Use of fluorescence excitation-emission matrices coupled with parallel factor analysis to monitor C- and N-DBPs formation in drinking water recovered from cyanobacteria-laden sludge dewatering

This is the first time that correlations between the spectroscopic properties of algal organic matter (AOM) and cyanobacteria-related C- and N-disinfection byproduct (DBP) formation have been presented. Three types of coagulants, aluminium chloride (AC), chitosan (CTS) and a composite chitosan-aluminium chloride (CTSAC), were selected to assess and compare the performance of coagulation to control DBPs formation in dewatering water (DW). Fluorescence excitation-emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) indicated that four components dominated the EEM of the DW samples. Examination of C-, N-DPBs formation and attendant changes in the AOM parameters allows the establishment of strong linear relationships between yields of the trihalomethanes, haloacetonitriles and trichloronitromethane and the relative changes in the fluorescence compounds. Stronger linear correlations were found between trihalomethanes and tryptophan-like substance C1 (r = 0.918), between haloacetonitriles and C1 (r = 0.934), and between trichloronitromethane and amino acid-like substance C2 (r = 0.915) than other AOM parameters, suggesting that tryptophan-like substance and amino acid-like substance in AOM play major roles in generating cyanobacteria-related DBPs upon chlorination. Furthermore, because the CTSAC composite was effective in removing fluorophores and caused little cell lysis during the first 4 days of sludge storage, the production of C-, N-DBPs in the DW was lower than those in the AC or CTS systems for the same storage period. This indicates the feasibility of surrogate monitoring of the production of cyanobacteria-related C-, N-DBPs via online measurements of water EEM fluorescence. CTSAC composite coagulant is thus recommended, and the sludge should be disposed of within 4 days to obtain DW with lower DBPs formation potentials.