title: Floc morphology and cyclic shearing recovery: comparison of alum and polyaluminum chloride coagulants.
abstract: This study investigated the floc formation and re-aggregation potential for alum, polyaluminum chloride (PACl) and a blend of these coagulants. Bench-scale testing included floc morphology characterization for well-developed floc, post-shear floc, and non-settleable (filter influent) floc. Different applications of coagulants were observed to produce non-settleable floc that was morphologically different. The alum treatment had a decrease in average floc size from coagulated to non-settleable conditions, whereas the PACl and PACl/alum treatments resulted in similar sized floc between these processes. Zeta potential distribution measurements showed that the alum treatment resulted in a negative shift from coagulated to non-settleable conditions whereas the PACl and PACl/alum treatments had no significant shift. A photometric dispersion analyzer (PDA) was employed to compare the differences between coagulant treatments with respect to shear induced aggregate breakup and recovery. The PDA allowed a dynamic monitoring of initial floc aggregation and measured the degree of recovery from cyclic shearing. The degree of recovery from shearing was greatest for the PACl/alum treatment likely as a result of increased collision efficiency due to more effective charge neutralization.
authors.affiliation: Department of Civil Engineering, Colorado State University, Fort Collins, CO 80523-1372, USA.
authors.forename: Kevin
authors.initials: K
authors.lastname: McCurdy
authors.forename: Kenneth
authors.initials: K
authors.lastname: Carlson
authors.forename: Dean
authors.initials: D
authors.lastname: Gregory
mesh_terms: D000534:Alum Compounds / Q000737:chemistry*; D000536:Aluminum Hydroxide / Q000737:chemistry*; D004784:Environmental Monitoring; D005427:Flocculation; D011108:Polymers; D014872:Water Movements; D018508:Water Purification / Q000379:methods*
chemical_list: D000534:Alum Compounds; D011108:Polymers; C016213:aluminum oxychloride; C041524:aluminum sulfate; D000536:Aluminum Hydroxide