Floating oil in a wastewater pit is usually a surface-separation problem first
Hydraulic oil, lubricants, fuel, grease and process oils can enter industrial wastewater and accumulate as a separate floating phase in pits, sumps, basins and process-water tanks.
When the oil has already separated and risen to the surface, continuously removing that concentrated oil layer can often be more efficient than repeatedly pumping large volumes of oily water away for external treatment or disposal.
The correct solution depends on how the oil behaves, how much is present, the geometry of the pit or sump, changes in liquid level, floating debris, temperature and what happens to the water after the oil is removed.
How does oil enter industrial wastewater?
Oil in industrial wastewater does not always originate from one clearly identifiable process stream.
In many plants, pits and sumps act as collection points for water from several operations. Hydraulic leaks, machine lubrication, wash water, maintenance activities, process drainage and equipment cleaning can all introduce oil into the same system.
First determine whether the oil is actually free-floating
Surface skimming works on oil that has separated from the water and is available at the surface.
Free-floating oil
A visible oil layer, film or accumulation is present on the water surface and can physically contact a collector tube or other surface-skimming device.
Dispersed or emulsified oil
Small oil droplets remain distributed through the water instead of forming a separate recoverable surface layer. Additional separation or wastewater-treatment technology may be required.
Important: an oil skimmer is primarily a free-oil recovery device. Removing surface oil can be an important treatment step, but it should not automatically be considered complete wastewater treatment.
Why remove the oil while it is concentrated at the surface?
Once oil has separated naturally and risen to the surface, the contaminant is present in a much more concentrated form than when it is mixed through the total water volume.
Continuously removing that floating layer can reduce the amount of oil carried into downstream treatment stages and can reduce reliance on periodic manual removal.
How does a tube oil skimmer work in a wastewater pit?
A tube-type skimmer uses a continuous closed-loop collector tube that floats on the wastewater surface.
Free-floating oil adheres to the outside of the tube as it moves through the contaminated area. The tube then returns to the skimmer, where scraper components remove the recovered oil.
The cleaned tube returns to the water surface and continuously repeats the process.
Why pits and sumps benefit from a free-floating collector tube
Wastewater collection areas rarely operate under perfectly constant conditions.
Liquid levels can rise and fall as processes discharge, pumps switch on or off, wash cycles begin and storage volumes change.
Floating debris can also be present in outdoor pits, scale pits and general industrial wastewater systems.
The collector follows the surface
Because the collector tube floats, it can rise and fall with the working water level instead of requiring one fixed skimming height.
The tube is not on a rigid path
The flexible collector can move around changing surface conditions and floating debris rather than relying on one fixed belt or pickup position.
Model 6V: the industrial workhorse for pits, sumps and wastewater
For many industrial wastewater applications, the Model 6V Brill® is the primary tube-skimmer starting point.
Heavy-duty vertical tube oil skimmer
The Model 6V is designed for continuous removal of free-floating petroleum oils, animal and vegetable oils, fats, greases and oily waste from industrial water and wastewater.
When does a Model 7V make more sense than a Model 6V?
The Model 6V is suitable for a wide range of industrial oil-removal duties, but some pits and tanks have higher or more variable oil loads.
In those applications, the Model 7V adds higher recovery capacity, a larger collector tube and complete variable-speed control.
Model 6V
- 4–100 US gal/h (15–379 L/h)
- 3/4 in (19.1 mm) collector tube
- Vertical tube operation
- Standard and High Speed configurations
- Strong starting point for industrial wastewater, pits and sumps
Model 7V
- 10–200 US gal/h (38–757 L/h)
- 1 in (25.4 mm) collector tube
- Complete variable-speed control
- Greater collector surface area
- Useful where oil load or viscosity changes significantly during operation
Selection principle: the Model 7V is not automatically the better choice simply because it has a higher capacity. The actual oil load, oil characteristics, pit geometry and required operating range determine whether the added capacity and variable-speed control are useful.
What information is needed to size an oil skimmer for a pit or sump?
A correct skimmer selection starts with the physical application.
| Parameter | Why it matters |
|---|---|
| Oil type | Petroleum oil, hydraulic oil, fuel, vegetable oil, fats and grease can behave differently on the surface and on the collector tube. |
| Liquid temperature | Temperature changes oil viscosity and can be especially important for heavy oils, fats and materials that become less fluid as they cool. |
| Pit length and width | Surface dimensions help determine collector-tube travel, equipment placement and whether a standard mounting arrangement is practical. |
| Liquid depth | Defines the basic geometry of the pit or sump and helps evaluate operating conditions. |
| Liquid-level variation | The system needs to remain effective across the actual minimum and maximum operating level. |
| Surface to mounting point | The available mounting height influences model, collector-tube length and system arrangement. |
| Oil quantity | Estimated litres or US gallons per hour, day or batch help determine the required oil-recovery capacity. |
| Floating debris | Leaves, scale, solids and other floating material can affect the choice of recovery technology and mounting. |
| Process flow | Continuous inflow, batch dumping or intermittent operation can create very different surface conditions and oil loads. |
| Electrical supply | Available site power must be considered when the final motor configuration is selected. |
The pit itself can be as important as the amount of oil
Two wastewater pits containing the same quantity of oil may require different equipment if their geometry and access conditions are different.
