Search

The application of membrane bioreactor (MBR) technology was investigated with the aim of evaluating its potential for cytostatic drug and cytotoxicity bioremoval. The toxicity removal was assessed from biomarker test. CP removal of up to 80% was achieved under the operating conditions studied (HRT of 48 h and a SRT of 50 days). The increase of TMP was associated with an increase of supernatant toxicity as if fouling led to retention of the toxicity. Peaks of supernatant cytotoxicity were correlated with peaks in supernatant humic acid contents. It may suggest that molecules with a toxic effect may be adsorbed or entrapped in humic acids substances. Our study then points out that advances in wastewater treatment using an MBR can provide a suitable process for lowering CP concentrations before discharge into the aqueous environment. However, a tertiary treatment is necessary if complete elimination of toxicity is targeted., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The aim of this work is to evaluate the influence of cyclophosphamide and its principal metabolites (CPs) on microbial behaviour in a membrane bioreactor system. Two laboratory-scale membrane bioreactors (MBR) were run in parallel with a sludge retention time of 70 days (one with the cytostatic drugs, MBR-CPs, the second without, MBR-control). The microbial activity was measured by respirometric analysis. The endogenous and exogenous respirations of heterotrophic micro-organisms were evaluated. Micro-organisms exposed to CPs showed higher endogenous respiration rates and lower exogenous respiration rates than micro-organisms present in MBR-control. The effects were observed several days after adding the cocktail. Reduced sludge production was observed in MBR-CPs compared to MBR-control. This reduction of sludge production and the increase in the endogenous respiration rate in relation to MBR-control suggest that the chemical stress caused by CPs led to a diversion of carbon and/or energy from growth to adaptive responses and protection. In addition, the inhibitory effect on the assimilation of exogenous substrate (reduced exogenous respiration rate) suggests an inhibition of catabolism and anabolism despite the low CPs concentration studied (microg/L). However, this inhibitory effect can be offset by the biomass still active under low ratio (substrate/biomass) conditions in the bioreactor (due to complete retention of biomass and high sludge age), which helped to maintain high overall performance in the removal of conventional pollution.

In submerged-membrane bioreactors (SMBRs) for wastewater treatment, aeration with coarse bubbles is applied to limit fouling. The understanding of the different mechanisms between aeration and fouling helps to manage the aeration policy. The impact of aeration (macro scale) on shear stress and mixed-liquor properties (local scale) is evaluated. Experimental characterization of gas-liquid flow in membrane modules, computational fluid dynamics simulation, and controlled breakdown of SMBR mixed-liquor samples are reported. Mean bubble velocities were significantly lower in mixed liquor than in water and the shear stress was one order of magnitude higher in mixed liquor than in water. The floc size decreased and soluble protein concentrations increased with higher shear stress values. Considering the known impacts of these mixed-liquor properties on fouling, the obtained local results explain stronger fouling when coarse bubble aeration increases. [ABSTRACT FROM AUTHOR]

Membrane bioreactor technology has become relatively widespread as an advanced treatment for both industrial and municipal wastewaters. The main problem of these installations is that they do not operate at the maximum of their potential, mainly because of membrane fouling. Experimental research with this kind of installation requires resources and is time consuming. The use of a computer simulator, as in the present work, allows the fouling behaviour in a bench-scale submerged membrane bioreactor to be investigated over a wide range of operating parameters: average specific aeration intensity (0.041–0.277 L m−2 s−1), filtration flux (0.032–0.160 m3 m−2 d−1) and filtration and coarse bubble aeration cycles (filtration and aeration times: 60–1080 s, with/without ratio: 0.33/10). A quadratic optimization method applied to the energy consumption (EC) was first carried out: minimum values of 0.27 and 0.32 kW h m−3were obtained for EC in the sequential and non-sequential operating modes, respectively. Using the optimal operating conditions and the most influent parameters found in the first part, the second part details their influence on both membrane fouling and EC for each operating mode. The mean filtration flux and the mean aeration intensity have opposite effects on fouling and EC, which implies that a more global, economic optimization, including chemical cleaning, is needed. The detailed study of filtration and coarse bubble aeration cycles showed that they had little influence for a with/without ratio superior to 1. Using the quadratic optimization method within silicoexperiments gave reliable first approximation results. [ABSTRACT FROM PUBLISHER]

