A study on membrane fouling due to algal deposition

Batch filtration experiments in dead-end mode were carried out to investigate the membrane fouling phenomenon due to Chlorella deposition and to analyse the effectiveness of pretreatment techniques to control membrane fouling. Experiments were also conducted to identify efficient and effective physical and chemical methods for cleaning the membrane. For both cellulose acetate and PVDF membranes, the effect of algal concentration was found similar. Initially when the deposition was less, the flux was high and the resistance was very low or negligible. As the deposition increased, the resistance increased exponentially. With further increase in deposition, the resistance increases linearly at a constant rate. Among the three pre-treatment techniques studied, coagulation with alum and ozonation were effective in controlling the fouling of membrane. Chlorine pretreatment was not effective in reducing the algal cake resistance because it brought about an extensive cell lysis. Photographs taken by Scanning Electron Microscope (SEM) showed damage to the cell surface architecture and release of organic matter to the medium after chlorination. Ozone pretreatment was more effective than chlorine in disintegrating only the extracelluar organic matter (EOM) without causing cell lysis, thus bringing down the algal cake resistance. Cleaning experiments after algal filtration without pre-treatment showed that physical cleaning was less effective than chemical cleaning. All four chemicals tested for membrane cleaning could reduce the cake resistance by more than 99%.