Destratification and oxygenation efficiency of a water-lifting aerator system in a deep reservoir: Implications for optimal operation.

Thermal stratification is a common phenomenon in lakes and reservoirs and has a significant influence on water quality dynamics. Heihe Reservoir is a canyon-shaped reservoir in Shaanxi Province with strong thermal stratification. Therefore, eight water-lifting aerators (WLAs) were installed in this reservoir, which could overcome thermal stratification and increase oxygenation with gas flows between 20 and 50m/hr, and oxygenate the hypolimnion with gas flows less than 20m/hr. To examine the destratification efficiency of the WLA system, we used a three-dimensional hydrodynamic module based on MIKE 3 to simulate the thermal structure of Heihe Reservoir and compared the simulations with measured data. Results showed that operation of the WLA system promoted water mixing and effectively oxygenated the hypolimnion. Through the established energy utilization assessment method, the energy utilization efficiency of the WLA system was between 5.36% and 7.30%, indicating the capability of the technique for destratification in such a large reservoir. When the surface water temperature dropped to the theoretical mixed water temperature calculated by the energy utilization assessment method, reducing gas flow could save energy. This would prevent anaerobic conditions from occurring in the bottom water and maintain good water quality in Heihe Reservoir.