Design, simulation, and laboratory test of a single sludge drainage pipe for wastewater treatment sedimentation tank

This study develops a novel design scheme based on engineering fluid mechanics for the single-pipe-type sludge drainage mechanism of sedimentation tanks in the wastewater treatment industry. A laboratory-scale clarifier is fabricated for experimental verification. Sludge drainage ratio and suspended solids (SS) of inflow are selected as two factors for laboratory experiments, and SS values are measured to evaluate the performance of the sludge drainage pipe. Experiment data show that the designed single sludge drainage pipe can successfully achieve the supposed task with a coefficient of variation (CV) of SS less than 8.5%. The variation scope of CV from 1.5% to 8.3% suggests that the sludge drainage performance is relatively steady. Nine sets of 3D computational fluid dynamic (CFD) simulations, which is based on the inhomogeneous Eulerian-Eulerian multiphase model, were conducted for a comprehensive exploration and assessment. Results reveal noticeable deviations of the characteristics of the fluid in the outermost orifice of the sludge drainage pipe from the designed value. Although the fluid velocity through each orifice is matched with the designed values, the mass flowrate differs with a maximum of four times the designed value and a standard deviation of 0.4 of hole among the nine simulations. This study also suggests some considerations in the design process and routine operation of the single-pipe-type sludge drainage system.