Vancomycin sorption on activated sludge Gram+ bacteria rather than on EPS; 3D Confocal Laser Scanning Microscopy time-lapse imaging.

Antibiotics-bacteria interactions depend on antibiotic concentration at the scale of bacteria. This study investigates how vancomycin penetrates into activated sludge flocs and can be sorbed on the bacteria and extracellular polymeric substances (EPS). The 3D structure of flocs was imaged using EPS autofluorescence. The green fluorescent BODIPY® FL vancomycin was introduced in a microscopic chamber containing activated sludge and penetration of vancomycin into the flocs by diffusion was observed using time-lapse microscopy. The penetration depended on the floc structure, as long and large pores could go through the whole flocs making preferential path. The antibiotic concentration into the flocs was also found to depend on the sorption rate. BODIPY® FL vancomycin was found to bind preferentially into Gram+ bacteria than on EPS. The vancomycin adsorption constant on bacteria according to the linear adsorption model, Kdbacteria was estimated to be 5 times higher (SD 2.6) than the adsorption constant on EPS KdEPS. These results suggest that antibiotic removal by sorption into wastewater treatment plants could change according to the amount of bacteria in the sludge. Moreover, antibiotic concentration at the scale of bacteria could be significantly higher than the concentration in the bulk solution and this should be taken into account when studying antibiotic activity or biodegradation.

Treatment of highly concentrated tannery wastewater using electrocoagulation: Influence of the quality of aluminium used for the electrode.

This paper deals with the ability of electrocoagulation (EC) to remove simultaneously COD and chromium from a real chrome tanning wastewater in a batch stirred electro-coagulation cell provided with two aluminium-based electrodes (aluminium/copper/magnesium alloy and pure aluminium). Effects of operating time, current density and initial concentration of Cr(III) and COD have been investigated. The concentrations of pollutants have been successfully reduced to environmentally acceptable levels even if the concentrated effluent requires a long time of treatment of around 6h with a 400A/m(2) current density. The aluminium alloy was found to be more efficient than pure aluminium for removal of COD and chromium. Dilution of the waste has been tested for treatment: high abatement levels could be obtained with shorter time of treatment and lower current densities. Energy consumption of the electrocoagulation process was also discussed. The dilution by half of the concentrated waste leads to a higher abatement performance of both COD and chromium with the best energy efficiency.

Assessment of field fluorometers.

Two field fluorometers, devoted either to natural organic matter (NOM) or to tryptophan-like fluorescing substances, were tested for the characterization of a large set of water samples (n = 263) impacted to various degrees by untreated or poorly treated urban sewage. Both fluorometers yielded consistent results when testing discrete samples. A nonlinear correlation (coefficient of determination = 0.98) was found between the tryptophan concentration given by the tryptophan field fluorometer and the fluorescence intensity given by a bench-top fluorometer (excitation = 285 nm, emission = 335 nm), corresponding to tryptophan-like fluorescing substances. A linear correlation with a mediocre coefficient of determination (0.63) was found between the NOM concentration given by the NOM field fluorometer and the fluorescence intensity given by the bench-top fluorometer (excitation = 355 nm, emission = 405 nm). This could be related to the diversity of NOM present, as illustrated by the different shapes of synchronous fluorescence spectra collected for the same samples.

Benchmark simulation models, quo vadis?

As the work of the IWA Task Group on Benchmarking of Control Strategies for wastewater treatment plants (WWTPs) is coming to an end, it is essential to disseminate the knowledge gained. For this reason, all authors of the IWA Scientific and Technical Report on benchmarking have come together to provide their insights, highlighting areas where knowledge may still be deficient and where new opportunities are emerging, and to propose potential avenues for future development and application of the general benchmarking framework and its associated tools. The paper focuses on the topics of temporal and spatial extension, process modifications within the WWTP, the realism of models, control strategy extensions and the potential for new evaluation tools within the existing benchmark system. We find that there are major opportunities for application within all of these areas, either from existing work already being done within the context of the benchmarking simulation models (BSMs) or applicable work in the wider literature. Of key importance is increasing capability, usability and transparency of the BSM package while avoiding unnecessary complexity.

