title: Chemical pretreatment of combined sewer overflows for improved UV disinfection.
abstract: The aim of this research was to better understand chemical pre-treatment of combined sewer overflows (CSOs) for subsequent ultraviolet (UV) disinfection. Approximately 200 jar tests were completed. Alum (Al2(S04)3·12H2O) resulted in a higher UV light transmission (UVT), and equivalent total suspended solids (TSS) removal, than ferric chloride (FeCl3). An alum dose of 20 mg/L increased the UVT of the raw CSO from 30 to 60% after settling. The addition of 100 mg/L of alum maximized UVT reaching approximately 85%. Flocculation did not increase UVT. However, it did improve the removal of TSS. Cationic polymers worked quickly compared with metal coagulants, but only reached a UVT of 60%. A high positive charge density on the polymer improved the removal of turbidity when compared with low charge, but did not affect UVT. If the goal is to maximise UVT, a very high alum dose may be preferred. If the goal is to minimize coagulant dose with moderate UV performance, cationic polymer at approximately 3 mg/L is recommended.
authors.affiliation: Environment Canada, Wastewater Technology Centre, Canada Centre for Inland Waters, 867 Lakeshore Road, Burlington, ON, Canada L7R 4A6 E-mail: jgibson@rogers.com; Present Address: Department of Civil Engineering, University of Toronto, 35 St. George St., Toronto, ON, Canada M5S 1A4.
authors.forename: J
authors.initials: J
authors.lastname: Gibson
authors.affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College St., Toronto, ON, Canada M5S 3E5.
authors.forename: R
authors.initials: R
authors.lastname: Farnood
authors.affiliation: Environment Canada, Wastewater Technology Centre, Canada Centre for Inland Waters, 867 Lakeshore Road, Burlington, ON, Canada L7R 4A6 E-mail: jgibson@rogers.com.
authors.forename: P
authors.initials: P
authors.lastname: Seto
mesh_terms: D000534:Alum Compounds; D002412:Cations; D002712:Chlorides; D004203:Disinfection; D004323:Drainage, Sanitary; D005290:Ferric Compounds; D005427:Flocculation; D011108:Polymers; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid; D062065:Wastewater; D018508:Water Purification / Q000379:methods*
chemical_list: D000534:Alum Compounds; D002412:Cations; D002712:Chlorides; D005290:Ferric Compounds; D011108:Polymers; D062065:Wastewater; C041524:aluminum sulfate; C024555:ferric chloride