title: Effects of velocity gradient and mixing time on particle growth in a rapid mixing tank.
abstract: Effects of velocity gradient (G value) and mixing time (t) on the coagulation of particles were investigated by monitoring particle counts in a rapid mixing process. Total particle counts after mixing of 30 s at G value of 200 s(-1) were similar to the summation of clay particles and alum precipitates at alum dose of 30 mg L(-1). Although small particles (microflocs less than 5 microm) were formed within the mixing time of 30 s, macroflocs larger than 8 microm did not increase significantly until the mixing time of 60 s. However, macroflocs larger than 8 microm started to increase after mixing of 75 s and they reached the maximum counts at 150 s. On the other hand, macroflocs larger than 8 microm decreased after mixing time of 180 s due in breaks of the macroflocs, which resulted in resuspension of small particles. The rapid mixing conditions for the maximum growth of macroflocs were the G value of 200 s(-1) and the mixing time of 150 s, which confirmed the best performance of turbidity removal in jar tests. Growth and break of particles and flocs in a rapid mixing step would influence significantly on the sequential flocculation and sedimentation processes for turbidity removal.
authors.affiliation: Department of Environmental Engineering, Chungbuk National University, Korea.
authors.forename: S M
authors.initials: SM
authors.lastname: Park
authors.forename: H B
authors.initials: HB
authors.lastname: Jun
authors.forename: M S
authors.initials: MS
authors.lastname: Jung
authors.forename: H M
authors.initials: HM
authors.lastname: Koo
mesh_terms: D000534:Alum Compounds; D000538:Aluminum Silicates; D000077215:Clay; D005427:Flocculation; D010316:Particle Size; D014865:Waste Disposal, Fluid / Q000379:methods*; D018508:Water Purification / Q000379:methods*
chemical_list: D000534:Alum Compounds; D000538:Aluminum Silicates; C041524:aluminum sulfate; D000077215:Clay