Abstract: The performance of the microfiltration in a specifically designed membrane bioreactor operating under various transmembrane pressures with periodic backwashing was investigated for model media. These media were representative of some usual components of a fermentation medium: BSA solution (2gL−1), yeast suspension (8gL−1, dry mass) and a mixture of BSA/yeast (2gL−1/8gL−1). In this system, the separation was provided by a 0.1μm polysulfone hollow fiber membrane. The net permeate fluxes observed for yeast/BSA mixture were proportional to the transmembrane pressure applied (ΔP) but were less than those obtained with water osmosis, showing that, in spite of the periodic backwash, a small amount of irreversible fouling remained. This fouling can be assumed to be due to internal fouling by protein and/or external fouling by a residual yeast cake. Moreover, the net permeate flux obtained with the yeast/BSA mixture was higher than that obtained with the BSA alone, showing that a thin yeast cake probably acted as a primary filtration layer that could protect the polysulfone membrane against protein fouling. These experiments enable operating recommendations to be made for the use of this specific bioreactor concerning the transmembrane pressure value and the possible addition of inert particles. [Copyright &y& Elsevier]

The presence of melanoidins in molasses wastewater leads to water pollution both due to its dark brown color and its COD contents. In this study, a bacterial consortium isolated from waterfall sediment was tested for its decolorization. The identification of culturable bacteria by 16S rDNA based approach showed that the consortium composed of Klebsiella oxytoca, Serratia mercescens, Citrobacter sp. and unknown bacterium. In the context of academic study, prevention on the difficulties of providing effluent as well as its variations in compositions, several synthetic media prepared with respect to color and COD contents based on analysis of molasses wastewater, i.e., Viandox sauce (13.5% v/v), caramel (30% w/v), beet molasses wastewater (41.5% v/v) and sugarcane molasses wastewater (20% v/v) were used for decolorization using consortium with color removal 9.5, 1.13, 8.02 and 17.5%, respectively, within 2 days. However, Viandox sauce was retained for further study. The effect of initial pH and Viandox concentration on decolorization and growth of bacterial consortium were further determined. The highest decolorization of 18.3% was achieved at pH 4 after 2 day of incubation. Experiments on fresh or used medium and used or fresh bacterial cells, led to conclusion that the limitation of decolorization was due to nutritional deficiency. The effect of aeration on decolorization was also carried out in 2 L laboratory-scale suspended cell bioreactor. The maximum decolorization was 19.3% with aeration at KLa = 2.5836 h−1 (0.1 vvm). [ABSTRACT FROM AUTHOR]

The study of microbial interactions often requires fastidious and sometimes expensive analytical methods. A reactor specifically designed to carry out studies of interacting populations was developed. Its basic principle consists in keeping both strains of the mixed culture separate by the way of a porous membrane, allowing substrates and metabolites to pass through. As the different strains grow separately, they can be sampled and analyzed distinctly. The culture medium is shared by both strains, and interactions between them occur as if they were mixed in the same vessel. A specific application in winemaking killer yeast interactions is described. The membrane bioreactor made it possible to carry out mixed killer/sensitive fermentations with a double physiological characterization of both killer and sensitive strains. [Copyright &y& Elsevier]

Highlights: [•] A computer simulator of a Submerged Membrane Bioreactor was developed. [•] The implemented model integrates biological degradation and separation by membranes. [•] The simulator performance was described showing its advantages for teaching. [•] The simulator use in teaching was presented through a simulated laboratory. [•] The simulated laboratory was successfully accepted by the students. [ABSTRACT FROM AUTHOR]

