Key Takeaways:  

  • Effective FOG management in food service operations is essential to prevent potential consequences such as sewer blockages and environmental pollution.
  • A grease trap is a device designed to separate and capture grease, oils, and fats from wastewater, preventing them from entering the sewer system.
  • There are various types of grease traps including passive manual, automatic, and gravity traps. Each with its own pros and cons.
  • Maintaining and cleaning traps regularly is crucial to ensure their proper functioning and prevent blockages.
  • Proper FOG management is not only important for compliance with legal requirements but also for protecting the environment and future-proofing businesses against stricter regulations.
  • Investing in the correct type and size of grease management solution for individual business requirements and in different water authority areas is critical to staying inline with regulations and safeguarding businesses and the environment.


When it comes to running a successful food service operation, effective management of FOG (fats, oils, and grease) is of utmost importance. Without proper management, the consequences can be alarming. Did you know that clogged pipes and sewer backups caused by FOG accumulation can lead to expensive repairs and regulatory fines? Here we layout the basics including what grease traps are, how they work and the types of grease management solutions that are available. 

What is a grease trap?  

Grease traps play a crucial role in the effective management of fats, oils, and grease (FOG) in food service operations. Their purpose is to prevent FOG from entering the sewerage system where it can cool and solidify causing blockages and to limit environmental pollution. If FOG is allowed to accumulate in pipes, it can cause blocks and backups that result in costly repairs. 

Typically having a box design, a grease trap, depending on the type, will have multiple inner compartments and mechanisms to filter out contaminants. The basic equipment functions by intercepting and separating FOG from wastewater, allowing cleaner water to flow through drainage pipes. This ensures that the sewer system remains free of clogs and reduces the risk of costly repairs to pipework, inconvenience for the surrounding community and environment or fines due to non-compliance with regulations. Regular maintenance and cleaning are essential to keep fat traps operating efficiently.

As food service and catering businesses create the largest volume of used cooking oil, fats, grease and food juices, they are the main contributors to any blockages. Over time, accumulated FOG caused blockages in drainage systems, which when combined with solid waste that can be found in sewers such as toilet paper, wet wipes, sanitary products, condoms, nappies and even used syringes, can lead to extensive plumbing damage and costly repairs. It is critical for all food service businesses to understand the importance of effective grease management solutions and implement accordingly.

Common terms used to refer to grease traps

  • Fat traps: This term emphasises the primary function of grease traps, which is to trap and contain fats.
  • Grease interceptors: This name highlights the role of these devices in intercepting and capturing grease before it can cause problems in the plumbing system.
  • Grease separators: This term reflects the separation process that occurs within traps, where solid waste settles at the bottom while FOG floats to the top.
  • Grease removal units or grease recovery units (GRU's): Used as an alternative term for automatic grease traps. Automatic grease removal units (AGRU's) may also be referenced.
  • Oil-water separators: In some cases, particularly in industrial settings, grease traps may be referred to as oil-water separators due to their ability to separate oil and water effectively

It is worth noting that these terms may be used interchangeably depending on regional preferences or industry-specific terminology. However, they all refer to the same device that helps manage FOG in food service and catering operations.

How does a grease trap work?

Understanding how a grease separator works is essential to understanding it's importance and how it can benefit a catering and food service business, as well as the level of cleaning and maintenance that is required.

Understanding the principles behind grease trap operation  

Grease traps are designed to intercept wastewater from kitchen sinks and dishwashers before it enters the sewer system. The basic principle allows the grease to rise to the surface or filter out into a separate container while trapping solids and sediment at the bottom, allowing uncontaminated water to continue through to the main system. Depending on the type of trap this separation is achieved through a combination of gravity and buoyancy or via a small heater system.

As wastewater flows into the trap, it slows down, allowing the heavier solids to settle at the bottom. Grease and other fatty substances, being lighter than water, float to the surface or are separated into a separate basket/container from the cleaner water. The trap's design includes baffles that help to slow down the flow further and facilitate better separation.

The process of grease separation and capture in a manual and automatic trap  

The primary mechanism involved in basic manual or passive grease traps is gravity and a series of chambers. As wastewater containing FOG enters the trap, it undergoes a slowing down process, allowing the less dense fats and oils to rise to the top while solids settle at the bottom. This separation occurs due to the difference in density between water and FOG.

