What is a FOG

FOG is an acronym that stands for Fats, Oils, and Grease — a collective term used to describe organic substances commonly found in kitchen waste and food preparation by-products that often end up in drainage systems. In the context of wastewater management and plumbing, FOG refers to the accumulation of these substances within pipes, sewers, and treatment infrastructure, where they can cause serious operational and environmental issues.

FOG originates from both residential and commercial sources and is considered one of the primary contributors to drain blockages, sewer overflows, and wastewater treatment inefficiencies.

Sources of FOG

FOG can enter the drainage system from a wide variety of everyday activities and industrial processes. Key sources include:

Residential:

  • Cooking oil and pan drippings
  • Butter, lard, and margarine
  • Food scraps and dairy products
  • Sauces and gravies washed down the sink

Commercial:

  • Commercial kitchens and restaurants
  • Food processing and packaging plants
  • Cafeterias, bakeries, and takeaways
  • Abattoirs and meat handling facilities

In most cases, FOG is discharged into drains through sinks, dishwashers, and floor drains — particularly when hot water or detergents are used, which temporarily emulsify the grease and allow it to flow.

Behaviour in Drainage Systems

Once FOG enters the drain system, it begins to cool and solidify, adhering to the inner walls of pipes. Over time, this build-up:

  • Narrows the pipe diameter
  • Reduces flow efficiency
  • Traps other debris such as food particles, hair, and sediment
  • Eventually leads to complete blockages and sewer backups

In larger sewer networks, FOG can combine with non-biodegradable solids (e.g. wet wipes, sanitary products) to form large congealed masses known as “fatbergs” — some of which have reached several tonnes in weight and required industrial-scale removal operations.

Impacts of FOG on Wastewater Infrastructure

The accumulation of FOG in drainage and sewer systems can have serious consequences:

  • Blocked sewers and overflows: One of the leading causes of sanitary sewer overflows (SSOs), posing health and environmental risks.
  • Increased maintenance costs: Blockages and pump failures result in expensive emergency call-outs and repair work.
  • Damage to treatment plants: Excess FOG disrupts biological treatment processes and can clog screens, tanks, and pipes.
  • Odours and pest issues: Stagnant grease promotes foul smells and attracts rodents and insects.
  • Health and safety hazards: Overflowing manholes and kitchen drain backups pose slip and contamination risks in food service settings.

For these reasons, managing FOG is a priority for utility providers, local authorities, and facility managers.

FOG Management and Prevention

Preventing FOG-related issues requires a combination of source control, mechanical solutions, and public education. Common strategies include:

1. Grease Management Practices

  • Scraping food waste into bins before washing dishes
  • Avoiding pouring oils or fats down sinks or toilets
  • Using strainers to capture solids in kitchen sinks

2. Grease Traps and Grease Interceptors

  • Installed under sinks or in external drainage systems
  • Capture FOG before it enters the sewer, allowing for periodic removal
  • Required by law in many commercial kitchens and food service establishments

3. Regular Maintenance

  • Routine cleaning of grease traps and drainage systems
  • Use of biological dosing systems in some applications to break down FOG using bacteria

4. Public Awareness Campaigns

  • Water companies and councils often run “Stop the Block” campaigns to educate households on proper waste disposal
  • Labelling and in-kitchen signage in commercial settings

Regulation and Compliance

In the UK and many other jurisdictions, improper management of FOG can lead to fines, enforcement notices, or prosecution. Food service establishments are often required by environmental health officers or water utilities to:

  • Install approved grease management systems
  • Maintain cleaning and service records
  • Demonstrate compliance during inspections

Failure to comply not only leads to penalties but can also damage reputations and cause business interruptions.

Conclusion

FOG — fats, oils, and grease — may seem harmless when hot and in liquid form, but once introduced into drainage systems, they become a leading cause of blockages, overflows, and infrastructure damage. Managing FOG effectively requires a combination of responsible behaviour, proper equipment, and regulatory oversight. For households, businesses, and water authorities alike, proactive FOG control is essential for maintaining reliable, hygienic, and sustainable drainage systems. As urban populations grow and food services expand, FOG management remains a critical priority in modern wastewater operations.