Occurrence of eight household micropollutants in urban wastewater and their fate in a wastewater treatment plant. Statistical evaluation.

The occurrence in urban wastewater of eight micropollutants (erythromycin, ibuprofen, 4-nonylphenol (4-NP), ofloxacin, sucralose, triclosan, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS)) originating from household activities and their fate in a biological wastewater treatment plant (WWTP) were investigated. Their concentrations were assessed in the liquid and solid phases (sewage particulate matter and wasted activated sludge (WAS)) by liquid chromatography-tandem mass spectrometry. The analysis of sewage from two different urban catchments connected to the WWTP showed a specific use of ofloxacin in the mixed catchment due to the presence of a hospital, and higher concentrations of sucralose in the residential area. The WWTP process removed over 90% of ibuprofen and triclosan from wastewater, while only 25% of ofloxacin was eliminated. Erythromycin, sucralose and PFOA were not removed from wastewater, the influent and effluent concentrations remaining at about 0.7 µg/L, 3 µg/L and 10 ng/L respectively. The behavior of PFOS and 4-nonylphenol was singular, as concentrations were higher at the WWTP outlet than at its inlet. This was probably related to the degradation of some of their precursors (such as alkylphenol ethoxylates and polyfluorinated compounds resulting in 4-NP and PFOS, respectively) during biological treatment. 4-NP, ofloxacin, triclosan and perfluorinated compounds were found adsorbed on WAS (from 5 ng/kg for PFOA to 1.0mg/kg for triclosan). The statistical methods (principal component analysis and multiple linear regressions) were applied to examine relationships among the concentrations of micropollutants and macropollutants (COD, ammonium, turbidity) entering and leaving the WWTP. A strong relationship with ammonium indicated that some micropollutants enter wastewater via human urine. A statistical analysis of WWTP operation gave a model for estimating micropollutant output from the WWTP based on a measurement of macropollution parameters.

Impact of certain household micropollutants on bacterial behavior. Toxicity tests/study of extracellular polymeric substances in sludge.

The impact of eight household micropollutants (erythromycin, ofloxacin, ibuprofen, 4-nonylphenol, triclosan, sucralose, PFOA and PFOS (PFAAs)) on the laboratory bacterial strain Escherichia coli MG1655 and on activated sludge from an urban wastewater treatment plant was studied. Growth-based toxicity tests on E. coli were performed for each micropollutants. The effect of micropollutants on activated sludge (at concentrations usually measured in wastewater up to concentrations disturbing the bacterial growth of E. coli) was examined in batch reactors and by comparison to a control reactor (without micropollutants). The bound extracellular polymeric substances (EPS) secreted by the sludge were measured by size exclusion chromatography and their overexpression was considered as an indicator of bacteria sensitivity to environmental changes. The chemical oxygen demand (COD) and the ammonium concentration were monitored to evaluate the biomass ability to remove the macropollution. Some micropollutants induced an increase of bound EPS in activated sludge flocs at concentrations depending on the micropollutant: erythromycin from 100 µg/L, ofloxacin from 10 µg/L, triclosan from 0.5 µg/L, 4-nonylphenol from 5000 µg/L and PFAAs from 0.1 µg/L. This suggests that the biomass had to cope with new conditions. Moreover, at high concentrations of erythromycin (10 mg/L) and ibuprofen (5 mg/L) bacterial populations were no longer able to carry out the removal of macropollution. Ibuprofen induced a decrease of bound EPS at all the studied concentrations, probably reflecting a decrease of general bacterial activity. The biomass was not sensitive to sucralose in terms of EPS production, however at very high concentration (1 g/L) it inhibited the COD decrease. Micropollution removal was also assessed. Ibuprofen, erythromycin, ofloxacin, 4-nonylphenol and triclosan were removed from wastewater, mainly by biodegradation. Sucralose and PFOA were not removed from wastewater at all, and PFOS was slightly eliminated by adsorption on sludge.

On the use of electrokinetic phenomena of the second kind for probing electrode kinetic properties of modified electron-conducting surfaces.

