Oil water separator is a requirement, not an option

Oil separator

Keeping the water cycle free of impurities such as oil is an important aspect of environmental protection.

These pollutants can enter the water supply in a variety of ways.

Some are flagrant violators of environmental regulations, such as throwing oil down the drain after an oil change.

Others are far more subtle. Trace amounts of oil, for example, can be discovered in the condensate from lubricated air compressors.

This is why it is critical to keep polluted condensate out of wastewater before it is treated, i.e., before the oil is separated from the water.

What is an oil-water separator?

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Simply, an oil-water separator separates oil and suspended solids from water so that they can be skimmed off, as implied by the name.

Oil tends to float to the top because it is lighter than water.

However, some oil particulates, particularly microscopic droplets, can get hooked up due to the nature of wastewater, which is permeated with all different types of pollutants.

Based on the gravity difference between oil and water, oil-water separators are specifically made to target oil, allowing heavier solids (sludge) to settle to the bottom while oil rises to the top, leaving additional effluent in the middle layer.

The wastewater can then proceed for additional treatment after the sludge has been scraped off and the oil has been skimmed off the top.

How do Oil-Water Separators Work

There are numerous different oil-water separator designs.

The majority of wastewater separators are “gravity type” separators, either standard or improved.

Wastewater is directed into the oil water separator for treatment after passing through filters to remove the biggest solids.

The majority of the time, the wastewater passes through several chambers.

These chambers aid in creating three discrete compartments for oil, water and sludge.

Heavy suspended particles and muck sink to the bottom.

Oil particulates are tumbling over the surface of the wastewater as it travels through the chambers, allowing them to gather and solidify into larger globules that are more buoyant.

As a result, more oil separates and rises to the surface of the water.

Importance of oil-water separators

Keeping contaminants like oil out of the water cycle is crucial to environmental protection.

These pollutants can enter the water supply through a variety of channels.

Some of them are flagrant environmental law infractions, like just pouring used oil down the drain after an oil change.

Others are far more subtle. For instance, the condensate from lubricated air compressors contains traces of oil.

Because of this, it’s critical to stop the contaminated condensate from contaminating wastewater before it’s treated, or before the oil and water are separated.

Oil water separators types 

OWS are classified into three types: gravimetric, parallel plate (also known as coalescing plate) and American Petroleum Institute (API).

Conventional Gravity Separators (API) Traditional gravity separators use gravity to separate water from pollutants like oil.

Oil is less dense or heavier than water, therefore this works.

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Because of this, when oily water is added to a separator, the oil rises to the top, the particles and silt sink to the bottom and the water is left in the center.

The water can freely flow through an exit on the side of the tank for additional processing or environmental release while the oil is skimmed off the top and discarded.

Scraped off the bottom and pumped into a sludge pump for disposal are solids and the sediment layer.

Parallel Plate Gravity Separators Corrugated plates made of oleophilic material are arranged parallel to one another in a tank with a distance between them of between 6 and 12 millimeters in this sort of water oil separator system.

The tank’s interior and the spaces between these plates are thus left open to the passage of water and oil.

The water’s oil is drawn to and adheres to the plates.

Oil droplets grow in size as more join together, finally rising to the surface where they are gathered and released into a used oil tank.

The water can now flow through the tank and into a clean water exit where it can be released for various purposes as it is no longer contaminated with oil.

Hydrocyclone water oil separator system when oily water is injected at an angle into the tank, an active vortex forms, which is exploited by a hydro cyclone water oil separator system.

The spiral or cyclone shape is produced when the speed of the centrifugal force increases.

Because water is heavier than oil, it is pushed to the edges and allowed to fall into an outlet that leads to more processing or into the environment.

The lighter oil is forced upward through the top of the used oil tank and toward the center.

This sort of separator is appropriate for highly effective oil removal from water, such as in factories and heavily contaminated waters.

Flotation Separators The final water oil separator system, also known as DAF (dissolved air flotation), accelerates the pace at which the oil rises by using dissolved air.

Oily water and water that has dissolved air are combined in the separator to produce tiny air bubbles.

These bubbles carry the water’s oil to the top of the separator, where the oil, sludge and particles are skimmed off and collected in a different tank.

