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How to dispose of fats, oils, and greases for off mains drainage and sewage treatment systems

By: Andrew Baird on Feb 26, 2024

What is off mains drainage and sewage treatment?

Up to 3% of properties in the UK have off-mains drainage and sewage treatment systems. These properties are typically homes or businesses situated in more remote, rural, locations where a connection to the main sewer is not possible.

Wastewater is taken away from a property in two ways:

  • The house is connected to a pipe network leading to a main sewer and centralised treatment works, or
  • The building has its own private pipes and treatment system, known as off-mains drainage and sewage treatment.

Using these systems means that it is exceptionally important to dispose of fats, oils, and greases (FOGs) correctly to avert plumbing, environmental, and economic problems.

A common misconception about cooking oil disposal

It is a common misconception that you can wash FOGs away with soap and warm water, but water and FOGs cannot mix as water is denser with means they remain in the pipes causing damage and putting more washing-up liquid down the sink to counter the problem causes pipes to harden and the washing-up liquid to stick to other debris.

What happens when FOGs are poured down the sink and enter an off mains drainage and sewage treatment system?

Clogging: FOGs solidify and stick to the sides of pipes, forming a clog that blocks water from flowing. This can lead to slow-moving or completely stalled off main treatment systems.

Burning pipes: Pouring hot oil down a sink can burn plastic piping by eroding the inside.

Odours: FOGs decompose over time and produce unpleasant odours in the treatment system.

Environmental issues: When FOGs enter a treatment system, they can disrupt the treatment process, causing overflowing. If they enter bodies of water, they can cause severe damage to the environment and human health.

Economic issues: Not correctly disposing of FOGs can cost home and business owners a lot on plumbing repairs.

Rules for disposing of FOGs for commercial off mains sewage treatment systems

Restaurants and bars operating in the UK's food industry are legally required to dispose of FOGs correctly. Non-compliance can result in fines and forces closures - as stipulated in the Food Safety Act (FSA) 1990.

Installing a grease trap can prevent a build-up of FOGs and commercial food services should be aware of regulatory requirements regarding their use and maintenance to ensure compliance and prevent environmental damage.

What is a grease trap?

A grease trap, or grease interceptor, prevents blockages in off mains drainage and sewage treatment systems caused by FOGs. Grease traps efficiently collect FOGs before they enter the treatment system, storing them in a separate container to be discarded correctly and legally.

A wide selection of grease traps are available to suit different businesses for different reasons including above and below ground grease traps, grease dosing systems, and grease removal units.

Rules for disposing of FOGs for domestic off main sewage treatment systems

There are several different ways of disposing of FOGs:

  1. Allow the oil to cool before disposal. Hot oil can be a fire hazard, and it can also cause waste containers to break or melt.
  2. For small amounts of FOGs it can be spooned directly into the general waste bin when it cools, or paper towels can be used to absorb excess oil from greasy surfaces.
  3. For large amounts of FOGs pour into a tight sealed container, such as a plastic takeaway container, bottle, or jar. It's a good idea to leave a container next to the sink to use several times and then dispose of it when it is full.
  4. Dispose of the FOGs correctly in the general waste bin or by using a food waste recycling service that handles FOG disposal. These services use specialist equipment to recycle FOGs into biodiesel or other products.

Can I reuse cooking oil?

If you have a large amount of oil, and it is still in good condition and has not been contaminated, you can reuse it for cooking.

  • Strain the oil to remove any food particles using a sieve
  • Store it in a clean, airtight container for reuse. Oil can generally be reused several times but dispose of it if it becomes dark or smells bad.

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Topics: Wastewater Treatment

Andrew Baird

Written by Andrew Baird

Andrew is the Technical Director at WCS Environmental Engineering. Andrew has worked for WPL (now a part of WCSEE) since 2006 and has nearly 30 years’ experience in the water and wastewater treatment industry. Andrew has a background in traditional engineering and technical business development and has worked on technical projects for BAE Systems, North West Water & Yorkshire Water to name a few. Andrews’s commercial awareness goes hand in hands with his excellent knowledge in industrial effluent treatment and broad knowledge of Europe’s water and wastewater treatment needs in manufacturing and process industries.

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