A Revolution in the design of Sedimentation Tank using Computational Fluid Dynamics method

Dr. Thiyam Tamphasana Devi *

Innovation frequently takes the shape of ground-breaking technologies that improve the productivity and sustainability of essential infrastructure in the constantly expanding fields of civil and environmental engineering.

In recent years, the use of computational fluid dynamics (CFD) modeling has emerged as a game-changing technique in the design and optimization of sedimentation tanks, providing engineers with never-before-seen insights into fluid dynamics and sediment behaviour. This article explores the revolutionary potential of CFD modeling for sedimentation tank design and its application to water and wastewater treatment.

The Age-Old Challenge: Sedimentation Tank Design

Sedimentation tanks, a crucial component of water and wastewater treatment facilities, have been used since ancient times. They are used to facilitate the settling of suspended particles through gravity, which clarifies the water or wastewater. These tanks are essential for preparing water for safe release into the environment, reuse, or consumption.

Although there are distinctions between water and wastewater treatment in terms of the influent characteristics and sedimentation tank aims, both treatments share the same basic design concepts, hydraulic considerations, and sludge removal processes. Engineers have, however, consistently struggled with the design of an effective sedimentation tank that increases particle removal while minimizing energy use.

Traditional design methods often relied on empirical equations and physical scale models. Despite the fact that these techniques have been effectively applied for many years in the construction of sedimentation tanks, they have drawbacks in terms of accuracy, adaptability, and the capacity to take intricate factors into account.

Empirical equations are based on assumptions that may not always be true and can lead to inaccuracies in the design, and scale models can be costly and time-consuming to create and test. This is where CFD modeling has come into play, providing a more sophisticated and economical approach to sedimentation tank design and providing more precise and adaptable design solutions.

The Power of CFD Modeling

CFD modeling is a computational technique that simulates and analyses fluid flows, heat transfer, and other phenomena related with fluid. It has gained traction in numerous industries, including aerospace (e.g., design of wings), automotive engineering (e.g., combustion, engine cooling etc.,), chemical engineering (e.g., mixing and separation), hydraulic and hydrology (e.g., Flows in rivers, grounds etc.), biomedical (e.g., blood flow in arteries and veins), and environmental science (e.g., distribution of pollutants and effluents in air or water) etc., for its ability to simulate complex fluid dynamics with high precision.

In sedimentation tank design, CFD models are used to simulate the flow of water and sediment particles within the tank, enabling engineers to visualize and analyse various design configurations.

Key benefits of CFD modeling in sedimentation tank design include

1. Flow Pattern Analysis: CFD enables engineers to analyze the flow distribution within the sedimentation tank, ensuring that influent water is distributed uniformly inside the tank. This ensures uniform settling of particles and reduces the risk of short-circuiting.

2. Optimizing Tank Geometry: CFD enables engineers to evaluate several geometries of tank, including inclined plate settlers and lamella clarifiers, and can then determine which design is most effective for a given application. It helps identify areas for improvements in tank shape, dimensions, and component placement.

3. Cost Savings: By eliminating the need for physical scale models and extensive trial-and-error testing, engineers can optimize sedimentation tanks using CFD and reduce the overall cost of construction, operation, and maintenance, while still meeting performance requirements.

4. Retrofitting Existing Tanks: CFD can be applied to assess and improve the performance of existing sedimentation tanks, making them more cost-effective and efficient without the need for physical modifications.

5. Particle trajectory analysis: CFD can track the trajectories of particles within the tank, allowing engineers to understand how different particle sizes settle and interact with tank components. This information aids in optimizing the performance of the sedimentation tank.

6. Baffle and weir Design: Properly designed baffles and weirs can enhance sedimentation by controlling flow patterns and preventing short-circuiting. CFD allows for the optimization of baffle placement, size, and configuration to maximize sedimentation efficiency.

7. Inlet and Outlet Design: CFD can help engineers design efficient inlet and outlet structures. By optimizing these components, it is possible to minimize disturbances in the tank that can hinder sedimentation and ensure a consistent flow rate through the tank.

