Humic Acid Removal from Water with Polyaluminum Coagulants: Effect of Sulfate on Aluminum Polymerization

Humic acid (HA) removal from water with inorganic polyaluminum coagulants is reported in this paper. Polyaluminum chloride (PAC) and three kinds of polyaluminum chloride sulfate (PACS) with a [SO42-]/[Al3+] (S) molar ratio of 0.02, 0.06, and 0.10 were prepared. The coagulation behaviors of these coagulants were investigated in the view of coagulant dosage, initial pH, and aging time. PACS (S=0.06) showed the best HA removal efficiency, and there was no restabilization within a broad effective dosage range. The proper initial pH range was broad and was 4.0-9.0 for PACS (S=0.06). The stability of PACS (S=0.06) reduced with a long aging time, so the proper aging time should not exceed 1 month. The aluminum species distribution, particle mean size, charge neutralization, and infrared spectrum of prepared coagulants were tested. Results showed that SO42- addition promoted the hydrolysis/polymerization of aluminum and reduced the charge neutralization capacity of PACS. Besides charge neutralization, the bridge-aggregation and sweep-flocculation mechanisms may play important roles for HA removal. The coexisting Ca2+ and kaolin slightly promoted the HA removal with polyaluminum coagulants. DOI: 10.1061/(ASCE)EE.1943-7870.0000412. (C) 2012 American Society of Civil Engineers.