Removal of natural organic matter and trihalomethane minimization by coagulation/flocculation/filtration using a natural tannin

Abstract

Natural organic matter (NOM) is found in all surface, ground, and soil waters. The presence of NOM causes many problems in drinking water treatment processes. Minimization of the disinfection byproducts precursors or effective removal of NOM has emerged as a critical issue in the production of high quality drinking water from surface water. The objective of the present investigation is to explore the capacity of tannin to remove NOM in coagulation/flocculation/filtration/chlorination process from surface water in order to minimize total trihalomethanes (TTHM) formation. For the tests, raw water from Pirapó River Basin (Maringá, Paraná, Brazil) was used. Optimization of coagulation/flocculation tests was performed in jar test with dosage of Tanfloc 0.5% as coagulant ranging from 2.5 to 15 mg L−1. The parameters analyzed were color, turbidity, compounds with absorption at UV-254 nm, dissolved organic carbon (DOC), and zeta potential. In view of the statistical analysis results, Tanfloc with dosage of 7.5 mg L−1 was chosen as coagulant for the follow-up tests of coagulation/flocculation/filtration/chlorination. The implementation of slow sand filtration after the sedimentation stage achieves almost 100% removal of turbidity. Besides, the combination of coagulation/flocculation/filtration/chlorination using this tannin improved NOM removal according to UV254nm and DOC parameters, minimizing TTHM formation. The amount of TTHM in drinking water varied from 31.3 to 47.7 μg L−1, while the amount of raw water TTHM was found to be 4.0 μg L−1. Although these values lie below the ones stipulated by Ordinance no. 2914/2011 for TTHM limits, it is advisable to check periodically this parameter. In view of these results, this tannin can be recommended as a promising agent for surface water treatment.