Biofuoling in RO membrane systems Part 1: Fundamentals and control

Abstract

Membrane separation systems are widely used to purify water of different qualities including brackish water, seawater and wastewater. Dissolved and particulate matter in the feed water can deposit on the membrane surface. This phenomenon is identified as fouling. Several types of fouling can occur in the membrane systems, e.g. inorganic fouling or scaling, particulate and colloidal fouling, organic fouling and finally biological fouling or biofouling. Biofouling is usually ascribed to the accumulation of microorganisms such as bacteria, algae and fungi on the membrane surfaces forming the harmful biofilms, via multi-step and complex formation process. In fact; biofouling has a lot of adverse effects on the RO membrane systems like flux decline of the RO plant, significant increase in the pressure drop of the RO modules, increase in salt passage and membranes biodegradation and failure. No doubt that biofouling is one of the most serious problems associated with the RO membrane systems which has not yet been effectively solved. Moreover, this biofouling phenomenon is most critical in RO systems operating with feed water above 25°C which is typical of RO plants in the Gulf countries like Saudi Arabia. In the present work, more attention is given to the fundamental and engineering aspects of this biofouling phenomena covering the basic various mechanisms of its multisteps formation processes and its negative effects on the plant performances. The interaction between feed water quality and membrane biofouling is also discussed and analyzed. Corrosion problems induced by biofouling are also tackled in the present work due to their harmful effects in the actual practice of RO plants. Finally, various techniques for befouling minimization and control are recommended with special attention to the proper pretreatment systems by which feed water properties are precisely adjusted before entering to the membrane modules.