NOM removal and residual Al minimization by enhanced coagulation: roles of sequence dosing with PACl–FeCl 3 Ming-Han Tsai, Lap-Cuong Hua, Kochin Huang and Chihpin Huang ABSTRACT To remove higher proportions of natural organic matter (NOM) in water treatment plants, over dosing of Al-based coagulant is frequently applied. However, this leads to the risk of an excess of coagulant residue in the clean water. In this study, sequential coagulation with polyaluminum chloride (PACl) and FeCl 3 was proposed to improve the removal of NOM as well as to minimize residual Al. Single dosing with either PACl or FeCl 3 in particular was compared with sequential coagulation, with different dosing sequences of PACl–FeCl 3 (P–F) or FeCl 3 –PACl (F–P). At optimum dosage, sequential coagulation P–F showed twice as much dissolved organic carbon (DOC) removal from water containing algogenic organic matter, compared to single dosing of PACl and sequential coagulation F–P. However, sequential coagulation F–P was the most effective approach for humic substance removal that improved DOC removal up to >70% compared to other dosing approaches (<60%). Practical treatment with real water also showed the advantages of sequential coagulation with P–F in improving the removal of low SUVA NOM by 18% compared to the traditional single dosing of PACl. As expected, the Al residues found in both sequential coagulation (0.07 mg/L) were significantly reduced compared to single dosing with PACl (0.15 mg/L), indicating the promising application of sequential coagulation for future safe water treatment. Key words | coagulation, FeCl 3 , NOM, PACl, residual Al HIGHLIGHTS • Coagulation behavior was firstly clarified for sequential coagulation. • PACl-FeCl 3 dosing improved the removal of algogenic organic matter. • Effective removal of humic acid was observed by FeCl 3 -PACl dosing. • Residual soluble Al was minimized significantly with sequential coagulation. • Reservoir water confirmed PACl-FeCl 3 in having higher organics removal than PACl. Ming-Han Tsai Lap-Cuong Hua Kochin Huang Chihpin Huang (corresponding author) Institute of Environmental Engineering, National Chiao Tung University, Hsinchu 300, Taiwan E-mail: cphuang@mail.nctu.edu.tw INTRODUCTION Humic substances (HS) and algogenic organic matter (AOM) are commonly occurring natural organic matter (NOM) in the aquatic environment. Seasonal occurrence of algal blooms and the release of high concentration of AOM often occur as a result of excess nutrients in natural water (Henderson et al. ). Generally, AOM comprises large amounts of nitrogenous organics and hydrophilic (HPI) substances, including free amino acids, peptides and proteins with low specific ultraviolet absorbance (SUVA) value (<2 L/mg C m) (Pivokonsky et al. ). By contrast, HS, typically humic acid (HA), either released by soil or produced by the biodegradation of dead plants contains hydrophobic organics with relatively high aromaticity (SUVA value >2 L/mg C m) (Edzwald ). Both AOM 616 © IWA Publishing 2020 Journal of Water Supply: Research and Technology—AQUA | 69.6 | 2020 doi: 10.2166/aqua.2020.010 Downloaded from http://iwaponline.com/aqua/article-pdf/69/6/616/746605/jws0690616.pdf by guest on 10 September 2021