city sewer system. black water transport.

[gil]

I am asking for your opinion, since on matter I am quite ignorant.

in my city you are thinking about the realization of a sewer system, capable of bringing black waters, of an entire neighborhood to the city purifier. However, the purifier is about 13 km away. do you think it is best to make a pumping system of this length or is it better to make one closer? the capacity of the plant must be adapted for 20,000 residents and in summer 60,000 other tourists. You will understand that we are not talking about a tube from a few inches of diameter.

Is it better for you to move fluids to the central system or make a second closer?

 

[menodizero]

the calculation of the only loss of load for residents (winter period) and for the extent that should be lifted from the neighborhood until the purification plant can be based on the following data:
- population no 20,000
- water supply l/ab*d 250
- inflow coefficients % 80
- max capacity to treat 5 qm
- qm 20.000 * 250/1000 * 80% = 4.000 m3/d
- qx 4.000 * 5 = 20.000 m3/d = 833 m3/h = 231 l/
- pipe diameter 450 mm
- speed in the pipe ~ m/" 1,46
- load loss ~ m 60,00 (without considering the geodetive prevalence I do not know)
if the lifting pump yield is 0.75, the power absorbed by the machine is ~ 180 kw.
logical that it is not possible to install only one pump (if they consider at least three with reduced flow to 1/2, so that they always have a reserve machine), but I think that the energy expenditure (with meteoric flow) is excessive.
also considering the only winter flow in dry weather, theoretical energy consumption would be about:
36 kw * 24 * 365 = ~ 315.000 kwh/year
It should be noted that a lifting plant suitable for winter use has been hypothesized, while the summer population is quadrupled with everything that follows.
said this, it is preferable to build a purification plant at the service of the neighborhood.
the calculation, although approximate, has considered that a system of lifting of the sewer is indispensable: other thing would be if it was possible to deliver the sewage to the centralized system with a gravity pipe.
Bye, good day.

 

[gil]

Thanks for the answer.

the pumps will be necessary because the starting fee is approximately 20 meters lower than that of arrival. Moreover taking into account that the distance between the two points is 13km, that the conduct should be at least 16km (you can not always pass for the shorter stretch), with the obvious load losses presuppose it serves more than a pumping system.

I didn’t understand how you calculated the power of the plant, but I’m interested in it, so to do so I would like to ask you to deepen. Can you explain to me how you counted?

in the plant do not pass meteoric water, finally I think that for the user can go well an average estimate of 200 liters per capita day.

 

[menodizero]

In view of the geodetic prevalence and the greater length of the pipe, I believe that the prevalence of the pumps is approached to 90 meters with a considerable increase in the power absorbed by the machines.
the formula used in this case is suitable for a preliminary calculation, to be refined later according to the manufacturer of the pump and the model to be installed.
In the specific case it is to be analyzed, as you already admit, if you are not forced to prepare an intermediate lifting, with attacking however of the costs, both installation and subsequent management.
the generic formula:
p = (p * 9,81 * q * h) / (1000 * nu)
where:
p = power in kw
p = specific weight of liquid (1 dmc)
q = flow rate
h = prevalence in meters
nu = pump performance

Good evening.