Autopsy of RO desalination membranes Part 2. Chemical characterisation

Recent advanced in membrane technologies allow a large application of this process and reverse osmosis systems show today a dazzling development in desalination, contributing to more than 50% of the world installed capacity. Despite progress realised on membrane materials, a degradation of membrane performances appears with time. This major problem is mainly due to the fouling phenomenon and depends for a large part on the physico-chemical characteristics of the used resource. Several mechanisms are responsible for this fouling. Desalination membranes have the particularity of retaining salts. Precipitation phenomena can appear at the membrane surface because of the increase in salts concentration. Antiscalants could prevent this scaling problem. Deposits could also come from colloidal particles of organic origin which will accumulate (interactions with inorganics, co-precipitation) near the membrane to form a gel layer or a cake leading to a higher flow resistance (secondary membrane). Finally, adhesion and microorganism development at membrane surface constitute another type of fouling called biofouling. This biofouling is often initiated by a primary film containing proteins and sugars (bacterial or algae exudates). Membrane fouling is a complex phenomenon including sorption and precipitation mechanisms in which microbial activity (biofouling) plays an important role in particular in the case of seawater.