Czestochowa University of Technology, Department of Chemistry, Water and Wastewater Technology, Faculty of Infrastructure and Environment, Czestochowa, PL
EFFECTIVENESS OF REMOVING ORGANIC MATTER FROM SURFACE WATER USING POLYALUMINIUM CHLORIDE
The aim of this study was to evaluate the effectiveness of the coagulation process using highly alkaline polyaluminium chloride 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 organic carbon - TOC and DOC, oxygen consumption, absorbance in the ultraviolet UV), the potential for trihalomethanes creation THM was also determined. SUVA index was calculated as the ratio of absorbance at UV254 to the DOC content. Connecting the values of absorbance and DOC into single coefficient SUVA enables to determine properties of dissolved organic matter in water, and vulnerability to their removal in the coagulation process.
Water collected in September 2016 and January, April, July 2017, from the Stradomka river in Częstochowa was used in the study. Surface water was characterized by colour equal to 25-60 mgPt/dm3. The TOC and the DOC content amounted to respectively 7.2-16.8 and 6.6-15.1 mgC/dm3, the oxygen consumption – 5.3-16.2 mgO2/dm3, and the absorbance at UV254 – 0.145-0.443. The SUVA value was equal to 2.2-2.9.
Lowering the TOC content in water after the coagulation was in the range of 31-39%, the oxygen consumption in the range of 47-63%, and the value of the absorbance UV254 – 61-68%. The SUVA value was equal to 1.1 -1.5. This confirms that in water after the coagulation, organic substances remained, which are unsusceptible to the removal in this process. In water after the coagulation process subjected to chlorination, CHCl3 concentration ranged from 54 to 281 μg/dm3 and the concentration of CHCl2Br ranged from 14 to 26 μg/dm3. These were values by 54-62% lower than THM concentration obtained in untreated surface water subjected to chlorination.
Keywords: organic matter, coagulation, polyaluminium chloride, surface water