The volumes of wastewater
150
100
50
Influent to treatment plant
m 3 /h.
- - - - -- -Maximum 244 % of average
600
2400
soo
Hour
Fig 1.1
Influent to Tuelso wastewater treatment plant (Denmark, July 10-11, 1980) /1/.
The maximum hourly flow rate, Qh,maXt can be calculated on the basis of a number
of maximum hourly flows rates.
The average maximum hourly flow rate, Oh,ma» is, among other things, used as a
basis for the hydraulic design of sewers and ponds. The average hourly volume of
water, Oh,aw or the diurnal volume of water, Qd,av' is for example used for the
calculation of operating expenses.
1.1.2 Statistics
By processing the data statistically a more detailed picture of wastewater variations
is obtained. The different volumes of water (volume, maximum hour, maximum
second, etc. over a 24-hour period) will often be normally distributed or log-normally
distributed. Data sets for wastewater are never ideal as there will be irregularities
which may, if they are too excessive, result in a special treatment of the data.
Fractile diagrams can be an important tool in the design of treatment plants. Fig 1.2
gives an example of such a diagram. The 60 per cent fractile is frequently used as an
average load and a fractile of 85-90 per cent as a maximum load.
A number of irregularities in wastewater data can be revealed visually by listing the
collected data in order of time (a time series). Hence irregularities such as
-jumps
- trend (increasing or decreasing)
-variation (for example weekly or seasonal variations)
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