Monitoring of slaughterhouse wastewater biodegradation in a SBR using fluorescence and UV-Visible absorbance.

The aim of this study was to demonstrate that the effectiveness of slaughterhouse wastewater treatment by activated sludge could be enhanced through the use of optical techniques, such as UV-Visible absorbance and fluorescence spectroscopy, to estimate the hydraulic retention time necessary to remove the biodegradable chemical oxygen demand (COD). Two experiments were conducted. First, a batch aerobic degradation was performed on four wastewater samples collected from four different cattle processing sites in order to study the changes in the spectroscopic properties of wastewater during biodegradation. Second, a sequencing batch reactor was used in order to confirm that the wastewater fluorescence could be successfully used to monitor wastewater biodegradation in a pilot-scale experiment. Residual blood was the main source of organic matter in the wastewater samples. The absorbance at 416 nm, related to porphyrins, was correlated to the COD during wastewater biodegradation. The tryptophan-like/fulvic-like fluorescence intensity ratio was related to the extent of biodegradation. The COD removal efficiency ranged from 74% to 94% with an hydraulic retention time (HRT) of 23 h. A ratio of tryptophan-like/fulvic-like fluorescence intensities higher than 1.2 indicated incomplete biodegradation of the wastewater and the need to increase the HRT.

Comparison of photocatalytic degradation of dyes in relation to their structure.

The photocatalytic degradation of a series of six acid dyes (Direct Red 80, Direct Red 81, Direct Red 23, Direct Violet 51, Direct Yellow 27, and Direct Yellow 50) has been tested compared in terms of color removal, mineralization, and toxicity (Lactuca sativa L. test) after photocatalysis on immobilized titanium dioxide. The dyes were examined at their natural pH and after hydrolysis at pH 12. Results show that hydrolysis decreases strongly the efficiency of color removal, that full mineralization takes much longer reaction time than color removal, and that toxicity is only very partially reduced. Some structural parameters, related to the structure and the topology of the dye molecules, could be correlated with the apparent color removal rates at natural pH.

Spectrophotometric characterization of human impacted surface waters in the Moselle watershed.

In order to characterize the pollution discharged into the Moselle River and some of its tributaries, spectroscopic techniques, namely UV-vis spectroscopy and synchronous fluorescence spectroscopy, have been combined. UV-visible spectra were analysed using the maximum of the second derivative at 225 nm (related to nitrates), the SUVA254 and E2/E3 indices (related to the nature of organic matter). Synchronous fluorescence spectra (delta lambda = 50 nm) presented different shapes depending upon the type of pollution. The pollution results from anthropogenic activities: untreated domestic sewage due to misconnections in a periurban river, effluent from urban WWTPS, agricultural runoff (nitrates) in several streams, discharge from a paper mill (humic-like substances due to wood processing) and from steel mills (PAHs).

Arsenic mass balance in a paper mill and impact of the arsenic release from the WWTP effluent on the Moselle River.

Rivers used for drinking water production might be subject to anthropogenic pollution discharge upstream of the intake point. This problem was investigated in the case of the Moselle River, used for water production in Nancy (350,000 inhabitants) and which might be impacted by industrial activities 60 km upstream. The arsenic flux of a pulp and paper mill discharging in the Moselle River at this location has been more specifically investigated. The main sources of arsenic in that mill seemed to be the recovered papers and the gravel pit water used as feed water. The arsenic input related to wood and bark was limited. The main arsenic outputs from the plant were the paper produced on site and the deinking sludge. The arsenic concentration in the effluent of the wastewater treatment plant (WWTP) was not correlated to the one in the gravel pit water, but may depend on the operating conditions of the WWTP or the changes in processes of the mill. The impact of this anthropogenic source of arsenic on the Moselle River was slightly larger in summer, when the flowrate was lower. Globally the impact of the paper mill on the Moselle River water quality was limited in terms of arsenic.

Comparison of four methods to assess biofilm development.

