Simulation Of Oscillating Grid Turbulence And Its Effect On Mass Transfer In Biofilms

Biofilm mass transfer has been a hot topic in the research of biofilms.At present,the research on the influence of hydraulic conditions on the mass transfer and growth characteristics of biological films focuses more on the influence effect of hydraulic shear force,flow velocity and other factors,while the number of related studies on the influence of pulsation velocity is less.Cultivation of biological membrane in this paper,by means of vibration grating device,is determined by particle image velocimetry the flow field inside the device,the statistical characteristics of turbulent flow field and the change law of simultaneous determination of biofilm dry weight,thickness,density,and the content of extracellular polymer components,through the statistical features of the turbulent flow field associated with biofilm growth index,analyze the turbulent flow field and mass transfer effect on biofilm growth.The main research results are as follows:(1)the distribution law of RMS velocity and effective turbulence intensity in the ordinate direction is basically similar.In the horizontal direction,the distribution of root mean square velocity fluctuates up and down around the mean value,with little overall change and relatively uniform distribution.In the vertical direction,the RMS velocity and the effective turbulence intensity decrease with the increase of the vertical coordinate under the same vibration condition.At the same height,each parameter increases with the increase of vibration frequency.(2)by fitting the experimental results of particle image velocity measurement,various parameters in the turbulence model of vibration grille are modified,and the expressions of mean square velocity and effective turbulence intensity are obtained.The turbulence model can be used to calculate the effective turbulence intensity at a specific position in the biofilm culture experiment under the same experimental conditions.(3)the greater the effective turbulence intensity and turbulence pulsation degree is,the more dry weight and density of the biofilm cultured in this region will be,the better the growth status of the biofilm will be,and the structure of the biofilm will be smoother and denser.When the grating vibration frequency is low,the Reynolds number of turbulent flow is low,and the thickness of biofilm gradually thickens with the increase of effective turbulent intensity.With the increase of the grid vibration frequency and the increase of the Reynolds number,the thickness of the biofilm changes little with the increase of the effective turbulence intensity.(4)under the action of turbulence pulsation,in the region closer to the grid,the concentration difference boundary layer outside the biofilm becomes thinner and the mass transfer resistance decreases due to the influence of stronger turbulence,which promotes the growth of biofilm to a certain extent.When the degree of turbulence increases,the turbulence fluctuation velocity increases correspondingly,which improves the rate of microbial desorption and adsorption on the biofilm and the rate of biofilm self-renewal.