8. Varying Operating Conditions: CFD simulations can assess the impact of operational changes, such as changing influent water quality and flow rates on sedimentation tank. This aids in making informed decisions for optimizing existing sedimentation tanks.

9. Scale-Up and Scale-Down: CFD simulations can be used to scale up or down sedimentation tank designs for different flow rates and sizes, ensuring that the tanks work efficiently under various conditions.

10. Environmental Impact: CFD can be used to predict the environmental impact of sedimentation tank operations, such as the dispersion of particles, and pollutants in the effluent, helping ensure compliance with environmental regulations. Also, Optimized sedimentation tank designs reduce energy consumption and chemical usage, thereby contributing to a more sustainable and eco-friendly treatment process.

In conclusion, CFD offers a more detailed and comprehensive approach to sedimentation tank design compared to traditional methods. It provides valuable insights, helps optimize design parameters, and reduces the risk of operational issues, ultimately leading to more efficient and cost-effective water and wastewater treatment processes.

Real-World Applications

Numerous case studies highlight the real-world impact of CFD modeling on sedimentation tank design. For instance, a case study is conducted at a rectangular sedimentation tank for water treatment of a steel rolling company using baffles. In this study, baffles of different sizes and numbers are placed at different locations of the tank to analyze their effects on the performance of the tank.

It is essential to research the ideal placement and size of the baffles in settling tanks because improper usage of baffles would produce tanks that perform worse than tanks without baffles. The baffle installations are made in two categories based on height (3m and 4.1m) to analyse their effects on the settling efficiency of the tank to determine the optimum size and number of the baffles.

In each category, the number of baffles increases one by one from the outlet side towards the inlet side at a distance of 5m. Simulation is first carried out in the original tank and validated with the experimental data of settling efficiency. After simulations of various cases of baffle arrangements, it is found that the baffle arrangement for 3m height is ineffective while that of 4.1m is effective.

It is also observed that for the baffles of 4.1m height, the efficiency increases with the number of baffles. The highest efficiency of 50.27% is obtained by installing 6 baffles of height 4.1m, which is much higher than that of the original tank (i.e., 39.92%). Therefore, CFD modeling can be used to improve the performance of the sedimentation tank.

Similarly, the performance of a water treatment plants located around Imphal city where population density is high and hence having space constraints for constructing large sedimentation tanks (in terms of its length). Therefore, it is suggested that for optimising the performance of these existing sedimentation tanks, CFD techniques can be effectively applied for fulfilling the ever-increasing demands of treated water.

Furthermore, CFD modeling has enabled engineers to tackle challenges posed by varying influent conditions. For instance, during heavy rain events, sedimentation tanks can become overwhelmed by increased flow rates and sediment loads. CFD simulations help in designing tanks that can adapt to changing conditions, ensuring consistent performance.

Future Prospects

As technology continues to advance, the integration of artificial intelligence and machine learning with CFD modeling promises even greater advances in sedimentation tank design. These technologies can optimize tank operations in real-time by adjusting influent flow rates, sediment removal mechanisms, and chemical dosing, leading to unprecedented levels of efficiency and environmental sustainability.

In conclusion, the combination of Computational Fluid Dynamics modeling with sedimentation tank design represents a significant leap forward in the field of water and wastewater treatment. By providing engineers with the tools to design more efficient, cost-effective, and environmentally friendly sedimentation tanks, CFD modeling is poised to play a crucial role in meeting the growing demands of clean water resources in an increasingly urbanized world.

As we look to the future, it is clear that the impact of CFD modeling on sedimentation tank design will continue to be a driving force in advancing our approach to water treatment and environmental stewardship.

Acknowledgements

This article is an outcome of the research project sponsored by the Department of Science and Technology - Science and Engineering Research Board (DST-SERB), New Delhi, Government of India under the scheme of Core Research Grant (Grant no. CRG/2020/001341).

This project is currently undergoing under the direction of the Principal Investigator, Dr. Thiyam Tamphasana Devi, Associate Professor, Department of Civil Engineering, National Institute of Technology Manipur, Langol, Imphal West, Manipur - 795004, India.