The enhanced reduction of C- and N-DBP formation in treatment of source water containing Microcystis aeruginosa using a novel CTSAC composite coagulant.

Abstract

This study investigated the effect of a chitosan-aluminium chloride (CTSAC) composite coagulation process on reducing the formation of algal organic matters (AOM) related carbonaceous disinfection by-products (C-DBPs) and nitrogenous disinfection by-products (N-DBPs), by removing or adsorbing their precursors. Compared with aluminium chloride (AC) and chitosan (CTS) alone, CTSAC significantly enhanced the removal of dissolved organic matter (DOC), polysaccharide, protein and humic acids, attaining removals of 64.95%, 80.78%, 70.85% and 44.50%, respectively. Notably, the three-dimensional excitation and emission matrix (3D-EEM) combined with molecular weight (MW) fractionation analysis revealed that CTSAC was not only effective for removing high-MW AOM, but also for the low-MW fractions that are important in forming DBPs. In addition, the CTSAC coagulation was proven to enhance the removal of aromatic polypeptide/amino acid-like materials and aliphatic amines, which have high N-nitrosodimethylamine formation potential. Efficient AOM removal by the CTSAC coagulation resulted in significant reduction of both AOM-related C-DBPs (63.54%) and N-DBPs (71%), while AC coagulation did not substantially reduce the formation of tribromomethane, 1,1,1-trichloropropanone or N-nitrosodimethylamine, and CTS coagulation alone did not achieve any obvious reduction in trichloronitromethane. Fourier transform infrared (FT-IR) spectroscopy analysis confirmed the interaction of CTS and AC in the CTSAC composite coagulation, which contributed to the improved AOM removal performance of CTSAC, and, in this case, reduced the formation of C- and N-DBPs.