Using Dissolved Humic Acid To Remove Hydrophobic Contaminants from Water by Complexation−Flocculation Process

Abstract

Dissolved humic acid (DHA) can be used as a complexing agent to remove hydrophobic contaminants from water by complexation−flocculation process. The treatment process is composed of two stages: (a) DHA is added to the contaminated water and allowed to interact (bind) with the dissolved contaminants to form DHA−contaminant complexes (complexation stage). (b) A flocculant (alum or ferric chloride) is added, resulting in precipitation and flocculation of the DHA and the associated contaminant (flocculation stage). Flocculation of DHA at concentrations of 1−50 mg/L OCHA was highly efficient with both alum and ferric chloride. The removal of three polycyclic aromatic hydrocarbons (PAHs) was studied using this process. DHA−PAH complexes did not disintegrate upon addition of Al(III) or Fe(III) salts, they were efficiently removed by flocculation, and the experimental results corresponded to those predicted by computations of the bound fractions. The proposed process is effective in removing pollutants of medium to high hydrophobicity (log Kow > 4.5). It is simple, does not require special treatment facilities, can be coupled with common water treatment technology, and has a potential to be useful in cases of periodic contamination events. Additionally, the efficient removal of DHA−contaminant complexes by flocculation emphasizes the importance of enhanced coagulation, not only to reduce the formation of disinfection byproducts (DBPs), but also to remove organic micropollutants associated with dissolved organic matter.