Frequently Asked Questions About Fats, Oils, and Grease (FOG)

What is FOG?

FOG refers to fats, oils, and grease produced in most catering environments during the preparation of food.  Because of its poor solubility in water and its tendency to congeal and separate from liquid solutions, FOG requires active interception and treatment to prevent costly environmental problems.

Is FOG a problem?

In a word, YES!  Excessive FOG in wastewater congeals in collection system pipes, thereby decreasing their capacity and increasing the need for frequent, costly, and time consuming pipe cleaning to keep things flowing along.  It may also necessitate replacing some piping sooner than otherwise expected.  The resulting downtime and bottlenecks in your kitchen will have a financial impact, as well as an impact on the ability of your staff to perform their normal duties. 

Fats, oils and grease also have an impact on wastewater treatment plants.  Grease congealing in settling tanks form rancid skins, and blockages in digesters and other pipe works may necessitate shutting down wastewater treatment units.  Problems caused by catering waste have resulted in legislation governing the discharge and disposal of grease matter into waste water systems.  This type of waste requires the installation of preliminary treatment facilities, commonly known as grease traps or interceptors.

What is a grease trap / interceptor / separator, and how does it work?

A grease trap is a reservoir built into the wastewater piping a short distance from the grease producing area. Baffles in the reservoir retain the wastewater long enough for the grease to congeal and rise to the surface. The grease can then be removed and disposed of properly.

Grease traps can range in size from small under counter units at the point of use, to large units with a few thousand gallons capacity serving multiple cleaning points.  Larger units are often located on the exterior of the building. The important thing is that the capacity of an interceptor, and the rate of flow provides adequate residence time for the wastewater to cool, thereby allowing the grease time to congeal and rise to the surface where it accumulates until it is pumped out.

What is a skimming / positive separation device, and how does it work?

A grease positive separation device is similar to a grease trap, but in addition to separating the FOG, it uses a mechanical process to remove it off the surface, making it easier to dispose of without opening and emptying the greasetrap each time.

What is a dosing system and how does it work?

A dosing system injects enzyme and grease digesting bacteria into your waste system.  Dosing systems are generally fully automated, and provide a regular and measured release of enzyme into your system at appropriate timed intervals, greatly reducing the likelihood of expensive repair and maintenance through improper or irregular use.  There are certain systems which also introduce water during the dosing cycle to help evenly distribute the enzyme through the whole system.

Do I need a grease management system?

Any establishment that introduces FOG into the sewage system in quantities large enough to cause line blockages or hinder sewage treatment is required to have a grease management system.  Grease interceptors are usually required for high volume restaurants and large commercial establishments such as hotels, hospitals, factories, or school kitchens. Grease traps are required for smaller establishments. Medium volume establishments may be required to install an interceptor depending upon the size of the establishment and its catering activity.  Dosing units will introduce active enzymes and grease digesting bacteria into the system which will help to break down solid fats and other contaminants.  A dosing regimen used in conjunction with an intercepting device, will increase the effectiveness of the system.

How do I clean my grease trap?

Cleaning a grease trap or interceptor is dirty work.  It requires special receptacles, and the waste must be legally disposed of.  Smaller units can be scooped out, but larger units require special pumps.  Great care needs to be taken to avoid spillage, which can contaminate other areas of the kitchen.  Ideally this is a job for a specialist contractor who can empty, clean and service your units at regular intervals.

Can you recommend a maintenance schedule?

How regularly equipment is cleaned and maintained depends entirely on the volume of use, and how food waste is handled and disposed of on the premises. If an establishment has to empty and clean their equipment too often, the owner should evaluate the effectiveness of food and grease handling practices, and should consider installing a larger trap or interceptor or a dosing system. All grease interceptors should be cleaned at least twice each year. If a grease trap is not maintained regularly it will not provide effective grease removal. The establishment should work out a specific cleaning schedule that is right for its volume of business and specific circumstances. All grease traps need to have the grease cleaned out periodically and no one likes to do the job. It is a dirty job. Running extremely hot water down the drain only moves the problem further down stream. It does not go away. Catching the grease at the source, and cleaning it regularly is the most economical means to reduce all costs.

What if I don’t install a grease management system?

If an establishment uses grease and oil in food preparation, it will eventually encounter a maintenance problem with a blocked building sewer line. The blockage can create a sewer backup situation and ultimately a potential health problem in the establishment. Someone will have to pay for removing the blockage. If the problem is in the building sewer line, then the establishment has direct responsibility for paying for the maintenance. If the blockage or restriction is in the public sewer and it can be proven that the establishment has caused the blockage, it may have to pay for the public sewer to be maintained. Blocking a sewer line is also a violation of various laws and local bylaws.

How do I determine whether I need a grease trap or interceptor?

Environmental legislation requires the producer of the waste to get rid of it in an acceptable manner.  If there is a possibility that FOG from your establishment can create blockages or foul water treatment systems, you are legally responsible for ensuring that it is treated or intercepted.  If blockages or other complications occur you will be legally liable for the costs involved in solving the problem, and you may also incur a fine.

What are the criteria for inspecting grease traps?

Any food service establishment suspected of causing problems to the collection system or treatment facilities will be inspected.  In 2007/2008 Thames Water alone cleared over 60,500 blockages, of which 60% were as a result of FOG being released directly into the waste water system.  This led to over 2500 visits to various sites, and a number of fines for non-compliance. FOG in the system can be traced back directly to the polluter.  Depending on the amount of FOG entering the waste water system, and the condition and capacity of the grease management system, an establishment may be expected to increase it's maintenance schedule, and/or improve its grease management equipment. In some cases prosecution may result in considerable fines, or even imprisonment, and the closure of a facility.

Why should I choose FOG to manage my grease waste?

If you have re-occurring problems you will need an experienced contractor to work with you in finding suitable solutions.  We take a proactive approach to treatment, and will work with you to solve your problems and reduce your maintenance costs, rather than just jetting your sewer lines every time they become blocked.  Major companies, catering establishments, and restaurant chains use our proactive treatment program.

We offer the following:

Education: We will work with kitchen and maintenance staff to identify sources of FOG, and look for the most effective ways of eliminating them.  We are able to inform kitchen staff of alternatives to their current practices, and train them in the correct procedure and schedule for their chosen grease management systems.  We provide printed reference documentation and checklists (where appropriate) for the equipment we install and service.

Maintenance: We help you establish and manage a maintenance schedule and log for your whole treatment programme that specifically takes into account the demands made on your systems.  We also ensure that relevant staff are assigned duties of cleaning and caring for your grease management devices.

Follow up: We check back periodically to insure that your grease management program is working effectively.  This includes checking interceptors, dosing units, log books, and talking with the kitchen staff. We provide you with an integrated program that will reduce the amount of jetting required for keeping your lines clear, thereby reducing your annual maintenance cost and the likelihood of being in breach of your regulatory obligations.

Pre-treatment Devices: Small devices require frequent maintenance and are less efficient.  Larger devices allow for a greater storage time and more grease retention. Mechanical separators are fairly small units and work well as long as they are cleaned and maintained on a regular basis.

Registered Waste Contractors: We are registered with the Environment Agency to collect, manage, and dispose of your FOG waste legally, and provide you with the necessary waste transfer documentation for any waste we remove from your site.

Nationwide Reach:  We are a truly national company who work across the length and breadth of mainland UK.


For further guidance see "Guidance on Grease Traps" by Water UK