title: Novel Ion-Exchange Coagulants Remove More Low Molecular Weight Organics than Traditional Coagulants.
abstract: Low molecular weight (MW) charged organic matter is poorly removed by conventional coagulants but contributes to disinfection byproduct formation during chlorination of drinking waters. We hypothesized that CIEX, a new Al-based hybrid coagulant with ion-exchange functional groups, would be new mechanistic approach to remove low MW organic matter during coagulation and would perform better than polyaluminum chloride (PACl) or metal-salt based coagulants. We measured coagulation performance using dissolved organic carbon (DOC) in a high hardness surface water. CIEX achieved excellent turbidity removal and removed 20% to 46% more DOC than FeCl3, Al2(SO4)3, or PACl, depending on dose. The improved DOC removal was attributable to better removal of low MW organic matter (<2 kDa). We further studied removal mechanisms in a model water containing a low MW organic acid (salicylic acid (SA)). CIEX achieved high removal of organic acids (>90% of SA) independent of pH, whereas removal by metal salts was lower (<15%) and was strongly pH dependent. CIEX ion-exchange capability is facilitated by its covalently bound quaternary ammonium group, which conventional coagulants lack. Plus, unlike other cationic polymers that react with chloramines to form N-nitrosodimethylamine (NDMA), CIEX has a low molar yield (9.3 × 10(-7) mol NDMA per mol CIEX-N).
authors.affiliation: Department of Environmental Engineering, Peking University , Beijing 100871, China.|The Key Laboratory of Water and Sediment Sciences , Ministry of Education, Beijing 100871, China.
authors.forename: Huazhang
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Department of Environmental Engineering, Peking University , Beijing 100871, China.|The Key Laboratory of Water and Sediment Sciences , Ministry of Education, Beijing 100871, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: School of Sustainable Engineering and the Built Environment, Arizona State University , Tempe, Arizona 85287-3005, United States.
authors.forename: David
authors.initials: D
authors.lastname: Hanigan
authors.affiliation: School of Sustainable Engineering and the Built Environment, Arizona State University , Tempe, Arizona 85287-3005, United States.
authors.forename: Paul
authors.initials: P
authors.lastname: Westerhoff
authors.affiliation: Department of Environmental Engineering, Peking University , Beijing 100871, China.|The Key Laboratory of Water and Sediment Sciences , Ministry of Education, Beijing 100871, China.
authors.forename: Jinren
authors.initials: J
authors.lastname: Ni
mesh_terms: D000536:Aluminum Hydroxide / Q000737:chemistry; D002244:Carbon / Q000032:analysis; D002712:Chlorides / Q000032:analysis; D003102:Colloids / Q000737:chemistry; D005427:Flocculation; D007474:Ion Exchange; D046529:Microscopy, Electron, Transmission; D008970:Molecular Weight; D009930:Organic Chemicals / Q000302:isolation & purification*; D010316:Particle Size; D020156:Salicylic Acid / Q000737:chemistry; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D002712:Chlorides; D003102:Colloids; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; C016213:aluminum oxychloride; D000536:Aluminum Hydroxide; D002244:Carbon; D020156:Salicylic Acid