Liquid Environmental Solutions


We’re always happy to take time to answer your questions. Below are some of the most common ones we encounter. Got another? Just contact us using one of the links at the bottom of this page.

Grease Trap

My Grease trap is overflowing. What do I need to do?

If you are experiencing a backup where there is grease trap waste overflowing from the grease trap manhole cover this usually indicates a clog in the outgoing grease line. You may also experience drains backing up within the establishment. In this instance, pumping the grease trap will not alleviate the problem. Calling a plumber to perform a jetting service will be necessary.

If you have an interior grease trap that is overflowing, first call a plumber. Typically clogs are in the lines and can be cleared with a jetting service. However, if the interior trap continues to be an issue a pumping may be necessary.

I noticed that my grease trap is full? What should I do?

The grease trap should always be full. If a plumber has told you that your grease trap is full, or if you lift up the lid to your grease and see water levels nearly reaching the top of the trap, you may think that your grease trap is full and needs to be pumped. This is almost never the case. Exterior interceptors work by using gravity within the tank to separate out the Fats, Oils, and Greases (FOG) from the water. If the trap were not full it would not be working properly. For most drain and backup issues, grease trap pumping is not the solution.

What is a grease trap?

A grease trap is a device that wastewater flows through prior to entering your city’s sanitary sewer system. The device traps Fats, Oils and Greases (FOG), preventing it from flowing into the sewer line and clogging it. When the wastewater goes through the grease trap, the FOG rises to the surface and floats on top of the water, while the solids sink to the bottom. The FOG is then trapped inside the grease trap while the rest of the water exits to the sewer line.

How do I maintain my grease trap?

It is important to have your grease trap serviced regularly and in compliance with any municipal pumping requirements.  This will help prevent costly backups and overflows, as well as possible fines from local municipalities.

Why is there an odor after I have had my grease trap serviced?

There are several reasons why your grease trap cleaning may leave an.

If an odor lingers for a short while right after a trap service has been completed, this is typically due to the water flowing back into the trap and the odor will soon dissipate as the trap fills up. 

Odors coming from the floor drains could be due to a backup in the line leading to the trap. Pouring very hot water down the drains will often help alleviate the odor.  If the odor persists after pouring water down the drains, you may need to contact a plumber to snake the lines.

Grease trap odors can also escape through a worn or corroded gasket around your manhole cover allowing gases to escape.

A plumber said that my grease trap is full and must be emptied before he jets or snakes the lines. What should I do?

This is almost never true. A plumber can usually access lines to jet or snake without having the grease trap emptied. However, if the plumber has to enter the grease trap to perform a repair, then a coordinated service will need to be scheduled with LES and the plumber so that the trap can be emptied for repairs to be completed.

Oil Water Separator

What analysis method is recommended for determining oil concentration in water?

MSR suggests the use of USEPA analytical Method 1664, which is a spectrophotometric method. Most environmental laboratories can perform this test and it is usually not expensive. It is accepted by most regulatory authorities.

What are the ideal inlet conditions for an oil water separator? I’d like to make it work as well as possible.

Ideal inlet conditions for an oil-water separator are:

⋅ Gravity flow (not pumped) in the inlet piping
⋅ Inlet piping sized for minimum pressure drop
⋅ Inlet piping straight for at least ten pipe diameters upstream of the separator (directly into nozzle)
⋅ Inlet piping containing a minimum of elbows, tees, valves and other fittings

What can I do with the oil recovered in a separator?

Removing the oil from the separators is not enough to protect the environment, it must also be recycled to ensure that it is disposed of properly. Current U.S. law can hold the owner of the oil-water separator responsible if this oil is not properly disposed of, even if the owner has paid for proper disposal. There are many local firms involved in recycling hydrocarbons. Most will be able to tell you what the local regulations are and usually offer a pick-up service.

What can I do about dissolved hydrocarbons?

In general, hydrocarbons are only marginally soluble with the notable exception of Benzene and some other aromatic hydrocarbons. Even these are removable using coalescing plate separators or other physical means as long as they are either removed so quickly that there is no time for the dissolution to occur or if they are present in concentrations greater than the solubility. Dissolved hydrocarbons are, strictly speaking, not covered by the Clean Water Act since they do not cause a sheen on the water. Many analysis methods will detect dissolved hydrocarbons and some jurisdictions are concerned about them, so it may be necessary in some cases to treat for their removal. Physical methods such as coalescing plate separators will not remove dissolved hydrocarbons and other methods such as biological treatment or absorbents are required.

What is the benefit of using separators over absorbents?

The biggest problem with the use of absorbents is that they are quickly used up, and since there no way to determine if they are exhausted without laboratory testing, they are often left in place long after their useful life is done. The used absorbents are sometimes considered hazardous waste and will result in a disposal cost.

I have dirt and/or grit in my flow stream. What will that do to the system?

Small quantities of dirt and grit will not harm the operations of the separator; they will only cause some eventual plugging that must be removed periodically. If large quantities of solid particles are expected, it is wise to provide a grit removal chamber before the separator. These chambers should be designed according to normal design parameters for grit removal as used in sanitary sewer plant design. MSR will be glad to offer suggestions on this design.

Can I use soaps and detergents and still have my separator work well?

