Flow control innovations in wastewater treatment

Wastewater treatment facilities face increasingly complex challenges in managing diverse chemical processes, ensuring environmental compliance and optimising operational efficiency. As the industry evolves to meet stricter regulations and sustainability goals, the demand for sophisticated flow control equipment has grown. This article explores recent developments in flow control technology for wastewater treatment, including contributions from companies such as Valmet. 

Wastewater treatment involves multiple stages: preliminary treatment, primary sedimentation, secondary biological treatment, and tertiary filtration and disinfection. Throughout these stages, various chemicals are used, including pH neutralizers, anti-foaming agents, coagulants, flocculants and disinfectants. Each chemical presents unique challenges in terms of pH levels, viscosity and material compatibility. Controlled chemical dosing is crucial for efficient treatment. Optimal dosing improves performance, reduces costs and minimises environmental impact. Key requirements include adjustable dosing based on real-time monitoring, accuracy, chemical compatibility and reliability in harsh environments.

Precise chemical dosing

Accurate chemical dosing is crucial in wastewater treatment. Excessive dosing can lead to unnecessary chemical costs and potential environmental issues, while insufficient dosing may result in ineffective treatment. Key factors in optimal dosing include:

1. Adjustability based on influent quality and flow rate
2. High accuracy across various flow rates
3. Chemical compatibility to prevent equipment degradation
4. Reliability in corrosive environments
   Advanced flow control solutions must address these factors to ensure efficient, cost-effective and environmentally sound wastewater treatment.

Metering pump advancements

Metering pumps play a vital role in precise chemical dosing in wastewater treatment. Recent advancements in this technology, as exemplified by pumps such as those in Valmet’s Flowrox™ FXM series, include:

• Multiple control options: Local or remote operation via various signal types allows for integration with plant control systems.
• Positive displacement design: This ensures consistent output volume regardless of discharge pressure, which is critical for maintaining treatment efficacy.
• Self-cleaning mechanisms: Features such as compression points that act as non-clogging valves can reduce maintenance requirements and ensure reliable operation.
• Multi-chemical compatibility: The ability to handle a range of media makes these pumps suitable for various treatment stages.

Modern metering pump designs often incorporate additional features to enhance operational safety and efficiency, such as:

• Only the tube and tube fittings are in contact with the process medium 
• Integrated leak detection systems
• Energy-efficient motors with variable speed drives

These features can improve dosing accuracy while also contributing to reduced downtime and lower operational costs.

Peristaltic pump technology

Peristaltic pumps represent an alternative approach to fluid handling in wastewater treatment. Their operating principle is straightforward:

1. A flexible hose is fitted inside a circular pump casing.
2. Rollers attached to a rotor compress the hose.
3. As the rotor turns, the compressed part of the hose forces fluid through.
4. The hose’s restitution creates a vacuum, drawing in more fluid.

This design offers several advantages in wastewater applications:

• Reduced contamination risk: The hose is the (main) contact element with fluid.
• Versatility: Suitable for handling abrasive slurries, corrosive chemicals and fluids with high solid content.
• Dry running capability: The pump can run dry without sustaining damage.
• Gentle fluid handling: Suitable for shear-sensitive fluids and beneficial for media containing live microorganisms used in biological treatment processes.

Some peristaltic pumps, such as those in Valmet’s Flowrox LPP series, feature a single roller design that may offer additional benefits:

• Improved process performance and efficiency: Capability to pump 24/7. No overheating at high continuous flow rates due to the roller design that minimises friction and heat.
• Reduced friction: This can minimise wear on the hose, potentially extending its lifespan.
• Improved energy efficiency: Lower friction may translate to reduced power consumption.
• Reduced pulsation: Smoother flow characteristics can improve dosing accuracy and reduce pipe stress.

These pumps have proven particularly effective in sludge transfer applications, where their ability to handle high-viscosity fluids with suspended solids is valuable.

