Review of Mechanism of Bioflocculation and Settleability of Activated Sludge Bioflocs

Abstract:

Bioflocculation of activated sludge is crucial to overall performance and efficiency of the treatment process as well as the settleability. The bindings between flocs are due to the intermolecular interactions, which can be mainly categorized into 3 interdependent and interactional types including bridging of extracellular polymeric substance (EPS), DLVOtype interactions and hydrophobic interactions. Flocs and EPS carry negative charges and zeta potentials that not only produce the electrostatic interactions but create bridges among cells by means of divalent and trivalent cations. EPS contains more protein and carbohydrate than any other substances, the low concentration of which is believed to correlate with good settleability but poorly hydrophobic interactions. Moreover, low hydrophobicity which is also affected by surface charge, is associated with poor flocculation. Also high ionic strength contributes to good performance of bioflocculation. The goal of this study is to gain a comprehensive insight into sludge floc characteristics and to identify the key factors which determine the solidliquid separation properties of activated sludge.

Key words:activated sludge flocs; bioflocculation; settleability; EPS; DLVO; hydrophobicity