Abstract: To explore the feasibility of micro-vortex coagulation technology in tunnel wastewater treatment process, a numerical simulation is conducted to investigate the the characteristics of the coagulation flow field produced by the grid micro vortex generator with different characteristics.Furthermore, a hydraulic flocculation validation experiment is conducted using the optimal combination of grating-types for simulated tunnel wastewater with turbidity of 1 300 NUT. The results show that the thickness of the grid bars primarily affects the turbulent kinetic energy of the fluid in the flow field and the consumption degree of turbulent dissipation in the initial coagulation stage. The square grid bars with a side length of 5 mm are better suited to maintain the kinetic energy required in the whole coagulation process in the flow field. The spacing of the grid bars alter their blocking effect of the grid bars on the fluid. When the spacing is 11 mm, the fluid can provide higher turbulent kinetic energy and turbulent dissipation for flocculation reaction. The length of grid bars mainly affects the energy evolution of the flow field in the axial direction. The grid bars of 400 mm, 600 mm and 800 mm extend the energy distribution distance of the fluid in the flow field, providing sufficient energy for aggregation of the flocs in the rear section of the reactor. The hydraulic flocculation verification experiment of simulated tunnel wastewater with turbidity of 1 300 NTU was carried out using the optimal combination of grid bars, resulting in a stable effluent turbidity of the wastewater of less than 50 NTU.

Key words: vortex flocculation technology, numerical calculations, gridded micro-vortex generators, turbulent kinetic energy, turbulent energy dissipation rate