Separators have a watertight concrete body (See: Concrete chambers and tanks) and usually do not need extra load. Depending on the separator's location cast iron or cast iron and concrete manholes classes A15, B125, C250 and D400 or higher are used. In order to adjust the location of the separator's manhole slab to ground elevation there is an additional top element used made of concrete rings corresponding to the diameter of the separator's body. When the sewer system is located deep in the ground, a reduction slab and a chimney made of Dw = 1000 rings can be used. The inlet and outlet are located in the axis of the separator. It is also possible to deviate inlet and outlet axes (consult the catalogue for details) as well as connect several inlets.
A separator placed in a concrete tank with foundation on bearing soils up to 10 m below ground level does not need special foundation and does not need static calculations. Normally, excavation death is prepared using minimum 10 cm C8/10 (B10) concrete substructure or well-compacted layer of gravel or other course non-cohesive soil.
Separators should have gravitation inflow. In case of the need for wastewater pumping it is recommended that the pumping station is located after the separator. A separator must be located in a place providing access for a suction vehicle.
In order to reduce maintenance costs and improve ecological safety there is a possibility to connect a separator to alarm systems (See: Monitoring Systems) such as sediment level sensors, oil and overflow sensors. Regular monitoring of the device limits the necessity to physically control the device and shortens the reaction time of maintenance teams in case of a failure.
In grease separators organic oils are separated by means of gravity in the process of flotation. Due to lower density of grease particles than water particles, grease accumulates on the surface of water. The unique shape of deflectors placed inside the separator's body (at the inlet and outlet) forces a certain direction of wastewater flow and prevents the separated grease particles from leaving the separator. All impurities of higher density that flow into the separator settle on the bottom of the device.
Grease Separators with Settling Tank
Wastewater with suspended solids should be pretreated in a settling tank. A correctly designed settling tank should provide optimal treatment effectiveness and sufficient storage capacity for suspended solids (choosing a separator with a settling tank). Large solids suspended in wastewater have to be separated by baskets, sieves or other separating devices.
A settling tank can be a single-standing device (See: Settling Tanks) or can be integrated with a grease separator.
The purpose of using a set of integrated devices reduces space required for installation while providing high level of grease and suspended solids separation. Such devices can be found mainly in highly-urbanised areas.
Selecting a Grease Separator
The selection of a grease separator should be done on the basis of the quality and amount of wastewater to be treated by the device, simply – for mass catering facilities following the specifications featured in Tab. 8 or on the basis of the separator's throughput calculated (NS) according to PN-EN 1825-2.
In case of selecting a grease separator with a settling tank further calculations should be done (Tab. 9).
|Restaurants and other facilities
/ number of meals served daily
|up to 200||2|
|201 to 400||4|
|401 to 700||7|
|701 to 1000||10|
|1001 to 1500||15|
|1501 to 2000||20|
|2001 to 2500*||25|
* When exceeding 2500 meals a day the following have to be added to the separator's throughput value:
0.75 for every 100 meals (from 2500 to 3500 meals a day)
0.50 for every 100 meals (from 3501 to 4500 meals a day)
0.25 for every 100 meals (over 4500 meals a day)
Tab. 8. Guidelines for selecting a simplified version of a grease separator for mass catering facilities.