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Division of wastewater flow
Water Research Pergamon Press 1972. Vol. 6, pp. 371-373. Printed in Great Britain
DIVISION OF WASTEWATER FLOW WOLFGANGSTALZERand WILHELMVON DER EMDE Institut fur Wasserversorgung, Abwasserreinigung, und Gewasserschutz, Technische Hochschule Wien, Karsplatz 13, A-1040 Wien, Austria AT (1) (2) (3) (4)
LARGEtreatment plants there are, among others, the following possibilities: simple division by separating channels division by flowmeters and gates controlled by the flowmeters hydraulidy by using weirs (e.g. circular distribution weirs) before the tanks hydraulicly by utilizing the head losses that exist at the inlet or outlet to or from the primary or secondary clarification tanks.
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Tonks
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(1) Simple division by a symmetrical separation of the channels has the advantage of a hydraulicly clear situation--whereas three-fold and multiple partition offers no clear situations--nevertheless long inlet conduits are required for appropriate radii of curvature and long exit channels are required to ensure uniform flow in the cross section before the separation. (Much space and expensive conduits are necessary.) (2) A division of the wastewater by flowmeters often cannot be avoided in the case of numerous tanks; this solution is expensive and intensive maintenance will be necessary. Where flow measurement involves significant head losses and where large fluctuations of the flow exist, large head losses have to be considered. O) Division by weirs before the tanks (e.g. circular distribution weirs) has the advantage of a hydraulicly clear solution. Additional head losses and long lengths of the conduits have to be accepted. When applying circular distribution weirs, sufficient radii and uniform flow towards the weir has to exist. (4) Division by utilizing the head losses at the inlet and the outlet does not cause additional head loss. A prerequisite with rectangular tanks is a wide distribution 371
372
WOL~O.~OSTALZI~and Wna-n~Myon DEM.E~E
channel which is situated in front of the battery of tanks and where low flow velocities exist. By this means small friction losses and a small regain of the velocity head, respectively, will lead to a small difference between the water level at the beginning and the end of the distribution channel. The advantage of such a distribution channel is that large particles will settle out or float to the surface. The disadvantage is that it is necessary to collect the separated particles or to aerate the channel. Furthermore, an exact and equal level of all outlet weirs has to be established since this forms the basis for the hydraulic distribution (a check by filling the tanks is absolutely necessary). This method of hydraulic distribution only works if free flow exists over the outlet weirs. The change in water level caused by different flows can be applied for flow measurement. (a) Utilizing the inlet head losses The velocity distribution in a sedimentation tank has to be uniform. By accelerating the wastewater and its contents 0arge velocity head), successive dispersion of the water contents (head loss) and equalization of flow across the section of the tank in the inlet construction. The objective of attaining uniform flow can be achieved. The head loss in the inlet construction will be much larger than the difference in the water level between the beginning and end of the distribution channel, and this is why the influence of the difference in the water level will be negligible with respect to the flow distribution e.g. "Stuttgarter Inlet" according to WEIDI~mR(1967). Velocity in the distribution channel: v~ = 0.1 m s- 1 Velocity in the acceleration part of the inlet construction v2 = 1.0 m s- ~ Head loss according to h~ = ~V~2g "Stuttgart Inlet" ~ = 1.6 Head loss: h,, = 8 cm. Velocity head and friction losses in the distribution channel around 1 era. Such inlet structures are used with advantage in final clarifiers. (b) Utilizing the outlet head losses When applying a relatively large weir load a relatively large difference in the water level of the tanks will be established, too, if there is a fluctuation of flow. Where an uneven distribution of the flow to the tanks occurred, this would be caused by a relatively large difference in the water level at the beginning and end of the distribution channel. This difference will not exist when the distribution channel is properly designed.
Example Velocity head and friction losses in the distribution channel: Weir load Necessary head for free flow When head for free flow 0.19 m, flow 156 1. m -1 s -1 When head for free flow 0.17 m, flow 132 1. m -1 s - t
0.22 m 1441.m-is - t O-18m
Division of Wutewater Flow
373
Maximal deviation in the flow distribution: 12.01. m - t s -1 ---- ± 8 per cent. Such outlet structures are used with advantage in primary clarifiers, since small entrance openings can clog. The clogging is avoided by this solution. REFERENCES SCHR6DER-PR]E?,U(1966) Hydromechanik ira Wasserbau. Wilhelm Ernst u. Sohn, Berlin. WEIDNmt S. (1967). ZufluB, DurchfluB trod Absetzwirkung zweckmdflig gestalteter Rechteckbecken Stuttgarter Berichte xur Siedlungswasserwirtschaft, Heft 30. R. Oldenbourg, Miinchen.
w.m. 6: 4/5---=
DIVISION OF WASTEWATER FLOW WOLFGANGSTALZERand WILHELMVON DER EMDE Institut fur Wasserversorgung, Abwasserreinigung, und Gewasserschutz, Technische Hochschule Wien, Karsplatz 13, A-1040 Wien, Austria AT (1) (2) (3) (4)
LARGEtreatment plants there are, among others, the following possibilities: simple division by separating channels division by flowmeters and gates controlled by the flowmeters hydraulidy by using weirs (e.g. circular distribution weirs) before the tanks hydraulicly by utilizing the head losses that exist at the inlet or outlet to or from the primary or secondary clarification tanks.
