9-fold, as compared with assays without AC. Optimum rates were obtained at pH 5 except for MY10, higher at pH 7. In general, rates increased with increasing the pH of point zero charge (pH(pzc)), following the trend AC(HNO3) < AC(O2) < AC(0) < AC(N2) < AC(H2). The highest reduction rate was obtained for MY10 with AC(H2) at pH 7, which corresponded to the double, as compared with non-modified AC. In a biological system using granular biomass, AC(H2) also duplicated and increase 4.5-fold the decolourisation rates of MY10 and RR2, respectively. In this last experiment, reaction rate was independent of AC concentration in the tested range 0.1-0.6 g L(-1).

Immobilized redox mediator on metal-oxides nanoparticles and its catalytic effect in a reductive decolorization process.

Different metal-oxides nanoparticles (MONP) including α-Al(2)O(3), ZnO and Al(OH)(3), were utilized as adsorbents to immobilize anthraquinone-2,6-disulfonate (AQDS). Immobilized AQDS was subsequently tested as a solid-phase redox mediator (RMs) for the reductive decolorization of the azo dye, reactive red 2 (RR2), by anaerobic sludge. The highest adsorption capacity of AQDS was achieved on Al(OH)(3) nanoparticles, which was ∼0.16 mmol g(-1) at pH 4. Immobilized AQDS increased up to 7.5-fold the rate of decolorization of RR2 by anaerobic sludge as compared with sludge incubations lacking AQDS. Sterile controls including immobilized AQDS did not show significant (<3.5%) RR2 decolorization, suggesting that physical-chemical processes (e.g. adsorption or chemical reduction) were not responsible for the enhanced decolorization achieved. Immobilization of AQDS on MONP was very stable under the applied experimental conditions and spectrophotometric screening did not detect any detachment of AQDS during the reductive decolorization of RR2, confirming that immobilized AQDS served as an effective RMs. The present study constitutes the first demonstration that immobilized quinones on MONP can serve as effective RMs in the reductive decolorization of an azo dye. The immobilizing technique developed could be applied in anaerobic wastewater treatment systems to accelerate the redox biotransformation of recalcitrant pollutants.