| Dissolved organic matter (DOM) in water has complex structure and diversity of physical and chemical properties. DOM is not only the main material that can cause color and odor, but also can be transformed into disinfection by-products in the chlorination process. These substances cause hazard to human health.Coagulation, as an important part of water treatment, is one of the most effective, convenient and economical process technologies to remove DOM. Enhanced coagulation, as a cost-effective treatment of organic micro-polluted raw water, is through the use of new coagulant, optimizing coagulant dosage, adding coagulant aids or adjusting the pH of the raw water to improve the removal efficiency of pollutants, so that the removal of disinfection by-products precursors is kept a maximum and water quality could reach the standard. The paper focused on the removal effect of DOM in water through the coagulation process by aluminum salts. Physical and chemical fractionations were utilized to characterize the DOM in the Pearl River raw water and after enhanced coagulation.The main contents and results are as follows:(1) Investigate the removal efficiency of DOM in the Pearl River raw water by coagulation process and the change of the Zeta potential in the process with different conventional coagulants (polyaluminum chloride, aluminum sulfate). Studies showed that polyaluminum chloride performed better than aluminum sulfate at low coagulant dosage(30 mg/L). In range of 10 to 60 mg/L, the difference in removal efficiency of DOM was not significant. 22% DOC can be removed with coagulant at a dose of 30 mg/L.(2) Research the removal of DOM by enhanced coagulation with diatomite as a coagulant aid. Results showed that at the coagulant dose of 30 mg/L and diatomite dose of 0.5 g/L, DOC could be removed from 22.5 % to 26.3 %. By adjusting the pH of the raw water to investigate the effects of pH values on coagulation. It indicated that coagulation with aluminum sulfate, the optimum pH was 6~6.5; while with PAC, the optimum pH was 5~6.(3) Characterization the DOM in raw water from the Pearl River. Physical distribution showed that the fractions with molecular weight (MW) <4 kDa was predominant component, more than 50%; followed by >30 kDa, accounting for about 25 %. Chemical fraction showed that hydrophobic acids (HoA) and the hydrophilic matter (HiM) are richer than others, about 35% and 30%, respectively; followed by hydrophobic neutral (HoN). The lowest concentration was hydrophobic base (HoB).(4) Fractionation the water which sink after enhanced coagulation. when the coagulant dosage was 30 mg/L, characterized the solubility of the effluent after coagulation by a comprehensive classification. It demonstrated that two Al-based coagulants were effective and feasible for removal of high MW organic compounds. PAC performed slightly effectively than Al2(SO4)3.18H2O in organic compounds removal at low MW dosage. We could conclude that the removal performance of DOM with different molecular weight and chemical component can be improved on varying degrees by enhanced coagulation. |
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