LEADING THE FUTURE OF WATER & WASTEWATER TREATMENT SOLUTIONS

Modular Versus Concentric Circle Design for Wastewater Treatment

Close-Up of Wastewater Treatment Plant
The choice between modular and concentric circle designs for wastewater treatment depends on factors including the specific needs of the community, available space, budget constraints, and future scalability requirements.

Space constraints, treatment goals, and scalability needs are considerations

When planning a wastewater treatment plant, choosing the type of design is a crucial consideration for efficiency, site constraints, scalability, operations preferences, and cost-effectiveness. Two popular designs, modular and concentric circle (often called a bulls-eye design), offer unique benefits and cater to different needs. Whether you’re looking for flexibility in expansion or optimizing space, understanding the strengths and challenges of each design can help you make an informed decision. Explore our detailed comparison to discover which approach best suits your community’s requirements and treatment goals.
 

Design and Layout

Modular design, often used in decentralized treatment, involves constructing wastewater treatment facilities in separate units or modules. Each module has a treatment function, and depending on the type of treatment offered, it can operate independently or as part of an integrated system. Since they can be prefabricated and installed on-site, modules can be tailored to fit site constraints and configurations.  Package plants of modular design require more space than concentric circle plants, though construction costs can be optimized because of the ability to add modular tanks as a community grows.
 

Modular Wastewater Treatment Plant

Modular design offers flexible, scalable wastewater treatment with prefabricated units tailored to fit site constraints and evolving needs.

 
The concentric circle design (often called a bulls-eye design) is a traditional wastewater treatment plant layout that features basins with a central core (the clarifier) and surrounding treatment stages arranged in an outer ring. This arrangement maximizes space efficiency and optimizes the treatment process. The treatment units in the outer ring handle different stages, typically starting with primary treatment on the outside, moving to the clarifier in the center, and ending with tertiary treatment in the outer core of the tank. As each of the stages of treatment takes place within the concentric circular system, the common wall construction — which features taller tank walls compared to modular units — reduces the footprint of the plant, making it suitable for sites where space is limited. The compact layout and reduced need for piping can lower construction costs, making it a more cost-efficient option, particularly for larger plants.
 

Flexibility and Scalability

Since modular plants are prefabricated and shipped to the site, they provide greater flexibility to adapt to changing needs than concentric circle plants, which typically require extensive civil engineering work and are constructed on-site. With modular plants, capacity can be increased by adding more modules as demand increases or treatment requirements change. Modular plants can also facilitate a phased installation that aligns with construction stages in a development such as a master-planned community, allowing for expansion according to project growth as well as better financial planning and budgeting. One project in Fort Bend County, Texas, used modular units to reduce initial costs and expand treatment capacity alongside community growth. The developer started with a single 200,000 GPD unit, gradually increasing to 600,000 GPD as demand rose. Concentric circle designs don’t have the same flexibility as there is only a single tank unit with a common wall.
 

Performance and Efficiency

 

Concentric Circle Wastewater Treatment Plant

Concentric circle design maximizes space efficiency and optimizes the treatment process with a central core and surrounding treatment stages.

 
Concentric circle plants are robust, tried-and-tested systems that rely on basic biological treatment. They tend to be effective in treating conventional pollutants, but they can limit the ability to add different treatment units in the future. With a modular design, each module can be optimized for a different treatment stage. Modular plants offer an easier way to incorporate advanced treatment processes, if needed in the future, in treating a wide range of pollutants commonly found in municipal wastewater treatment systems, producing high-quality effluent that meets stringent regulatory requirements.
 

Maintenance and Operation

Because modular plants consist of clearly defined and separate treatment units, they can be easier to operate and maintain than concentric circle plants, since troubleshooting and maintenance can be performed on individual modules without shutting down the entire system. They also add a layer of redundancy because if one module fails, others can continue to operate, enhancing reliability and reducing the risk of total system failure. Modular systems also allow for cost-effective and efficient upgrades since maintenance and improvements can be implemented in individual modules without overhauling the entire plant or taking the entire plant offline.
 
Concentric circle plants streamline operations by simplifying the flow of wastewater through the treatment stages. This makes it easier to manage and monitor the treatment process from a central control point. However, they can be more challenging to maintain and operate than modular plants for several reasons. Due to the interdependent nature of the treatment stages, it can be difficult to isolate sections for maintenance without affecting overall operations. Furthermore, any maintenance, repairs, or failure in one treatment unit can disrupt the entire treatment process, posing a higher risk of system failure.
 

Deciding on the Best Approach for Wastewater Treatment Design

Choosing between modular and concentric circle designs for wastewater treatment involves weighing their unique advantages and challenges. Modular designs excel in flexibility, scalability, and redundancy, making them ideal for projects anticipating growth and needing adaptable solutions. On the other hand, concentric circle designs maximize space efficiency and can be more cost-effective for larger plants, especially in areas with limited space. Your choice should reflect a comprehensive evaluation of your community’s needs, available space, budget constraints, and long-term objectives. Ready to find the perfect fit for your wastewater treatment project? Contact AUC Group today to explore our time-tested wastewater treatment solutions and cutting-edge technologies designed to meet your specific requirements.
 

Alok Shah, P.E. (TX)

Author Alok Shah, P.E. (TX)

Alok is a Water/Wastewater Engineer with AUC Group working on wastewater treatment plants for clients across Texas and the surrounding region. He has experience in the design of wastewater collection systems, lift station, treatment plants, and worked previously on condition assessment projects, and master planning projects. He has previously worked at Arcadis and Jacobs Engineering. Alok graduated with a master’s degree in petroleum engineering from Louisiana State University and a bachelor’s degree in environmental engineering from the University of Georgia.

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