Performance of titanium salts compared to conventional FeCl.sub.3 for the removal of algal organic matter (AOM) in synthetic seawater: Coagulation performance, organic fraction removal and floc characteristics

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2017.06.025 Byline: L. Chekli (a), E. Corjon (a), S.A.A. Tabatabai (b), G. Naidu (a), B. Tamburic (c), S.H. Park (d), H.K. Shon (a) Abstract: During algal bloom periods, operation of seawater reverse osmosis (SWRO) pretreatment processes (e.g. ultrafiltration (UF)) has been hindered due to the high concentration of algal cells and algal organic matter (AOM). The present study evaluated for the first time the performance of titanium salts (i.e. titanium tetrachloride (TiCl.sub.4) and polytitanium tetrachloride (PTC)) for the removal of AOM in seawater and results were compared with the conventional FeCl.sub.3 coagulant. Previous studies already demonstrated that titanium salts not only provide a cost-effective alternative to conventional coagulants by producing a valuable by-product but also minimise the environmental impact of sludge production. Results from this study showed that both TiCl.sub.4 and PTC achieved better performance than FeCl.sub.3 in terms of turbidity, UV.sub.254 and dissolved organic carbon (DOC) removal at similar coagulant dose. Liquid chromatography - organic carbon detection (LC-OCD) was used to determine the removal of AOM compounds based on their molecular weight (MW). This investigation revealed that both humic substances and low MW organics were preferentially removed (i.e. up to 93% removal) while all three coagulants showed poorer performance for the removal of high MW biopolymers (i.e. less than 50% removal). The detailed characterization of flocs indicated that both titanium coagulants can grow faster, reach larger size and present a more compact structure, which is highly advantageous for the design of smaller and more compact mixing and sedimentation tanks. Both titanium coagulants also presented a higher ability to withstand shear force, which was related to the higher amount of DOC adsorbed with the aggregated flocs. Finally, TiCl.sub.4 had a better recovery after breakage suggesting that charge neutralization may be the dominant mechanism for this coagulant, while the lower recovery of both PTC and FeCl.sub.3 indicated that sweep flocculation is also a contributing mechanism for the coagulation of AOM. Author Affiliation: (a) School of Civil and Environmental Engineering, University of Technology, Sydney, Post Box 129, Broadway, NSW, 2007, Australia (b) Water Desalination and Reuse Center (WDRC), 4700 King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia (c) Plant Functional Biology and Climate Change Cluster (C3), Faculty of Science, University of Technology Sydney (UTS), Sydney, NSW, 2007, Australia (d) Department of Civil Engineering, Dong-A University, 37 Nakdong-Daero 550beon-gil, Saha-gu, Busan, 604-714, South Korea Article History: Received 25 March 2017; Revised 7 June 2017; Accepted 12 June 2017