INTERACTIONS BETWEEN ALUM AND ORGANICS IN COAGULATION

The coagulation-sedimentation process, i.e. a major pretreatment for f iltration, has the potential to remove organic contaminants. However, interactions between coagulants and organics in the absence of suspend ed solids have only received limited attention. This study aims to mod el alum-organics' interactions corresponding to the behavior of organi cs during coagulation. Two typical organic materials, humic acid and s alicylic acid, are investigated. Experimental results indicate that th e removal of organics by coagulation is directly related to the molecu lar weight. The interaction of alum with humic acid involves complexat ion, charge neutralization, precipitation and adsorption. The coagulat ion of salicylic acid with alum arises from adsorption and entrapment. Results of this study confirm a stoichiometric relationship between t he initial concentrations of humic acid and optimal alum dosages.