Interactions between alum and organics in coagulation

The coagulation-sedimentation process, i.e. a major pretreatment for filtration, has the potential to remove organic contaminants. However, interactions between coagulants and organics in the absence of suspended solids have only received limited attention. This study aims to model alum-organics' interactions corresponding to the behavior of organics during coagulation. Two typical organic materials, humic acid and salicylic acid, are investigated. Experimental results indicate that the removal of organics by coagulation is directly related to the molecular weight. The interaction of alum with humic acid involves complexation, charge neutralization, precipitation and adsorption. The coagulation of salicylic acid with alum arises from adsorption and entrapment. Results of this study confirm a stoichiometric relationship between the initial concentrations of humic acid and optimal alum dosages.