Long-term evaluation of a sequential batch reactor (SBR) treating dairy wastewater for carbon removal.

Many dairy industries have been using SBR wastewater treatment plants because they allow optimal working condition to be reached. However, to take advantage of SBR capabilities, strong process automation is needed. The aim of this work is to study the factors that influence SBR performance to improve modelling and control. To better understand the whole process we studied the kinetic modelling, the carbon removal mechanism and the relation between reactor performance, aerobic heterotrophic activity and bacterial population dynamics (by terminal restriction fragment length polymorphisms of 16S rDNA, T-RFLP). The heterotrophic activity values presented high variability during some periods; however, this was not reflected on the reactor performance. As sludge health indicator, the average activity in a period was better than individual values. Although all the carbon removal mechanisms are still unclear for this process, they seemed to be influenced by non-respirometric ways (storage, biosorption, accumulation, etc.). The variability of heterotrophic activity could be correlated with the bacterial population diversity over time. Despite the high variability of the activity, a simple kinetic model (pseudo ASM1) based on apparent constant parameters was developed and calibrated. Such modellisation provided a good tool for control purposes.     

Determination of the potency of hexyl‐ciprofloxacin molecules that interact with gold nanoparticles in a reversible manner

This work determined the potency of hexyl‐ciprofloxacin molecules that reversibly interact with gold nanoparticles (AuNPs) passivated with 11‐mercaptoundecanoic acid (MUA) on Escherichia coli cells. For this, partition of modified antibiotic between different compartments of the gold colloid was determined using analytical techniques. First, concentration of hexyl‐ciprofloxacin was determined in the continuous phase of the colloid. Subsequently, the colloid was exposed to a volume of organic immiscible solvent and concentration of the transferred molecules was determined in the organic phase. Comparison of the amount of hexyl‐ciprofloxacin in each phase revealed that interaction between molecules and nanoparticles was reversible. Later, this work determined the potency of a population of hexyl‐ciprofloxacin molecules contained in a volume of the colloid, and the potency of other population of molecules that only interact with the continuous phase of the colloid. The absolute difference between these two values was proportional to the potency of a number of molecules that interact with the nanoparticles of the colloid.Inspec keywords: organic compounds, nanoparticles, gold, colloids, microorganisms, molecular biophysics, drug delivery systems, nanomedicineOther keywords: continuous phase, hexyl‐ciprofloxacin molecules, gold nanoparticles, gold colloid, 11‐mercaptoundecanoic acid, Escherichia coli cells, modified antibiotics, RP‐HPLC, organic immiscible solvent, reversible interaction, Au     

Monitoring of carboxylic carbon nanotubes in surface water by using multiwalled carbon nanotube-modified filter as preconcentration unit

In this paper, for the first time, the possibility of preconcentrating and determining carboxylic single-walled carbon nanotubes (c-SWNTs) from environmental water samples is demonstrated. The method is based on the preconcentration of c-SWNTs and their further electrophoretic analysis. The preconcentration of c-SWNTs has been successfully performed on a filter modified with multiwalled carbon nanotubes (MWNTs), which allows the use of high preconcentration rates. MWNT-modified filters were fabricated in the laboratory from a surfactant dispersion of MWNTs. The main variables affecting the preconcentration of analytes are studied and discussed in the paper. Electrophoretic separation of carboxylic SWNTs was accomplished by using a 50 mM ammonium acetate solution at pH 7.5 as a background electrolyte and a potential of 15 kV. Under these conditions, separation was completed within only 5 min. Recoveries for the analysis of spiked samples ranged from 70 to 85% and the precision from 6.4 to 7.3%.     

ATR-FT-IR membrane-based sensor for integrated microliquid-liquid extraction and detection

A novel straightforward membrane-based sensor, which uses attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy has been developed. The flow cell designed permits the on-line microliquid-liquid extraction of the target analyte into a organic solvent layer (OSL), which was deposited on the ATR surface using a sequential injection manifold. The aqueous and organic phases are separated via a commercial hydrophobic membrane placed on the PTFE piece of the cell. The main advantage of the proposed device is that the OSL can be created and regenerated in a continuous manner using the automatic manifold without opening the cell. The analytes are enriched into the OSL after diffusion through the membrane, which excludes the typical absorption bands of water. In addition, the behavior of different organic solvents was evaluated in order to increase the applicability and versatility of the proposed system. Finally, the analytical performance of the design was established for the detection and quantitation of Triton X100 in water.     

Autoanalyzer for milk quality control based on the lactose,fat, and total protein contents

A novel autoanalyzer was developed to assess the quality of milk samples according to the percentage of lactose, fat, and total protein they contain. The module comprises two pumps (one of high pressure), an injection valve, a filter, and an evaporative light-scattering detector. A volume of 15 microL of dilute milk was injected in an ethanol-water (50% v/v) stream for precipitation/retention of protein/fat, being the lactose content determined in the filtrate. The fat fraction was calculated using an ethanol stream, and total protein was finally dissolved by means of a 1.7 mol/L acetic acid solution. The simplicity of the proposed automatic module lies in the universal response of the detector, which permits the determination of the three macrocomponents in milk. In addition, the flow injection method allows their sequential analysis in the same injected sample by using selective reagents for each compound. The proposed method was validated with an SRM milk sample as well as by comparison of the results obtained with those provided by the IR method. In addition, the proposed analyzer is cheaper than its counterpart that is based on infrared technique.     

