DIN 1999-100 and DIN EN 858-2
The risk of backwater must also be taken into account in the case of wastewater containing mineral oils. The release of water-polluting substances from the separator must be prevented. Under no circumstances must stored liquid escape, even in the event of backwater.
To date, DIN 1999-100, Section 5.5.3 Inspection Facilities, stipulates: “Where necessary, protection against backwater must be provided.”
Furthermore, the requirement regarding ‘special conditions’ as set out in DIN 1999-100: Section 15.3.3 can only be met if no backwater into the separator system can occur and, at the same time, the following applies:
- no extraneous water can enter the separator system in the area not tested for tightness (above the tank area)
- and, when the automatic closure device is activated, the liquid level in the separator system cannot, by design, rise above the tank area
- Approval by the competent authority
According to DIN EN 858-2, the principle applies that light liquids must not escape from the separator system or the upper sections. Derived from this is the requirement that separator systems must be installed in such a way that the upper edge of the cover (ground surface) is positioned sufficiently high relative to the relevant level of the area to be drained.
What is an ELEVATION OF THE INLET POINTS? = Required structural height difference between the relevant level of the drainage elements connected to a separator system and the lowest manhole structure.
The relevant level of the drainage points and surrounding area is defined as:
- The top edge of the lowest connected drain, if only wastewater
- the maximum possible rainwater backflow level, if rainwater is also discharged
- Backwater level from the downstream sewage system
The reference level of the manhole structure is defined as:
- a safety margin of 30 mm from the top edge of the cover or
- a calculated distance taking into account the displaced volume of the cover
RWS: Calm water level, RSE: Backwater level, B: Petrol separator, P: Sampling system
RWS: Calm water level, RSE: Backwater level, B: Petrol separator, P: Sampling system
Taking the backwater level into account
In particular, the requirement regarding the backwater level has not yet been explicitly stated, but must be strictly adhered to in order to prevent the escape of stored light liquids.
What is an EXCESS ABOVE THE BACKWATER LEVEL? = The required structural height difference between the backwater level acting on a separator system and the upper edge of the lowest cover, plus a safety margin of 30 mm or a precise volumetric assessment of the cover.
If this is not structurally feasible, a backflow prevention system must be installed on the backflow side if there is no elevation. Please note the following:
- Lifting stations in accordance with DIN EN 12050 Parts 1 and 2 are always suitable
- If the inlet cannot be interrupted, a double lifting system is required
- Backwater valves may only be used if the inlet flow can be interrupted or
- there is a rise on the inlet side
- Backflow pump or lifting stations may be used in accordance with the relevant scope of application as specified in the approval
A build-up warning device is always required whenever backwater is to be expected. This also applies even if a sufficient elevation above the backwater level has been maintained.
Once a backflow has occurred in the separator due to a backflow event, the following measures must be carried out:
- Separate maintenance must be carried out in accordance with DIN 1999-100
- Documentation in the log book
- In the event of frequent backflow occurrences, a backflow prevention system is recommended.
- If there is no sufficient head (on the inlet and outlet sides), a warning device for sludge thickness and build-up is required.
Protection against backwater using a backwater valve is permitted if the inlet can be shut off or if a sufficient head is maintained on the inlet side. Where space is limited, the backwater valve can also be installed in the sampling system.
RWS: Calm water level, RSE: Backwater level, B: Petrol separator, P: Sampling system
When using a backwater pumping station, no interruption to operations is required.
RWS: calm water level, RSE: backwater level, B: Petrol separator, P: sampling system
