How Oil Water Separators Work

Oily Water - Oil Water Separators

Because of the highly damaging effects of oil hydrocarbon pollution on waterways and the environment in general, businesses are required by law to ensure their wastewater and stormwater runoff are pre-treated for oil pollution before entering the sewer system. The first line of oil wastewater treatment is the Oil/Water Separator. Find out how oil/water separators work, what they offer, and how enhanced oil/water separators differ from the rest.

How Do Oil Water Separators Work?

  1. Wastewater is stored in a holding tank (usually underground).
  2. A pump draws the wastewater from the holding tank and delivers it to the separator in a non-emulsified state.
  3. Wastewater enters the Separator through the inlet and then passes through the Vertical Tube Coalescing (VTC) pack.
  4. As oil is lighter than water, the gravity forces oil droplets to the top of the separator.
  5. The water continues to flow under a baffle and then through 100-micron filters.
  6. After filtering, the water exits the separator and enters the sewer system.

Despite being useful in keeping crucial human activities running smoothly, unfortunately, oils are notorious environmental pollutants. If not priorly treated and separated, the hydrocarbons from both industrial and everyday use can easily enter waterways through stormwater runoff and sewer systems, creating havoc as they accumulate.

The fact that oil and water do not mix creates a specific type of pollution that disperses across the water’s surface. This way, the hydrocarbon pollutants can travel long distances and have a far and wide negative effect on the aquatic systems, as well as on the environment surrounding them.

The chemical and physical properties of many oil products make this type of pollution a grave long-term danger for humans and wildlife. The shorelines and the inhabitant seabirds tainted with the black crude oil have become iconic anthropogenic pollution images. However, smaller amounts of oil from everyday activities can accumulate and create substantial environmental and health hazards.

Therefore, all developed countries’ local environmental laws strictly require treatment of oily wastewater and stormwater runoff for all businesses that produce it. The treatment usually starts with the device known as the oil-water separator.

What Is An Oil Water Separator?

Oil Water Separator

An oil/water separator is a wastewater treatment device designed to separate oil and water in the circumstances when the two components are mixed.

Oil/water separators extract diesel, gasoline, crude oil, vegetable oil, and the associated particulates, along with the suspended solids heavier than water.

The main goal of oil-water separators is to remove the oils and other contaminating particles prior to releasing the treated water into the sewer system.

As oils represent a significant group of waterway pollutants with a high impact on the environment, oil-water separators are an essential part of modern business wastewater treatment. They are usually legal minimum pre-treatment systems required by local Councils and safety authorities.

As typical oil-water separators, Fox FX Series Oil/Water and Solid Separators are also designed for removing the floating hydrocarbons in the forms of oil, diesel, and hydraulic fluid, as well as the suspended solids from the wastewater created by your business activities. To achieve this, they utilize a widely-accepted Vertical Tube Coalescing (VTC) technology.

How Do Oil Water Separators Work?


Regardless of the exact model, there are several common steps in filtering wastewater via Fox oil-water separators:

  • The wastewater is previously stored in a holding tank (usually underground).
  • A Fox Diaphragm Pump draws the wastewater from the holding tank and delivers it to the separator in a non-emulsified state.
  • Wastewater enters the Separator through the inlet and then passes through the Vertical Tube Coalescing (VTC) pack.
  • Here is where gravity kicks in as oil is lighter than water, the gravity forces oil droplets to the top of the separator.
  • The water continues to flow under a baffle and then through 100-micron filters.
  • After filtering, the water exits the separator and enters the sewer system.

What is Gravity Separation?

The concept that the gravity separator machines are based on is deeply rooted in fundamental physics. The settling of the solid particles in a liquid medium is governed by the Stokes’ Law, described by the English mathematician George Stokes in 1845.


Relevant to the oil-water separators, the same principle also governs the rising of insoluble lighter liquid droplets in other, heavier liquids.

The law describes the relationship between six main values:

  • The viscosity of medium
  • Fall, settling, or terminal velocity
  • Acceleration of gravity
  • The density of particle
  • The density of the medium
  • Particle diameter

As we can see, gravity is the main force in any process driven by the Stokes’ Law.

