Pre-cleaning in rainwater management is important in order to remove pollutants and impurities from roof or road runoff water. This protects the environment and bodies of water, prevents infiltration systems from clogging and protects technical systems. Pre-treatment measures are now mandatory in many areas.
In Germany, the following regulations, among others, must be observed:
- Code of practice DWA-M153
- Since December 2020: DWA-A102
- Since October 2024: DWA-A138
Stormwater treatment DWA-A102 vs. DWA-M153 vs. DWA-A138-1
The most fundamental change in DWA-A102 is the categorisation of connection areas into only three categories with different levels of pollution. A further subdivision is made according to the type of utilisation of the areas.
For the retention of pollutants, the following parameters can be tested in the test in accordance with DIBt:
"DIBt ZG_Niederschlagswasserbehandlungsanlagen_Teil_1_Mai_2023"
- Particle retention (AFS)
- Hydrocarbon retention (MKW)
- Heavy metal retention, zinc and copper
- Redissolution behaviour of heavy metals when exposed to de-icing salts
AFS63, defined as particles <63 μm of Millisil W4, which is widely used as a test material for rainwater treatment plants, is an important key parameter for contamination. The unit of measurement for the pollution of the surfaces is kg/ha. It has been defined as 280, 530 and 760 kg/ha for the three different surface types. In addition to contamination with solids, it is assumed that a large proportion of the dissolved dirt loads are present in particulate form and thus adhere to the AFS63. Due to their small size, they make up the largest surface share of the total particulate load. The aim of stormwater treatment is to reduce pollution to below the specified 280 kg/ha for Category I areas. DWA-A102 refers to the discharge into surface waters. This can be lakes, rivers or drainage ditches. For the area of infiltration, M153 remains valid until the publication of DWA-A138, which is currently in yellow print.
| AFS | Zinc and | MKW | Testing |
|---|---|---|---|---|
Sedimentation, filter and separation systems | ||||
| PLURAFIT filter with sedimentation, filter and separator insert PFB-F-100-SF | XX | X |
|
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| PLURAFIT filter with substrate PFB-F-Sub | XX | X | XXX |
|
| DRAINMAX Sedimentation, filtration and separation area DM-F-250 ES | XX | X | X | * |
| Sedimentation and filter shafts SF 1000 - 2500 | XX | X | X |
|
Trough drain systems | ||||
| DRAINMAX trough trench systems | XXX | XXX | XXX | ** |
| DRAINMAX trough-trench systems with capillary subsurface irrigation | XXX | XXX | XXX | ** |
Technical pre-cleaning systems | ||||
| Substrate filter channels | XXX | XXX | XXX | Depending on make |
| Substrate filter shafts | XXX | XXX | XXX | Depending on make |
* Testing AFS 63 Retention in preparation
** Testing not required / possible
Xsatisfactory - XX good - XXX very good
Sedimentation, filter and separation systems
The INTEWA sedimentation, filter and separation systems perform several tasks simultaneously. The heavy pollutants settle in the sedimentation area. As the overflow water runs through an immersion pipe into the drainage system, floating contaminants such as grease and oil are also retained in the sedimentation area. There is a filter element in the immersion pipe that prevents contaminants from entering the downstream drainage system.
Passage values (D) and reduced connection areas (A,u) according to DWA-M-153 for different rainfall intensity and filter shaft diameters (DN)
| Reduced connection area (A,u) | |||||
|---|---|---|---|---|---|---|
Typ | Ared (m²) | Qin (l/s) | critical rainfall intensity=15 l/s*ha | critical rainfall intensity=30 l/s*ha | critical rainfall intensity=45 l/s*ha | rainfall intensity (15,1) 100 l/s*ha |
SF 100 | 0.07 | 0.35 | 236 | 118 | 79 | 35 |
SF-ET2000 | 1.90 | 9.50 | - | - | - | 950 |
DN1000 | 0.79 | 3.93 | 2,618 | 1,309 | 873 | 393 |
DN1500 | 1.77 | 8.84 | 5,890 | 2,945 | 1,963 | 884 |
DN2000 | 3.14 | 15.71 | - | 5,236 | 3,491 | 1,571 |
DN2500 | 4.91 | 24.54 | - | 8,181 | 5,454 | 2,454 |
1x DM-T | 2.67 | 13.35 | 8,900 | 4,450 | 2,967 | 1,335 |
2x DM-T | 5.34 | 26.70 | - | - | 5,900 | 2,670 |
3x DM-T | 8.01 | 40.05 | - | - | - | 4,005 |
The PLURAFIT filter with sedimentation, filter and separator insert is usually used for the pre-treatment of run-off water from low-pollution areas upstream of rainwater infiltration systems and for retrofitting existing rainwater cisterns (sealing is then required). The dirt particles in the incoming water settle in the filter basket. The water then flows in an upward flow through an immersion bend with a stainless steel sieve into the overflow. Grease and oil are separated outside the immersion bend. For maintenance purposes, either the stainless steel strainer can be removed individually or the entire insert can be removed. The filter basket with the collected dirt can then be easily emptied.