Once separated, the captured grease remains floating on top of the water while relatively clean water exits through the outlet pipe of the trap. The trapped FOG can then be manually removed or pumped out for proper disposal as per local regulations.

Automatic traps or grease removal units (GRUS) use a small heater to prevent FOG from cooling and solidifying. Non-mechanical traps use a form of pressure to force FOG into a separate connected chamber which can then be emptied as required. Mechanical GRUs allow the FOG to cool and solidify in the same way that a passive grease trap does yet has a skimming mechanism that removes the top layer from waste water periodically into a separate container.  

It is worth noting that the efficiency of grease separation and capture largely depends on regular maintenance and cleaning of the trap. When left unchecked, accumulated FOG can solidify, causing blockages and reducing trapping capacity over time. Similarly, where separate chambers are used to capture FOG, these will reach capacity and cause health and safety concerns. 

The different types of grease traps  

When it comes to grease trapping equipment, there are several types to choose from. Each type of trap has its own features and benefits so that every requirement can be met. Understanding the different types of grease management solution available is vital to understanding the type of fat trap most suitable for your specific needs.

Passive grease traps

Passive or manual grease traps are an essential component in effective FOG management. Operating with a basic level of function, stainless steel grease traps or outdoor epoxy grease traps use hydrodynamic processes to separate and capture grease.

Key Points:

  • Passive hydro mechanical grease traps are designed with a simple yet efficient mechanism that allows for the separation of grease from wastewater.
  • These types of grease interceptors typically consist of baffles or plates that slow down the flow of wastewater, allowing gravity to aid in the separation process.
  • The captured grease is then trapped within the device, preventing it from entering the sewer system and causing blockages.

Passive or manual traps offer a cost-effective solution for FOG management, ensuring compliance with environmental regulations without relying on complex machinery or automation. Stainless steel materials are strong and durable, perfect for indoor positioning. Epoxy coated steel traps are also weatherproof making them ideal not only for indoors but also outdoor or underground placement.

Some reports by Aqua Mundus have suggested that, depending on the size and output of the kitchen, passive hydro mechanical (manual) grease traps can effectively remove between 50% and 90% of fats, oils, and greases from wastewater.

Gravity grease traps are also available however are typically installed outdoors and have a much greater flow rate making them perfect for larger establishments.

Automatic grease traps

Automatic grease traps, also known as grease removal units or grease recovery units (GRUs) or automatic grease removal units (AGRUs), are advanced systems designed to efficiently separate and capture fats, oils, and grease (FOG) from wastewater in food service operations. These innovative devices utilise cutting-edge technology to automate the process of FOG removal, ensuring a high level of efficiency and effectiveness. 

Many automatic GRU's are designed with the grease container being removed vertically. This is perfect when used in conjunction with high level equipment with plenty of vertical space between the top of the trap and the equipment it is placed under, if applicable. When grease removal units are used with low-level equipment such as commercial combination ovens or wok cookers, there may not be enough room for vertical removal of the full FOG chamber. As grease traps may be fixed, and therefore unable to be pulled out, an alternative solution is required. Goslyn have a low-profile trap, Goslyn GOSLOC20 Low Level Automatic Grease Trap, that allows the fat collection basket to be removed horizontally rather than vertically, to allow for applications that are limited by space. 

Key Features:

  • Enhanced Efficiency - Incorporates sensors to detect and skim FOG from wastewater within the trap. Non-mechanical GRU's using pressure to force FOG into a separate fat collection container.
  • Large Capacity - Not only a large tank for overall water volume but also equipped with sizable connected storage tanks, sometimes referred to as baskets, that can accommodate significant quantities of FOG.
  • Real-time Monitoring - Levels of FOG are clearly visible to monitor when emptying is required.
  • Easy Maintenance and Less Down-Time - Unlike passive manual traps, automatic grease GRUs do not need to be completely opened during cleaning so there is less disruption to the business. This allows for continuous operation without frequent shutting down for emptying and cleaning.
  • Compliance - Meets all relevant industry standards and regulations for FOG management in food service establishments. Helps businesses stay in compliance with legal requirements to avoid penalties or fines. 

