Effect of nano Fe3O4-(CMC-Na)-PFS coagulant on coagulation–ultrafiltration process for treatment of algae -rich water

Abstract

A novel composite flocculant (PCNF) was prepared using nano Fe3O4 as the condensed core, sodium carboxymethyl cellulose (CMC-Na) as the binder, and polyferric sulfate (PFS). The results indicate that the mass ratio of Fe3O4 to PFS is the key factor determining the flocculation effect of PCNF. When the mass ratio of Fe3O4 to PFS is 1:3, the Zeta potential value is approximately − 1.5 mV, indicating better removal of algae through adsorption electroneutralization. The resulting floc, characterized by negative charge and a loose structure, forms a filter cake layer that is easily backwashed on the surface of the ultrafiltration membrane. This floc also creates strong electrostatic repulsion with the membrane surface. Experimental results demonstrate that the specific flux decreased to 0.69, the total relative pollution was 0.33, and the proportion of irreversible pollution was only 34.65%, all of which were superior to traditional flocculant like PACl. Through microinterface mechanism analysis, it is concluded that the new PCNF flocculant, in combination with algal matter, forms a floc structure critical for mitigating ultrafiltration membrane pollution caused by high algal content in natural surface water.