Flowrox LPP-D peristaltic pumps are ideal for dosing and flow control. They provide accurate dosing in all process conditions as the pump discharge flow does not depend on the pipeline pressure.

Pinch valve innovations

Pinch valves have emerged as an alternative solution for sludge control and other challenging wastewater applications. The pinch valve’s operating principle is straightforward:

1. A flexible, elastomeric sleeve is housed within a robust designed body.
2. When open, the sleeve provides an unobstructed flow path.
3. During closing, two pinch bars squeeze the valve sleeve shut on the centre line with various types (e.g. mechanical, pneumatic or hydraulic) of actuators.

This design offers several advantages in wastewater treatment:

• Unobstructed flow: This minimises pressure drop and reduces the risk of blockages with suspended solids.
• Effective closure: Achieves reliable shut-off even with abrasive or scaling media present.
• Wear resistance: Suitable for handling corrosive chemicals and abrasive slurries.
• Simplified maintenance: The sleeve is typically the primary wear component, which can simplify maintenance procedures.

Some pinch valve designs, such as those offered by Valmet, incorporate additional features:

• Sleeve materials optimised for specific chemical compatibilities
• Positioners for flow control applications
• Diagnostic capabilities for maintenance planning

These valves have demonstrated long service lives in demanding applications, with some installations operating for extended periods without sleeve replacement.

In the wastewater industry there are over 18,000 Flowrox valves and pumps installed in over hundreds of municipal/industrial wastewater treatment plants across the globe. Each valve is designed to reduce clogging, ensure purity and increase reliability.

Case Studies

Camden Wastewater Treatment Plant, USA

Challenge: The plant needed to transition from gas chlorine to liquid sodium hypochlorite for disinfection and use sodium bisulfite for dechlorination, requiring a reliable dosing system with a small footprint.

Solution: Valmet supplied wall-mounted packaged Flowrox metering pump systems. Key features included:

• Space-efficient design
• Integrated containment for enhanced safety
• Capability to handle off-gassing in sodium hypochlorite service

Outcome: The installation addressed the plant’s chemical dosing needs whilst improving safety and reliability. The system’s effectiveness led to its specification for a second site.

Czajka Wastewater Treatment Plant, Warsaw, Poland

Challenge: This large-scale plant required precise sludge flow control across its treatment process

Solution: Twenty electrically actuated Flowrox pinch valves were installed for sludge flow control. The solution offered:

• Gentle handling of bacteria-rich sludge, important for maintaining biological treatment efficacy
• Wide flow control range, adapting to varying process conditions
• Extended maintenance intervals, reducing operational disruptions

Outcome: The valves have operated without sleeve changes for over a decade, demonstrating durability in a demanding application. This longevity has reduced maintenance costs and improved overall plant reliability.

Future developments in wastewater treatment

Several trends are shaping the future of flow control technology in wastewater treatment:

1. Increased use of sensors and connectivity: This is enabling real-time monitoring and informed maintenance planning.
2. Focus on energy efficiency: Pump and valve designs are being optimised to reduce power consumption without compromising performance.
3. Emphasis on chemical reduction: Control systems are being developed to optimise dosing and minimise chemical usage whilst maintaining treatment efficacy.
4. Resource recovery: Flow control solutions are being adapted to support the extraction of valuable resources from wastewater streams.

Industry suppliers, including Valmet, are working to develop solutions that address current challenges and anticipate future needs.

Conclusion

The wastewater treatment industry continues to face challenges in managing complex processes, ensuring environmental compliance and optimising operational efficiency. Advanced flow control solutions, such as those offered by various manufacturers including Valmet, play a crucial role in addressing these challenges. By offering improved accuracy, reliability and efficiency, these technologies enable wastewater treatment plants to meet regulatory requirements while minimising costs and environmental impact. 

Text by Melonie Dodaro. Originally published in Valve World November 2024 issue. For more information, visit valve-world.net