PLURAFIT substrate filter shafts are used to remove arsenic, phosphorus, heavy metals and organic impurities (mineral oils) on the basis of iron hydroxide as part of rainwater treatment. The PF 300-SUB T+R substrate is filled into the PF 300-Sub C substrate cartridge, which is then placed in the PF 300-100 Base element. The PLURAFIT PF 300-SUB T+R substrate is able to remove and permanently bind substances dissolved in water by means of adsorption processes. The high capacity for the above-mentioned pollutants results in long filter service lives and therefore optimum cleaning performance with minimised investment costs. For maintenance purposes, only the substrate needs to be replaced and not the entire cartridge. This minimises maintenance costs. The PLURAFIT filter with sedimentation and filter and separator insert can be used as a pre-filter, for example. If the filter is operated in upflow mode (advantage: low height offset and uniform substrate flow), the water flows through the substrate from bottom to top. A height offset of > 10 cm must be taken into account between the inlet and outlet in order to overcome the flow resistance in the substrate. As the filter material must not stand in water all the time, a small drain must be installed to ensure that the filter drains after rainfall events.
With our tunnel infiltration systems, the polluted rainwater is first channelled into the sedimentation, filtration and separation area integrated into the system. The dirt is retained here. The water is then buffered in the large-volume tunnels and from there seeps into the ground. The special feature of this system is that the sedimentation, filtration and separation area is hydraulically connected to the downstream system in such a way that it can run empty. This means that its infiltration or retention volume is actively available as storage volume and is not lost. The tunnel elements are laid on a special high-pressure flushable fabric. Compared to other systems, the tunnel system is therefore the only system in which the infiltration trench floor can also be cleaned to ensure permanent infiltration capacity. This system is particularly cost-efficient in terms of transport, purchase, installation and operation.
The plastic pre-cleaning chambers are suitable for cleaning rainwater from small and medium-sized roof areas. They allow connection diameters of DN150 and DN200 and - equipped with the appropriate manhole - can be loaded up to lorry trafficability.
Features:
- Completely ready for connection
- No height offset between inlet and outlet
- Suitable for harmless and tolerable rainwater runoff in accordance with DWA-A 138-1
| VRS Plastics | ||
|---|---|---|
| Perm. traffic load | walkable/ car passable | Truck passable |
| Perm. overlap to tank shoulder [mm] | 425 to 670 | 800 to 1,000 |
| Height incl. dome set truck [mm], cover and frame on site | --- | 2,931 |
| Height with telescope dome [mm] | 2,500 to 2,749 | --- |
| Max. installation depth [mm] | 2,500 to 2,749 | 3,101 |
| Connections | DN150 / DN200 | |
| max. pipe crown [mm] | 1,760 | |
| Base tank height [mm] | 2,075 | |
| Weight [kg] | 120 | |
The concrete pre-cleaning chambers from INTEWA are ideal for larger construction projects. They are suitable for cleaning rainwater from large roof areas and open spaces with harmless and tolerable runoff. The main advantages are the robust design and the minimised product and installation costs. Concrete sedimentation/filter shafts allow connections up to DN400 and heavy-duty trafficability.
- Pre-cleaning chamber
- Inlet
- Outlet
Maintenance instructions
Each pre-cleaning system must be regularly monitored and maintained. We recommend checking the sedimentation, filter and separation systems for contamination twice a year. To do this, the filter basket is removed from the immersion pipe of the shaft and rinsed if necessary. The sludge content should be checked once a year. From a sludge height of 0.25 m to 1 m, depending on the system, a specialist company should be commissioned with the extraction. The sludge level can be measured reliably using a dipstick with a dip disc. Firstly, the dipstick is immersed to the bottom without the disc. The part protruding from the tank is measured. The process is repeated with the dipstick disc. The difference between the measurements gives the sludge layer thickness. From the maintenance vehicle, a DN100 suction hose is inserted through the immersion pipe and the sludge is sucked out with the water. The dirt in the edge areas is fed into the suction hose with a high-pressure rinsing hose. If any residue remains, the flushing hose is fitted with a suitable nozzle that allows it to be propelled into the relevant zone.
