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.

An antibiotic-resistant class 3 integron in an Enterobacter cloacae isolate from hospital effluent.

Hospital effluents are involved in dissemination of antibiotic-resistant integrons. We describe here a new class 3 integron, In3-5, detected in an Enterobacter cloacae isolate retrieved from a random French hospital effluent sample collected in 2009. In3-5 carries two gene cassettes: the new blaOXA -256 and an aac(6')-Ib variant, respectively conferring resistance to ß-lactams and aminoglycosides. In3-5 is located on an IncQ-like backbone plasmid. Class 3 integrons could thus be involved in the dissemination of antibiotic resistance in both clinical settings and the environment, and could participate in the exchange of antibiotic-resistance genes between these two ecosystems.

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.

Urban wastewater treatment plants as hotspots for antibiotic resistant bacteria and genes spread into the environment: a review.

Urban wastewater treatment plants (UWTPs) are among the main sources of antibiotics' release into the environment. The occurrence of antibiotics may promote the selection of antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB), which shade health risks to humans and animals. In this paper the fate of ARB and ARGs in UWTPs, focusing on different processes/technologies (i.e., biological processes, advanced treatment technologies and disinfection), was critically reviewed. The mechanisms by which biological processes influence the development/selection of ARB and ARGs transfer are still poorly understood. Advanced treatment technologies and disinfection process are regarded as a major tool to control the spread of ARB into the environment. In spite of intense efforts made over the last years to bring solutions to control antibiotic resistance spread in the environment, there are still important gaps to fill in. In particular, it is important to: (i) improve risk assessment studies in order to allow accurate estimates about the maximal abundance of ARB in UWTPs effluents that would not pose risks for human and environmental health; (ii) understand the factors and mechanisms that drive antibiotic resistance maintenance and selection in wastewater habitats. The final objective is to implement wastewater treatment technologies capable of assuring the production of UWTPs effluents with an acceptable level of ARB.

Urban wastewater treatment plants as hotspots for the release of antibiotics in the environment: a review.

Urban wastewater treatment plants (UWTPs) are among the main sources of antibiotics' release into various compartments of the environment worldwide. The aim of the present paper is to critically review the fate and removal of various antibiotics in wastewater treatment, focusing on different processes (i.e. biological processes, advanced treatment technologies and disinfection) in view of the current concerns related to the induction of toxic effects in aquatic and terrestrial organisms, and the occurrence of antibiotics that may promote the selection of antibiotic resistance genes and bacteria, as reported in the literature. Where available, estimations of the removal of antibiotics are provided along with the main treatment steps. The removal efficiency during wastewater treatment processes varies and is mainly dependent on a combination of antibiotics' physicochemical properties and the operating conditions of the treatment systems. As a result, the application of alternative techniques including membrane processes, activated carbon adsorption, advanced oxidation processes (AOPs), and combinations of them, which may lead to higher removals, may be necessary before the final disposal of the effluents or their reuse for irrigation or groundwater recharge.

Impact of copper and cadmium on aerobic and anaerobic digestibility of sonicated sludge.

The effects of the introduction of a sludge reduction process such as ultrasound on batch aerobic and anaerobic biodegradability after exposition to two metals (copper and cadmium) were investigated. The specific energy of ultrasonic treatment applied to the sludge was 200,000 kJ kg TS(-1). Ultrasonic treatment led to floc size reduction and to organic matter solubilization. Low copper (< 5 mg L(-1)) and cadmium (< 1 mg L(-1)) concentration improved aerobic biodegradability. For high metal concentration the maximal instantaneous biogas production rate q(max) inhibition by copper and cadmium was modeled by a saturation-type relationship under aerobic and anaerobic conditions. Under aerobic conditions, respiration inhibition was not affected by sonication. Cadmium inhibition (74%) was more than copper (58%). The positive effect of sonication on CO2 production was maintained after metal introduction. Under anaerobic conditions, metal introduction cancelled out the positive effect of the treatment. The sonicated sludge was 16% less sensitive to copper inhibition but 10% more sensitive to cadmium inhibition compared to non sonicated sludge.

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.

Techno-economic evaluation of thermal treatment, ozonation and sonication for the reduction of wastewater biomass volume before aerobic or anaerobic digestion.

Aerobic and anaerobic digestions were compared with different sludge reduction processes such as ultrasonic, ozone, and thermal treatments. Each treatment was tested under the following conditions to improve batch aerobic or anaerobic digestion: ultrasound (200,000kJkgTS(0)(-1)), thermal (40 degrees C, 60 degrees C, 90 degrees C for 90 min, 120 degrees C 15 min, 1 bar), and ozonation (0.1gO(3)gTS(0)(-1)). The different pretreatments induced organic matter solubilisation and intrinsic sludge reduction (total suspended solids): ultrasound (47%), thermal 90 degrees C (16%), ozone (15%), thermal 60 degrees C (9%), thermal 40 degrees C (5%), autoclave (120 degrees C) (4.2%). TSS (and also VSS) solubilisation were found to be highly correlated to the pretreatment ability to break the flocs rather than to specific energy input. The total values of TSS reduction ranged from 57% to 71% under aerobic conditions and from 66% to 86% under anaerobic conditions. TSS solubilisation after pretreatment can be considered as a predictive parameter of sludge volume reduction enhancement after aerobic or anaerobic digestion while specific energy input did not show anything or negligible impact. In our experimental conditions, ultrasound and ozone led to the best TSS removal improvement after both aerobic (30% and 20%) and anaerobic digestion (20%). Ultrasonic and ozone pretreatments prior to aerobic or anaerobic digestion led to the best reduction of the specific energy required for removing 1 kg of TSS compared to the control. Anaerobic digestion was globally more effective (compare to aerobic digestion) in enhancing sludge production reduction.