Automatic grease removal or recovery units offer numerous advantages over traditional manual or passive hydromechanical grease interceptors. Their automated operation ensures a consistent level of performance, minimising the risk of human error in FOG management. Additionally, these systems provide real-time data on FOG levels, allowing for better monitoring and control.

 Bio-dosing solutions

Bio-dosers are not required yet may be used in conjunction with a standalone trap. Using bacteria rather than chemicals to tackle FOG directly in your drain, these solutions, such as GreasePak, distribute the bacteria into pipes that coats the inside walls and breaks down fats, oils and grease as they flow through. Bio-dosing equipment, such as GreaseBeta, can also be used to break down FOG within your existing trap which can reduce cleaning frequency. GreasePak Bio-Enzymatic Fluid Refills, GreaseBeta Liquid Fat Digester and GreaseBeta ECO20 Fluid refills are available to allow for continued use. It is advised that bio-dosers always be used alongside a functioning manual FOG trap when being used directly for waste pipes. 

Pros and cons of each type of grease management solution  

Grease traps play a crucial role in FOG management, but each type has its own advantages and disadvantages. Here we discuss the pros and cons of different models.

Type of System

Passive hydromechanical (manual) grease traps


  • Low initial cost.
  • Simple installation.
  • No dependency on electricity or mechanical parts.


  • Requires frequent manual maintenance.
  • Inefficient at trapping smaller food particles.
  • Potential odour issues if not properly cleaned.

Automatic grease traps

  • Semi-automatic operation
    Increased efficiency in capturing FOG.
  • Reduced maintenance frequency compared to manual traps.
  • Higher upfront investment.
  • Possibility of mechanical failures that require repairs or replacements.
  • Potential power supply requirements for operation.


  • An additional defence against FOG build-up.
  • Can be used with existing grease management solutions.
  • Can be expensive to purchase and will have an ongoing cost with fluid refills.

Pro Tip: Before making a decision, consider factors such as budget, space availability, maintenance requirements, and potential future regulations. It is advisable to consult professionals for guidance tailored to your specific needs and circumstances and to enquire with your local water authority before making an investment, to ensure that your choice will meet required regulations.

What types of food service premises should have a grease trap? 

Grease interceptors have various applications in different settings such as restaurants, commercial kitchens, and food processing facilities. They are designed to handle specific volumes of wastewater based on the size of the establishment and the level of FOG production.

  • Commercial kitchens, takeaways and restaurants: These types of premises are one of the major contributors and producers of FOG, and so grease separators are essential to prevent FOG from clogging the sewer system by capturing grease and solids before they enter the drainage system.
    • Food service operations: Grease separators are commonly used in food processing plants, catering companies, and other similar establishments to trap FOG and prevent its discharge into the wastewater system.
    • Industrial facilities: Industries that generate large quantities of FOG, such as slaughterhouses or oil refineries, utilise fat traps to ensure proper management and disposal of FOG waste.
    • Institutional buildings: Hospitals, schools, and government buildings also benefit from grease interceptors to maintain proper wastewater management by removing FOG from the drainage system.

    In addition to these settings, grease management systems can also be found in elderly care homes where large quantities of meals are prepared in a commercial kitchen setting. Such applications highlight the importance of implementing effective FOG management strategies across a range of environments.

    Research carried out by Collin, Thomas et al. in "Towards a risk ranking for improved management of discharges of fats, oils, and greases (FOG) from food outlets" highlights the importance of educating food service businesses and commercial catering settings on the dangers posed by FOG in wastewater, employing effective grease management system and utilising other grease limiting practices.

     The importance of effective FOG management in food service operations  

    As a main user and producer of cooking oil, fats and grease food service businesses contribute a high volume of the FOG that ends up in the mains water system. Appropriate grease management will benefit in many ways.

