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How can I test Fats, Oil and Grease (FOG) in water and wastewater?

In the UK alone, there are around 200,000 sewer blockages per year – with an estimated 75% of these caused by Fats, Oil and Grease – commonly known as FOG.

When fats and oils solidify inside water pipes they form blockages and reduce the capacity – ultimately resulting in costly down time for cleaning and clearing, or even burst sewer pipes.

Fat blocking a sewer in Kingston, London, UK in 2013
Fat blocking a sewer in Kingston, London, UK in 2013

In recent years large fat deposits in sewers have made the news – particularly the London “fatberg” in 2013, where over 15 tonnes of fat was removed from a London Sewer. Thames Water commented at the time; “If we hadn’t discovered it in time, raw sewage could have started spurting out of manholes across the whole of Kingston”

Off-shore oil platforms have tsted FOG for many years with portable analysers – these help to ensure the water they discharge does not contain high levels of oils, in a rapid on-site test.

With the effects being so significant both in cost and environmental impact, testing and monitoring of wastewater is important.

Below we have explored the legislation that applies to FOG discharge, and the methods available to test your wastewater samples for FOG levels.

What legislation applies to Fats, Oil and Grease (FOG) in water?

Several pieces of legislation exist in the UK to prevent fat, oil and grease from getting into drains and sewers, including;

  • The Water Industry Act (1991) – makes it an offence to pass any matter which may interfere with the free flow of wastewater to public sewers.
  • The Building Act (1984) – allows local authorities to demand owners have satisfactory provision for drainage, for example by installing a grease trap.
  • The Food Safety Act (1990) – allowing local authorities to inspect premesis. Problems caused by fat and oil in drains can result in failure to comply with these regulations.
  • The Water Resources (Scotland) Act 2013 – makes it an offence to pass fat, oil or grease into a public sewer system which interferes with the sewage treatment and disposal process.

Some countries have begun to impose discharge limits, such as in the USA where the Clean Water Act states a limit of FOG that industrial sites must adhere to. This approach could be extended to other countries if FOG contamination continues to be a costly problem.

How can I test for FOG in water and wastewater?

Koehler Instruments K25552 IR Analyzer for FOG, TPH and TOG testing of water, wastewater and soils
Koehler Instruments K25552 IR Analyzer for FOG, TPH and TOG testing of water, wastewater and soil

The fastest way to test for FOG content in water is using an Infrared Analyzer, such as the K25552 model by Koehler Instruments.

The overall method of testing is as follows;

  1. Take a set volume of sample (usually 100ml) and add to a separating funnel with a set ratio amount of solvent (usually 10ml)
  2. Shake for 2 minutes to extract FOG into the solvent portion
  3. Leave the separating funnel in a retort stand with retort ring, and allow the water and solvent portions to separate
  4. Fill the quartz cuvette with solvent, place into the analyzer and test

Not only does this method get results fast (10-15 minutes per sample, including the extraction) but working at room temperature ensures all volatile hydrocarbons remain in the sample and are measured.

This analyzer can also be used for TPH (Total Petroleum Hydrocarbons) and TOG (Total Oil and Grease) testing, by modifying the test method.

What solvent should I use for FOG testing?

The FOG content of a sample is dependent on the procedure and the solvent used. Working to a standard test method will also ensure all samples are tested in the same manner every time, across different shifts or locations. The ASTM method D7066-04 is one of the most popular for rapid tests and uses S-316 (chlorotrifluoroethylene) as the solvent, though other methods such as EPA methods can be used.

The test method used will state which solvent you should use – common choices are S-316 or perchloroethylene.


For more information on FOG testing in wastewater by IR analysis, just follow the links above or contact us with any questions;

One thought on “How can I test Fats, Oil and Grease (FOG) in water and wastewater?

  1. I need to measure FOG in wastewater samples, the instrument must be follow standard methods A-F-PE FTIR or ISO 11394

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