title: Influence of Al³⁺ addition on the flocculation and sedimentation of activated sludge: comparison of single and multiple dosing patterns.
abstract: In this study, the flocculation and sedimentation performance of activated sludge (AS) with single and multiple dosing of trivalent aluminum (Al(3+)) were studied. The AS samples were cultivated in sequencing batch reactors at 22 °C. The dosages of Al(3+) were 0.00, 0.125, 0.5, 1.0, and 1.5 meq/L for single dosing, and 0.1 meq/L for multiple dosing. Under single dosing conditions, as Al(3+) dosage increased, the zeta potential, total interaction energy, and effluent turbidity decreased, whereas the sludge volume index (SVI) increased, indicating that single Al(3+) dosing could enhance sludge flocculation, but deteriorate sedimentation. By comparison, adding an equal amount of Al(3+) through multiple dosing achieved a similar reduction in turbidity, but the zeta potential was higher, while the loosely bound extracellular polymeric substances (LB-EPS) content and SVI remarkably declined. Although the difference in the flocculation performances between the two dosing patterns was not significant, the underlying mechanisms were quite distinct: the interaction energy played a more important role under single dosing conditions, whereas multiple dosing was more effective in reducing the EPS content. Multiple dosing, which allows sufficient time for sludge restructuring and floc aggregation, could simultaneously optimize sludge flocculation and sedimentation.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China. Electronic address: weny@tongji.edu.cn.
authors.forename: Yue
authors.initials: Y
authors.lastname: Wen
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China.
authors.forename: Wanlin
authors.initials: W
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Department of Environmental Health Sciences, School of Public Health, University of Michigan, Ann Arbor 48104, MI, USA.
authors.forename: Yundi
authors.initials: Y
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China; Shanghai Municicpal Engineering Design Institute (Group) CO., LTD., Shanghai 200092, PR China.
authors.forename: Asheng
authors.initials: A
authors.lastname: Cao
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, PR China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D019149:Bioreactors; D005427:Flocculation; D012722:Sewage / Q000032:analysis*; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D012722:Sewage; D000535:Aluminum
keywords: Activated sludge; Aluminum ion; Extracellular polymeric substances; Flocculation; Interaction energy; Sedimentation