Feedwater coagulation to mitigate the fouling of a ceramic MF membrane caused by soluble algal organic matter

• Impact of four coagulants on AOM fouling of a ceramic MF membrane was investigated.
• Improved flux was primarily due to the removal of high MW biopolymers by coagulation.
• Reduction in high MW molecules mitigated the formation of a cake layer.
• ACH appeared to be more cost-effective than the other coagulants tested.

Soluble algal organic matter (AOM) resulting from the cyanobacterial blooms in water catchments can cause severe fouling of ceramic membranes in water treatment. The effect of feedwater coagulation using alum, aluminium, ACH, ferric sulphate and ferric chloride for reducing the fouling of a commercial ceramic MF membrane (ZrO2–TiO2) caused by the AOM released from Microcystis aeruginosa was investigated. At their optimum dosages (i.e., 5 mg Al3+/L and 10 mg Fe3+/L), all coagulants could significantly mitigate the membrane fouling, with the hydraulically reversible and irreversible fouling resistance reduced by over 90% and 65%, respectively. ACH, ferric chloride and ferric sulphate performed similarly in reducing the flux decline, and considerably better than alum did. The reduction in AOM fouling of the membrane was primarily due to the effective removal of the very high MW biopolymers (≫20,000 Da). There were much greater removals in carbohydrate (74–77%) than protein content (15–28%) by the coagulation. The hydrophobic compounds in the AOM solution were more susceptible to the coagulation treatment than the hydrophilic and transphilic compounds. Among the tested coagulants, ACH appeared to be more cost-effective in maintaining the permeate flux and minimising the irreversible fouling for the ceramic MF membrane.