    1. FOG management prevents blockages: Proper management ensures that FOG does not clog the sewerage system or drainpipes, preventing costly and time-consuming blockages.
    2. Environmental protection: Effective FOG management reduces the environmental impact by preventing FOG from contaminating water bodies and affecting aquatic life.
    3. Compliance with legal requirements: Implementing proper FOG management practices ensures compliance with regulations governing wastewater discharge, avoiding penalties and reputational damage.
    4. Operational efficiency: By efficiently managing FOG, businesses can avoid disruptions caused by clogged drains or sewers and ensure uninterrupted food service operations.
    5. Future-proofing against stricter regulations: As regulations surrounding FOG management are expected to become more stringent in the future, implementing effective strategies now can help businesses stay ahead of compliance requirements.

    Potential consequences of inadequate FOG management  

    Blockages are likely when a grease management solution isn't in use or isn't correctly implemented. These blockages can impact the surrounding community when drains become clogged leading to sewage backups and overflows. The environment is also affected, with any incident posing serious health risk, contamination of water sources, and potentially long-term ecological consequences. Inadequate handling of hazardous FOG's will also incur fines, penalties or even the closure of the offending business should appropriate measures not be in place. 

    Additionally, as regulations surrounding FOG management continue to evolve and become more stringent, it is crucial for businesses to future-proof themselves against potential consequences. By implementing effective strategies for managing FOG, businesses can ensure compliance with current and future regulations while also protecting their reputation.

    To avoid these potential consequences of irresponsible practices and fog management, it is imperative for food service operations to prioritise proper methods of handling fats, oils, and grease. Investing in a suitable trap for the size of the business is vital. Regular maintenance and cleaning of grease traps are essential to prevent blockages and minimise environmental impact. By investing in suitable grease trapping systems and adhering to best practices for disposing of FOG waste, businesses can mitigate the risks associated with inadequate fog management.

    Best practice for grease management in food service settings  

    While investing in a suitable FOG trap is a major step forward in responsible grease management, there are other practices that should also be implemented. 

    Regular maintenance and cleaning of grease interceptors are essential for effective FOG management. Properly maintained traps ensure that they continue to function efficiently in capturing and separating FOG from wastewater. Grease trap cleaning should be performed by licensed professionals who can dispose of the collected FOG properly. 

    In order to reduce environmental implications further, businesses should consider encouraging additional strategies alongside grease separator usage. This may include educating employees about proper disposal practices for fats, oils, and grease, as well as implementing preventive measures such as installing food scrap collectors or using strainers in sinks. Even small actions such as wiping used plates with kitchen towel before rinsing in the sink can have a big impact. The kitchen towel removes residual FOG from the plate which can then be disposed of in the bin rather than being rinsed down the sink.

    Environmental implications of FOG in the sewer system

    FOG (Fats, Oils, and Grease) in the mains sewer system can have significant environmental implications. These substances can cause blockages and clogs in the pipes, leading to sewage backups and overflows. The presence of FOG can also contribute to the build-up of harmful bacteria and odour issues. Additionally, when FOG enters water bodies through untreated sewage discharges, it can harm aquatic life and disrupt ecosystems. Proper management of FOG is crucial to minimise these environmental impacts.

      Legal requirements and potential action for non-compliance  

    In addition to their practical purpose, there are legal requirements for proper FOG management. There are regulations in place that mandate businesses to implement effective FOG management strategies, including the use of suitable grease managing equipment. Failure to comply with these regulations can result in penalties or even closure of operations. It is crucial for businesses to prioritise proper FOG management not only to meet current requirements but also to future-proof their operations against increasingly stringent regulations.

    What is the standard for grease traps in the UK? 

    UK Building Regulations state: (Part H 2.21) -Drainage serving kitchens in commercial hot food premises should be fitted with a grease separator with EN1825-1 and designed in accordance with EN 1825-2 or other effective means of grease removal.

    The legal obligations and potential repercussions associated with failing to meet regulatory standards are vital aspects to consider when it comes to complying with laws and guidelines. Failure to adhere to the necessary legal requirements can result in serious consequences, both in a financial and reputational aspect. It is imperative for businesses to understand and comply with these regulations, as non-compliance can lead to penalties, fines, and even legal action.

    • Businesses must be aware of the specific legal requirements related to FOG management, particularly in the food service industry. This includes understanding local regulations regarding the installation, maintenance, and inspection of grease traps.
    • Failing to comply with legal requirements can have consequences for businesses found to be non compliant or contravening regulations. In addition to potential fines and penalties imposed by regulatory authorities, non-compliant businesses may also face reputational damage. Negative publicity could harm future sales and customer trust.
    • Moreover, non-compliance can result in environmental harm as FOG enters the sewerage system. The accumulation of FOG may cause blockages in pipes and wastewater treatment facilities, disrupting the proper functioning of the system.

