RAI Legal

Grease Trap Law

Grease Traps. Ick. I know you don’t want to think about them but there’s some stuff you need to know. Like they can do stuff that can cause your business serious harm. Ever seen a foul water flood in a commercial kitchen? You don’t want to. Trust me on this.

[important]Grease Trap Basics[/important]

They trap grease. Duh! Fats, Oils and Greases (FOGs) float to the top to stop them going down the sewer. Here’s why you need one (or replace / enhance it with a biological system):

  • It’s illegal to discharge FOGs to the sewer (here’s why) plus you could get a blocked drain as well as a fine from the water board or both
  • You need to empty the grease trap (ICK!!) BUT you can’t chuck the crap in the rubbish or you get fined
  • It needs to be removed by a Licenced Waste Pikey (expensive!) – who prob then buries it in someone’s garden  – but that’s the law
  • There is an EN standard for grease trap size (wow! who’da thunk it!) and just about every one I’ve ever seen is undersized. So another possible fine there, then.

[important]Biological Systems[/important]

Many people are moving to biological systems. Many new builds don’t even bother with grease traps anymore. Essentially these things automatically poot a cupful of ‘friendly’ bacteria down the waste pipes each night who then get to work eating away at the FOGs. No more icky grease trap, no blocked drains and no smells.

But there are good systems and crap ones. Some don’t work at all. The best of the bunch is a product called Bio GD and when set up properly a biological system will:

  • Eat away the FOGs in pipes and grease traps (but won’t eat napkins, cocktail sticks and non-FOGs
  • Get rid of smells – especially important during the summer; if the beer garden whiffs of drains it will cost you business
  • Remove (or dramatically reduce) the need for grease trap emptying
  • Only cost 1-2p per meal vs fines, emptying costs (direct and indirect.

What the bugs won’t do is sort out dodgy drains. They’re not plumbers or brickies.

One type of system that makes me laugh is those that use a ‘bio-generator’ to activate and grow up a live culture of bacteria before injection into a drain. While this concept sounds like a good idea the slurry used for the bio-generator needs to contain a food source for the bacteria – usually a cheap source of carbohydrate such as molasses. The theory is that the bacteria grow up in the generator feeding on molasses so you get loads more for your money.

This sounds eminently sensible and plausible but where it all falls down is that when these bacteria get set free in the drain they are ‘looking for’ molasses – that is they are generating enzymes to digest carbohydrates. But a funny thing about drains and grease traps is that they tend to contain grease. Not molasses. Clue’s in the name: grease trap. So the bugs need to go through several generation cycles as they reprogramme themselves to produce lipases to digest the fats, oils and greases you find in a drain or grease trap. While the notion of a biogenerator in a drain system sounds persuasive the basic science behind them is half-baked to say the least. The best place to grow the bacteria is in the drain or trap. I’ve yet to find anyone that can come up with a scientifically convincing argument to counter this view.

By all means contact me with grease trap / biological questions. But I might bore you to death with a  diatribe on biofilm ecology. You have been warned.

[notice]Legals That’ll Screw You Up[/notice]

There are several pieces of legislation relevant to the disposal of Fats, Oils, Grease and associated kitchen waste into the Drainage system. One or all of these can be used by the authorities. If you get it wrong it can cost. You may not know it but you have an ‘environmental permission to discharge’ – that is, you are allowed to chuck some stuff down the drain but if you’re contributing to some FatBerg somewhere they can (and will) fine the bejeezus

EN1825 – Grease Trap Size

The new European design standard for Grease Traps and Separators EN1825 stipulates that to calculate the correct Nominal Size (NS) then 4 factors must be considered. They are:

  • Maximum flow rate of water.
  • Maximum temperature of water
  • Density of grease or oils to be separated or trapped
  • Influence of cleaning and rinsing agents used

The rule of thumb is that maximum flow rate in litres per second x 1.5 gives a rough estimate of the minimum size. For example, an installation with a maximum flow rate of 1.5 litres per second would give a calculation of 1.5 x 1.5 which would require a grease trap of nominal size of 2.25.

The standard then specifically requires that the unit then must have a minimum volume for sludge of 100 times the nominal size for all installations except abattoirs and similar processing plants where it needs to be 200 times. So for the above calculation then the grease trap or separator size would have to be in excess of 250 litres.

There is clearly a large element of FPM (Fag Packet Maths) at work here, but to give an idea:

Meals per Day Flow (l/sec) Min Size (l) Actual Size (l)
50 0.75 148.5 150
100 1.50 198 250
200 2.00 297 350
300 2.25 396 400
400 2.50 495 500

Most grease traps in food businesses are between 200 and 450 litres – the latter being able to cope with 350l of grease and 100l of water. A meat processing plant would typically need a minimum of 5,000 litres. In terms of physical size a 250l grease trap would be a metre long, 50cm high and 50cm deep. Undersizing is incredibly common.