The electrokinetic features of electron-conducting substrates, as measured in a conventional thin-layer electrokinetic cell, strongly depend on the extent of bipolar faradaic depolarisation of the interface formed with the adjacent electrolytic solution. Streaming potential versus applied pressure data obtained for metallic substrates must generally be interpreted on the basis of a modified Helmholtz-Smoluchowski equation corrected by an electronic conduction term-non linear with respect to the lateral potential and applied pressure gradient-that stems from the bipolar electrodic behavior of the metallic surface. In the current study, streaming potential measurements have been performed in KNO(3) solutions on porous plugs made of electron-conducting grains of pyrite (FeS(2)) covered by humic acids. For zero coverage, the extensive bipolar electronic conduction taking place in the plug-depolarized by concomitant and spatially distributed oxidation and reduction reactions of Fe(2+) and Fe(3+) species-leads to the complete extinction of the streaming potential over the entire range of applied pressure examined. For low to intermediate coverage, the local electron-transfer kinetics on the covered regions of the plug becomes more sluggish. The overall bipolar electronic conduction is then diminished which leads to an increase in the streaming potential with a non-linear dependence on the pressure. For significant coverage, a linear response is observed which basically reflects the interfacial double layer properties of the humics surface layer. A tractable, semi-analytical model is presented that reproduces the electrokinetic peculiarities of the complex and composite system FeS(2)/humics investigated. The study demonstrates that the streaming potential technique is a fast and valuable tool for establishing how well the electron transfer kinetics at a partially or completely depolarised bare electron-conducting substrate/electrolyte solution interface is either promoted (catalysis) or blocked (passivation) by the presence of a discontinuous surface layer.

Characterization of activated sludge exopolymers from various origins: a combined size-exclusion chromatography and infrared microscopy study.

High-pressure size-exclusion liquid chromatography and infrared microscopy were coupled to investigate the molecular weight and nature of extracellular polymeric substances (EPS) from various activated sludges. Six main families of compounds (proteins, polysaccharides, organic acids, lipids, mineral phases) were found either as a single molecule or as associations. The molecular weight of proteins varied from small (10 kDa) to large (600 kDa) sizes, while all polysaccharides were smaller than 1 kDa. Association of different molecules implied the presence of species large in size. The EPS chromatographic fingerprints of sludge from various origins remained stable in normal operating conditions, but were drastically modified during settling crises. In poor settling conditions, the EPS with smaller molecular sizes always prevailed and large polymers were underrepresented. The EPS identified in activated sludge were collected in a chemical database which provides the basis for comparison of municipal and industrial wastewater treatment plants (WWTP).

Investigation of activated carbon surface heterogeneity by argon and nitrogen low-pressure quasi-equilibrium volumetry.

Surface heterogeneity can be assessed by adsorption of different gaseous probes on solid materials. In the present study, four types of activated carbons were analyzed by classical N2 Brunauer-Emmett-Teller (BET) measurements and by low-pressure quasi-equilibrium volumetry (LPQEV) (Villieras, F.; Michot, L. J.; Bardot, F.; Cases, J. M.; Francois, M.; Rudzinski, W. Langmuir 1997, 13, 1104). Three methods of data evaluation were applied: (a) the Frenkel-Halsey-Hill method for estimation of fractal dimensions from BET data, (b) the Horwath-Kawazoe method to calculate the pore size distribution from LPQEV Ar and N2 adsorption isotherms, and (c) the derivative isotherm summation (DIS) method to describe the solid's surface heterogeneity by a concept of local derivative isotherms. Similar Ar and N2 adsorption energy distributions were obtained on all carbons, which indicates the presence of mainly nonpolar surfaces. When adsorption was described by the van der Waals equation, the ratio between the interaction energy of different energetic sites with argon and nitrogen was 0.88. This value corresponded very well with a slope obtained when Ar and N2 positions of local isotherms by the DIS method were compared. This relationship has an important impact because it enables one to constrain the modeling of local isotherms. This study, besides the surface information, showed large possibilities of the DIS method for the surface analysis not only in terms of solid heterogeneity characterization but also in terms of polarity assessment.

Kinetics of salicylic acid adsorption on activated carbon.

