The amount of rainfall sewage
Nominal flow (amount of sewage requiring pre-treatment)
Qnom = qnom·F·ψ
Qnom – intensity of precipitation [/ (s · ha)]; in accordance with the Regulation of the Ministry of the Enviroment from November 18, 2014:
– 77 dm3/(s·ha) for storage areas and gas stations
– 15 dm3/(s·ha) for industrial areas, transport bases, harbours, airports, cities, Category G national, provincial or county roads, as well as car parks with a surface area of over 0.1 ha
F – watershed [ha]
ψ – outflow factor
| Type of water catch basin | Outflow factor ψ | |
| Roofs | roof pitch over 15º | 1,00 |
| roof pitch below 15º | 0,80 | |
| gravel | 0,50 | |
| Asphalt | 0,8-0,90 | |
| Cobblestone | 0,8-0,85 | |
| Gravel | 0,15-0,30 | |
| Roof gardens | 0,30 | |
| Ramps and car washes | 1,00 | |
| Pressed concrete, covered by tar paper or concrete | 0,90 | |
| Chodniki pokryte płytami | 0,60 | |
| Pavements without paving blocks, yards, alleys | 0,50 | |
| Playgrounds and sports fields | 0,25 | |
| Greenery, gardens | 0,10-0,15 | |
| Parks | 0,05 | |
Maximum flow
Qmax= qmax·ψ·φ
qmax – maximum rainfall density / maximum severe rainfall density [/(s·ha)]
| qmax = | 6,631 * 3√H2*C |
| t 2/3 |
H – annual normal precipitation (average 600 mm) [mm]
t – duration of rainfall [min]
C – frequency of rainfall [years]
P – probability of rainfall [1/year]
| P | C | Qmax [dm3/s·ha] fot t [min] | |
| [1/year] | [years] | t =10 min | t =15 min |
| 100,0 | 1,0 | 100,0 | 77,0 |
| 50,0 | 2,0 | 126,0 | 97,0 |
| 20,0 | 5,0 | 172,0 | 132,0 |
| 10,0 | 10,0 | 216,0 | 166,0 |
| 5,0 | 20,0 | 273,0 | 210,0 |
F – watershed [ha]
ψ – outflow factor (see “Nominal flow”)
φ – delay factor (retention) depending on size, shape and fall of water catch basin
| φ = | 1 |
| n√F |
where n = 4-8
The more compact the water catch basin is (with a similar shape to a circle) and falls greater- the greater the n. The flatter and longer the water catch basin, the smaller the n.
Industrial wastewater
On the basis of PN-EN 858-2 norms
Qnom device = 2 · Qs· fd
Qs – amount of industrial wastewater; on the basis of PN-EN 858-2 norms
Qs = Qs1· Qs2· Qs3· Qs4· Qs1· Qs1 [dm3/s]
Qs1 – amount of wastewater from water access points
Qs2 – amount of wastewater from car washes. For one device Qs2 ≥ 2 dm3/s; for more than one device: 2 dm3/s for the first device and 1 dm3/s for the rest of the devices.
Qs3 – amount of wastewater from high pressure washers. For one device Qs3 ≥ 2 dm3/s; for more than one device: 2 dm3/s 2 for the first device and 1 dm3/s for the rest of the devices.
Qs4 – amount of industrial wastewater
| Diameter of valve taps | |||
| Water access point | DN 15 (1/2”) | DN 15 (1/2”) | DN 25 (1”) |
| Amount of wastewater Qs1 [dm3/s] | |||
| 1 | 0,50 | 1,00 | 1,70 |
| 2 | 0,50 | 1,00 | 1,70 |
| 3 | 0,35 | 0,70 | 1,20 |
| 4 | 0,25 | 0,50 | 0,85 |
| ≥5 | 0,10 | 0,20 | |
| Density of separated fluid [g/cm3] | fd |
| to 0,85 | 1,00 |
| over 0,85 do 0,90 | 1,50 |
| 0,90 do 0,95 | 2,00 |
SELECTING THE SIZE OF THE SEPARATOR
| Rainfall sewage | ||
| Coalescence separators | Qnom separator (NS) > Qmax sewage | |
| Lamella separators | Qnom separator (NS) > Qmax sewage | Qmax separator (NS) > Qmax sewage |
| Coalescence separators with by-pass | ||
| Industrial wastewater | ||
| Coalescence separators | Qnom separator (NS) > Qmax sewage | |
Capacity of settling tank
| Estimated sample amount of sewage sludge | Minimum volume of settling tank | |
| None | - condensate | Not needed |
| Small | - Industrial wastewater with a small amount of sewage sludge - all areas precipitation water where there is a small amount of sludge from traffic etc. |
100 · NS a |
| Medium | - gas stations, car washes - places for washing buses - wastewater from garages and parking lots - power plants, service stations |
200 · NS b |
| High | - washing devices for off-road vehicles, construction machinery, agricultural machinery - places for washing lorries and trucks |
300 · NS b |
| – automatic car washes |
300 · NS c |
|
| a Does not apply to separators smaller or equal to NS 10 b Minimum volume of sedimentation tanks 600 l c Minimum volume of sedimentation tanks 5000 l |
||
| Diameter of valve taps | |||
| Water access point | DN 15 (1/2”) | DN 15 (1/2”) | DN 25 (1”) |
| Amount of wastewater Qs1 [dm3/s] | |||
| 1 | 0,50 | 1,00 | 1,70 |
| 2 | 0,50 | 1,00 | 1,70 |
| 3 | 0,35 | 0,70 | 1,20 |
| 4 | 0,25 | 0,50 | 0,85 |
| ≥5 | 0,10 | 0,20 | |
| Density of separated fluid [g/cm3] | fd |
| to 0,85 | 1,00 |
| over 0,85 do 0,90 | 1,50 |
| 0,90 do 0,95 | 2,00 |
SELECTING THE SIZE OF THE SEPARATOR
| Rainfall sewage | ||
| Coalescence separators | Qnom separator (NS) > Qmax sewage | |
| Lamella separators | Qnom separator (NS) > Qmax sewage | Qmax separator (NS) > Qmax sewage |
| Coalescence separators with by-pass | ||
| Industrial wastewater | ||
| Coalescence separators | Qnom separator (NS) > Qmax sewage | |
Capacity of settling tank
| Estimated sample amount of sewage sludge | Minimum volume of settling tank | |
| None | - condensate | Not needed |
| Small | - Industrial wastewater with a small amount of sewage sludge - all areas precipitation water where there is a small amount of sludge from traffic etc. |
100 · NS a |
| Medium | - gas stations, car washes - places for washing buses - wastewater from garages and parking lots - power plants, service stations |
200 · NS b |
| High | - washing devices for off-road vehicles, construction machinery, agricultural machinery - places for washing lorries and trucks |
300 · NS b |
| – automatic car washes |
300 · NS c |
|
| a Does not apply to separators smaller or equal to NS 10 b Minimum volume of sedimentation tanks 600 l c Minimum volume of sedimentation tanks 5000 l |
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