Abstract
In a primary treatment tank of on-site wastewater systems (small-scale johkasou), sludge separation and accumulation efficiency depend on water flow. Prediction of water flow using computational fluid dynamics (CFD) might be effective to optimize the design of a tank. In this study, a model primary treatment tank was used to test reliability of CFD. The water flow (simulated by CFD) was compared with the water flow measured experimentally by an acoustic Doppler velocimeter (ADV). The simulated flow pattern agreed well with the experimental result. The water flowed from the inlet baffle, down to the bottom of the tank, across the bottom and up into the outlet baffle. The simulated velocity was approximately equal to the measured velocity with the correlation coefficients of 0.68 and 0.93 for 20 L/min and 50 L/min inflow rates, respectively. Furthermore, the simulated flow direction was agreed well with the measured flow direction except the data whose velocities were small enough less than 0.5 cm/sec. The similarities of the simulation and the experiment suggested that CFD will be a useful tool for small-scale johkasou design.
