Inducing an extended naturally complete mixing period in a stratified reservoir via artificial destratification

Nan Li; Tinglin Huang; Yang Li; Fan Si; Haihan Zhang; Gang Wen

doi:10.1016/j.scitotenv.2020.140958

Inducing an extended naturally complete mixing period in a stratified reservoir via artificial destratification

Sci Total Environ. 2020 Nov 25:745:140958. doi: 10.1016/j.scitotenv.2020.140958. Epub 2020 Jul 17.

Authors

Nan Li¹, Tinglin Huang², Yang Li³, Fan Si¹, Haihan Zhang¹, Gang Wen¹

Affiliations

¹ Key Laboratory of Northwest Water Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, China; Shaanxi Key Laboratory of Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
² Key Laboratory of Northwest Water Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, China; Shaanxi Key Laboratory of Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China. Electronic address: huangtinglin@xauat.edu.cn.
³ Key Laboratory of Northwest Water Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, China; Shaanxi Key Laboratory of Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China; School of Energy and Environment, Zhongyuan University of Technology, ZhengZhou 450007, China.

PMID: 32738682
DOI: 10.1016/j.scitotenv.2020.140958

Abstract

Naturally complete mixing (i.e., ΔT <1 °C across the entire water column) driven by convection in winter is an ideal state for maintaining good water quality, as it spontaneously redistributes dissolved oxygen (DO) over the entire water column and prevents hypolimnetic anoxia and associated pollution. A complete mixing duration is quite short under natural mixing conditions, whereas artificial destratification systems can artificially induce an earlier occurrence of complete mixing, thereby prolonging the span of the naturally complete mixing period by several months. Based on multi-year in situ water quality measurements and meteorological data during natural and artificial mixing periods, this study evaluates the effects of water-lifting aerators (WLAs) and climatic factors on convective mixing processes and their duration. WLA-supplied turbulent kinetic energy (TKE) and WLA-induced hypolimnion warming significantly decrease the water stability and extend the naturally complete mixing period for 2.6-fold. The results indicate that an optimal WLA implementation should immediately achieve complete mixing when surface mixing occurs in autumn. By evaluating the influence of WLAs and other factors on convective mixing, this study provides insights for successful destratification system operations (i.e., WLAs) to replenish oxygen concentrations across the water column and minimize operating costs by taking advantage of climatic conditions. Although our study focuses on WLA-induced mixing, these observations can be applicable to other destratification systems in most of the stratified reservoirs and lakes.

Keywords: Complete mixing; Destratification; Hypolimnetic anoxia; Hypolimnion warming; Reservoir management.