The essential guide to headworks construction in wastewater treatment plants

When planning and building a wastewater treatment facility, the headworks is one of the most important areas to get right. It is the first stop for incoming flow and sets the tone for everything downstream.

Yet, despite its importance, many of the most critical equipment and design decisions are not obvious until operations begin. Early planning and smart collaboration can prevent complications and future problems for the system, while also increasing efficiency.

Following are some key considerations for owners, designers and contractors to keep in mind during headworks construction, using lessons learned from major municipal wastewater facilities in various parts of the United States.

More than screens: Thinking through the first line of defense

Screens, whether coarse bar screens or fine screens, are the gatekeepers of a wastewater treatment plant. They protect downstream equipment by removing large solids and debris, but their performance is highly dependent on hydraulic conditions and installation decisions made well before startup.

At a large municipal facility in Arizona, fine screens were installed to remove solids from the flow. Initially, operators encountered issues related to the high velocity of water running through the screens and as a result, passing too much material through, which threatened to foul downstream equipment. The cause of the issue were water elevations in the IPS that were lower than the upstream water elevation at the screens. To resolve the issue, the team adjusted the influent pump station elevation, slowing water velocity and improving screen performance.

Key practices for evaluating screen selection:

• Plan elevations early: The hydraulic profile, especially the upstream and downstream elevations of pump stations, must be modeled with screening flow velocities in mind.
• Get the right screen type: Work closely with engineers to determine whether coarse or fine screens — or both — are needed and in what sequence. Eliminating coarse screens may simplify the process but can increase pressure on the fine screens, located downstream, affecting performance.
• Plan for serviceability: Design for future serviceability — how will screens be removed, replaced or maintained? Make that part of early design conversations.

Grit happens: Plan for removal, not just capture

Grit removal is often underestimated in importance, but poorly managed grit wreaks havoc on treatment plants. It damages pumps, clogs lines and shortens the life of key infrastructure. Specialized vortex grit systems are commonly used to capture and isolate fine solids like sand and silt, however, issues may arise with the process.

At a treatment plant in Arizona, a gravity-fed stacked tray vortex system replaced traditional grit tanks and mixers, dramatically increasing removal efficiency, capturing up to 95% of particles larger than 75 microns. However, initial design challenges affected flow balance across multiple trains. To address this, the project team made modifications to the plan, such as installing or removing equipment to equalize distribution and improve performance.

Fine-tuning and equipment evaluation of grit systems matters:

• Balance flow across trains: For that Arizona plant, one channel received significantly more grit than the others. The fix? Simple flow baffles installed in the influent channels helped equalize distribution across three concentrators.
• Valves matter: The team found that actuated valves on the teacup discharge were not necessary. When the valves remained closed, grit accumulated and cycled back into the process, undermining performance. Once left open, performance improved dramatically.
• Leave room for commissioning: Grit systems often require more fine-tuning than expected. Building extra time into the commissioning schedule — beyond what is required by specs — helps to ensure optimal settings for pumps and flow controls.

Startup is a process, not an event

Headworks commissioning is not just about flipping a switch. It is an ongoing, often repetitive process that requires alignment between the contractor, equipment vendors and operators.
On a wastewater treatment project in the Midwest, the grit washers were tested with the vendor’s participation during commissioning, but performance testing was not completed to the needs of the construction team. The vendor was called back to prove compliance with performance specs, specifically in achieving 95% grit removal at 250 gallons per minute (GPM) and 93% at 300 GPM.

Best practices for startup success:

• Schedule vendors early: Vendor site visits often require months of notice. By clarifying expectations with the vendor in advance and again when they arrive on-site, the process can be more effective. Determine how many trips are needed; what specific performance testing they are required to complete; and what happens if work is not complete.
• Coordinate performance testing: Confirm who is responsible for testing and what metrics are being measured. Vendors should be contractually obligated to prove removal rates, not just power up equipment.
• Include operator: Operators bring valuable insight and responsibility. Their input during startup helps ensure the equipment performs not just according to spec, but in a way that integrates with the plant’s daily operations.

Final details can make or break performance

Headworks construction is about more than just equipment. Supporting infrastructure must be carefully coordinated to ensure long-term reliability and to minimize maintenance. Often it is the people behind the projects that make or break it. Building a cohesive, collaborative team that includes the owner, engineer, general contractor, equipment vendors and operators is critical. Every project will encounter unique challenges that require a solutions-oriented team to resolve any issues, which will lead to other considerations listed below.

Go beyond the drawings

Site-specific knowledge from operators can highlight areas at risk that may not be obvious to designers. For example, at the Midwest facility, McCarthy engaged operators in an evaluation meeting where they identified the need for coating additional headworks areas in concrete during a collaborative session that showed where hydrogen sulfide (H2S), a byproduct of wastewater that is both dangerous and corrosive, would accumulate.

The project team was able to address this early enough in the project that construction delays and future potential issues that may have been caused were avoided and the long-term performance of the facility was adaquately maintained.

Set expectations early

Operations teams often inherit systems they did not help select. Establishing clear handoff and commissioning processes — like the 30-day continuous presence during startup at the Arizona plant — can help build trust and ownership.

Leak testing

Headworks structures often have complex joints and corners, requiring extra diligence during waterproofing and concrete placement. McCarthy’s project teams find that leak testing allows for addressing potential issues prior to commissioning.

Force main cutovers

It should be a standard practice to coordinate early with plant operations to plan force main cutovers, ensuring minimal disruption to any existing facility.

Building a foundation: Headworks lay the groundwork for plant performance

Whether it is screens, grit concentrators or washer compactors, the headworks is not just the beginning of wastewater treatment — it is the beginning of everything. By taking a holistic, operations-focused approach to planning, designing and constructing these critical systems, project teams can avoid costly rework, improve plant performance and empower operators to take ownership from day one. Success in headworks construction lies not just in selecting the right equipment, but in the timing, coordination and collaboration it takes to bring it all together.