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The amount of waste water produced over time varies depending on water consumption from industry and households, precipitation (in particular rain), ... . Variations can be daily, weekly and seasonal and depend a great deal on the size of the catchment area. Whereas for example in small settlements without any industry the waste water peaks are very pronounced in the morning, at midday and in the evening, cities have only slight peaks.

Variations in water consumption:

In a village










In a town


In a city

                               
          
 
Large sewer systems delay and lessen the peaks arising in the sewage plants – the amount of waste water arriving at sewage plants in cities is levelled. In a small (short) sewer system, peaks which arise largely arrive directly at the sewage plant.  The sewer system must be designed for the directly arising quantities taking into account peak drainage values and variations – dimensioning to the maximum arising quantities would however be uneconomical. Dimensioning values are defined for the individual structures.

water demand per unit and day:

households 65-275 [l/(Pxd)]
small companies 50-250 [l/(Exd)]
restaurants 50 [l/((E+G)xd)]
agriculture 50-100 [l/(CHxd)]
hotels 200-400 [l/((E+G)xd)]
schools 40 [l/((S+T)xd)]
hospitals 300-500 [l/((PA+E)xd)]
green lands 0,1 [l/(m²xd)]
municipal size [PE]
water demand incl. business (no industry)
Qd [l/(PExd]
< 5.000 60 – 150
5.000 – 10.000 100 – 200
10.000 – 250.000 150 – 250
> 250.000 150 - 300
P:         person             E:         employee         CH:      cattle and horses unity  PA: patient
G:        guest               S:         scholar             T:         teacher

The water demand of a region is determined by a number of factors. For example, climate, water supply, other sources of water, water composition, water price, local sewers, economic structure, standard of living, piping network losses and the like. Consumption Q is indicated by year, month, day, hour and second (indices a, m, d, h and s). The mean daily consumption is calculated by dividing Qa by 365 and is approximately 200 l/(P x d) in Austria. In tourist regions consumption can however be much higher (frequent washing of laundry, many restaurants, etc.).

water delivery-duration curve

  water consumption per month -- seasonal fluctuation [% of Qa]
locality january april july september november
village 5 8 12,5 10 6
small town 6 8 11 10 7
big town 7,8 8,3 8,9 8,5 8,2

The consumption in april is about the annual mean.

water delivery/ day:                          



water delivery/ hour:



                        

Qd:       average daily water delivery

Qd,max:   water delivery on the day with the highest consumption             Qh,max:   max. hourly water delivery

fS(d):     daily peak factor, dependent on the size of the supply area, the precipitation distribution and - height and the fraction of industry and business

fS(h):     hourly peak factor, dependent on the size oft he supply area, the structure of the supply area and the tourism

Peak consumption at weekends is 0.80 – 0.95 of that during the week.

example dimensioning example dimensioning
sewage pipe on Qh,max sewage plants with equalizing reservoir on Qd,max
rainwater buffer basin (bei Mischwasserkanalsystemen z.B. vor Kläranlagen) on Qd sewage plants without equal. reservoir on Qh,max
supply area fS(d) fS(h) fS(d)*fS(h) supply area fS(d) fS(h) fS(d)*fS(h)
country community 2,0-3,0 2,9 5,8-8,7 bigger town 1,5-2,5 2,0 3,0-5,0
small town 1,7-2,7 2,4 4,1-6,5 big town 1,5-2,0 1,5 2,3-3,0



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