Circulation induced by diffused aeration in a shallow lake

Arthur Ja Toné,Iran E Lima Neto,Carlos Ha Pacheco

doi:10.4314/wsa.v43i1.06

Abstract

Field surveys were carried out to investigate the surface jet flows and the resulting circulation patterns generated by diffused aeration in a shallow lake. In conrast to previous studies, the experimental conditions included point-source bubble plumes with very high air flow rates (100–400 L/min) relative to the shallow water depth (1.5 m). The results indicate that the surface jet velocity can be described by linear profiles. The decay of this velocity with distance displayed a similar behaviour to that reported in the literature, but the surface jet spread much faster under the present conditions. Combining our results with published data allowed for the generation of dimensionless correlations for the velocity and depth of the surface jet. A good agreement between the total circulation flow rates predicted by using the proposed correlations and integral modelling was also obtained. Lastly, a simple returning flow model was proposed to describe the circulation flow patterns induced by the bubble plumes. The results were also applied to assess the impact of circulation on vertical algae migration, which is important for water quality management. Keywords : aeration, algae migration, bubbles, jets, plumes

Highlights

Bubble plumes generated by diffused aeration are widely used for treating wastewater and ameliorating water quality problems in lakes and reservoirs (Bombardelli et al, 2007; Socolofsky et al, 2008; Lima Neto, 2012a,b; Lima Neto and Parente, 2016)
The aims of the present paper are: (i) to investigate the surface flows generated by axisymmetric bubble plumes with relatively high air flow rates in a shallow lake, (ii) to propose a method to describe the circulation patterns induced by the bubble plumes, and (iii) to apply the results to assess the impact of circulation on vertical algae migration
Dashed lines represent fitted linear curves, which were adjusted to the data with a coefficient of determination R2 ranging from 0.94 to 0.99. This confirms that, for the sake of simplicity, the surface jet flow induced by axisymmetric bubble plumes can be described by linear velocity profiles

Summary

Introduction

Bubble plumes generated by diffused aeration are widely used for treating wastewater and ameliorating water quality problems in lakes and reservoirs (Bombardelli et al, 2007; Socolofsky et al, 2008; Lima Neto, 2012a,b; Lima Neto and Parente, 2016). In addition to supplementing the dissolved oxygen levels and reducing internal phosphorus loading in water bodies, bubble plumes generate water circulation patterns that can prevent or destroy stratification (Wüest et al, 1992; Singleton et al, 2010; Lima Neto et al, 2016). The behaviour of these circulation patterns must be well understood in order to promote positive effects such as the elimination of undesired algae, as well as to avoid negative effects such as resuspension of bottom sediments and nutrients (Imteaz and Asaeda, 2000; Jungo et al, 2001). To the authors’ knowledge, only Goossens (1979) has performed experimental studies involving measurement of the circulation flows generated by axisymmetric bubble plumes, which is the focus of the present investigation (see Fig. 1), while Wen and Torrest (1987), Fanneløp et al (1991) and Riess and Fanneløp (1998)

Objectives

Methods

Results

Conclusion