Interaction Between EPS And Chromium In Aerobic Activated Sludge

The biochemical tailwater of tannery wastewater contains a certain concentration of Cr(Ⅲ),which can be adsorbed and stabilized with the proteins and polysaccharides in the activated sludge extracellular polymer(EPS).When the adsorbed Cr(Ⅲ)in the sludge reaches the adsorption equilibrium,Cr(Ⅲ)can be more stabilized in the dissolved Cr in the tailwater with the release of the soluble components in the EPS.The interaction,binding process,structural characteristics and destabilization mechanism of Cr(Ⅲ)release between protein,polysaccharide and Cr(Ⅲ)in EPS of tannery wastewater biochemical system are not clear yet,which cannot provide an effective means to control the total amount of Cr(Ⅲ).In this study,sodium alginate and bovine serum albumin were selected as the simulants of protein and polysaccharide in aerobic activated sludge EPS,and the interaction between protein-polysaccharide-Cr(Ⅲ)and the formation process,structural characteristics and removal law of the mixed ligand complex were studied by simulating the mixed ligand complex formed by activated sludge EPS and Cr in the biochemical treatment of tannery wastewater,and the effect of Cr(Ⅲ)on the changes of EPS components and structural characteristics in each structural layer of activated sludge,and investigated the conformational changes,aggregation dissociation and destabilization mechanism of protein-polysaccharide-Cr(Ⅲ)mixed complexes before and after ultrasonic treatment.The main results of the study are as follows:(1)Sodium alginate and bovine serum albumin were selected to simulate protein and polysaccharide in aerobic activated sludge EPS,and the complexation behaviors of polysaccharide,protein and Cr(Ⅲ)and the removal laws of alkali precipitation,isoelectric point precipitation and coagulation precipitation were analyzed and discussed.The results showed that polysaccharides and proteins formed polysaccharide-protein complexes by electrostatic interaction and hydrogen bonding,and Cr(Ⅲ)occurred multi-point coordination by influencing the complex depolymerization,and a stable and complex complex complexation of protein-polysaccharide-Cr(Ⅲ)existed.When the mass ratio of polysaccharide to Cr(Ⅲ)was 3:1 and the mass ratio of protein to Cr(Ⅲ)was 4:1 the complex was formed with high stability,and the removal rate of mixed ligand complexes with alkali precipitation and coagulation precipitation of Cr was about 83%.(2)The protein-polysaccharide-Cr(Ⅲ)mixed ligand complexes were studied to investigate the mechanism of the effect of ultrasound on the conformational changes and destabilization of chromium release from the complexes,and the laws of ultrasound synergistic with alkali precipitation,urea treatment and chelate precipitation removal.The results show that ultrasound destroys the internal and intermolecular hydrogen bonds,destabilizes the structure of mixed ligands,dissociates the macromolecular agglomerates into uniformly distributed small molecule complexes,exposes the Cr wrapped inside the macromolecules,and promotes the removal process of synergistic chelating agent and coagulation precipitation,resulting in a total Cr removal rate of 99.12%.Urea has an effect on hydrogen bonding and coordination bonding in the complexes.(3)The effect of protein-polysaccharide-Cr(Ⅲ)complexes that have been produced in biochemical treatment on EPS in each structural layer of activated sludge was investigated by simulating the interaction process of ligand complexes with municipal aerobic activated sludge.The results showed that the protein-Cr(Ⅲ)complex promoted EPS secretion by microorganisms,inhibited protein secretion and promoted polysaccharide secretion;the polysaccharide-Cr(Ⅲ)complex inhibited EPS secretion,and the polysaccharide and protein in the mixed ligand complex slowed down the reaction rate with activated sludge EPS.The ligand complexes bound to S-EPS,LB-EPS and TB-EPS in order,and the most stable one was bound to TB-EPS;dissociation,complexation and aggregation with activated sludge EPS caused molecular conformational changes to re-coordinate Cr in the system and form hydrogen bonds between molecules to form more stable and complex complexes.