Design of an Artificial Destratification System To Control Cyanobacteria Growth in Reservoirs

Abstract

This study aims at designing an artificial destratification system to control cyanobacteria growth in the reservoirs. Previous applications for artificial destratification in reservoirs were based on trial and error on site, where neither the effect of air bubble size and configuration nor the effect of air density in the bubble plume could be investigated. This study seeks for the optimized design. We have tackled this task at four steps. Firstly, we setup an experimental system that mimics a thermally stratified reservoir experiencing hypoxia and oxygenate/mix the water column. We maintain a stable stratification by a novel setup designed for this study enabling to form consistent and desired stratified layers along the water column. Next, we investigate the effects of bubble size, bubble slip velocity and other parameters on destratification efficiency. Nondimensional numbers involving bubble diameter, bubble diffusing area, air rate and stratification rates are used to quantify destratification efficiency for the best design of aeration systems. Then, we simulate the hydrodynamics during the mixing of thermally stratified water columns by air diffusers via a 3-D numerical model. The Eulerian multiphase model and k-. turbulence model are found to be suitable for the purposes of the study. In the final part, the numerical model is validated with the experiments. Based on the error analysis of comparisons of the model and observations, the best configuration of air diffuser is proposed, and the numerical model is found to be successful in simulating the destratification of thermally stratified water columns by air diffuser.