[ I [ I I
[
I
I
IIttIItl
I I I I I I I I I
Tonks
Tanks
Fro. A.
Ro. B.
1 I I I I I Tanks
Flo. C.
I
1,1,1,1,1,1,1,1, I I I [
I
]
I
I
RG. D.
(1) Simple division by a symmetrical separation of the channels has the advantage of a hydraulicly clear situation--whereas three-fold and multiple partition offers no clear situations--nevertheless long inlet conduits are required for appropriate radii of curvature and long exit channels are required to ensure uniform flow in the cross section before the separation. (Much space and expensive conduits are necessary.) (2) A division of the wastewater by flowmeters often cannot be avoided in the case of numerous tanks; this solution is expensive and intensive maintenance will be necessary. Where flow measurement involves significant head losses and where large fluctuations of the flow exist, large head losses have to be considered. O) Division by weirs before the tanks (e.g. circular distribution weirs) has the advantage of a hydraulicly clear solution. Additional head losses and long lengths of the conduits have to be accepted. When applying circular distribution weirs, sufficient radii and uniform flow towards the weir has to exist. (4) Division by utilizing the head losses at the inlet and the outlet does not cause additional head loss. A prerequisite with rectangular tanks is a wide distribution 371
372
WOL~O.~OSTALZI~and Wna-n~Myon DEM.E~E
channel which is situated in front of the battery of tanks and where low flow velocities exist. By this means small friction losses and a small regain of the velocity head, respectively, will lead to a small difference between the water level at the beginning and the end of the distribution channel. The advantage of such a distribution channel is that large particles will settle out or float to the surface. The disadvantage is that it is necessary to collect the separated particles or to aerate the channel. Furthermore, an exact and equal level of all outlet weirs has to be established since this forms the basis for the hydraulic distribution (a check by filling the tanks is absolutely necessary). This method of hydraulic distribution only works if free flow exists over the outlet weirs. The change in water level caused by different flows can be applied for flow measurement. (a) Utilizing the inlet head losses The velocity distribution in a sedimentation tank has to be uniform. By accelerating the wastewater and its contents 0arge velocity head), successive dispersion of the water contents (head loss) and equalization of flow across the section of the tank in the inlet construction. The objective of attaining uniform flow can be achieved. The head loss in the inlet construction will be much larger than the difference in the water level between the beginning and end of the distribution channel, and this is why the influence of the difference in the water level will be negligible with respect to the flow distribution e.g. "Stuttgarter Inlet" according to WEIDI~mR(1967). Velocity in the distribution channel: v~ = 0.1 m s- 1 Velocity in the acceleration part of the inlet construction v2 = 1.0 m s- ~ Head loss according to h~ = ~V~2g "Stuttgart Inlet" ~ = 1.6 Head loss: h,, = 8 cm. Velocity head and friction losses in the distribution channel around 1 era. Such inlet structures are used with advantage in final clarifiers. (b) Utilizing the outlet head losses When applying a relatively large weir load a relatively large difference in the water level of the tanks will be established, too, if there is a fluctuation of flow. Where an uneven distribution of the flow to the tanks occurred, this would be caused by a relatively large difference in the water level at the beginning and end of the distribution channel. This difference will not exist when the distribution channel is properly designed.
Example Velocity head and friction losses in the distribution channel: Weir load Necessary head for free flow When head for free flow 0.19 m, flow 156 1. m -1 s -1 When head for free flow 0.17 m, flow 132 1. m -1 s - t
0.22 m 1441.m-is - t O-18m
Division of Wutewater Flow
373
Maximal deviation in the flow distribution: 12.01. m - t s -1 ---- ± 8 per cent. Such outlet structures are used with advantage in primary clarifiers, since small entrance openings can clog. The clogging is avoided by this solution. REFERENCES SCHR6DER-PR]E?,U(1966) Hydromechanik ira Wasserbau. Wilhelm Ernst u. Sohn, Berlin. WEIDNmt S. (1967). ZufluB, DurchfluB trod Absetzwirkung zweckmdflig gestalteter Rechteckbecken Stuttgarter Berichte xur Siedlungswasserwirtschaft, Heft 30. R. Oldenbourg, Miinchen.
w.m. 6: 4/5---=