Removal of five selected pharmaceuticals by coagulation in the presence of dissolved humic acids and kaolin

Abstract

Coagulation behaviour of five pharmaceuticals, i.e. acetaminophen (ACE), carbamazepine (CBZ), 17β-estradiol (E2), naproxen (NAP) and diclofenac (DCF), was investigated through jar tests in deionized water, tap water, kaolin containing water and humic acid containing water, respectively, using aluminium sulphate as a coagulant. The effects of dissolved humic acids (DHAs) and kaolin on the removal efficiency of these compounds were studied particularly. The results showed that neither ACE nor CBZ was removed effectively (less than 10%), indicating that compounds with low hydrophobicity (log Kow < 3) are difficult to be removed in coagulation process. In deionized water, DCF achieved the highest removal efficiency due to its relatively strong hydrophobicity. However, in tap water, the removal efficiencies of these pharmaceuticals were much lower than those in deionized water except E2 and CBZ. In the presence of humic acid, the removal efficiencies of acidic pharmaceuticals (NAP and DCF) were much higher than those of neutral pharmaceuticals (ACE, CBZ and E2), especially with high dosage of DHA. The maximum removal efficiencies of NAP and DCF reached 61 and 59%, respectively. In terms of E2, its removal efficiency decreased surprisingly with increasing dosage of DHA. The presence of kaolin enhanced the removal efficiencies of E2, NAP and DCF because they were more readily adsorbed onto the surface of kaolin. DHA and kaolin improved the removal of certain pharmaceuticals during coagulation process.