The use of the membrane bioreactors (MBR) has gained an important place in the treatment of urban and industrial wastewater in the last years, due mainly to their advantages over conventional processes of wastewater treatment, such as: higher quality of treated water, less environmental impact if compare with other processes, and better process control. In this work, an analysis of the modelling evolution of such complex systems is presented. The advances in last years in modeling biological and filtration systems in MBR are discussed. The importance of Computational Fluids Dynamics in the study of systems functioning, specifically in the modelling of membrane fouling process is underlined. The current trend to use models that integrate biological degradation with the hydrodynamic and membrane filtration process, achieving a more phenomenological description of the MBR functioning is explained. Finally, the importance of integrated models in the optimization of the MBR functioning with a considerable saving of resources and time is described. [ABSTRACT FROM AUTHOR]

Abstract: Membrane bioreactor (MBR) is already a well-developed wastewater treatment process for both municipal and industrial applications. Nonetheless, membrane fouling remains a significant problem for its wider development. In the case of submerged membrane bioreactors (SMBRs), one of the most efficient strategies to limit fouling is the use of a gas/liquid two-phase flow to enhance the mass transfer. However, the effect of aeration still remains incompletely understood. The complexity of flows and of the nature of activated sludge makes a theoretical approach difficult. Aeration is the source of a large part of the operating costs in most industrial scale plants and its optimization is a necessity to make the process really efficient. This paper first deals with hydrodynamics in MBRs, then it reviews the parameters of aeration and their impact on filtration performance. Finally, the effects of aeration mechanisms on biological media are described. [Copyright &y& Elsevier]

Abstract: The influence of cyclophosphamide and its principal metabolites (CPs) on the physicochemical properties of the mixed liquor of a cross-flow membrane bioreactor and the consequences for membrane fouling were investigated. The influence of CPs was determined by comparing the performance of two bioreactors running in parallel, MBR-CPs (with CPs) and MBR-control (without CPs). The physicochemical properties of the mixed liquor were characterized by soluble extracellular polymeric substances (soluble EPS content), particle size distribution and specific cake resistance. Results suggested that the CP toxicity altered the characteristics of the biological matrix of the activated sludge. Micro-organisms exposed to CPs showed higher endogenous respiration rates than MBR-control micro-organisms. The accumulation of soluble EPS and the formation of small particles (in MBR-CPs after cross-flow velocity was raised) increased the resistance to filtration. The fouling potential of the supernatant seemed to be linked more closely to the concentration of polysaccharides than of proteins and humic substances. Modifications of the membrane performance were observed. Under operating conditions, membrane fouling was faster in MBR-CPs than MBR-control. Moreover, the membrane played an important role in the permeate quality and the overall performance of the process, making possible the biological treatment of such an effluent. [Copyright &y& Elsevier]

Abstract: A mathematical model was developed to simulate filtration process and aeration influence on submerged membrane bioreactor (SMBR) in aerobic conditions. The biological kinetics and the dynamic effect of the sludge attachment and detachment from the membrane, in relation to the filtration and a strong intermittent aeration, were included in the model. The model was established considering soluble microbial products (SMP) formation-degradation. The fouling components responsible of pore clogging, sludge cake growth, and temporal sludge film coverage were considered during calculation of the total membrane fouling resistance. The influence of SMP, transmembrane pressure, and mixed liquor suspended solids on specific filtration resistance of the sludge cake was also included. With this model, the membrane fouling under different SMBR operational conditions can be simulated. The influence of a larger number of very important process variables on fouling development can be well quantified. The model was developed for evaluating the influence on fouling control of an intermittent aeration of bubbles synchronized or not with the filtration cycles, taking into account the effects of shear intensity on sludge cake removal. [Copyright &y& Elsevier]