Experimental Study On The Basic Physical Properties Of Sediment Particles After Biofilm Vegetating

Microorganism exists in the form of biofilm on all solid surface in the wetland environment such as rivers, lakes, and so on. In recent years, because of the nutrient surpluses of many rivers and lakes, the adsorption of large quantities of nutrient materials on sediment particles'surface provides more favorable conditions for the bacterial sorption and biofilm growth. On the one hand, bacterial growth and biofilm formation would change the transfer laws of nutrient materials in aquatic environment and influence parematers of water quality model. On the other hand, the geometrical features and mechanical properties of sediment particles would also change because of the biofilm growth. Although the importance of biofilm in water, soil and biotic environment has gradually been recognized, the previous research usually focuses on its environmental effect, and little is about the influence on the basic physical properties of sediment particles in aquatic environment, which is the important aspect of sediment transport mechanics.This dissertation would focus on the basic physical properties'changes of sediment particles after biofilm vegetating. The research work is based on the culture experiment of biofilm vegetating on sediment particles'surface. The required data are obtained through high-precision apparatus, and then the changes of biofilm sediment properties are studied and analyzed, including particles'geometrical features, bulk properties of density, physical properties of rheology, and so on.The geometrical features'changes of sediment particles after biofilm vegetating are studied from two aspects of projection profile and micro-morphology. Based on the statistics of abundant ESEM pictures, the methods of Fourier analysis and Wavelet analysis are used to build the project profile model of sediment particles after biofilm vegetating, the first-order operator and second-order operator are applied to analyze the surface micro-morphology of biofilm sediment, and further the"mathematical sediment"is built. The research shows that sediment particles become smoother after biofilm vegetating. The research on bulk properties of density is directed respectively through the dry bulk density and wet bulk density of bioflocculation sediment. Based on the observation of growth process of bioflocculation sediment using the confocal laser scanning microscopy, some image processing methods are used to analyze the structural properties, and the Logistic growth curve equation is applied to describe the growth and variation of biofilm over time. A dry bulk density formula of bioflocculation sediment is proposed and the wet bulk density is modified according to the change of grain size, laying a foundation for the calculation of sediment transport.MCR300 advanced extension rheometer is used to study the difference of rheological properties between original sediment and biofilm sediment, and the influence on rheological properties of fine-grained sediment from biofilm is investigated. The research shows that the rheological properties of fine-grained sediment change greatly due to biofilm growth, assuming the properties of plastic fluid with thixotropy, which is different from that of hyper-concentration flow. Also the rheological equation of biofilm sediment and expressions of rheological parameters over time are proposed.