Effect of the efficiency of organic matter removal by coagulation on THM concentration in chlorinated water

The aim of this study was to evaluate the effectiveness of the coagulation process using pre-hydrolyzed salts in reducing the level of pollution of surface water with organic substances. Apart from the typical indicators used to evaluate the content of organic compounds (total and dissolved carbon, ultraviolet absorbance at 254 nm), the potential for trihalomethanes formation was also determined. The TIM formation potential reflects the amount of precursors present in water, capable of generating THMs. The coagulants used in the study were Al-2(SO4)(3)center dot 18H(2)O, AlCl3 center dot 6H(2)O and pre-hydrolyzed polyaluminium chlorides (commercial agents PAX-XL 19F and PAX-XL1910S). Surface water was collected in March 2016, from the Pilica River (Poland). L owering the DOC content in water after the coagulation was in the range of 32-45%, and the UV254 absorbance in the range of 36-63%, depending on the used coagulant. The largest reduction in values of those indicators were stated using pre-hydrolyzed polyaluminium chlorides. In the chlorinated surface water, presence of CHCl3 and CHCl2Br was demonstrated, CHBr3 and CHClBr2 were not detected. CHCl3 and CHCl2Br concentration was equal to 73.8 and 3.5 mu g/dm(3), respectively. In the chlorinated water after the coagulation process, CHCl3 concentration ranged from 72.4 to 48.9 mu g/dm(3), while CHCl2Br from 5.6 to 4.6 mu g/dm(3). The lowest concentration of these compounds were obtained in the water subjected to chlorination after previous treatment using PAX-XL19F and PAX-XL1910S. TEEM formation potential in purified water was by 32 and 29% lower than in surface water.