Dual coagulation with floc breakage to alleviate ultrafiltration membrane fouling caused by algae organic matter

A novel coagulation strategy, where floc property was regulated by varying dosing sequence of dual coagulants of aluminum sulfate (AS) and chitosan (CS) with floc breakage, was applied as the pre-treatment of ultrafiltration to treat algae-laden water. The river water (TW), and TW spiked with intracellular organic matter (IOM) and extracellular organic matter (EOM) respectively (TW-IOM and TW-EOM) were tested. The results indicate that floc breakage applied in successive dosing of AS and CS in TW and TW-IOM water samples formed compact flocs through charge neutralization and bridging, generating dense cake layer to control irreversible fouling; and mitigated irreversible fouling (Rir) caused by protein-like and humic-like species in the molecular weight (MW) of 950–3000 Da. For TW-EOM water sample, the successive addition of CS and AS can relieve Rir by removing protein-like species and soluble by-products in the MW of 500–3000 Da via charge neutralization, sweeping flocculation and bridging together, while the applied breakage aggravated membrane fouling. The obtained results provide a novel coagulation strategy to control membrane fouling during algae-laden water treatment.