Comparison of iron (III) and alum salt on ultrafiltration membrane fouling by alginate

• Sodium ions exacerbate the fouling caused by alginate coagulated with iron/alum salt.
• Calcium ions mitigate the fouling caused by alginate coagulated with iron/alum salt.
• Flux decline is depended on the ratio of sodium ions to calcium ions in the system.
• Alum salt behaves better than iron salt when membrane fouling is caused by alginate.

Compared with humic acids or proteins, polysaccharides usually cause more severe flux decline. Here, the ultrafiltration (UF) membrane fouling caused by alginate coagulated with iron (III)/alum salt was investigated in the absence/presence of ionic strength (NaCl), calcium ions and their combinations in the system. The results showed that flux decline was significantly reduced only in the presence of high dose of iron/alum salt. With increasing ionic strength, the membrane flux caused by alginate coagulated with high dose of iron/alum salt was decreased, while that was dramatically increased in the presence of calcium ions. When ionic strength and calcium ions were presented with high dose of iron/alum salt, flux decline was determined by the ratio of sodium ions to calcium ions. Alum salt behaved much better than iron salt on reducing membrane fouling with/without ionic strength, calcium ions and their combinations in the solution. Membrane flux was high at coagulation conditions that resulted in low concentration of alginate after filtration, which was in the presence of high dose of alum salt, especially in combination of calcium ions.

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