If I-CONNECT is installed, the operator of the system receives information about the sludge level, fill level, infiltration or throttling capacity of his system via his browser platform. This saves the cost and effort of on-site appointments and increases the safety of the system and can therefore pay for itself within a few years.
Trough drainage systems
According to DWA-A 138-1, infiltration via the vegetated soil zone is considered a treatment measure. A minimum thickness of the vegetated soil zone and a maximum material and hydraulic surface load must be observed. For example, with a thickness of > 30 cm and an area load according to category II, the swale area must be > than 1/50 of the connected, reduced, sealed area. For a 1000 m² reduced area, > 20 m² of swale area is therefore required.
Advantages
- Greened sponge city element directly on site, for example as a design element
- Lower investment costs compared to technical pre-filters
- Lower maintenance costs due to substrate replacement compared to technical pre-filters
- Greater operational reliability, lower risk of clogging
Disadvantages
- The surface of the trough can no longer be used
- Maintenance work, such as green maintenance for the trough, is required
- For deep troughs: Safety precautions must be taken to prevent access in the event of water accumulation due to heavy rainfall events
- Not always feasible due to topographical conditions
Standard trough trench drain system
Typical structure of a DRAINMAX trough trench drain system:- DRAINMAX tunnel
- Lateral and upper tunnel backfill
- Geotextile
- tunnel cover
- Topsoil
- Infiltration trench
- Groundwater gap
- revitalised soil zone
- Maximum water level
- Overflow and ventilation shaft
- Swale slope
- Rainwater inlet
Trough trench system with capillary subsurface irrigation
Similar to the classic swale infiltration system, the contaminated runoff water is first filtered and cleaned via the revitalised soil zone of a swale during pre-cleaning using capillary subsurface irrigation. From there, the water enters the storage area. This empties itself via the capillary underfloor irrigation system, watering the plants in the system and cooling the surroundings through evaporation. The excess water is channelled via the overflow into the connected infiltration trench, where it is safely returned to the groundwater.
1. Planting 2. Evaporation Minimization 3. Root Zone 4. Geotextile 5. Ventilation 6. Waterproofing, Membrane 7. Soil Zone 8. Water Storage Elements 9. Drain/Distribution Pipes | 10. Drainage Device 11. Groundwater 12. Drainage Layer 13. Conductivity Sensor 14. Water Storage Zone 15. Air Layer 16. Retention Basin 17. Dosing
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Technical pre-cleaning systems
Sedimentation filter systems are used in most rainwater management applications. Here in particular for run-off water from low or uncontaminated surfaces, such as roof run-off water. Technical pre-cleaning systems are used when a higher cleaning performance is necessary or required, e.g. for heavily contaminated rainwater, limited space, special pollutants or strict legal requirements. In these cases, we offer the following special solutions for pre-cleaning:
Gutters are used as pre-cleaning systems in stormwater management because they retain coarse debris such as leaves, sand and rubbish, control water runoff and thus protect downstream systems from blockages. They also contribute to water pollution control by removing pollutants from rainwater at an early stage.
- Location: At the edge of roads or car parks
- Construction:
- Concrete or plastic channel
- Grid cover for protection and safety
- Slight gradient for controlled runoff
Location: Residential areas, commercial areas or car parks with limited sealing
A substrate filter shaft is a compact and effective solution for cleaning rainwater in urban areas. The water first passes through a sedimentation area in which coarse particles are retained before passing through a substrate layer that specifically removes pollutants such as heavy metals and phosphates. Substrate filters are used in rainwater management wherever stormwater runoff needs to be cleaned before being discharged into water bodies, groundwater or an infiltration system. Typical areas of application are traffic and industrial areas where pollutants such as heavy metals, oil residues or tyre abrasion can get into the rainwater. They are also used in large car parks, logistics areas or petrol stations, as well as on roof surfaces with metallic or bituminous coverings. Substrate filters are also particularly relevant in areas with infiltration systems, where the water must be treated before entering the ground, and wherever water legislation stipulates limit values for pollutants.