The influence of the design of the mixing device on the efficiency of mass transfer during pneumo-mechanical aeration of wastewater

Summary

Aeration is the most energy-intensive process in wastewater treatment. The expenditures for air oxygen supplied for biological treatment are about 60% in the treatment cost structure. Thus, the efficiency of mass transfer and reduction of air consumption is an urgent task for the enterprises that look for improving the economic efficiency of their activities. The purpose of this work is to determine the effectiveness of a pneumo-mechanical aeration system using a turbine mixer and a new conical mixer designed by the authors, as well as to compare the efficiency of gas dispersion in pneumatic and pneumo-mechanical aeration systems. As a criterion for comparison, SOTE (Standard Oxygen Transfer Efficiency) indicator that is the main process parameter that provides for comparing the effectiveness of different aeration systems, is selected. The second efficiency criterion is SAE (Standard Aeration Efficiency) indicator, i. e. the ratio of the amount of oxygen dissolved in liquid to the amount of the electrical energy consumed. As a result of experimental studies, it was found that the conical mixer was as efficient as the turbine one in the rate of saturation of water with oxygen, while consuming much less electrical energy. With the development of a bevel wheel mixing in the «gas-liquid» system in large-sized apparatus became possible owing to the low resistance of the blades, which is especially important for aeration tanks with a small depth in the process of biological wastewater treatment under the conditions of the significant reduction in the effectiveness of the pneumatic system.

Key words

wastewater treatment , pneumo-mechanical aeration , mixing device , sulfite method , criterion of the aeration efficiency , mass transfer