Optimal location of artificial aeration in a tidal river for water quality improvement

Artificial aeration is one of the alternatives proposed for the improvement of DO level of the Shing Mun River in Hong Kong. This study employs Saint Venant equations and one-dimensional water quality models to simulate the hydrodynamics and DO distributions in the river, respectively. Processes affecting the river quality, such as biochemical degradation, oxygen production and consumption by algae and sediment oxygen demand are considered in the models. In-situ and laboratory tests were conducted to determine the values of reaction rates of these processes. By comparing the simulated results of DO concentration under different locations of the aeration equipment along the river with the present DO condition during spring and neap tides, the optimal position of artificial aeration is determined based on the effectiveness of water quality improvement. The effect of intermittent aeration and that of continuous aeration are compared and it is found that the increase of DO in the intermittent aeration case is about 50% of that in the continuous case on the cross-section of aeration. The influence of water temperature on the aeration is also discussed.