Two nondestructive methods of biofilm quantification (optical density via a flatbed scanner and biofilm thickness) have been evaluated and compared to two destructive methods (Crystal Violet staining after biofilm disintegration and dry weight). The methods were tested on biofilms that developed on a modified rotating biological contactor (RBC) that was inoculated with urban wastewater and fed with a synthetic medium that mimicked slaughterhouse wastewater. The results of the different methods were highly correlated (coefficient of correlation greater than 0.8). This validation experiment confirms the ability of the scanning method to easily monitor the biofilm's development over large surfaces without destruction of the biofilm.

Suspended particles in wastewater: their optical, sedimentation and acoustical characterization and modeling.

Wastewater regulation and treatment is still a major concern in planetary pollution management. Some pollutants, referred to as particulate matter, consist of very small particles just suspended in the water. Various techniques are used for the suspended particles survey. Few of them are able to provide real-time data. The development of new, real time instruments needs the confrontation with real wastewater. Due its instability, the modeling of wastewater in terms of suspended solids was explored. Knowing the description of real wastewater, we tried to produce a synthetic mixture made of basic organic ingredients. A good agreement in terms of turbidity and settling velocity was observed between the artificial wastewater matrix and the real one. The investigation of the individual contribution of the different compounds to the acoustical signal showed a more complex dependence. Thus the modeling of wastewater with reference to turbidity and settling velocity is not sufficient to describe it acoustically. Further studies should lead to a good comparison of the acoustical and turbidity behavior of wastewater.

Benchmark Simulation Model No 2: finalisation of plant layout and default control strategy.

The COST/IWA Benchmark Simulation Model No 1 (BSM1) has been available for almost a decade. Its primary purpose has been to create a platform for control strategy benchmarking of activated sludge processes. The fact that the research work related to the benchmark simulation models has resulted in more than 300 publications worldwide demonstrates the interest in and need of such tools within the research community. Recent efforts within the IWA Task Group on "Benchmarking of control strategies for WWTPs" have focused on an extension of the benchmark simulation model. This extension aims at facilitating control strategy development and performance evaluation at a plant-wide level and, consequently, includes both pretreatment of wastewater as well as the processes describing sludge treatment. The motivation for the extension is the increasing interest and need to operate and control wastewater treatment systems not only at an individual process level but also on a plant-wide basis. To facilitate the changes, the evaluation period has been extended to one year. A prolonged evaluation period allows for long-term control strategies to be assessed and enables the use of control handles that cannot be evaluated in a realistic fashion in the one week BSM1 evaluation period. In this paper, the finalised plant layout is summarised and, as was done for BSM1, a default control strategy is proposed. A demonstration of how BSM2 can be used to evaluate control strategies is also given.

Photocatalytic decolorisation and mineralisation of orange dyes on immobilised titanium dioxide nanoparticles.

In this paper the photocatalytic decolorisation and mineralisation of three orange dyes (AO10, AO12 and AO8) in neutral, alkaline and hydrolysed solutions under UV light irradiation in the presence of TiO(2) nanoparticles has been compared. The investigated photocatalyst was Millennium PC-500 TiO(2) (crystallites mean size 5-10 nm) immobilised on non-woven paper. All the experiments were performed in a circulation photochemical reactor equipped with a 15 W UV lamp emitting around 365 nm. Results indicated that complete decolorisation of 250 mL pure dye solutions with initial dye concentration of 30 mg/L could be achieved in 140 min. Photocatalytic mineralisation of the neutral, alkaline and hydrolysed dye solutions was monitored by total organic carbon (TOC) decrease and ammonium ion formation. Results indicated that the photocatalytic decolorisation and mineralisation of the dyes was less efficient with the hydrolysed and alkaline dye solutions in comparison with the neutral pure dye solutions. The amount of NH(4)(+), as N-containing mineralisation product, during UV/TiO(2) process was analysed. The electrical energy consumption for photocatalytic decolorisation of the dyes was calculated and related to the treatment costs.

Tylosin abatement in water by photocatalytic process.

The photocatalytic degradation of a macrolide (tylosin) has been studied using immobilized titanium dioxide as photocatalyst in a laboratory reactor under UV illumination (365 nm). The degradation of the antibiotic and of the reaction intermediary product was monitored by UV spectrophotometry and HPLC. Three photocatalysts (P25 from Degussa and PC105 and PC500 from Millennium) immobilized on glass plates were compared. A slightly better degradation was obtained with P25. Then the tylosin degradation kinetics were investigated with the P25 photocatalyst. The kinetic model of Langmuir-Hinshelwood is satisfactorily obeyed at initial time and in the course of the reaction. Adsorption and apparent rate constants were determined. These results suggest that, although an intermediary by-product was detected during the reaction, complete degradation of tylosin can be achieved, which confirms the feasibility of such a photocatalytic treatment for tylosin elimination from wastewater.

