Effects of ozonation, photocatalystic oxidation, and sequential oxidation on coagulation of humic acids

Abstract

In this study, coagulation behavior of untreated and treated humic acids with two different types of metal coagulant and two types of polyelectrolyte as coagulant aid were investigated. The aim of this study was to understand the coagulation efficiencies of different type of coagulant and the mechanisms underlying the contribution of pretreatments to coagulation. Pretreatment were done by ozonation, photocatalytic oxidation and sequential oxidation in which ozonation was applied as pretreatment stage for partial oxidation of humic acids prior to photocatalytic oxidation using TiO2.The coagulation properties of humic acid were evaluated according to Color436 and UV254 values. These parameters were calculated for treated and untreated humic acid samples as well as for alum, ferric chloride, and combination of metal coagulant with anionic and nonionic polyelectrolyte. Coagulation efficiencies decreased with pretreatments regardless of the type of the coagulants used. However, anionic and nonionic polyelectrolytes were effective coagulant aids for the coagulation of humic acid. Especially, polyelectrolyte more effective for untreated humic acid than treated humic acid. Removal percentages of UV254 and Color436 values increased with using metal salts combining with anionic and nonionic polyelectrolyte. Nevertheless, applied high dosage of primary coagulant combining with low synthetic polyelectrolyte led to higher removal percentages of humid acid than applied low dosage of primary coagulant combining with high dosage of synthetic polyelectrolyte. Furthermore, using metal salts combining with anionic and nonionic polyelectrolyte lead to decrease in used primary coagulant.