Reduction of organic matter and disinfection byproducts formation potential by titanium, aluminum and ferric salts coagulation for micro-polluted source water treatment

Abstract

Typical Chinese source water has high content of low molecular weight and aromatic protein-like organic matter which is difficult to remove and poses a great challenge to conventional coagulation/flocculation. To investigate coagulation performance of this typical water, this research focused on organic matter removal characteristics and the associated disinfection byproducts formation potentials (DBPFPs) during the coagulation process by titanium salts compared with traditional aluminum and ferric salts. Results showed that based on the dissolved organic matter (DOM) removal, the optimal coagulant dosages of AlCl3, FeCl3 and TiCl4 were 0.5 mM and the optimal initial pH values were 8, indicating that the DOM in the typical Chinese water could be effectively removed through sweeping and adsorption by metal hydroxides rather than the complexation and charge neutralization effect under acidic conditions. Compared these three coagulants, the highest ultra violet absorbance at 254 nm removal rate of 72.9% was achieved by TiCl4. The three-dimensional excitation emission matrix results showed that the removal ability of humic acids by AlCl3 was poorer than FeCl3 and TiCl4. The removal rate of low molecular weight components (1600 Da) by TiCl4 was 20% higher than using AlCl3 and 14% higher than FeCl3. Comparing with AlCl3 and FeCl3, TiCl4 had a better performance on the control of DBPFPs, especially for chloroform and dichloroacetic acid, due to its higher removal ability of aromatic organics. The trihalomethane formation potentials removal rate by TiCl4 was three times higher than that by AlCl3 and twice by FeCl3, by which could be inferred that titanium salts achieved better removal of low molecular weight organic matter than aluminum and ferric salts.