Water Industry Act 1991

Each local utility company will set a ‘consent level’ to discharge to drain. This will normally include flow rate, temperature, suspended solids, Chemical Oxygen Demand (COD). It may also include Fats, Oils and Grease and Biological Oxygen Demand (BOD). The relevant legislation with regard to this is the Water Industry Act 1991. Section 111, Part 1 of the legislation states:

‘…. no person shall throw, empty or turn, or suffer or permit to be thrown or emptied or to pass, into any public sewer, or into any drain or sewer communicating with a public sewer any matter likely to injure the sewer or drain, to interfere with the free flow of its contents or to affect prejudicially the treatment and disposal of its contents’

Water Resources Act 1991

If you are not connected to the mains drains then you would normally have on site a treatment plant which would have an outflow to a public stream, river, ditch etc. If this is the case then the Environment Agency will be the relevant authority to issue consent levels for the discharge and check that these are being complied with. The relevant legislation here is the Water Resources Act 1991. Part IIIII of this legislation relates to ‘Control of Pollution of Water Resources’ Section 85 states:

‘….A person contravenes this section if he causes or knowingly permits any poisonous, noxious or polluting matter or any solid waste matter to enter any controlled waters. A person contravenes this section if he causes or knowingly permits any trade effluent or sewage effluent to be discharged into any controlled waters. A person contravenes this section if he causes or knowingly permits any trade effluent or sewage effluent to be discharged from a building or from any fixed plant—

(a) on to or into any land; or

(b) into any waters of a lake or pond which are not inland freshwaters.’

Buildings Act 1984

If your drain pipework is then connected to the public sewer but is causing a problem to the public sewer then the Local Authority may serve a notice under the Building Act 1984. Section 59 states:

‘….that if it appears to a Local Authority that in the case of any building a cesspool, private sewer, drain, soil-pipe, rain water pipe, spout, sink or other necessary appliance provided for the building is insufficient or in such a condition as to be prejudicial to health or a nuisance they shall by notice require the owner of the building to make satisfactory provision for the drainage of the building, or, as to case may be, require either the owner or occupier of the building to do such work as may be necessary for renewing, repairing or cleaning the existing cesspool, sewer, drain pipe, spout, sink or other appliance, or for filling up, removing or otherwise rendering innocuous the disused cesspool, sewer or drain.”

In addition, Local Environmental Health Officers in many areas – particularly where food preparation and cooking is creating a FOG (fat, oil & grease) problem within a public or private sewer – will stipulate that the offender treat their waste (which is considered to be trade effluent) with a biological treatment.

Local Government (Misc Provisions) Act 1982, Public Health Act 1936

If you have blocked drains (serving one property) then the local authority can serve a notice on you to cleanse and repair under Local Government (Misc Provisions) Act 1982 section 27 and / or Public Health Act 1936 section 343. Also, if you have a blocked private sewer (serving two or more properties) then the local authority can serve a notice to cleanse and repair under Local Government (Misc Provisions) Act 1976 section 35 and / or Public Health Act 1936 section 343.

Building Regulations 2000

If you have had a new build or extension to your kitchens then you may fall be liable under Building Regulations 2000. Part H Section 2.21 states:

‘Drainage serving kitchens in commercial hot food premises should be fitted with a grease separator complying with BS EN 1825-1:2004 and designed in accordance with BS EN 1825-2:2002 or other effective means of grease removal’

It is considered that Biological Treatment of FOG complies under these regulations.


Any premises operating under ISO14001 should also consider the following:

‘ISO 14001:1996 is the current Environmental Management System (EMS) standard, providing a model for companies to follow to create and achieve their environmental policy, thereby effectively managing the complete business. It is designed to help companies achieve consistent environmental regulatory compliance together with continuous improvements in environmental performance. It can also lead to increased efficiency and can yield cost benefits.’

How you use water on your site and how you dispose of waste water forms part of ISO 14001. It also requires businesses to demonstrate they are using the latest techniques and equipment to constantly improve the methods and equipment they use as part of their environmental management systems’. So, the compliance burden is a heavy one. Essentially business are required to deal with biological waste sensibly and responsibly. You are no longer allowed to just flush the problem away or empty the grease trap into the rubbish as this is now controlled waste. Luckily compliance in this case works out to be less expensive than flouting the law. A biological system can eliminate FOGs and scale as well as keeping a business on the right side of the law as well as eliminating any foul odours and taking out overall cost.