WHY ABOVE GROUND
Mercer designs oil-water separators to live above ground on purpose. When equipment is visible and accessible, it gets inspected, maintained, and kept in balance. Operators can see what’s happening, clean the plate pack, verify flow conditions, and address issues before performance degrades—without excavation, confined space entry, or hidden failures.
Above-ground systems give engineers and operators full control over hydraulics and long-term separation performance. Every critical component is accessible. Nothing is buried. Nothing is assumed. Mercer’s above-ground units deliver the same engineered plate pack performance, hydraulic control, and provable oil removal as our in-ground systems—and they represent the majority of what we build. That’s why they are trusted across industrial plants, maintenance and fueling facilities, and vehicle operations where performance has to be proven, not promised.
No one else does. Before you buy anything, we evaluate your actual wastewater — either on-site or through controlled testing — using your worst-case influent conditions. We document removal performance, validate the math, and show you exactly what the system will do in the field. Only after the results are verified do we issue a written performance guarantee.
See WhyENGINEERED SYSTEMS BY FLOW RATE
From 5 GPM to 4,000+ GPM, each system is designed for long-term reliability under real-world operating conditions.
Our "low flow" series offers an industrial-duty design in a compact size. This separator series is ideally suited for smaller vehicle wash stations. These separators are also well suited for wastewater from small sumps, small stormwater treatment applications, groundwater pump and treat systems, and various other low-flow applications. Our "low flow" series incorporates the same features in our standard sized separators that have helped Mercer build its sterling reputation—but in a compact design.
view detailsOur low-flow separator series delivers industrial-duty performance in a compact design, incorporating the same proven features as Mercer’s standard separators that have built its strong reputation. These units are widely used in vehicle wash operations, automotive repair shops, dealerships, transportation agencies, and utility companies, where they serve as stand-alone treatment or as primary treatment ahead of larger systems, valued for reliability and ease of maintenance. Mercer’s low-flow separators have also been successfully applied across diverse industries, including scrap yards, chemical and fertilizer processing, boiler and bilge water treatment, hydraulic fluid leakage control, and food and beverage processing for grease, fat, and oil removal.
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Our 50–100 gpm Compliance Master™ separators step up from low-flow units with a true V-shaped coalescer and full-width Chimney-Zone™, efficiently processing solids out of the coalescer for cleaner effluent and longer maintenance intervals. Designed for demanding applications in the Food, Chemical, and Oil & Gas industries, these units deliver field performance that closely matches theoretical design by excelling at solids removal and extended run times. Proven over three decades across hundreds of industrial installations, they are especially cost-effective in “muckier” applications, from produced water piloting and chemical manufacturing to truck washing, food processing, and waste handling.
view detailsThis mid-range separator series is widely used in oil and gas, electric utilities, transportation, and heavy industrial operations where wastewater contains oil, elevated temperatures, and high solids loading. Proven applications include crude oil de-salting, heated #6 fuel oil and heat-exchanger systems, railcar and large bus wash facilities, military multi-bay vehicle washing, ballast water treatment at naval shipyards, and primary stormwater treatment. Mercer has also successfully applied these separators in specialized processes such as tall oil separation during sterol production and aluminum smelting component manufacturing, consistently delivering reliable effluent performance with significantly reduced maintenance.
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At higher flow rates, Mercer’s large separators with the Multi-Pack™ coalescer are widely deployed across the oil and gas and electric utility industries, where they are used for frac flowback, produced water, de-salting, and complex heated oil systems. Major energy producers and service companies such as Chevron, ExxonMobil, Schlumberger, Baker Hughes, EOG Resources, Con Edison, Duke Energy, NRG Energy, and the New York Power Authority rely on Mercer’s designs for consistent effluent compliance and reduced maintenance. Mercer systems are also specified by leading global engineering and consulting firms—including Arcadis, Bechtel, AECOM, and HDR—and are trusted by industrial manufacturers, transportation companies, and refiners such as DuPont, Dow, Alcoa, Coca-Cola, UPS, and Harley-Davidson to replace underperforming separator technologies.
view detailsWe’ve designed solutions of this size for large rail maintenance facilities, centralized wastewater trucking terminals, and high-volume mining operations. This flow family incorporates an internal split-flow configuration that divides wastewater into two parallel treatment trains. This design maximizes use of the separator tank while reducing velocity through the coalescers, allowing Mercer to maintain strict performance criteria at very high flow rates. The split-flow approach also provides operational flexibility, enabling one half of the system to be taken offline for maintenance while the other half continues to operate.
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High-solids, high-oil wastewater at large flow rates is especially challenging, yet Mercer has successfully treated streams from coal conveyor belt washdown, coker de-sludging, tank bottom cleaning, and oil field services. Mercer’s high flow above-ground separators deliver high efficiency, low maintenance, and field-customized solutions using the Compliance Master™ design with the adjustable Multi-Pack™ coalescer. Unlike cheap corrugated “me-too” coalescers that plug, foul, and require frequent replacement, Mercer’s Multi-Pack™ is easily cleaned, resists solids loading, and is typically used for the life of the separator.
view detailsIn upstream wellhead operations or downstream crude and petrochemical refining, Mercer has deployed modular large-flow units to handle produced waters with challenging solids from flowback. For our largest pre-fabricated separators, we use a “double-split flow” design that maximizes coalescer and tank efficiency for optimal treatment performance. These units are divided into four separate chambers with a shared clear well, ensuring effective separation and flexibility in operation.
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Mercer International offers competitively priced plastic oil/water separators for flows up to 100 gpm, constructed from corrosion-resistant polyethylene and buryable up to 30" below grade. These separators use a removable, cleanable “coalescer ball” system, where polypropylene balls attract and capture oil from the wastewater. Ideal for gas stations, vehicle maintenance facilities, auto dealerships, airplane hangars, and wash racks, this solution is also favored by several statewide Departments of Transportation for cost-effective oil removal.
view detailsBecause performance claims mean nothing without proof. We validate separation performance against your real influent characteristics — oil type, solids loading, temperature, flow variation. Once the data confirms compliance targets, we issue a formal written guarantee tied to documented performance.
See the ProofSelection starts with flow rate, solids loading, wastewater source, and available pad space. Our engineering team provides free sizing based on your actual operating conditions.
Yes. Mercer uses the same engineered plate pack, baffling, and hydraulic controls across both configurations to ensure guaranteed removal performance.
Yes. Above-ground units offer full visual access, making solids inspection and cleaning significantly easier than in-ground systems.
Absolutely. Mercer routinely configures custom tank dimensions, materials, access platforms, and integration with pumps or pre-treatment.