Nucleotide sequence and chromosomal localization of the gene encoding the old yellow enzyme from Kluyveromyces lactis

A 6·6 kb genomic DNA fragment from the yeast Kluyveromyces lactis was isolated. Sequence analysis of this fragment revealed the presence of two incomplete open reading frames (ORFs) in one strand, one coding for the carboxyl terminus of the plasma membrane H⁺-ATPase and the other for the amino terminus of an unidentified product. In the complementary strand, a full-length ORF which encodes for a protein homologous to the yeast NADPH-dependent Old Yellow Enzyme was found. The deduced amino acid sequence of this ORF predicts a protein of 398 residues with 84% similarity in its full length to OYE1 from Saccharomyces carlsbergensis and OYE2 from Saccharomyces cerevisiae. In addition, an internal region showed considerable similarity to the bile acid-inducible polypeptide from Eubacterium sp., to the NADH oxidase from Thermoanaerobium brockii, to the trimethylamino dehydrogenase from bacterium W₃A₁ and to the estrogen-binding protein from Candida albicans, suggesting a functional or structural relationship between them. Inactivation of the KYE1 (K luyveromyces Y ellow E nzyme) gene by deletion of 0·6 kb fragment between positions +358 and +936 produced viable cells with a slight increase in their generation time. Haploid cells carrying the disrupted allele showed one-third of the NADPH oxidase activity, compared to wild-type cells. Southern blotting analysis of digested DNA and chromosomes separated by contour-clamped homogeneous electric field electrophoresis from K. lactis indicated that this is a single-copy gene and it is localized on chromosome II, whose molecular size has been estimated to be approximately 1·3 Mb. The sequence reported in this paper has been deposited in the GenBank data base (Accession No. L37452).     

Water-induced coacervation of alkyl carboxylic acid reverse micelles: phenomenon description and potential for the extraction of organic compounds

Coacervates made up of alkanoic (C8-C16) and alkenoic (C18) acid reverse micelles were described for the first time, and their potential for the extraction of organic compounds prior to liquid chromatography was examined. The coacervation process occurred in miscible binary mixtures of water and a variety of protic and aprotic solvents. The phase behavior of alkyl carboxylic acids was found to be a function of both the Hildebrand solubility parameter, delta, and the hydrogen-bonding capability of the solvent. The best solvents for analytical extractions were those featuring the lowest delta values. The phase behavior of alkyl carboxylic acid/water/tetrahydrofuran (THF) ternary systems as a function of component concentration, pH, ionic strength, and temperature was investigated. The efficiency and the time required for phase separation depended on the experimental procedure used (i.e., standing, centrifugation, stirring, and sonication). The formation of alkyl carboxylic acid reverse micelles in THF was proven using both hydrophilic fluorescent probes and scattered light measurements. The structure of the coacervates consisted of spherical droplets dispersed in a continuous phase. Phase volume ratios were a function of both alkyl carboxylic acid and THF concentration. The low volume obtained (e.g., 1.5 microL per mg of decanoic) compared to that obtained by other coacervates (e.g., 5.1 microL per mg of dodecane sulfonic acid and 11.3 microL per mg of Triton X-114) greatly improved the concentration factors reached by coacervation-based extractions. Parameters affecting the extraction efficiency were assessed. Analytes in a wide range of polarity were efficiently extracted on the basis of the hydrophobic (e.g., PAHs) and hydrogen bond (e.g., chlorophenols, bisphenols, pesticides, phthalates, nonionic surfactants, dyes, and photographic developers) interactions that reverse micelles can establish. The coacervates were compatible with the chromatographic determination of analytes following UV or MS detection. They were successfully applied to the extraction of alkylphenol ethoxylates (octyl and nonyl) and alcohol ethoxylates (C12-C16) from influent and effluent wastewater and river water samples. Nonionic surfactants in the coacervate were directly separated and quantified by liquid chromatography-ion trap mass spectrometry. Concentration factors were around 160. The recovery of nonionics in the environmental water samples ranged from 90 to 104%.     