Activated sludge behaviour in a batch reactor in the presence of antibiotics: study of extracellular polymeric substances.

The influence of Erythromycin, Roxithromycin, Amoxicillin, Tetracycline and Sulfamethoxazole on municipal sludge in batch reactors was investigated. The study was focused on extracellular polymeric substances (EPS) as indicator of bacteria sensitivity to toxic agents. The EPS were analysed by UV-Vis and FT-IR spectroscopies and by size exclusion chromatography. It was found that Erythromycin and Roxithromycin induced a significant increase of bound EPS in flocs. This was attributed to a protection mechanism of the bacteria. Erythromycin was the only antibiotic which inhibited COD and nitrogen removal.

Adverse effects of erythromycin on the structure and chemistry of activated sludge.

This study examines the effects of erythromycin on activated sludge from two French urban wastewater treatment plants (WWTPs). Wastewater spiked with 10 mg/L erythromycin inhibited the specific evolution rate of chemical oxygen demand (COD) by 79% (standard deviation 34%) and the specific N-NH4+ evolution rate by 41% (standard deviation 25%). A temporary increase in COD and tryptophan-like fluorescence, as well as a decrease in suspended solids, were observed in reactors with wastewater containing erythromycin. The destruction of activated sludge flocs was monitored by automated image analysis. The effect of erythromycin on nitrification was variable depending on the sludge origin. Erythromycin inhibited the specific nitrification rate in sludge from one WWTP, but increased the nitrification rate at the other facility.

Evaluation of bioaugmentation efficiency for the treatment of run-off water under tropical conditions: applications to the Derby-Tacaruna canal (Recife/Brazil).

An evaluation of the efficiency of bacterial biomass augmentation was performed at lab-scale for the pollution treatment of the Derby-Tacaruna canal. The canal is located at the central area of Great Recife, alongside an important urban corridor. The characterization of the canal water in different tidal conditions showed that the actual pollution is organic and inorganic (heavy metals). Degradation experiments of water from the canal and rain-off system polluted by synthetic wastewater were performed, using activated sludge and an industrial bioadditive. Continuous reactors under two different conditions were evaluated: with diffuse aeration and without aeration. The channel reactor was operated under steady state conditions at a flow rate of 2.5 L h(-1) and with an average residence time of 22 h without aeration and 17 h with aeration. The organic matter removal was in the range of 60% for the system inoculated with the bioadditive and 85% with activated sludge. It was concluded that the water of the Derby-Tacaruna canal may be treated by activated sludge without being affected by its salt content, while the bioaugmentation technique was not satisfactory due to inhibition by inorganics.

Acute sensitivity of activated sludge bacteria to erythromycin.

The presence of antibiotics in water resources has been disturbing news for the stakeholders who are responsible for public health and the drinking water supply. In many cases, biological wastewater treatment plants are the final opportunity in the water cycle to trap these substances. The sensitivity of activated sludge bacteria to erythromycin, a macrolide widely used in human medicine was investigated in batch toxicity tests using a concentration range of 1-300 mg L(-1). Erythromycin, a protein synthesis inhibitor, has been found to significantly inhibit ammonification, nitritation and nitratation at concentrations higher than 20 mg L(-1). The degree of inhibition increased with greater concentrations of the antibiotic. Exposure to erythromycin also clearly affected heterotrophs, particularly filamentous bacteria, causing floc disintegration and breakage of filaments. Cell lysis was observed with the concomitant release of organic nitrogen (intracellular proteins) and soluble COD. Although erythromycin exhibits properties of a surfactant, this characteristic alone cannot explain the damage to heterotrophs: the effects from erythromycin were greater than those of Tween 80, a commonly used surfactant. Floc disruption can lead to the release of isolated bacteria, and possibly antibiotic resistance genes, into the environment.

