Experimental Study of the Quantitative Impact of Flow Turbulence on Algal Growth

Haiping Zhang,Yuehong Zhang,Feipeng Li,Yafei Cui,Hanling Xu

doi:10.3390/w13050659

Abstract

Flow turbulence has been widely accepted as one of the essential factors affecting phytoplankton growth. In this study, laboratory cultures of Microcystis aeruginosa in beakers were carried out under different turbulent conditions to identify the quantitative relationship between the algal growth rate and the turbulent intensity. The turbulent intensity (represented by energy dissipation rate, ε) was simulated with the software FLUENT. Daily measurement of the two parameters (algal biomass and chlorophyll-a concentration) was carried out during the experimental period to represent the algal growth rate. Meanwhile, the rates of photosynthetic oxygen evolution and chlorophyll fluorescence intensity were calculated to investigate the photosynthetic efficiency. The results indicated that the growth rate of Microcystis aeruginosa became higher in the turbulent environment than in the still water environment under the designed experimental conditions. The peak growth rate of Microcystis aeruginosa occurred when ε was 6.44 × 10−2 m2/s3, over which the rate declined, probably due to unfavorable impacts of strong turbulence. In comparison, the maximum rate of photosynthetic oxygen evolution occurred when ε was 0.19 m2/s3. Based on the findings of this study, an exponential function was proposed in order to incorporate the effect of flow turbulence into the existing algal growth models, which usually just consider the impacts of nutrient availability, illumination, and temperature.

Highlights

Rapid industrialization has resulted in severe environmental pollution, and bluegreen algal blooms have become a global phenomenon with increasingly remarkable intensity and frequency throughout the world in recent decades
The energy dissipation rates (ε) of the magnetic rotor under different rotor speeds were estimated by FLUENT (Table 2)
Laboratory cultures of Microcystis aeruginosa in beakers were carried out under different turbulent conditions to identify the quantitative relationship between the algal growth rate and the turbulent intensity

Summary

Introduction

Rapid industrialization has resulted in severe environmental pollution, and bluegreen algal blooms have become a global phenomenon with increasingly remarkable intensity and frequency throughout the world in recent decades. Microcystis aeruginosa is the most typical bloom-forming freshwater cyanobacteria in freshwater all over the world [1]. Microcystis blooms can initiate severe environmental and ecological events, causing blockage of drinking water supply systems, producing unpleasant odors, reducing water clarity, removing dissolved oxygen during decomposition, and so on [2]. Some species of Microcystis aeruginosa are potentially toxic and can produce microcystins, which may pose severe health risks to humans and other mammals [3]. Many studies have been conducted to explore the influence mechanism to solve algal blooms [4,5]. It is generally believed that significant influence factors of water eutrophication are climate [6]

Results

Discussion

Conclusion