Contact Us

(United Kingdom) 0844 372 7344
(International calls) +441327 871967

B & V Group

A division of
Global Chemical Technologies Ltd
The Control of Fats Oils & Grease
The Control of Fats Oils & Grease

Control of Fats, Oils & Grease (FOG) In Drainage Systems


The build-up of fats, oils and greases (FOG) in drainage systems can lead to malodours, and in extreme situations, blocked drain lines.  Process contamination or discharge of wash/rinse waters can rapidly give rise to problems.  Where this contamination is heavy or continuous, interceptors or similar devices are generally designed into the drainage system.

There are four basic types of drainage systems:

1.    Systems with grease traps or interceptor.

2.    Systems without grease traps.

3.    Systems that use a wet well prior to pumping to mains.

4.    A combination of 1 and 3 prior to pumping to mains or on-site treatment.

Optimum performance of FOG control measures may be achieved through careful product application.

1.    Systems with Grease Traps

Most establishments utilise a grease trap or interceptor.  These are prefabricated pits of varying size and construction, which depend on the basic principle that FOG will float on top of water (see below pictures).

Effluent enters the trap where a dip pipe or plate enables the water to be separated from the FOG, allowing relatively clean water to be discharged.

Problems begin to occur if the trap is not regularly cleaned and maintained.  A build-up of FOG can result in backing up of deposits, particularly where laminar flow is normal.  This causes restricted flow, and can eventually lead to blockages.  Grease traps and interceptors are relatively effective at concentrating FOG in one central location. 

effluent fat trapexample of the problems caused by fats in waste water

Problems associated with these devices include :

Undersizing : Probably the most common problem, where the grease trap has not kept pace with above ground extensions or increase in trade.  The most common result is overloading, this can lead to blockages, and/or high Suspended Solids (SS) in the final discharge.  The traditional remedy is to mechanically or manually empty the trap.

Food Debris : Many traps are fitted with catch all metal mesh baskets.  The food particles are caught in these, and if not emptied, regularly malodours result and blockages may occur.

Poor Design : Examples are: grease traps next to cleaning machines, which discharge hot water and debris into the system, the water being so warm that FOG is carried past the trap and deposited further down the line; open discharge pipes, allowing odours back into the work area.

2.    Systems without Grease Traps

Grease collects around “dead points” such as corners, low gradient pipes, manholes etc., these lead to the emission of unpleasant odours from rotting FOG, blockages may also occur.  In older sites with long sections of drainage pipe work, if this does lead to blockages, the actual physical and mechanical operation to unblock these lines can be very time consuming and disruptive to routine operations.

3.    Systems With Wet Walls

Wet walls or sumps are used generally by large premises where access to mains drainage is difficult.  All the effluent goes to the lowest point in the establishment where it is periodically pumped to a treatment plant or mains system.

These sumps are effectively large grease traps and here fouling of trip switches and pump breakdowns are the most common problems caused by FOG.

Regular maintenance is critical, as possible resultant flooding can prove very costly.

4.    Combinations Of Above

Each site system, although having similar pieces of equipment, will be unique in its layout.  Combinations of the problems highlighted above may occur, or it may be just one area in the operation which presents the problem, e.g. a batch cooker which is cleaned after each production run, may not present problems in its immediate area, but as FOG cools in the drainage line, problems may be caused further down the system.

5.    Enhancing System Performance

Bactiplus 60 is an effective means of introducing to a system a naturally occurring microbe that releases enzymes to break down FOG in the drain environment.  As a result of this, crust formation at sumps or grease traps is controlled, the system should be more aerobic and so does not give off the malodours, which would otherwise occur.  However, if malodours still occur then Odourguard 90 can be used to ensure that the normal malodorous gases, such as Hydrogen Sulphide, Methane and Ammonia, do not build-up.

The action of the microbes in these products, is to form a bio film on the walls of the drainage system, which continuously releases enzymes into the system, forming an effective barrier to FOG deposits.

The first sign of FOG degradation on an existing problem is the emulsification of the FOG, which swells and becomes translucent.  The fats are unable to solidify and pass further down the system for treatment in the sewage system.  The longer the fats are in contact with the enzymes, the further the effluent will be degraded.



Contact Us

Please use this form to contact us with any enquiry or comment you may have. We will endeavour to get back to you within 2 working days.

Please tick this box if you would not like to receive further information from B & V Water Treatment (this does not include communications related to your enquiry)

Connect with us