Like with other basic physics laws, the real-life conditions are much more complicated than the ideal model. Many additional calculations are applied to capture and predict all the necessary parameters relevant to the separation process in the field. That allows room for enhancement.

What are Enhanced Gravity Separators?

Fox Oil/Water Separators are classified as enhanced gravity separators.

The enhanced gravity separator machines originated from the mineral extraction industry, where extracting particles from a liquid flow is an essential part of ore processing and the mineral extraction.

Like the classic gravity separators, enhanced gravity separators rely on gravity to perform, but with one essential advancement. They utilize the centrifugal forces to enhance the separation of fine particles. This way, the enhanced gravity separators can capture fine and ultra-fine particles that are too challenging to tackle by the common water-based gravity separators.

Fox Enhanced Gravity Oil Water Separators effectively remove fine droplets of non-emulsified oils and fine suspended solids, reducing the effluent oil content to less than 30pmm or lower in controlled conditions.

Fox Oil Water Separators Properties and Advantages

  • Fox Oil Water Separators are made from high-quality stainless steel 304 Grade Stainless Steel for freshwater and 316 Grade Stainless Steel for marine applications and therefore are highly durable.
  • All Fox Separators come on a mounting frame with individually adjustable legs, enabling leveling on almost any surface.
  • Fox Oil Water Separators come complete with a pump, low voltage controllers, and float switches.
  • Fox Oil Water Separators are created with the system and local authorities’ safety requirements in mind.
  • All Fox pump controllers have an RCD safety switch for optimum protection from fallouts.
  • There are various options for the low voltage controllers to fulfill Local Council Trade Waste requirements, including high-level alarms and hour run meters.
  • With flow rates ranging from 1000 l/ph to 200,000 l/ph, Fox Oil Water Separators can cover any business requirements, with big or small wastewater output.
  • There is a 5-year warranty on Fox Oil Water Separators.
  • Fox Oil Water Separators are proudly made in Australia.

Oil Water Separator Applications

As said before, oil-water separators are applicable in all processes where wastewater contains oils. That can include wastewater and stormwater runoff. The applications are much more common than one may initially think.

Some of the businesses where oil-water separators can and should be applied are:

  • Automotive workshops
  • Car dealerships
  • Fuel stations
  • Mechanical workshops
  • Panel beaters
  • Plant and equipment hire

To suit all business needs, Fox Oil/Water Separators are available in standard sizes from 1000 to 15,000 l of processed wastewater per hour. Also, the supplier can manufacture custom systems that can treat up to 250,000 l per hour.

System Maintenance & Taking Care of the Effluent

  • For maximum Water/Oil Separator performance, the manufacturer recommends the use of Quick Break cleaners and degreasers.
  • Besides choosing the right device, effluent designs and system maintenance are critical to extract hydrocarbons safely and effectively and to comply with local regulations.
  • Take care to size the piping and other downstream facilities adequately the goal is to be able to process the quantity of wastewater and stormwater even in accidental events such as heavy storms. Precipitation overflows that are not accounted for can result in oil caught in spaces such as manholes to escape into the environment.
  • Effluent piping should have siphon breaks, which prevents siphoning oil and water from the separator in low-flow conditions.
  • Regular maintenance is key to successful filtration you have to ensure that the collected oil is removed from the separator regularly, if not continuously.
  • If not removed, the collected oil could fill the separator, causing an undesirably high oil content in the effluent, risking that the oils eventually re-enter the environment.
  • Once the oil is separated and removed from the separator, it must be treated not as common waste but as a hazardous waste per the local laws. Recycling or proper disposal is critical to prevent pollution and related problems elsewhere.

Final Thoughts

Oils are a critical source of aquatic and environmental pollution. As required by local regulations, this issue needs to be addressed by all businesses that produce wastewater or stormwater runoff contaminated with hydrocarbons. Oil/Water separators are the first and critical stage of ensuring safe and efficient oil wastewater treatment.

Enhanced gravity oil-water separators ensure that even the ultra-fine oil droplets and the related particles are caught and prevented from escaping into the environment.

Fox Oil/Water Separators offer durability, reliability, high efficiency, compliance with the local regulations, and a wide range of sizes suitable for every type of business in need.