The adsorption and desorption of salicylic acid from water solutions was investigated in HPLC microcolumns packed with activated carbon. The adsorption isotherm was obtained by the step-up frontal analysis method in a concentration range of 0-400 mg/L and was well fitted with the Langmuir equation. The investigation of rate aspects of salicylic acid adsorption was based on adsorption/desorption column experiments where different inlet concentrations of salicylic acid were applied in the adsorption phase and desorption was conducted with pure water. The concentration profiles of individual adsorption/desorption cycles data were fitted using several single-parameter models of the fixed-bed adsorption to assess the influence of different phenomena on the column behavior. It was found that the effects of axial dispersion and extraparticle mass transfer were negligible. A rate-determining factor of fixed-bed column dynamics was the kinetics of pore surface adsorption. A bimodal kinetic model reflecting the heterogeneous character of adsorbent pores was verified by a simultaneous fit of the column outlet concentration in four adsorption/desorption cycles. The fitted parameters were the fraction of mesopores and the adsorption rate constants in micropores and mesopores, respectively. It was shown that the former rate constant was an intrinsic one whereas the latter one was an apparent value due to the effects of pore blocking and diffusional hindrances in the micropores.

Study of tropaeolin degradation by iron--proposition of a reaction mechanism.

The degradation of tropaeolin by iron was studied under oxidizing and inert atmospheres. The products were identified by various chromatographic and spectroscopic methods. Under inert atmosphere, the proposed model of mechanism is based on the adsorption of tropaeolin by the sulfonate function on the solid iron, followed by a reduction of the [bond]Nz[double bond]N[bond] bond with formation of 1-amino-2-naphthol and sulfanilic acid. These two intermediaries were reduced to 1,2-dihydroxynaphthalene and benzene with NH(4)(+) and HSO(3)(-) liberation. Under oxidizing atmosphere, besides the reductions of tropaeolin, water and ferric ions, the existence of a homogeneous degradation was found. This process was explained (on the basis of surface iron potential monitoring) by a stepwise reduction of oxygen giving hydrogen peroxide. The initial stages of the mechanism were similar to those under inert atmosphere, but the degradation of the 1,2-dihydroxynaphthalene continued giving 1,2-naphthalenedione, then various polar monocyclic compounds leading to three unidentified volatile final products.

Activated sludge exopolymers: separation and identification using size exclusion chromatography and infrared micro-spectroscopy.

Extracellular polymeric substances were extracted from activated sludge using a resin exchange method and analyzed. The separation and identification of EPS were carried out by size exclusion chromatography and Fourier transform infrared micro-spectroscopy. Chromatograms of extracted EPS exhibited seven peaks. Proteins varying in molecular weights from 670 to 45 kDa were present in all the peaks. Polysaccharides corresponding to molecular weights of approximately 1 and approximately 0.5 kDa were present in only three peaks. Strong association of polysaccharides and proteins was observed. Infrared results revealed the presence of one type of polysaccharide and two types of proteins (A and B). Proteins differed mainly in the length of their associated alkyl chains and in the ratio of ester/acidic functionalities.

Use of the Gaussian Distribution Function as a Tool to Estimate Continuous Heterogeneity in Adsorbing Systems.

In environmental engineering, adsorption and desorption are phenomena commonly referred to as responsible for pollution dispersion, retention, or retardation in soils, aquifers, and hydrologic systems. They are also used to remove organic pollutants from water or odorous compounds in gas deodorization. Most often, the characterization of the aqueous adsorption systems that are of engineering interest involves a narrow adsorbate concentration range and low values of the adsorbate concentration. The practice is to use the Freundlich equation that best fits most data and is considered sufficient to design adsorption contactors. However, no physical or chemical meaning can be associated with the values taken by the parameters. The present paper gives a new way of analyzing adsorption data, using an extension of the Freundlich equation and the Gaussian distribution function that makes it possible to associate parameter values of this extension with the adsorbate-adsorbent normal interaction energy, its heterogeneity, and to some extent the adsorbate-adsorbate lateral interaction energy. Copyright 2001 Academic Press.