Study On Mechanical Properties Of Excess Sludge Bacterial Cell Based On ANSYS Model

Using microbiological methods for treatment of sewage will produce large amounts of sludge. The sludge take up a lot of space, and its dehydration and transport are not easy. The sludge disintegration is an important means of dealing excess sludge, and physical disintegration is one of the main methods of sludge disintegration. Nowadays, the widely used methods include ultrasonic, spray, and mechanical homogenization techniques. The current study is focused on the relationship between disintegration effect and physical parameters (ultrasonic frequency, ultrasonic time, spray pressure, etc.) These studies only observed the appearance of sludge disintegration without explanation of its inherent mechanism.The key to disintegrate excess sludge is to destroy the microorganisms in excess sludge, i.e. destroy the structure of bacteria, especially the bacterial cell wall. Understanding and mastering the mechanical mechanism of destroying of bacterial cell walls under the effect of mechanical force is the most basic and most critical issue in the research of physical disintegrating excess sludge.In this article, ANSYS was used to create a relatively simple single-cell bacteria finite element model:spherical shape, the cytoplasm is tightly wrapped by cell wall, and the force is transmitted by a rigid plate. With the result of numerical simulation, the effect of physical properties and geometric dimensions of the cell wall and cytoplasm on the cell deformation and impact stresses were discussed.It’s found that there are 3 main parameters that affect the stiffness of the cells significantly:cell diameter, the thickness of the cell wall, and the elasticity modulus of the cell wall. The smaller the cell size is, the thicker the wall is, or the greater the cell wall elastic modulus is, the more overall stiffness the cell performance. The impact of the other parameters on the overall stiffness is small, the affect the Poisson’s ratio is completely negligible, and the impact of cytoplasm elastic modulus is reasonable, controllable and acceptable. The larger the cell is, The larger the deformation is(with the same force), and the greater the stress is, and therefore, the easier to be damaged. And a small changes of the size of cell can cause great changes in stress distribution, it’s one of the key factors that affecting the disintegration. The thicker the wall is, the greater the resistance to deformation is. However, increasing of the wall thickness also makes the stress variation more intense on the top of cell wall. Increasing the Young’s modulus of cell wall will reduce the amount of compression. But, the reducing of deformation cause increasing of stress, maximum stress is increased significantly. If the ultimate tensile strength is proportional to Young’s modulus, then the larger the Young’s modulus is, the harder to broke the cell.Based on previous studies, using the finite element method analysis with ANSYS software, a simple three-dimensional cell model with cell wall and cytoplasm was created. And the mechanical behavior of cell with different physical parameters and geometric dimensions were analyzed. It helps to clarify the mechanism of the macroscopic mechanical behavior of bacterial cells.