Any silt or substance that is too heavy to rise descends to the bottom and collects in a drain.

After passing through an outlet, the DAF wastewater is prepared for reuse or further filtration.

Above-ground VS below ground oil-water separator

Oil Water Separators are either above or below-ground vaults made of steel or concrete that use gravity to separate oil and water.

Due to space constraints and layout, a below-ground oil water separator is often the best option.

There is no need for pumps or controllers because gravity may drain into a below-ground system and ultimately into the sanitary sewer system.

In other circumstances, a below-ground system has already been specified and the specifications cannot be changed.

One of the problems with a below-ground system is that it is frequently ignored after installation.

The efficiency of the separator declines as solids accumulates within it.

Which will ultimately fill up to the point where the separator will no longer separate the oil and will simply flow it through with the water.

If underground system leaks lack effective maintenance or have poor soil conditions, the potential clean-up expenses can be very high!

While the majority of underground tanks are double-walled, very few underground piping lines are, which is another source of possible groundwater leaks.

The longer the system remains underground, the greater the risk of leakage and the greater the liability.

Even if an aboveground oil water separator is in a building corner, it is still “in sight” and accessible, giving it a considerably better chance of being maintained.

Maintenance is far less expensive than for an underground system and typically consists of simply washing it out with a hose or pressure washer.

Maintenance of Above Ground Oil Water Separators

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1- To ensure that there is enough area for pumped or discharged material, check the amount of accumulated oil with a dipstick or an attached site glass.

2- Place oil absorbent pads around and under the oil decant valve of the oil water separator.

Place the waste oil drum beneath the oil decant valve or connect it to the drain line.

3- The oil should be emptied into a waste container.

4-To clean slanted coalescing plates, use a pressure cleaning spray.

5- The number of solids accumulated in the oil-water separators should be noted and documented.

6- Pump out the sediments while using a high-pressure water spray to liquidize them.

7- Replace coalescing plates as directed by the manufacturer.

8- Wipe out all repair tools with rags and oil-dispersing cleaners as needed. Maintenance of Buried Oil Water Separators

9- Determine whether or not confined space entry (CSE) is required.

10- To ensure appropriate capacity to receive pumped or drained material, use a dipstick to assess the level of accumulated oil.

11- Fill a garbage container with the collected oil.

12- Using a pressure washing spray, clean inclined coalescing plates.

13-Take note of and keep track of the level of collected solids in the oil-water separators.

14- A high-pressure water spray liquidizes and concurrently pushes away collected solids.

15- Note and record the level of accumulated solids in the oil-water separators before replacing coalescing plates.

16- Replace coalescing plates according to the manufacturer’s instructions.

17- As needed, clean all maintenance equipment using cloths and oil-dispersing cleansers.

Checking the oil/water separator

Many people believe that if the separator is still draining, it is still working.

An oil/water separator, like any “filter,” must be cleaned regularly.

The effectiveness of a separator is significantly influenced by settled oils and solids.

We recommend that you inspect your separator at least once a month.

A periodic examination may be required depending on how it is utilized.

There are other applications requiring oil-water separation.

For example, The worldwide MARPOL Convention requires oily water separators (OWS) to remove oil from bilge water accumulating on ships.

Oil and water separators are often used in electrical substations.

Substation transformers consume a lot of oil for cooling and unenclosed substations are surrounded by moats that are designed to catch any spilled oil as well as rainwater.

As a result, oil and water separators provide a faster and easier solution to clear up an oil spill.


[1] https://www.envirofluid.com/articles/quick-break-degreasers-safe-eco-friendly-heavy-duty-degreaser-technology/

[2] https://www.pewe-usa.com/blog/types-water-oil-separator-systems/

[3] https://www.liquidenviro.com/blog-news/what-are-oil-water-separators-how-do-they-work-and-why 4-

[4] https://www.atlascopco.com/en-lt/compressors/air-compressor-blog/oil-water-separators

[5] https://www.washbaysolutions.com/why-would-you-choose-an-above-ground-oil-water-separator-vs-a-below-ground-oil-water-separator.php

[6] https://www.stormwaterassociation.com/oilwaterseparators

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