Comparison of flocs characteristics using before and after composite coagulants under different coagulation mechanisms

Abstract

The flocs generated by different coagulants under various coagulation mechanisms produce fundamentally different floc characteristics. In this investigation, the fractal dimensions of aggregates produced by the different types of coagulants and coagulation mechanisms to drilling wastewater were described with image-based techniques. The flocs properties, which were evaluated in terms of floc strength, size and structure, formed by non-composite, polyferric chloride (PFC), and by a novel composite coagulant, polyferric chloride −polydimethyldiallylammonium chloride (PFC-PDM), were comparatively investigated. Besides, an intrinsic unity of relation among the floc properties under various coagulation mechanisms was also reported. It was found that the composite coagulant could exhibit better bridging capacity during coagulation process. Fractal dimension analysis revealed that PFC-PDM tended to form more regular and compact flocs with larger Dpf value than PFC formed. The results clearly demonstrated that the size of PFC-PDM-floc was larger than that of PFC-floc. Additionally, the PFC-PDM-flocs strength were higher than PFC-flocs, indicating that the aggregated flocs induced by the composite coagulant could be more resistant to shear and more recoverable than those induced by the non-composite coagulant. Those presented above results indicate that PFC-PDM may be used as alternative coagulant during wastewater treatment process with some capacities exceeding that of PFC, providing there is an economic and practical method to improve floc properties from its application.