The removal of silver nanoparticle by titanium tetrachloride and modified sodium alginate composite coagulants: floc properties, membrane fouling, and floc recycle

In this study, a modified sodium alginate (MSA) composited with TiCl4 was used to treat the synthetic Ag nanoparticles (AgNPs) water in coagulation-ultrafiltration process. The floc properties and membrane fouling of TiCl4 and MSA composite coagulants (TiCl4 + MSA) were investigated by a laser diffraction instrument and ultrafiltration fouling model. The recycle of the AgNP-containing flocs was evaluated by XRD and photocatalytic experiments. The results showed that TiCl4 + MSA could achieve better coagulation performance than TiCl4 alone with AgNP and DOC removal up to 97 and 59% at the optimum condition (pH = 5 and dosage = 12 mg TiCl4/L). TiCl4 + MSA produced larger and looser flocs than TiCl4 and TiCl4 + SA composite coagulant (TiCl4 + SA), which was benefit for the inhibition of subsequence membrane fouling. The strongly attached external fouling resistance (R (ef-s)) and the reversible internal fouling resistance (R (if-r)) of TiCl4 + MSA were only 43 and 39.2% of those achieved by TiCl4 at the optimal coagulation condition. Besides, the adopted AgCl-TiO2 could be recycled from AgNP-containing flocs. And MSA could promote the form of TiO2 anatase. It gives us a possible way for silver nanoparticle recycle.