Assessment of physiological state of microorganisms in activated sludge with flow cytometry: application for monitoring sludge production minimization.

Many sludge reduction processes have been studied for the minimization of sludge production in biological wastewater treatment. The investigations on most of these processes have monitored the increase of the soluble chemical oxygen demand, the sludge mass reduction, or the decrease of the floc size, but little information has been obtained on cell lysis and the change of the biological cell activity. However, employing any strategy for reducing sludge production may have an impact of microbial community in biological wastewater treatment process. This impact may influence the sludge characteristics and the quality of effluent. The objective of this study concerns the determination of the physiological state of activated sludge microorganisms during a sludge minimization process. A thermal treatment at 80 degrees C for 5, 20, 40 and 60 min was chosen in this study. Staining bacteria with CTC and SYTOX green was used to evaluate biological cell activity and viability of cell types contained in activated sludge, respectively. The monitoring of cell activity and viability was performed using flow cytometry (FCM) analysis before and after thermal treatment of activated sludge. Results indicated an increase in the number of permeabilized cells and a decrease in the number of active cells, subsequent to the thermal treatment. The study also confirms the potential of FCM to successfully evaluate the physiological heterogeneity of an activated sludge bacterial population. Moreover, the experimentally observed correlations between the FCM results and the organic matter solubilization in activated sludge samples during thermal treatment revealed that the increase in the soluble organic matter concentration was predominantly due to an intracellular material release. Identifying the increase in activated sludge hydrolysis requires a precise knowledge of the involved mechanisms, and this study indicated that the FCM, used in conjunction with specific probes, could be a useful tool.

[Rheological measurement used as a tool to assess sludges settleability]. / Apports des mesures rhéologiques pour la prévision des propriétés de décantation des boues activées.

The activated sludge process is the most widely used biological wastewater treatment method. The measurement of some physico-chemical parameters in aeration tanks do not still allow to avoid clarification operation failure. This study focus on the ability to apply rheological measurements on activated sludge at standard concentrations in order to assess sludge settleability. Measurements in shear flow show a pseudonewtonian region which corresponds to the maximum dispersion of the suspensions that can be detected with the rotational system used. The Bingham's viscosity and shear stress are used to characterise activated sludge. Different shear sensitivities of flocs seem to result from various operational conditions of activated sludge process. Significant relationships with different parameters of settleability point out the ability of Bingham's shear stress to express the compressibility of the activated sludge. According to the protocol of measurement of the study, Bingham's shear stress may influence the nature of the sludge on its settleability.

Setting-up a control simulation strategy for a sequencing batch reactor (SBR): application to municipal wastewater.

The use of a simulation model for setting up a control strategy for a sequencing batch reactor necessary for treating municipal wastewater is described. The model used is the ASM no 1 model. The objective of the pollution control treatment is the removal of carbon and nitrogen; the optimisation is concerned with the improvement in the biological removal of nitrogen. After experimental identification of the initialisation variables, the model enables different SBR control scenarios to be tested (time variation for each process) leading to the total elimination of nitrogen. The best simulation was tested in a laboratory reactor. On that scale, it was noted that denitrification is an endogenous process. Lastly, the control strategy was tested on a semi-industrial pilot working in a pollution control plant. Other control scenarios can be devised and tested by simulation, in order to improve the productivity of the reactor.

Use of image analysis and rheological studies for the control of settleability of filamentous bacteria: application in SBR reactor.

To monitor the ability of flocs to settle in Sequencing Batch Reactor sludge, two methods were tested during two operation cycles. Firstly, an automated image analysis procedure has been tested to quantify the floc size and the length and number of filaments. Secondly, rheological measurements (Bingham viscosity and shear stress) have been used to characterise the dispersion of the sludge which can reflect the cohesive strength of aggregates and so the influence of filamentous bacteria on rheological properties. These results were compared with settling parameters such as Sludge Volume Index or settling velocity. Correlations between the measured parameters with image analysis and parameters such as Sludge Volume Index have been obtained. If it is more difficult to analyze rheological results, it seems however that the thixotropy and the Bingham viscosity distinguish poor settlement owing to some filamentous bulking. The first results are promising, although they require confirmation in the long term.

Modeling of an industrial alcohol fermentation and simuiation of the plant by a process simulator.

The aim of the present study was the development of a general simulation module for fermentation within the framework of existing chemical process simulators. This module has been applied to an industrial plant which produces ethanol from beet molasses and fresh beet juice by Saccharomyces cerevisiae. An unstructured mechanistic model has been developed with kinetic laws that are based on a chemically defined reaction scheme which satisfies stoichiometric constraints. This model can be applied to different culture conditions and takes into account secondary byproducts such as higher alcohols. These byproducts are of prime importance and need to be correctly estimated because a sequence of distillation columns follow the fermentor in the plant. Important measurement campaigns have been performed on the plant to validate the model. Plant operation has been successfully simulated using the same kinetic model for both continuous and fed-batch modes of production. (c) 1995 John Wiley & Sons, Inc.