    It is crucial for businesses to stay up-to-date on evolving regulations and take proactive steps towards compliance. By implementing effective FOG management strategies, such as installing and maintaining appropriate grease traps, businesses can mitigate potential risks associated with non-compliance while ensuring a sustainable environment for all. 

    A real-life case involving inadequate grease management systems and potential contributing behaviours for fatbergs highlights the impact of non-compliance with FOG management regulations. A Nottingham restaurant was found to be repeatedly causing blockages in the area through inadequate grease management and failure to address the situation. A fine was issued for non-compliance, costs to cover remedial works and a victim surcharge. It serves as a stark reminder of the potential consequences that can arise from inadequate FOG management and non-compliance with legal requirements. 

    Choosing the correct grease trap to meet individual business requirements 

    There are many areas to consider before choosing the most suitable grease trap for resturants, catering kitchens and food service premises.

    • Size - the dimensions of the equipment in relation to the intended position e.g. grease traps under sinks, for commercial dishwashers or used in conjunction with specific cooking equipment such as combination ovens and wok cookers.
    • Type - passive/manual or automatic gru's.
    • Water Flow - the volume of wastewater that the kitchen deals with.
    • Number of sinks or pieces of equipment connected to the waste outlet.
    • Maintenance and cleaning - passive and manual traps will require complete cleaning of the whole unit while automatic traps with a separate FOG basket can simply remove and empty the attached container only according to disposal guidelines.
    • Additional filtration systems or pre-treatment devices - does the premises require additional bio-dosing equipment.

    A suitable grease interceptor is required for any equipment that may release FOG into the mains water system. The obvious culprits are sinks, but commercial dishwashers, combination ovens and wok cookers are also prime contributors. Did you know that some water authorities are recommending a 400 litre passive system for Chinese takeaways that use a wok cooker? The majority of kitchens would not be able to accommodate this, however an automatic grease trap is a suitable alternative. Don't think that you'll slip under the radar by installing just any sized grease trap - it must meet requirements to satisfy regulations. Why Installing Grease Traps is Essential for Chinese Restaurants & Takeaways

    Different water authorities may have different criteria, Thames Water and Severn Trent seeming to be the most diligent and so it is vital that you correspond and work closely with your local authorities to ensure your business meets the requirements for your area. 

    By considering these suggestions, businesses can effectively manage FOG in diverse settings while complying with environmental regulations and ensuring long-term sustainability. 

    Whether you've received a letter from your local authority advising that action be taken, you've had a personal visit and inspection of site and are acting on suggestions or are being proactive and addressing a potential issue before a problem occurs, it is advised to arrange a site consultation with an experienced company that can advise solutions based on your specific requirements. Before purchasing, check your proposed grease management solution with your local water authority before buying to make sure it meets requirements prior to spending money.

     Maintenance and cleaning requirements for grease traps

    To ensure continuous effectiveness in fog management strategies, regular maintenance and cleaning of grease traps to prevent build-up is vital, along with educating staff on proper disposal practices to minimise FOG contributions, installing appropriate grease interceptors based on business needs, and partnering with professional services for specialised cleaning.

    1. Regular inspection: Schedule routine inspections to assess the condition of the trap. Look for any signs of damage to the structure and seals or clogs that may hinder its efficiency.
    2. Periodic cleaning: Grease interceptors should be cleaned on a regular basis to prevent build-up and blockages. Remove accumulated fats, oils, and grease manually or through the use of specialised cleaning solutions or professional grease trap cleaning companies. As manual/passive grease traps must be completely opened during cleaning, the entire kitchen must be shutdown as bacteria and odours will escape into the surrounding area. Once cleaning has been completed the kitchen must undergo a deep clean before re-opening and resuming normal operation. Automatic grease traps are much easier to clean. Simply remove the FOG collection basket and clean out any debris or sediment from the tank; no need to shutdown the kitchen entirely.  
    3. Proper disposal: Dispose of the collected FOG waste in compliance with local regulations. This will help prevent environmental contamination and potential legal consequences.

