Bacterial community shifts in nonylphenol polyethoxylates-enriched activated sludge.

A molecular approach was used to evaluate the effect of nonylphenol ethoxylate surfactants on the bacterial diversity in lab-scale activated sludge reactors. Separate bench-scale units were fed synthetic wastewater with and without addition of branched nonylphenol ethoxylates (NPnEO). The performance of the reactors, in terms of carbonaceous removal was largely unaffected by the presence of NP10EO in the feeding solution. However, addition of NP10EO exerted a pronounced shift in bacterial community composition. In situ hybridization analyzing larger phylogenetic groups of bacteria with ribosomal RNA-targeted oligonucleotide probes revealed the dominance of clusters composed of Betaproteobacteria, accounting for up to one-third of 4',6-diamidino-2-phenylindol-dihydrochloride (DAPI)-stained cells in NP10EO amended reactors and only 5% of DAPI-stained cells in the controls. These shifts in populations of larger phylogenetic groups were confirmed by dot-blot analysis of rRNA. Members of gamma subclass of Proteobacteria were present in low numbers in all activated sludge samples examined, suggesting that only bacteria affiliated with the beta subclass of Proteobacteria may have a specific role in NP10EO degradation.

Kinetics and mechanisms of EDTA photocatalytic degradation with TiO2.

A complete study on the photocatalytic degradation of ethylenediaminetetraacetic acid (EDTA) over TiO2 has been initiated, to establish the influence of several parameters on the reaction rate, the nature of the intermediates and the kinetic regime. TiO2 (Degussa P25) suspensions containing EDTA at pH 3 at different concentrations were irradiated under near UV light. A Langmuirian behavior was observed, from which kinetic constants have been obtained. Experiments with 5.0 mM EDTA (zero order kinetic regime) were performed for 3 hours irradiation under different conditions. Under N2 bubbling, depletion of EDTA was very low. Under O2 bubbling, the concentration of EDTA decreased around 90%. However, the corresponding decrease of TOC ranged only between 4.5% and 9%. A higher TOC reduction (22% or more) was obtained by keeping the pH constant by HClO4 addition, or by hydrogen peroxide addition. Addition of 0.5 mM Fe(III) caused a dramatic increase on the initial rate of EDTA depletion and approximately a 32% TOC decrease. Analysis of the filtered solution was performed by ion chromatography and capillary electrophoresis to monitor the disappearance of EDTA and the formation of degradation products after different irradiation times. So far, glycine, ethylenediamine, formic acid, ammonium, iminodiacetic acid, oxalic acid and glyoxylic acid have been identified.

Determination of inorganic and organic anionic arsenic species in water by ion chromatography coupled to hydride generation-inductively coupled plasma atomic emission spectrometry.

The development of an analytical methodology for the specific determination of arsenite, arsenate and the organic species monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), is described. The method is based on an ion chromatographic separation, coupled on-line to post-column generation of the gaseous hydrides by reaction with sodium tetrahydroborate in acidic medium. Detection and measurement were performed by inductively coupled plasma spectrometry operated in the atomic emission mode. Arsenic emission was monitored at 193.7 nm. Different types and sizes of anion-exchange columns, silica and polymeric, were tested using EDTA as eluent. Composition, acidity and flow-rate of the mobile phase were optimized in order to obtain the required resolution. Complete elution and resolution of the four species was achieved in about 6 min. Linear calibration curves were obtained in the 0.05-2 microg ml(-1) range for As(III), As(V) and MMA, and between 0.1 and 2.0 microg ml(-1) for DMA. The absolute limits of detection for 200-microl sample injections were in the ng range, with DMA the compound measured with less sensitivity. Results of the analyses of natural samples, such as river and ground waters spiked with the studied species, suggested that analyte recoveries might be dependent on the sample composition.

Eriochrome Black T as a post-column reagent for the ion chromatographic determination of rare earths.

The use of Eriochrome Black T in an alkaline, 40% methanol solution was found to be appropriate as post-column reagent for the determination of rare earths by ion chromatography. Detection of individual lanthanides and lanthanum was carried out at 512 nm and 650 nm after separation by dynamic cation exchange chromatography with gradient elution on C18 column and employing a solution containing alpha-hydroxyisobutiric acid/sodium octanesulfonate at pH 3.8 as eluent. The effect of the presence of micelles in the post-column reagent was studied. Sensitivities obtained by the addition of the cationic surfactants cetylpyridinium chloride (CPC) and hexadecyltrimethylammonium bromide (CTAB) were lower than those measured without surfactant addition. In some cases, the signal was totally suppressed. No change in sensitivity was observed with non-ionic (Triton X-100) or anionic (sodium dodecylsulphate, SDS) surfactants but a slight improvement in the baseline noise was observed with the SDS. An evaluation of the influence of chemical and operational variables on the post column reaction (PCR) reagent was carried out either by spectrophotometric tests or by chromatographic experiments. A comparison was performed between three PCR reagents: Eriochrome Black T and xylenol orange in the presence of a cationic surfactant and arsenazo III. Calibration response was linear up to an analyte concentration of 5.0 micrograms ml-1. Absolute detection limits lower than 7 and 17 ng were obtained at the detection wavelengths of 650 nm and 512 nm respectively, for all the natural lanthanides and lanthanum.

Application of factor analysis to polarographic data: determination of the number of species present in metal ion-ligand systems.

It is shown that factor analysis is applicable to polarographic data, and can be used to find the number of complex species in solution. An analytical criterion for finding this number is proposed and applied to several calculated and experimental data sets. The range of use of the factor-analysis method is compared with that for spectrophotometric and potentiometric data.