Study on Propellers Distribution and Flow Field in the Oxidation Ditch Based on Two-Phase CFD Model

Yuquan Zhang,E Fernandez-Rodriguez,Huiwen Liu,Qinghong Tang,Yuan Zheng,Yanhe Xu,Chengyi Li

doi:10.3390/w11122506

Yuquan Zhang, E Fernandez-Rodriguez + Show 5 more

Open Access

https://doi.org/10.3390/w11122506

Copy DOI

Abstract

The oxidation ditch (OD) plays an important role in wastewater treatment plants. With increasing demand and production costs, the energy consumption and sludge deposition occurring in the OD must be diminished to enhance its development. In this paper, a two-phase computational fluid dynamics (CFD) model of water and activated sludge examined the flow field characteristics of an OD, consisting of two side-by-side propellers. The system was studied under five configurations, where the spacing between the propellers was set equal to −0.2, −0.1, 0, 0.1, 0.2 times the length of the OD. The viscosity and settling rate of activated sludge was imported in the numerical simulation through a user defined function (UDF). The optimal scheme of the propeller’s power consumption, velocity distribution, and sludge concentration distribution was obtained. The result shows that sludge concentrations are linked with dead zone velocity but not necessarily with low velocities. Experiments confirmed the validity of the velocity flow field simulated by the two-phase CFD model. Overall, these findings form the basis for the propellers distribution optimization and allow a deeper insight into the flow field of OD systems.

Highlights

To deal with the rapid increase in wastewater, lots of treatment plants have been installed to clean and reuse the water in industrial processes [1]
About 32.1% of the Chinese wastewater treatment plants employ the use of the oxidation ditch (OD) [2]
In view of the above, the aim of this paper is to study, through a two-phase computational fluid dynamics (CFD) model, the characteristics of flow and sludge distribution of a full-scale OD

Summary

Introduction

To deal with the rapid increase in wastewater, lots of treatment plants have been installed to clean and reuse the water in industrial processes [1]. About 32.1% of the Chinese wastewater treatment plants employ the use of the oxidation ditch (OD) [2]. Key aspects of ODs include their simplicity, low sludge production, and confidence in the market, including operation and maintenance processes [3]. They are one of the most widely used methods for activated sludge biological treatment [4]. Despite the existing research recognizes the critical role played by OD in the treatment plant’s production effectiveness and economics, old and inefficient technology still prevails in many OD systems; studies suggest their modernization will enhance the flow field and reduce costs and environmental impact [5,6,7,8]

Objectives

Results

Conclusion