Evaluation of fluorescence excitation–emission and LC-OCD as methods of detecting removal of NOM and DBP precursors by enhanced coagulation

Bench-scale tests were conducted to evaluate enhanced coagulation as a method for removing natural organic matter (NOM) from a surface water to reduce the formation of disinfection by-products (DBPs). Aluminium sulphate (alum) and two polyaluminium chloride (PACl) coagulants were used, as well as alum with pH depression. Using a PACl coagulant alone or alum with pH depression was shown to attain 35% removal of TOC at lower dosages (31 and 29 mg/L, respectively) when compared to the use of alum alone (43 mg/L). In addition to TOC and UV₂₅₄, a fluorescence excitation–emission matrix (FEEM) approach and liquid chromatography–organic carbon detection (LC-OCD) were used to further characterize the removal of NOM in both untreated and filtered waters. Principal component analysis of FEEM was able to identify the presence of humic-like substances (HS), protein-like substances (PS), and colloidal/particulate matter (CPM); HS were found to have a close correlation with TOC and UV₂₅₄. LC-OCD enabled the quantitative detection of hydrophobic and hydrophilic DOC; the latter was further separated into five components, the largest of which was HS. Strong linear correlations were calculated between TOC, UV₂₅₄, HS, and hydrophilic DOC (r² > 0.96); these parameters were also found to be closely correlated with the formation of trihalomethanes (THMs, r² > 0.78) and haloacetic acids (HAAs, r² > 0.92). Linear correlations with THMs and HAAs indicated that FEEM and LC-OCD provide good measures of DBP precursors when compared with TOC and UV₂₅₄.