    It's important to note that grease trap maintenance and cleaning requirements may vary based on specific regulations and business needs. Stay informed about any updates or changes to ensure ongoing compliance.

    In addition, adequate training should be provided to staff responsible for maintaining and cleaning grease traps to ensure proper procedures are followed.

    Poor cleaning and maintenance can have almost as much of a negative impact as not having a grease management solution at all. Once a trap becomes too full it will no longer work effectively, or at all.

    Expert Advice - Always work to the 25% rule - The total depth of the sediment layer and the floating fat layer should not exceed 25% of the total liquid depth if the grease trap is to operate adequately and effectively.  

     Recommendations for implementing effective FOG management strategies   

    In order to manage fats, oil and grease effectively in food service operations, there are several key strategies that can be implemented.

    1. Invest in appropriate equipment: Choosing the right type of grease trap for your specific needs is essential. Consider factors such as size, capacity, and ease of maintenance when selecting an appropriate system. Additionally, investing in monitoring equipment that can measure FOG levels in real-time can help identify any issues early on and ensure prompt action is taken.
    2. Implement regular maintenance and cleaning schedules: It is essential to establish a routine maintenance and cleaning schedule for grease traps. This includes regularly inspecting and cleaning the trap to prevent build-up of FOG. By adhering to a consistent schedule, potential issues can be identified and addressed before they become more serious problems.
    3. Train staff on proper FOG management procedures: Providing comprehensive training to staff members on the importance of FOG management is crucial. This includes educating them on the proper disposal of FOG and ensuring they understand the potential consequences of improper management. By empowering staff with this knowledge, they can actively contribute to effective FOG management practices.

    It is important to note that these recommendations for implementing effective fog management strategies are just a starting point. Each food service operation may have unique requirements that should be considered when developing a comprehensive strategy.

    Looking for more information on grease management solutions? Check out these sizzling comparisons on How Do I Know If I Should Get A Manual Or Automatic Grease Trap?, Grease Digesting Bio-Dosers: A Standalone Solution? and What Size Grease Trap Do I Need?

    Grease management FAQs  

    What is the impact of FOG on the UK sewerage system?  

    It is reported that approximately half a million tonnes of FOG is deposited into the UK mains drainage system annually. This may be from domestic and commercial premises, although primarily food service and catering premises where a large amount of used cooking oils, fats and oils are created. This grease and FOG when cooled, solidifies and sticks to pipe walls, leading to blockages and eventually fatbergs when combined with solid waste, while fats and oils damage waste water treatment equipment, costing authorities millions in repairs.

    Why is legislation being enforced for FOG management by food service operators?  

    Legislation is being enforced to ensure effective FOG management due to the serious environmental damage caused by fats, oils, and grease if they enter natural water courses. Polluters can face large fines or closure if FOG waste isn't managed properly.

    How does a grease trap work?  

    A grease trap is a receptacle that intercepts and traps fats, oils, and grease (FOG) from wastewater before it enters a drainage system. FOG floats on top of water allowing for separation. Grease rises to the top and is trapped using baffles, while clear water escapes under an outlet baffle. Solids settle at the bottom.

    What are the different types of grease traps?  

    There are three main types of grease traps: passive or manual, automatic, and gravity. Passive traps are manually cleaned, automatic traps re-heat and skim out FOG automatically, and gravity traps are large in-ground tanks. Additional bio-dosing equipment is also available to help break down FOG in grease traps or pipes.

    How often should a grease trap be cleaned?  

    The time between cleaning depends on wastewater production and the grease trap's size. Generally, it is recommended to clean/pump out the trap every 2-4 weeks. Adding a biological grease treatment fluid can extend this period to up to 8 weeks. Pay attention to the 25% rule - the total depth of the sediment and floating fat layer should not exceed 25% of the total liquid depth.

    What are the benefits of using an automatic grease trap?  

    Automatic grease traps, also known as grease removal units (GRU's or AGRU's), automatically re-heat and skim out FOG. This eliminates the need for manual measurements and checks. Although they have a higher initial cost, they are more efficient and have lower long-term running and servicing costs compared to manual grease traps.