Oxygen transfer in gravity flow sewers

Oxygen diffused to water in gravity sewer pipes was studied in a 21 m long, 0.15 m diameter model sewer. At first. the sodium sulfide was added into t he clean water to deoxygenate, then the pump was started to recirculate the water and the deoxygenated water was reaerated. The dissolved oxygen micro electrode was installed to measure the dissolved oxygen concentrations vari ed with flow velocity, time and depth. The dissolved oxygen concentration p rofiles were constructed and observed. The partial differential equation di ffusion model that considered Fick's law including the molecular diffusion term and eddy diffusion term were derived. The analytic solution of the par tial differential equation was used to determine the diffusivities by the m ethod of nonlinear regression. The diffusivity values for the oxygen transf er was found to be a function of molecular diffusion, eddy diffusion and fl ow velocity.