Selection of metal ions in different valence states on sludge conditioning: Analysis of hydrophobicity and evaluation of resource recovery capacity

In this study, we applied three types of metal ions in different valence states (Na⁺, Ca²⁺ and Fe³⁺) to compare their similarities and differences in adjusting sludge properties during the process of sludge conditioning. Under the same ion concentration, the addition of Na⁺ had strong capacity on damaging α-helix structure with the improvement of sludge hydrophobicity. However, the reduced hydrophobic polysaccharide and the increased hydrophilic protein result in the improvement of sludge hydrophilicity under the addition of Ca²⁺ and Fe³⁺. Meanwhile, three types of metal ions all had the better ability on damaging the two-dimension spatial structure of extracellular polymeric substance (EPS) protein due to the effective destruction of β-sheet. Additionally, the application of these three types of metal ions could achieve different resources (existed in sludge) recovery and enhance the value of sludge. This work will help us make a more correct choice when conditioning sludge with metal ions to meet actual needs.