Above-Ground Oil-Water Separators
OPERATING TIER
Mercer separators approaching the 4,000 GPM class are engineered for operating environments where oil-water separation is a core process tied directly to production continuity, environmental compliance, and downstream asset protection.
Systems at this scale are commonly applied in produced water treatment trains, frac flowback and early-life production, and as direct replacements for legacy API concrete tanks in refining, petrochemical, and energy infrastructure. These environments impose sustained high flows, elevated oil loading, solids variability, and changing water chemistry that traditional separation equipment is not designed to manage reliably over time.
Mercer systems in this class are built around deliberate hydraulic control, managed velocities, and serviceable internals so separation performance remains stable as operating conditions evolve.
Built To Scale
There is no single “4,000 GPM separator.”
Systems at this scale are engineered using Mercer’s large-system design philosophy, which may include multiple vessels or parallel process chambers configured to manage extreme throughput while maintaining controlled internal velocities.
Typical system architecture may include:
Please Note: Exact dimensions and configurations vary by application.
FIELD-PROVEN SYSTEMS
At this capacity, scale is visible and experience is not optional.
The installations shown represent Mercer systems operating at or near the 4,000 GPM class, deployed in environments where continuous duty, access, and serviceability determine long-term performance.
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
TRUSTED BY INDUSTRY LEADERS
A small sampling of companies with Mercer separators operating at or near the 4,000 GPM class through engineered system configurations.
ENGINEERED TO SOLVE
Flow rate is a label. Operating scale is the reality.
CORE TECHNOLOGY
A tank provides residence time.
Separation performance is determined by what happens inside the coalescer.
Mercer’s Multi-Pack™ coalescer is not generic media. It is a purpose-engineered separation system built around five core design elements that control oil rise, solids shedding, hydraulic stability, and real-world maintainability—especially in applications where small systems are easy to ignore until they fail.
The Multi-Pack™ uses flat, steep-angled plates rather than corrugated or honeycomb media. Flat plates support predictable droplet capture while allowing solids to shed cleanly instead of lodging in pockets that quietly choke performance over time.
Learn MorePlate spacing can be adjusted beyond or below standard spacing to tune separation performance to actual conditions—oil type, temperature and viscosity effects, solids behavior, and desired maintenance intervals.
Learn MorePlates are arranged in a herringbone configuration that organizes internal flow paths and segregates areas where oils rise from areas where solids settle. This stabilizes hydraulics when flows cycle on and off, which is common in low-GPM applications.
Learn MoreAs oil coalesces and solids shed from the plates, they enter dedicated Chimney Zones™ designed for separation—not turbulence. These quiescent chambers allow oils to rise and solids to settle without re-entrainment, even during solids spikes.
Learn MoreThe Multi-Pack™ is fully removable as a single assembly. Operators can remove the pack, visually inspect it, clean it, and return it to service without dismantling internals or replacing disposable media.
There has never been a Multi-Pack™ removed from a tank where operators could not see through to the opposite side before cleaning begins. Surface films may be present. Clogged pockets are not.
Learn MoreConventional corrugated plastic or tube-style media foul rapidly under sustained high solids loading. Once fouled, performance degrades and cleaning becomes impractical without full media replacement.
Large systems without deliberate access design force extended shutdowns, confined-space entry, or wholesale internal replacement to restore performance.
Systems specified solely by flow rate—without accounting for solids behavior, oil type, viscosity, temperature, redundancy, and maintenance constraints—routinely underperform at this scale.
All at no cost to you.
We walk your site, capture real influent data if needed, engineer a custom separator from your worst-case scenario, and validate performance before fabrication. Only after the data confirms it do we issue a written guarantee. That’s how risk is removed.
PROVEN LONGEVITY
Built to Stay in Service
Many of the systems shown below were installed years ago and remain in continuous operation today. These are not retired assets—they are active separators still managing oil and solids under real operating conditions.Longevity at this scale reflects internal designs that can be inspected, cleaned, and maintained over time rather than replaced.
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
Above Ground
4000 GPM
INDUSTRY APPLICATIONS
Above-ground systems approaching this scale are deployed where wastewater treatment is continuous—not intermittent—and where solids loading, oil characteristics, and access determine long-term performance more than nameplate flow.
Continuous oil-bearing wastewater with sustained solids loading from production, washdown, and process support activities.
Learn more
Produced water and oil-handling environments where oil type, temperature, and solids vary across operating cycles.
Learn more
Power plants and major utility facilities require separators capable of continuous operation with minimal downtime and straightforward maintenance access.
Large terminals, fueling operations, and hubs generating high-volume wastewater with operational uptime requirements.
At up to 4,000 GPM, oil-water separation decisions shape how a site functions — not just how it treats water. Mercer works with owners and project teams to define treatment architecture that aligns with long-term operational reality, future expansion, and institutional accountability.Engage Mercer early in master planning and system definition to ensure today’s decisions remain workable for the life of the facility.
Talk to Mercer about your application.At flows approaching 4,000 GPM, oil-water separation stops being an isolated treatment function and becomes a governing constraint on site layout, drainage strategy, and operational sequencing. Decisions made here influence how the entire facility manages water for decades.
Single-path solutions at this scale concentrate risk. Mercer approaches large-capacity systems with modular logic so treatment capacity can be distributed, isolated, or expanded without placing the entire operation at risk during maintenance, modification, or future upgrades.
Facilities operating at this scale will outlive original project teams, operators, and even ownership structures. Mercer designs systems that remain understandable, controllable, and defensible long after institutional knowledge has changed.
Tell us about your project and we’ll provide the right configuration drawings for your site and flow conditions.
Head to the design center
Provide your project details and we’ll share the full technical specs relevant to your operating conditions.
Head to the design center