Photocatalytic degradation of three azo dyes using immobilized TiO2 nanoparticles on glass plates activated by UV light irradiation: influence of dye molecular structure.

In order to discuss the effect of chemical structure on photocatalysis efficiency, the photocatalytic degradation of three commercial textile dyes (C.I. Acid Orange 10 (AO10), C.I. Acid Orange 12 (AO12) and C.I. Acid Orange 8 (AO8)) with different structure and different substitute groups has been investigated using supported TiO(2) photocatalyst under UV light irradiation. All the experiments were performed in a circulation photochemical reactor equipped with a 15-W UV lamp emitted around 365nm. The investigated photocatalyst was industrial Millennium PC-500 (crystallites mean size 5-10nm) immobilized on glass plates by a heat attachment method. SEM images of the immobilized TiO(2) nanoparticles showed the good coating on the plates, after repeating the deposition procedure three times. Our results indicated that the photocatalytic decolorization kinetics of the dyes were in the order of AO10>AO12>AO8. Photocatalytic mineralization of the dyes was monitored by total organic carbon (TOC) decrease, changes in UV-vis spectra and ammonium ion formation. The dye solutions could be completely decolorized and effectively mineralized, with an average overall TOC removal larger than 94% for a photocatalytic reaction time of 6h. The nitrogen-to-nitrogen double bond of the azo dyes was transformed predominantly into NH(4)(+) ion. The kinetic of photocatalytic decolorization of the dyes was found to follow a first-order rate law. The photocatalysis efficiency was evaluated by figure-of-merit electrical energy per order (E(EO)).

Flocs surface functionality assessment of sonicated activated sludge in relation with physico-chemical properties.

Flocs surface functional groups evolutions due to an ultrasonic treatment were investigated in respect with the mechanisms involved during sonication. Activated sludge surface functional groups changes were studied after treatment of a sample at different ultrasonic specific energies. Sludge functionality was qualitatively assessed by recording the infrared (FT-IR) spectra of centrifugation pellets. Potentiometric titration coupled with proton surface complexation modeling was used to assess the nature and quantity of ionizable functional groups present at the floc surface and in the aqueous phase. These evolutions were linked to changes of both mixed liquor biochemical composition (TSS, VSS, COD, proteins, humic like substances, polysaccharides) and physical properties (floc size and settleability). Observations carried out showed that activated sludge flocs were essentially mechanically disintegrated by ultrasonic waves: the nature of chemical bonds observed by FT-IR did not shift after ultrasonic treatment. Moreover, the total number of ionizable functional groups measured by potentiometric titrations remained constant during sonication. However, due to the solubilization of organic components induced by cavitation process, the corresponding ionizable functional groups (carboxyl, hydroxyl, amine) were transferred from particulate to soluble fraction. Moreover, due to the variable amount of proteins, humic like substances and polysaccharides solubilised, the relative contributions of carboxyl, hydroxyl and amine groups varied at floc surface.

Analyzing characteristic length scales in biofilm structures.

The quantification of biofilm structure based on image analysis requires a statistical measure like representative elemental areas (REA) to determine the necessary size of biofilm area to be imaged. In this study, REAs for biofilm structure were calculated for the descriptors Gray level and Correlation (COR) derived from a spatial gray level dependence matrix analysis (SGLDM). An important difference between these two descriptors is their response to structural features at different spatial scales. Gray level is a scale-independent descriptor, whereas COR is scale-dependent. For scale-independent descriptors, the size of the individual images is not relevant when determining REAs. This is in contrast to scale-dependent descriptors for which REAs can only be determined when the area of each image covers the range of structural variability of the biofilm. We used COR to analyze scale dependence of structural heterogeneity at different length scales. A characteristic length of 400 microm in biofilm images provides structural information relevant for mass transport phenomena in biofilms. Overall REAs for gray level and COR were on average 3.4 mm(2). The scale-dependent descriptor COR could not in all cases accurately be determined from combining individual image analysis results--even when the combined area resulted in the REA. Microscope and camera specifications define the upper and lower limit of detectable characteristic length that can be extracted from images and should therefore be considered in the experimental design when choosing an imaging technique.