Selecting the appropriate oil separator must be based on a detailed analysis of the installation site, as project conditions directly affect system sizing and configuration. Only a properly selected and dimensioned separator ensures optimal oil separation and compliance with applicable regulations.
An important component of oil separators is the sludge trap (sedimentation chamber). This is the part of the unit where solid particles (sand, sludge, and larger debris) settle at the bottom before the oil-contaminated water proceeds to further treatment stages.
The table below shows the minimum sludge trap volume depending on the installation location. The data is based on the SIST EN 858 standard.
IMPORTANT: The appropriate oil separator category is determined by the designer. The sludge trap volume must be defined in accordance with the table below.
| Category |
Application of oil separator |
Minimum sludge trap volume |
| Small |
For water with low sediment content – e.g. collection areas at petrol stations, lightly loaded parking areas |
(100 × NS) / fd a |
| Medium |
Petrol stations, manual car washes, garages, parking areas, industrial facilities, power plants |
(200 × NS) / fd b |
| High |
Truck washes, city buses, agricultural vehicles, automatic car washes |
(300 × NS) / fd b
(300 × NS) / fd c |
Notes:
a – the equation does not apply to separators smaller than NS 10, except for covered parking areas
b – regardless of the equation, the minimum sludge trap volume must not be less than 600 l
c – regardless of the equation, the minimum sludge trap volume must not be less than 5000 l
