Azuwater and Azuvoda

Grease Trap


Grease trap separator for domestic greywater (wastewater)

Category / type: wastewater pretreatment, organic oils and fats removing.
Application: restaurants, fast foods, kitchens, canteens, food industries.
Nominal Size – NS: 1, 2, 4, 7, 10, 15, 20, 25.
Normative references and guarantees: EN 1825-1 and 1825-2, d.o.p According to Regulation (UE) n.305/2011, local regulation.
Material: concrete, polyethylene, polypropylene, glass-reinforced plastic (GRP).

Organic oils and fats are usually part of civil and domestic wastewaters produced by kitchens, restaurants, fast foods, schools and workplace canteens. They also can be contained in industrial food processing wastewater as meat or fish processing.
The grease trap is a grey water (or gray water) pre-treatment used on separate sewers systems (in case of mixed sewer a septic tank is recommender).
Fat reduction is a necessary process to prevent pipe occlusion, often required by the sewerage management. It’s also required in any wastewater treatment plants to avoid problems in biological process: for example, fats decrease the bacteria contact with the organic matter and nutrients blocking their respiration.
The grease trap exploits the fats and oils flotation, (since they are lighter than water), and allows them to rise to the surface in a settling zone. The separation function and its efficiency are guaranteed only by a correct sizing and regular maintenance and if a correct cleaning maintenance procedure is done.
Grease trap works by gravity and therefore must be always kept full of water.
Different types with various specifications are available in the market; models equipped with sludge trap, able to retain the heavier solids settled, with air diffuser (grease floatation units) able to increase flow reducing space.
Grease traps are composed with baffles necessary to retain solids and floating materials avoiding sludge dragging and allowing clarified wastewater exit.


How It Works

The grease trap sizing is performed considering inlet flow, grease intake, fat type and it’s flotation velocity (depending on temperature). An appropriate volume is also needed to separate and accumulate material during a reasonably long period between cleaning operations.
There are several empirical design methods: an average rising rate of the floating material between 5 and 15 m/h should be considered. The required detention period is usually much lower compared to septic tanks.
Often technical sheets generically refer to population equivalent (PE) or to generic number of meals per day instead of nominal size.
Grease trap design and installation are regulated, according to European reference, by EN 1825-1 and EN 1825-2 standards: the first one defines principles of design (volumes, surfaces requests, etc.) depending on the nominal size (NS), the second one establishes the criteria for the selection of nominal size according to the user.
Some local regulations refer to a minimum volume per capita instead of nominal size.
Grease trap works exclusively by gravity, therefore oversizing: allows to reduce the frequency of cleaning operations and does not effect the trap efficiency.
Proper ventilation must be provided; if a ventilation column to the roof is present in the building, the gas can leak by the sewage pipes, otherwise a proper dedicated one directly connected to the tank must be provided.


Operation and maintenance

For grease trap any particular procedure or startup are needed; it must be filled with clean water up to the normal operating level before working.
Monitoring of accumulation of grease and sludge is important. Once the accumulation volume is saturated, a cleaning operation should be performed to avoid a reduction of the residence time and a decreasing of the efficiency. The maintenance and cleaning operations must be carried out by authorizated contractor and waste materials must be taken up to appropriate treatment systems.
All the light substances and gross bodies accumulated should be removed before cleaning operations. When finished, the tank must be filled with clean water up to the operating level in order to supply the medium useful for the separation processes.


Regulatory framework

The main regulations are EN 1825-1 “Principles of design, performance and testing, marking and quality control” and EN 1825-2 “Selection of nominal size, installation, operation and maintenance”. They specify that the main dimensional parameter is the nominal size (NS) and which are the mechanical and efficiency tests to obtain the CE mark.
A declaration of performance (DoP) is required, as indicated by the EU Regulation. 305/2011.
Standard EN 1825-1 “does not cover grease separators intended to treat domestic wastewater from kitchen areas of single family dwellings, where the separator has a nominal size less than 1” (1 – Scope).
Grease trap installation is always subject to authorization by institutions.


Features and benefits

Grease trap is used as grey water pre-treatment (kitchens, showers, sinks, dishwashers and washing machines) to restrain animal and vegetable fats or foams (soap).
It is normally placed on separate sewerage as close as possible to the discharge source to minimize pipe length and avoid fat and foam particles aggregation, since water temperature decreasing causes a significant increase in the amount of fat aggregates and consequently pipe clogging.
Grease separators are often requested by the public sewerage service and are essential as a pre-treatment for small wastewater treatment systems.
The European Standard EN 1825-2 requires that water containing organic fat and oils must be collected in a grease trap (7.1) while water with faecal material (black water), rain water and water containing light liquids (mineral oils) are not allowed.

Advantages (benefits)

  • treatment simplicity;
  • no power supply;
  • little space required (underground installation);
  • low operating costs;
  • long service life.


  • low efficiency (pretreatment);
  • periodic maintenance depending on the use.



Products in category Grease Trap