Natural organic matter removal by coagulation: effect of kinetics and hydraulic power

摘要

In this paper, the mechanism of NOM removal by coagulation is investigated using coagulantnpolyaluminium chloride (PACl), compared with AlCl3. The kinetics of Al ion hydrolysis, interactionnof hydrolyzed species of Al and NOM, and hydraulic power condition in coagulation process areninvestigated by programmable jar test, photometric dispersion analyzer and ferron assaying.nAfter the coagulant dosing, Al ion would hydrolyze very quickly, and then monomeric Al andnsmall polymeric Al would further hydrolyze to form larger polymer and precipitate, based on pHncondition, while the further hydrolyzed process is relative slow. Although complexation betweennNOM and Al appears to be several orders of magnitude slower than hydrolysis of monomericnforms of Al, it would be faster than further polymerization and precipitation of Al during aging.nHowever the further polymerization of fresh Al would benefit to Al-NOM complex aggregation andnsettlement. Therefore, PACl, with stabile preformed polymer shows significantly differentnperformance in NOM removal compared with AlCl3. Although the hydraulic power condition playsnsignificant role in collision frequency and efficiency of particles removal, the process of thenaggregation to form larger floc to settle down is relative slower than interaction of Al and NOM,nand it is not very correlative to the performance of NOM removal if only it can provide enoughnmixture.