Enhancement of ZnO particles aggregation and sedimentation using polysaccharide and amino acid: Importance in abiological granular sludge (ABGS) formation

• Polysaccharide and amino acid were used to enhance ZnO particles aggregation.
• A bridging and hydrophobic model is established based on extended-DLVO theory.
• SO42− is more suitable for bridging and hydrophobic model than F− and Cl−.
• This model helps the formation of ABGS with excellent settling performance.

Aggregation of particles is of paramount importance in nature and in diverse engineering applications. A simple and effective tunable mechanism for promoting aggregation of particles is highly desirable. Inspired by the important role of polysaccharide and amino acid playing in the formation of granular sludge, a new mechanism based on bridging and hydrophobic model was proposed to improve the aggregation of particles and enrich the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Effect of model polysaccharide (xanthan gum, XG), amino acid (l-tryptophan, Trp), and their mixture on ZnO particles aggregation kinetics was investigated as an example. Results indicate that ZnO particles aggregation is enhanced by adding these polymers, especially by adding Trp-XG mixture with high Trp/XG ratios. Moreover, impact of various anions such as F−, Cl−, and SO42− on ZnO particles aggregation was investigated. Results reveal that the order of ZnO particles aggregation to be improved is SO42− > Cl− > F−. Sulfate produces the smallest hydrated diameter and is of great benefit to bridging and hydrophobic mechanism. Furthermore, optimal conditions for ZnO particles aggregation were used in abiological granular sludge (ABGS) formation for practical application. Results confirm that Trp-XG is highly effective to promote the formation of ABGS with regular granular morphology and excellent settling performance.

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