Influence of Al3+ Addition on the Flocculation and Sedimentation of Thermophilic Activated Sludge

In this study, the flocculation and sedimentation performance of thermophilic activated sludge with single and multiple dosing of trivalent aluminum (Al3+) were studied. The thermophilic activated sludge samples were cultivated in sequencing batch reactors at 55 degrees C. The dosages of Al3+ were 0.125, 0.5, 1.0, 1.5, and 2.0 meq/L for single dosing, and 0.1 meq/L for multiple dosing. The experimental results indicated that single Al3+ dosing could enhance sludge flocculation, but deteriorate sedimentation. While multiple dosing, which allows sufficient time for sludge restructuring and floc aggregation, could optimize flocculation and maintain sedimentation simultaneously. LB-EPS played a more important role than interaction energy in the improvement. Although the responding of zeta potential was insignificant, better flocculability and settleability were achieved through Al3+ dosing.