A Guide to Below-Ground Grease Traps

Grease management requirements vary depending on the size, layout and output of a commercial kitchen. While smaller at-source systems can be suitable for lower-volume applications, larger sites often need a more centralised solution.

For commercial kitchens producing higher volumes of fats, oils and grease, a below-ground grease trap can provide a larger-capacity, centralised solution. Installed outside the kitchen and connected to the site’s wastewater system, these units are designed to manage FOG before it reaches the sewer network, making them particularly suitable for busy foodservice environments where compact at-source systems may not provide enough capacity.

Grease traps and grease interceptors are installed within commercial wastewater systems to capture fats, oils and grease before they enter the foul sewer network.

This guide focuses specifically on below-ground grease traps, also known as in-ground grease interceptors. These systems are typically installed externally and are designed for larger-capacity or centralised grease management requirements. If you are looking for a compact system installed close to the kitchen sink or wash-up area, see our under sink grease traps instead.

Below, we explain how below-ground grease traps work, when they are suitable, the main systems available and what to consider before installation.

Below-ground (in-ground) grease traps, as the name suggests, are generally buried underground, and as a result, benefit from larger capacities than compact under-sink or other at-source grease trap systems. They are typically made from metal, concrete, fibreglass, or PVC. Many business owners prefer this type, as they are far more aesthetically pleasing, and provide a much cleaner look for their establishment, as they are almost completely hidden. Be aware that these types of grease traps require more work during installation, given that metal or large concrete separators have to be lifted in place by heavy machinery.

There are a number of below-ground grease trap brands you can look at if this style of grease trap is going to be suitable for your kitchen. They include:

The Trapzilla is a below-ground grease trap that provides advantages that a traditional below-ground grease trap simply does not.

Traditional grease interceptors frequently suffer separation efficiency losses when grease layers exceed 25% of the internal liquid depth volume. This is why older grease interceptor models have very large footprints – to provide an adequate operating service period before reaching 25% full. The unique design of our Trapzilla model maintains peak separation efficiency well past the 25% full threshold, allowing it to store up to 90% of its own volume in fats, oils, and grease in a small footprint.

The most powerful feature of the Trapzilla is that it has a horizontal baffle that prevents thermal inversion. Thermal inversion occurs when warmer effluent entering the machine causes colder fluids to circulate the grease trap. This reverses the process of separation, making the grease trap process far less effective.

Trapzilla offers high grease capacity within a relatively compact footprint, which can make it suitable where space for a conventional below-ground interceptor is restricted. Installation requirements will depend on the model, drainage layout and site conditions.

As with our Trapzilla grease trap range, the LipuMax P Series is also a below-ground grease separator. Owing to its expert construction from compact and rigid roto-moulded polyethylene, the LipuMax has a structural stability that is guaranteed for 50 years, which is one of the longest guarantees offered out of all available models.    

Aqua Mundus offers four versions of the LipuMax P series, each with slightly different levels of automation. The main difference between the models is the level of manual labour required to operate and maintain each of the interceptors. Their specific differences are outlined further on our website.  

There are key features and benefits to be gained from the LipuMax series. The first is that they are fully BS EN 1825 certified. Secondly, they have a superior level of stability, as they have a unique built-in rib structure, which can be keyed into the surrounding concrete, and a buoyancy-proof shaft that extends to the top edge of the manhole cover.

Furthermore, the LipuMax has the highest level of construction of all available models, and in addition to offering resistance to upwelling, the top section of the separator permits simple onsite height adjustment – making them suitable for full load classes A15 to D400 – reducing your requirement for slab-reinforcement. 

Currently the UK’s leading independent grease trap and wastewater management specialist, Aqua Mundus has a wide range of high-quality solutions for you and your business. We install and service an extensive range of below-ground grease traps from trusted brands, all designed to be a valuable investment for years to come.

To discover more about our below-ground grease traps, site surveys, or other services we offer, please contact us! We’d love to hear from you and would be more than happy to help and start with free, impartial advice.