Insights into the Mechanism of Coagulation Pretreatment for Membrane Fouling Control from the Perspective of Organic Removal Based on a Sensitive SEC-DAD-FLD-OCD/OND Method

Organic matters, especially low molecular (LMW) ones, contribute to the serious membrane fouling, but the traditional coagulants cannot efficiently remove LMW substances. Herein, the coagulationultrafiltration combined process (C-UF) was applied to the actual lake water treatment, and a novel polyaluminum titanium composite coagulant (PATC) was used as a pretreatment reagent for membrane fouling mitigation. The results indicated that PATC performed better to efficiently remove organic matters than polyaluminium chloride (PAC) and polytitanium chloride (PTC). Notably, PATC could effectively remove building blocks and LMW substances, particularly the protein-like fluorescent substances. The removal mechanism of LMW substances by PATC was mainly the adsorption of amorphous hydrolysates, rather than the charge neutralization of positively charged hydroxy complexes. No matter with or without the cake layer, the control performance of the three coagulants on membrane fouling was consistent with their removal efficiency of organics. It indicated that although the cake layer played an important role in the interception of organics and small particles, it was not the decisive factor in lightning membrane fouling. Improving the removal efficiency of organic substances, especially the LMW component, is the key to alleviate membrane fouling. This work provides a new insight into the effects of the composite coagulant on the removal of various organics and the control of membrane pollution in actual lake water treatment.