Colliding with fatbergs in FOG 17 October 2018

Technical guidance about the sizing and use of industrial grease traps is needed to combat the modern fatberg epidemic, according to a new industry association. Penny Hitchin dives in

Public awareness of fatbergs in sewers is on the increase. In spring 2018 the Museum of London displayed chunks of the massive 250m-long, 130-tonne Whitechapel fatberg, which Thames Water had recently removed from the sewer at a cost of around £1 million. The exhibition proved a hit with the public.

A key fatberg component is FOG (fats, oil and grease), food preparation wastes often flushed down the drains. The hundreds of thousands of UK food service establishments are the main sources of FOG in wastewater. In drains and sewers, FOG mixes with solids and calcium from sewage to form a hard, soap-like solid that coats sewer walls, and in sufficient quantities can block them completely.

Dr Martin Fairley, research director of ACO Technologies, describes FOG as a 21st century ‘perfect storm’ as pressure on sewage infrastructure is exacerbated by urbanisation, population and economic growth as well as changing weather patterns causing floods and storms leading to overflowing sewers.

Flushing FOG down the drain contravenes Section 111 of the Water Industry Act 1991 (“No person shall throw, empty or turn...into any 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.”)

While wastewater companies can enforce compliance, neither they nor other regulators prescribe what equipment establishments should use to mitigate the outputs of sinks, drains, combi-ovens, dishwashers and coffee machines.

“What is not clear to restaurant operators is how to correctly size and maintain grease traps to satisfy the water utilities and regulations,” reports Edward Palin, co-chairman of new trade body The Grease Contractors Association. This is the issue that GCA, an association of 14 companies, seeks to address.

Food and FOG

Kitchens produce wastewater that contains some FOG as well as food debris. Wastewater from commercial kitchens tends to contain a higher proportion and volume of FOG than domestic. An example of a FOG industry code of practice is available online:

There are three main types of grease management product to trap FOG or treat wastewater to reduce the FOG contamination. Grease traps, separators or interceptors, physically trap the FOG within them and allow the cleaned wastewater to pass through (see left-hand graphic in box below). Grease removal units (see right-hand graphic in box below) trap the grease, and also use additional processes to place food debris and FOG into external containers for separate disposal. Dosing systems add a biological element to break down the FOG into less harmful products.

A combination of one or more of these elements can be installed in a kitchen. Local councils with many food outlets might consider deploying a large separator at a street or neighbourhood level.

All grease management equipment requires regular maintenance, and the waste collected in a grease trap or separator is classified as a controlled waste and must be disposed of appropriately. Water UK’s guidance on using grease traps ( argues that they should be checked weekly, emptied before they are completely full, and cleaning operations should be recorded.

Separators and grease traps come in different sizes, and smaller kitchens might struggle to find space to fit them. The only existing European standard for grease management in kitchens in commercial hot food premises is BSEN 1825, which came into effect in 2002. The standard is based on maximum flow rate and uses estimates of facility type, water volume use and meals per day.

However, Martin Fairley believes that further work on standards is necessary, as many products used are not covered by this. Under BS EN 1825, and US and Canadian Standards, a removal rate minimum is expressed only in relation to the maximum flow rate, but he argues that in reality items of kitchen equipment may not be operating at full flow.

His research specifically targeted smaller food service establishments and found that 50% of the maximum flow rate explained more than 62% of the volume discharged to sewer. Testing FOG removal devices at a range of flow rates (up to suggested maximum) will enable smaller devices to attain realistic performance levels. Fairley further established that it is necessary to test with appropriate media (or FOG proxy).

Also, Fairley argues no current test regime will adequately induce oil droplet sizes that challenge a separator: larger droplets separate easily; smaller droplets separate more slowly. Fairley’s use of optical imaging systems revealed that sink wastewater could be characterised by a droplet size of less than 30 microns – with a corresponding rise rate of only 5mm per minute.

Soft skills

Whatever the equipment standards may end up being, they are only part of the picture. Staff training has an important role in effective grease management; for example, greasy or oily plates should be wiped with a paper towel or cloth before being placed in the dishwasher. However, ensuring adequate ongoing training within a busy kitchen environment can be problematic. The catering industry workforce has a reputation for poor pay and often employs a fairly transient workforce.

More organised kitchens can send away waste cooking oil for recycling into biodiesel. If the infrastructure existed, the high calorific waste from grease traps, currently disposed of as controlled waste, could similarly be utilised rather than discarded. The introduction of financial incentives for this by-product would be a bonus for food outlet operators, who currently see grease management as a cost. Another incentive would be if the Food Standards Authority were to include grease management in its very visible Food Hygiene Rating scheme, which helps consumers choose where to eat.

For many small food outlets, the traditional way of dealing with fats, oils and grease has been flushing it away, so it becomes someone else’s problem. However, this is not sustainable. The GCA is setting out to provide a clear set of standards and a code of practice that will help food service outlets to deal with their FOG responsibly. This initiative should be welcomed by outlets and their various regulators who have lacked clear guidance on the sizing, installation and maintenance of appropriate equipment.

BOX OUT 1: Sizing guidance

The GCA is currently working on a grease trap sizing specification document, but it is not yet finished. In the meantime, the US IAPMO Uniform Plumbing Code ( offers recommendations in chapter 10, pp147-151.

Many sizing worksheets are available online; but most are in US units. Selected examples are below.

1 Derived from a previous version of the Uniform Plumbing Code: (1 gal=3.785L)

2 A UK supplier example:

BOX OUT 2: Dublin: world leaders in FOG

Since 2008, food businesses in Dublin have been designated in local regulations as trade effluent dischargers that are required to comply with a discharge and licensing management programme. They are liable to multiple annual inspections. Now, around 80-85% of Dublin’s licensed food service outlets are classified as a medium-to-low risk to the network, and sewer blockages have reduced significantly in line with this.

Spotting a gap in the market, a local engineer established a niche grease management technology platform accessible to both the inspectors and the food service outlets. SwiftComply offers access to a digital account that provides real-time visibility of FOG management status by monitoring and recording activity for restaurants and inspectors.

Adam Offord

Related Companies
ACO Technologies plc

This material is protected by MA Business copyright
See Terms and Conditions.
One-off usage is permitted but bulk copying is not.
For multiple copies contact the sales team.