Grease Trap Tour

Related Pages

	Pre-Treatment Fixtures

A typical grease trap consists of a rectangular concrete pit, with a concrete lid in two or three sections.

You may have seen one outside your premises.

In this photo, the lid at the inlet end of the trap is being opened.

This is the inlet to the trap. The sewer line (ie: drain pipe) from your commercial kitchen or process area discharges directly into the grease trap chamber.

Note that this grease trap has been left empty of water for demonstration purposes only. Under normal operation, the water level would be higher than this.

Your grease trap needs to have enough capacity to ensure that the water flows through it very slowly and very gently. There needs to be sufficient ‘retention time’ to allow all the grease particles to gradually coagulate and float to the surface.

You can see how much grease was captured and floating on the surface by the ‘bathtub ring’ left around the edges. (This would normally be scraped from the sides during the regular pump-out of your grease trap.)

Across the middle of the grease trap you will see one or two baffles, usually made from sturdy panels of grease-resistant PVC.

The grease, which floats on the surface of the water, is dammed up and trapped on the inlet side of the baffle, while the cleaner wastewater passes underneath the baffle.

If your grease trap is not re-filled after pump-out, it will not work. The grease will simply pass underneath the baffle. The bottom of the baffle needs to be submerged well below the water surface.

This photo is looking at the baffle from the outlet side of the trap. You will notice that the ‘bathtub ring’ on this side of the baffle is nowhere near as bad as on the inlet side. Some grease does stay in suspension, and pass under the baffle, but the vast majority is trapped on the upstream side of the baffle.

Grease traps also have a vent pipe, which allows any smelly air to escape. Unfortunately, we can’t see the vent pipe in these photos.

The smells are generated as the grease and food matter caught in your trap begins to break down. The vent pipe usually has its opening on the side wall inside the grease trap, and it is always above the normal water level in the trap. The pipe might then run underground and up the side (or inside) of a nearby building. Regardless, the other end of the vent pipe should always stick up in the air, above the level of any surrounding structures. Then, whenever the wind blows over the top of the vent pipe, it will work like a chimney to suck any smelly air out of the grease trap.

This is the outlet end of the grease trap. It has a T-square fitting as extra protection against any residual grease finding its way into the sewer.

The ‘clean’ wastewater discharging into the outlet is drawn from the bottom opening of the T-square. Its well below the surface of the water. (Any residual grease will be concentrated near the surface.)

But the bottom of the T-square is also well clear of the floor of the grease trap. Any bits of dirt or food particles in your wastewater will settle out in your grease trap, and fall to the bottom of the trap. The bottom of the T-square is clear of the floor to avoid any of this muck getting into the sewer.

The top of the T-square is about 10cm above the water level of the grease trap. Wastewater doesn’t normally flow through the top opening of the T-square. Instead, its purpose is to allow you to check the quality of the ‘clean’ wastewater that’s going into the sewer. You can see the surface of the water inside this T-square opening. It should be fairly clear, and much much clearer than the water surface within the rest of the Grease Trap.

But if the water surface inside the top opening of the T-square is not clear, and has an obvious layer of fat and grease on it, then it means your grease trap is fully loaded, and it needs to be pumped out. (If the grease trap starts to smell bad, then that’s also an indication that it needs to be emptied.)

The top opening of the T-square is also there as a back-up outlet in the event that the bottom end gets clogged with grease and fat, or settled solids. But regular maintenance and pump-out of your grease trap should avoid any risk of overflows.

This is the outlet end of the grease trap. It’s a bit dark inside, but you can just see the T-square outlet.

You can also see our sample point, downstream of the grease trap. It’s the little circular grate in the grass in front of the persons right foot.

The sample point is simply a length of pipe connected to the sewer pipe that rises to the surface. We can use this to take a grab sample of the ‘clean’ wastewater discharging from your grease trap, to see if your grease trap is doing the job its supposed to.

These sample points allow us to do random checks - to help us protect the environment and community health. Also, if we have a problem with grease or fat within a part of the sewer system, we can quickly check all the grease traps in the area to rule them out as a source of the contamination.

The sample point on your grease trap may look like this. Or it may be a solid metal cover sitting inside a square of concrete, or something similar.

Does this look familiar?

Before we go, we should mention drainage. It’s illegal to discharge stormwater or rainwater into the sewer, as the sewer system capacity is not designed to handle the high peak flows of stormwater from moderate or heavy rainfall events. To do so would be too costly for everyone, and its not an efficient way to deal with stormwater.

Consequently, your grease trap should be a little higher than the surrounding ground to ensure that rainwater runs off, rather than seeping into your grease trap. Also, you wouldn’t want your grease trap filling up with rainwater and overflowing, because the smelly mess would scare your customers away!

We require the grease trap lids to be at a level at least 75mm higher than the surrounding area. The one in the picture is less than ideal, as the ground between it and the wall is higher than the grease trap lids. But this is a very small area, its reasonably sheltered, and the general area drains away to the road. None the less, it would not be acceptable for a new installation.

And so ends our tour of a grease trap! By now, you should have a pretty good idea of what’s underneath those lids, and how it works.

You can also view our Pre-Treatment Fixtures page, to find out how your grease trap and our service go hand in hand.

Remember that it’s important to have your grease trap pumped out regularly. If you don’t stick to the maintenance schedule for your trap, the following negative consequences could result:

Your grease trap will develop a noticeable septic smell, that will drive your customers away
Cockroaches could start to breed in there, and crawl up the drain into your kitchen
Your grease trap will become ineffective, and you could cause a sewer blockage and overflow somewhere in the system, putting the environment and public health at risk
You will be in breach of your Industrial Waste Permit and DEP License conditions, and could risk prosecution

Of course, it’s a simple thing to stick to your pump-out schedule, and a well maintained grease trap should not cause you any of these problems or concerns.

If you have any more questions not answered in the brochures and web pages listed above, then please feel free to contact us and we'll be happy to help.

Downloads

For more information about grease traps, you can view and print the following publications:

Maintenance and Cleaning of Grease Arrestors

Acceptance Criteria for Food Outlets

Grease Arrestor Typical Design Drawing