An upscaled study of a membrane filtration process in presence of biofilms

During a membrane filtration process, a liquid medium is filtered through a membrane(selective barrier). The applied driving force between two sides of the membrane can be a gradient of pressure, temperature or a chemical/electrical potential.In pressure driven filtration processes (application of a pressure gradient as driving force between two sides of the membrane), certain components of the liquid medium pass through the membrane, while others are retained at the membrane surface. These processes are widely used as separation techniques in different industrial fields like waste water treatment, biotechnology, food and pharmacy. Compared to conventional techniquesof separation (distillation, crystallization, .), membrane processes offer more compact installations with more optimized operational costs. Moreover, membrane processes are mainly performed in absence of chemical additives and phase change. In this work we focus on the pressure-driven microfiltration membrane processes.The main disadvantage of these processes is the continuous accumulation of particles on the membrane surface. This affects the membrane selectivity, modifies the quality and the quantity of the liquid passing through the membrane and leads to an increase of energy costs. Membrane fouling occurs in all types of membrane processes and therefore is known as the major obstacle for widespread use of these processes. Different techniques are used to overcome the effects of fouling on the membrane performance : physical-chemical treatment of used membranes, modification of the operational conditions (tangential flow of the feed solution to the membrane is often applied for minimizing the particle accumulation to the membrane surface), use of membranes less susceptible to fouling, etc. Depending on the nature of the treated solutions, the deposited particles are highly variable. Microorganisms, natural organic matter such as proteins, polysaccharides, humid substances, inorganic oxides and salts contribute notably to membrane fouling.It should be noted that membrane fouling problem is a multi-physics (hydrodynamics,mass transport, physics, chemistry), multi-scale (different length scales are involved:molecules, pores and membrane surface) and time dependent (evolution of the membrane microstructure and the molecule-surface interactions) phenomena.In the last decades, a huge number of experimental studies have been invested to understand fouling mechanisms. It has been pointed out that membrane physicochemical properties, solution chemistry and operational conditions are the three major factors affecting the fouling mechanisms. In parallel, theoretical models have been proposed to confirm/describe the experimental observations.Modeling of membrane fouling is an essential tool for assessing the fouling mechanisms. It helps predicting the membrane performance and consequently finding adapted strategies to prevent their modification during the filtration process.In general, the models can be classified into two main categories: mass transport models which focus on solute permeation during the filtration process, and fouling models based on particle or solute blocking within the membrane porous structure. In most of the cases, models depend strongly on the empirical or semi-empirical parameters and thus remain phenomenological. Two main objectives have been set for the present work: 1. Get a better understanding of the membrane fouling mechanisms during filtration of a liquid medium containing suspended microorganisms. It should be pointed out that several Industrial streams and wastewaters belong to this kind of effluents.2. Propose a macroscopic model describing the observed fouling mechanisms. [. ]