Laser Light Scattering Studies For Microbial Extracellular Polymeric Substances

Microbial extracellular polymeric substances (EPS) have been recognized to play an important role in the field of wastewater treatment and received an increasing attention. The characteristics of EPS significantly influence the physicochemical properties of microbial aggregates, e.g., deposition, retention, flocculability, settling, dewatering and biofouling. However, information about the spatial configuration of EPS is very limited. In this work, we used laser light scattering to explore the configuration properties of EPS. Main contents and results are as follows:1. Both DLS and SLS can be used as a powerful and convenient tool to explore microbial EPS. The spatial configuration of EPS extracted from Bacillus megaterium TF10 is found in the form of colloids in neutral aqueous system and their shape is random coil with incompletely extending chains. The attraction interaction between EPS colloids is responsible for the high flocculability of B. megaterium TF10.2. With an integrated approach, the pH dependence of structure and surface property of microbial extracellular polymeric substances (EPS), excreted from Bacillus megaterium TF10, and accordingly its flocculation is elucidated. The deprotonated or protonated states of functional groups in EPS result in more dense and compact structure at a lower pH because of hydrophobicity and intermolecular hydrogen bonds. The EPS structure, surface properties and accordingly microbial flocculation are heavily dependent on pH in solution.3. The interaction between both cations and anions with SMP is evaluated. In the Hofmeister series, as "soft " ions, Cs+ and I- have larger polarisabilities, lower ion-water interactions, reducing the immediate water structure around ions. The presence of NaC1 results in dispersing, lower density, smaller size structure and higher translational diffusion coefficient <D>.