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International audience; Membrane bioreactors (MBRs) are widely used in wastewater treatment processes. However, membrane fouling mitigation remains challenging. Several strategies have been developed industrially to enhance MBR productivity, including coarse bubble aeration. The way such aeration participates in hydrodynamic patterns is an important research topic given its major contribution to the energy costs of such facilities. The methods currently used for hydrodynamic characterization suffer from several drawbacks, mainly due to the system’s complexity. Consequently, there is a need for a nonintrusive method that could be employed in reactors with complex internal geometry and in the presence of activated sludge. This article presents the evaluation and adaptation of the electrical resistivity tomography (ERT) to gain insights into hydrodynamic conditions and to determine how bubbles are distributed within membrane bioreactors in different aeration conditions. An approach used by geophysicists was adapted to a semi-industrial MBR: a numerical procedure was used to validate ERT’s ability to recover precise information in a complex geometry such as MBR membrane tank. Experiments were conducted in a semi-industrial membrane bioreactor with clear water and activated sludge. The resulting images were analyzed in terms of bubble dispersion over a section of the pilot. Heterogeneities were detected in all configurations studied in numerical simulations, although the results also emphasize the diffuse character of gas distribution obtained with the ERT method. Experimental results highlight how gas distribution is mainly localized inside membrane modules and its homogeneity over the module depends on activated sludge rheological properties and air flow rate. MBR operation could be optimized by considering the operating conditions which provide efficient gas distribution over the membrane module obtained at a scale representative of industrial reactors.

International audience; A fuzzy inference method was used to model the fouling evolution of a full-scale Membrane Bioreactor (MBR) treating rejection water from the sludge treatment of a water resource recovery facility (WRRF), using a dataset of 1.5 years. The six generated fuzzy rules replicate the fouling evolution with a promising correlation coefficient of 0.7.

International audience; 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−3 were 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 with in silico experiments gave reliable first approximation results.

A process modelisation for results analysis is presented. This modelisation has recovered concepts already used for design (aggregation of units, pinch technology, etc) and come up with specific ones of its own (aggregation of components, process objectives, etc). The understanding of the process has been enhanced by means of objective functions and path visualisation. General or user-specified automatic checking constraints allow the engineer to concentrate on important features of the process. These techniques may be extended to other procedures (test of alternatives, etc). A prototype containing the ideas presented in this paper is processed. The next step of the concepts development is a closer study of subfunctions, and an extension of constraints checking using automatic consistency checking.

International audience; This paper presents tools for analysis of CFD results adapted for flows in multi-stage stirred vessels through out two industrial cases. Those tanks fitted with double-flow impellers are used first to cool down highly viscous resins and subsequently for indirect emulsification. Since the simulation of these processes in their whole complexity would be unrealistic, it considers single-phase flows without heat transfer. The result analysis in order to prove that the mixing and the circulation are effective is not usual; in these cases, the circulation and impeller numbers are not adapted. The average axial flow numbers are relevant of the circulation in the whole tank and of the connection between the flows produced by the propellers in the given configuration. The velocity profiles give relevant results, but are not sufficient whereas the particle tracking validates that the propellers do not work together in one case and do work together in a second one.