Effect of using polydimethyldiallylammonium chloride as coagulation aid on polytitanium salt coagulation performance, floc properties and sludge reuse

• PDMDAAC was first used as coagulant aid with PTS in FA-kaolin water treatment.
• Effect of dosage, dosing sequence and solution pH on coagulation was studied.
• Residual turbidity was reduced by dual-coagulants, and FA removal efficiency was enhanced.
• Floc growth rate, size and recovery ability were increased by PTS + PDMDAAC.
• Sludge produced TiO2 of dual-coagulants showed better photocatalytic activity.

Polytitanium salt has attracted more and more attention recently, yet there is not much research on combining polytitanium salt with polymer flocculant. This study focused on the application of polydimethyldiallylammonium chloride (PDMDAAC) as coagulant aid with polytitanium sulfate (PTS) in fulvic acid (FA) water treatment. Effect of dosing sequence (PTS dosed first donated as PTS + PDMDAAC; PDMDAAC dosed first donated as PDMDAAC + PTS), dose and solution pH was investigated. Coagulation sludge of dual-coagulants was also reused to produce TiO2. Results showed that compared with use of PTS alone, turbidity and FA removal were both enhanced by dual-coagulants. In addition, this study revealed that floc size and floc growth rate of PTS + PDMDAAC were also significantly improved and floc strength and recovery ability were also increased by PTS + PDMDAAC. AS for PDMDAAC + PTS, floc size, growth rate, strength and recovery ability were similar to those of PTS. Floc fractal dimension of these three coagulants was in an order of PDMDAAC + PTS > PTS > PTS + PDMDAAC. Furthermore, TiO2 produced by dual-coagulants sludge showed higher photocatalytic activity than that produced by PTS sludge.