Aeration and hydrodynamics in submerged membrane bioreactors

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

Rheological characterization of mixed liquor in a submerged membrane bioreactor: Interest for process management

Rheological analyses of a submerged membrane bioreactor mixed liquor were performed in the aim of characterizing the mixed liquor present in the bioreactor and thus proposing a process management. These analyses pointed out that the mixed liquor was characterized by its viscoplastic property, which leads to a possible restructuring ability when a shear stress lower than the yield stress is applied. As the shear stress in the bioreactor is essentially generated by coarse bubbles, specific experiments were carried out in which coarse bubbles were injected in an intermittent way. The results of these experiments showed that this method could avoid damage to the mixed liquor. So working with intermittent coarse bubbles is useful to prevent fouling, keep good flocculation and minimize the energy cost

Aeration mode, shear stress and sludge rheology in a submerged membrane bioreactor: some keys of energy saving

Aeration mode, shear stress and sludge rheology in a submerged membrane bioreactor: some keys of energy savin

CFD analysis of industrial multi-staged stirred vessels

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

Submerged membrane bioreactor for waste water treatment: determination of the shear stresses produced by coarse bubbles

Submerged membrane bioreactor for waste water treatment: determination of the shear stresses produced by coarse bubble

Modelling of submerged membrane bioreactor: Conceptual study about link between activated slugde biokinetics, aeration and fouling process

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, trans-membrane 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

Analyse morphologique des boues biologiques d'épuration. Descriptifs les plus pertinents et propriétés physico-chimiques des boues d’épuration

Analyse morphologique des boues biologiques d'épuration. Descriptifs les plus pertinents et propriétés physico-chimiques des boues d’épuratio

Rheological study of sludge of membranes bioreactors for water treatment: protocol, limitations and link with the filtration

The submerged membranes bio-reactors (sMBR) are more and more visible in the field of waste water treatment. The membrane fouling, that causes a drastic fall of the performances, can be limited by the application of a swarm of bubbles close to the membrane surfaces. This aeration as a major factor of the energetic expense of these processes, lets numerous studies to focus on the understanding of the mechanisms linking the bubbles swarm with fouling.. In this background, the rheological tools appeared to be useful to understand the behaviour of sludge under shear stress. In order to be sure to get significant results, we used three types of rheological measurements: i) the influence of shear rate on shear stress; ii) the influence of upward then downward stages of shear stress on viscosity; iii) the influence of the alternation of two stages of shear stress with implementation times identical to those of sMBR aeration. Besides a viscoplastic behaviour previously observed, a phenomenon of hysteresis appeared. The transparent upper plan used on the rheometer exhibited formations of aggregative structures “in roll”. Sludges of a sMBR using different sequencing of aeration are compared: the developed protocols enabled to differentiate those sludges, with characteristic results depending on mechanical applications. The aim of this work is, eventually, to propose some correlations between usual characteristics of the process and aeration operating parameters, in order to propose an aeration policy improving energetic performances

Development of a Submerged Membrane Bioreactor simulator: a useful tool for teaching its functioning

Among the technologies used to treat wastewater, the Submerged Membrane Bioreactor (SMBR) has excellent prospects because of the possibility it provides for water reuse. In this work, an SMBR computer simulator is developed. A mathematical model was implemented, which integrated the biological degradation process using activated sludges with the physical separation process using membranes. The simulator functioning was validated with experimental results and its use in teaching was evaluated through the development of a simulated laboratory running for three and a half hours. This gave access to trends and orders of magnitude that would take more than fifteen months to obtain with real experiments. It was successfully used and accepted by the students

Weblab France-Brésil en génie des procédés

A Weblab is an experiment remotely operated via internet. A Weblab between the Chemical Engineering Department of the University of São Paulo Polytechnic School (EPUSP) and the Process Engineering Department of the Ecole Nationale Supérieurs d’Ingénieurs en Arts Chimiques et Technologiques (ENSIACET) is developed. The experiment consists of a tank level control. The main objective is to propose and test tunings for the system control loop. For this purpose, the students must work in synergy and propose models for the system in order to find the tuning parameters. Weblab is a showcase for new technologies and original experiences because it allows to perform a control action from anywhere in a supervision environment which is spreading out in the industry. The objectives and interests are mainly pedagogical as the Weblab favours the variety and diversity of intercultural experiences a student could experience during his undergraduate studies. Because of this, the Weblab perfectly integrates in an engineer curriculum that is open to international exchanges. Un WebLab est une installation commandée à distance via internet. Nous développons une expérience de Weblab entre le département de Génie Chimique de l’Ecole Polytechnique de l’Université de São Paulo (EPUSP) et le département Génie des Procédés et Informatique de l’Ecole Nationale Supérieurs d’Ingénieurs en Arts Chimiques et Technologiques (ENSIACET). L’expérience consiste en la régulation de niveau dans un bac. L’objectif de l’expérience est de proposer et de valider des réglages pour la boucle de commande du système. Pour cela, les étudiants de l’EPUSP et de l’ENSIACET doivent travailler en synergie et proposer des modélisations et un réglage du contrôleur. Le Weblab constitue une vitrine de technologies innovantes et d’expériences originales, car il permet, depuis n’importe où, d’effectuer une commande à distance dans un environnement de supervision qui est de plus en plus adopté dans l’industrie. Les objectifs et intérêts du WebLab se situent plutôt au niveau pédagogique car il peut être un facteur multiplicatif du nombre d’expériences interculturelles pouvant être vécues par un étudiant tout au long de son cursus. Pour ces raisons le Weblab s’intègre parfaitement dans une formation d’ingénieurs qui se doit d’être ouverte à l’international