Effect of in-situ ozonation on ceramic UF membrane fouling mitigation in algal-rich water treatment

• In-situ ozonation is highly effective to mitigate algal-related membrane fouling.
• Algal cake layer contributes most to the overall membrane resistance.
• In-situ ozonation forms cake layer more porous and thinner.
• In-situ ozonation reduces gel layer by degradation of high molecular weight polymers.
• Algal organics can be greatly degraded by ozone within the ceramic membrane pores.

The presence of seasonal algal blooms with harmful algae-derived organic matters threatens the performance of ultrafiltration in drinking water treatment. The hybrid process of in-situ ozonation with ceramic ultrafiltration membrane was proposed for the treatment of algal-rich water with effective removal of algal cells and mitigation of membrane fouling. The mechanism of membrane fouling mitigation with in-situ ozonation was systematically investigated from the perspective of cake layer, gel layer and membrane pore blocking. The results showed that in-situ ozonation treatment can effectively mitigate membrane fouling. For instance, transmembrane pressure was reduced by 75.8% with in-situ ozonation at 1 mg/L. In-situ ozonation resulted in the formation of a more porous and thinner cake layer due to the disintegration of extracellular organic matters that attached on the algal surface. Besides, the portion of very high molecular weight biopolymers (around 100 kDa) and the hydrophobic fraction of algae-derived organic matters, the main component intercepted by the ceramic membrane, were reduced with in-situ ozonation and thus leaded to less severe gel layer fouling. Furthermore, in-situ ozonation induced the accelerated organics degradation within the ceramic membrane pores, alleviating the membrane pore blocking.

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