Electrocatalytic reduction of nitrite on tetraruthenated metalloporphyrins/Nafion glassy carbon modified electrode

This paper describes the electrochemical reduction of nitrite ion in neutral aqueous solution mediated by tetraruthenated metalloporphyrins (Co(II), Ni(II) and Zn(II)) electrostatically assembled onto a Nafion film previously adsorbed on glassy carbon or ITO electrodes. Scanning electron microscope (SEM-EDX) and transmission electron microscopy (TEM) results have shown that on ITO electrodes the macrocycles forms multiple layers with a disordered stacking orientation over the Nafion film occupying hydrophobic and hydrophilic sites in the polyelectrolyte. Atomic force microscopy (AFM) results demonstrated that the Nafion film is 35 nm thick and tetraruthenated metalloporphyrins layers 190 nm thick presenting a thin but compacted morphology. Scanning electrochemical microscopy (SECM) images shows that the Co(II) tetraruthenated porphyrins/Nf/GC modified electrode is more electrochemically active than their Ni and Zn analogues.These modified electrodes are able to reduce nitrite at −660 mV showing enhanced reduction current and a decrease in the required overpotential compared to bare glassy carbon electrode. Controlled potential electrolysis experiments verify the production of ammonia, hydrazine and hydroxylamine at potentials where reduction of solvent is plausible demonstrating some selectivity toward the nitrite ion. Rotating disc electrode voltammetry shows that the factor that governs the kinetics of nitrite reduction is the charge propagation in the film.     

Electrooxidation of 2-chlorophenol and 2,4,6-chlorophenol on glassy carbon electrodes modified with graphite–zeolite mixtures

This work reports the behavior of zeolite–graphite electrodes for the oxidation of 2,4,6-trichlorophenol (2,4,6-TCP) and 2-chlorophenol (2-CP) in a pH 3, 0.5 M Na₂SO₄ electrolyte using cyclic voltammetry, chronoamperometry, electrochemical impedance and galvanostatic electrolysis. Three zeolites with different hydrophobic/hydrophilic balance were used, in order to determine the possible effect of this parameter. On glassy carbon (GC) modified with 80–20 % graphite–zeolite mixtures the voltammetric peak charge of 2-CP oxidation was higher than that on GC modified with graphite alone, clearly showing a catalytic effect of the zeolites. ZSM-5 was the more active zeolite, probably due to its hydrophobic character, which should favor its interaction with the also hydrophobic 2-CP. In agreement with this, the charge-transfer resistance of GC modified with a graphite-ZSM-5 mixture was about half that of GC modified with graphite alone, and its double-layer capacity about 50 % higher, indicating a modification of the interface which favours the reaction. On the contrary, for 2,4,6-TCP both the oxidation peak charge, and the charge-transfer resistance, for GC electrodes modified with graphite–zeolite mixtures was about the same as that of GC modified with graphite alone. This lack of catalytic action could be due to the fact that the oxidation of 2,4,6-TCP requires the release of at least one chlorine atom, this release being so difficult that it cannot be promoted by any of the zeolites studied. However, in prolonged galvanostatic electrolysis practically all the current went to the oxidation of 2,4,6-TCP, while in the case of 2-CP only a small fraction was oxidized. Probably with 2-CP at long times surface poisoning blocked the reaction, as reflected by the fact that the electrolysis potential rose to a value 0.2 V higher than that reached by TCP, and so high that most of the current went to oxygen evolution. The zeolites ZA and ZY decreased the mineralization of 2,4,6-TCP, since they promoted a one-electron oxidation reaction, so that its concentration at 80 min was about 80 % of that observed with graphite alone. The oxidation of 2-CP was not significantly affected by any zeolite as compared with that on graphite.     

Cobalt oxide nanoparticles on mesoporous MCM-41 and Al-MCM-41 by supercritical CO2 deposition

CoO and Co₃O₄ nanoparticles were uniformly dispersed inside mesoporous MCM-41 and Al-MCM-41 supports using supercritical CO₂ reactive deposition. This method represents a one-pot reproducible procedure that allows the dissolution of the organocobalt precursor and supports impregnation in supercritical CO₂ at 70 °C and 110 bar, followed by the precursor thermal decomposition into cobalt species at 200 °C and 160 bar. By the relative concentration of the cobalt precursor [cobalt (II) bis (η⁵-ciclopentadienil)], the load of cobalt nanoparticles was controlled and then determined by Inductively Coupled Plasma (ICP-OES). The synthesis of CoO and Co₃O₄ species inside the MCM-41 and Al-MCM-41 substrates was confirmed by X-ray Photoelectron (XPS) and Laser Raman Spectroscopies (LRS). By N₂ adsorption and Small Angle X-ray Scattering (SAXS), it was determined that the hexagonal arrangement as well as the surface area and pore size of the substrates changed after the addition of cobalt. By means of X-ray mapping from SEM images, a homogeneous distribution of cobalt nanoparticles was observed inside the mesopores when the cobalt loading was 1 wt.%. In addition, spherical cobalt nanoparticles of average diameter close to 20 nm were detected on the outer surface of MCM-41 and Al-MCM-41 supports when the cobalt content was higher. On the other hand, by Transmission Electron Microscopy (TEM), it was possible to measure the interplanar distance of the crystalline plane of the outer nanoparticles, which was later compared with the theoretical distance values which allowed identifying the CoO and Co₃O₄ phases.