Soaps and detergents (known collective as surfactants, which is a contraction of surface active agent) can cause emulsions that are very difficult to remove. Without careful attention to the amount and type of soaps and detergents used, it is likely that a system will NOT operate satisfactorily if they are used. The degree of emulsification of the oil is difficult to assess, but steps can be taken to discourage the formation of emulsions and encourage the breakup of emulsions that are inadvertently created. It may be necessary to substitute quick-break detergents for conventional detergents that also are emulsion causing. Quick-break detergents are those detergents designed to remove the oil (or grease) from the item to be cleaned and then quickly dissociate again from the oil, leaving the oil as free hydrocarbon droplets in the water. MSR will be glad to make design suggestions and / or send a copy of a study done by the U.S. Army Corps of Engineers on quick-break detergents. Note: The small amount of detergents in detergent motor oils will not cause problems with the operations of oil water separators.

What information do I need to gather for designing an effective, reliable separator?

Numerous factors must be considered in the selection and design of oil-water separation systems. Among these are:

⋅ Flow rate and conditions
⋅ Degree of separation required – effluent quality
⋅ Amount of oil in the water
⋅ Existing equipment
⋅ Emulsification of the oil
⋅ Treated water facilities
⋅ Recovered oil disposal method

For industrial and some municipal applications, flow rate, amount of oil, flowing temperature, and other conditions affecting separation – such as whether flow is laminar or turbulent – may be easily determined. For storm water applications, however, it may be necessary to estimate water flows. The degree of separation required is usually a matter of statutory or regulatory requirements, but if the water is discharged to a sanitary or industrial treatment plant, it may be negotiable. The amount of oil in the water may be known, especially in industrial applications, but it often will be necessary to estimate the quantity in storm water applications. MSR can provide guidance about quantities to be expected. Existing equipment such as API separators may affect the design of equipment to be used. Often, it is possible to retrofit existing equipment with more sophisticated internals to enhance separation quality. It is necessary to ensure that adequate size piping is provided for downstream treated water removal to avoid flooding the separator and perhaps filling the oil reservoir (if provided) with water. A downstream test point should be provided to allow for effluent testing. Adequate storage facilities for the removed oil should be provided and means for recycling the oil included. Careful records of removed and recycled oil should be kept to allow for preventative maintenance and avoid possible future regulatory problems.

If I have to pump into a separator, what is the best kind of pump to use?

The best type of pump to use is a positive displacement pump such as a diaphragm pump or screw pump. The worst are centrifugal pumps.

Why is it better to direct the flow into a separator by gravity flow than pumped flow?

Anything that decreases the average droplet size in the inlet of a separator will decrease the performance of the separator. The type of equipment that decreases the average droplet size is anything that causes shear in the inlet stream. This includes pumps, especially centrifugal pumps, valves, especially globe and other control valves, small or rough piping, and undue amounts of elbows or other fittings in the inlet pipe.

How can I be sure that the effluent from the separator will meet the requirements?

The first thing to do is to make very sure you know all of the possible inlet situations – maximum flow rate, minimum temperature and oil types and concentrations that may occur in the inlet. Consider if a spill condition may happen. Make a schematic flow diagram of the system and identify possible pressure drop causing equipment such as pumps and valves. With this information, MSR can estimate the oil droplet sizes that are likely to be present in the inlet water. We use this information in our proprietary computer program to predict operations of the system. We estimate a separator size and configuration and do a simulation calculation to see if the performance will meet the required effluent concentration. We then adjust the size larger or smaller to ensure a proper fit. Because the separation depends on Stokes’s Law and we are careful to ensure (in the separator design) that the conditions of this physical principle are met, the final design system will meet the required effluent. We try to be very conservative in estimating the droplet sizes so that the final design will be conservative and capable of handling variations in flow and other conditions. The physics work and Sir Isaac Newton’s gravity can be trusted to operate correctly and predictably every time. A very convenient property of coalescing plate separators not shared by some types of oil-water separators is that, at flow rates lower than the design flow, they just work better!

Used Cooking Oil

My used cooking oil is full. What should I do?

Do not add any more cooking oil to the tank.  Doing so will cause spillage to overflow onto the ground. If it is full, you can use a container to collect any additional oil until LES can arrive to service. Make sure you are storing the excess storage container in a safe area close to your UCO bin to avoid an employee from tripping or falling. Please do not put the oil in your refrigerator or freezers. The UCO needs to be soft for collection and refrigerating or freezing it will cause it to harden and solidify. Please contact LES at 866-694-7327 to schedule service.

To be sure that your bin is actually full, it is important to make sure your bin grate is free from debris. A clogged or obstructed grate will not allow the oil to pass into the bin.

Why do I need to collect my oil? Why can I not pour it down the drains?

Used cooking oil cannot be poured down the drain because it will build up in the pipes, causing clogs and then backups in your restaurant’s plumbing. This can pose a significant health and safety hazard in a restaurant environment. The used cooking oil will also cause high levels of grease to be discharged into the local sewer system which can cause clogs and backups in local sewer systems as well as result in violations and fines for you as the generator.

I have an oil spill around my bin. What do I do?

The best way to clean up an oil spill is to first block off the area so no one walks or drives through it. Then you will need to put down an absorbing agent to soak up the oil. This can be kitty litter, oil dry, or quick dry.  Allow the oil to be fully absorbed before sweeping up the absorbent and then discard in trash.