A small open sump with easy access is fundamentally different from a large scale pit, an enclosed tank, an outdoor pond or a deep wastewater basin with guard rails around the perimeter.
Mounting arrangements can therefore become part of the oil-removal system rather than being treated as an afterthought.
Useful application information: photographs showing the full pit, surrounding structure, guard rails, walls and possible mounting positions are often extremely useful during equipment selection.
Oil skimmer or oil-water separator?
Surface skimming and oil-water separation are related, but they are not identical processes.
Oil skimmer
Continuously removes a separate oil layer directly from the water surface.
This can be sufficient where the primary objective is controlling free-floating oil in the pit or sump.
Oil-water separator
Receives an oily-water stream and provides a dedicated separation stage before the treated water moves onward.
In some applications, active oil skimming can also form part of the separator system.
Which approach is appropriate depends on whether the problem is primarily accumulated surface oil or whether the complete oily-water stream needs a dedicated separation process.
Can the oil be evaluated before final equipment selection?
Yes. When the behaviour of an oil, grease or process fluid is uncertain, testing the collector material with the actual liquid can provide useful application information.
Tube Test Kit & Proof of Concept
For suitable applications, a Tube Test Kit can be used to evaluate collector-tube pickup using the actual oil and process liquid.
For selected larger or more difficult applications, Filtra International can also evaluate whether a temporary proof-of-concept arrangement is appropriate, subject to equipment suitability and availability.
Documented Oil Skimmers application experience
Floating oil in pits and sumps occurs across many industries. The following application examples illustrate how the problem and equipment configuration can differ even when all of the systems contain oily wastewater.
Oily wastewater in machinery pits
Scale pits and cooling water
Outdoor wastewater retention ponds
Difficult oil in a wastewater pit
Common engineering lesson: “oil in a pit” is not a complete equipment specification. The successful solution depends on the oil, water, pit geometry, operating pattern, debris, mounting position and what must happen to the recovered oil and remaining water.
Frequently asked questions
What type of oil can be skimmed from industrial wastewater?
Tube-type oil skimmers can recover suitable petroleum oils, hydraulic oils, lubricants, fuels, animal and vegetable oils, fats, greases and oily waste when the contaminant separates and remains available at the liquid surface.
Can an oil skimmer work when the wastewater level changes?
Yes. A free-floating collector tube can move with changes in the liquid surface rather than relying on one exact fixed water level.
The complete collector-tube length and mounting arrangement still need to match the operating range of the application.
Can a tube oil skimmer operate with floating debris?
The flexible collector tube can move over and around floating material instead of travelling along one rigid surface path. Applications containing large quantities of solids or unusual debris should still be reviewed individually.
Which oil skimmer is suitable for an industrial wastewater pit?
The Model 6V is a common starting point for industrial wastewater pits, sumps and tanks. It provides a recovery range of 4–100 US gal/h (15–379 L/h) and uses a 3/4 in (19.1 mm) collector tube.
Higher or more variable oil loads may justify evaluation of the Model 7V.
When should the Model 7V be considered?
The Model 7V should be evaluated when higher recovery capacity or variable-speed control is useful. It has a 1 in (25.4 mm) collector tube and a recovery range of 10–200 US gal/h (38–757 L/h).
Can an oil skimmer remove emulsified oil?
Surface oil skimmers are primarily intended for free-floating oil. Stable oil-in-water emulsions may require another separation or wastewater-treatment process.
Do I need an oil skimmer or an oil-water separator?
An oil skimmer is suitable when the main objective is continuously removing a free-floating oil layer.
If the complete oily-water stream requires a dedicated separation stage, an oil-water separator or complete engineered treatment system may be more appropriate.
What information should I send for an application review?
Useful information includes oil type, liquid temperature, pit length and width, liquid depth, liquid-level variation, distance from the surface to the possible mounting point, approximate oil quantity, process flow, floating debris and available electrical supply.
Need to remove floating oil from an industrial pit or sump?
Send us the oil type, wastewater temperature, pit dimensions, normal and minimum liquid levels, possible mounting position, approximate oil quantity and any photographs or drawings available.
Filtra International can review whether tube skimming is appropriate and help determine the required model, collector-tube configuration and mounting arrangement.