Ceramic membranes were used to separate Mg(OH)(2) precipitate from suspension in the chlor-alkali industry. Experimental results revealed that the ceramic membranes are capable of removing ultrafine Mg(OH)(2) precipitates and removal rate of Mg2+ cations was higher than 99.9%. The effect of suspension concentration on the permeate flux was more prominent than the transmembrane pressure. The presence of MgCl2 was found to affect the filtration performance more significantly than NaCl. The direct observation (DO) technique was introduced to monitor the processes of fouling deposition and removal. The relationship between the visual observation and the hydraulic performance values provided better understanding instead of assumptions in fouling deposition mechanisms. During backwashing, direct observation demonstrated that fouling layer first expanded and then left the membrane surface in large sections, indicating strong cohesion between Mg(OH)(2) particles in the cake layer. Using direct observation (DO) technique allows the non-invasive, in-situ visualization and quantification of fouling layer in real time compared with SEM. (C) 2013 Elsevier B.V. All rights reserved.