Definition of various Waste Water flow rates 

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Q avg:Qavg is the daily average flow based on yearly data. Q peak:Peak hourly flow rate of daily average flow (Qpeak = 1.5 x Qmax whereas, Qmax = 1.8 x Qavg,). Q min:Qmin is Minimum hourly flow of daily average flow (Qmin = 0.4*Qavg). Normally, the treatment units are designed on the basis of daily average flow while peak and minimum flows are used to check the capacities of basin and conduits in extreme flow condition. 
Mass Loading FactorMass Loading Factor takes care for the fluctuation in wastewater flows and the respective characteristics loading parameters. Mathematically; flow weighted average concentration Cw = (ΣCiQi) / (ΣQi)
Determination of weighted average Estimation of Flow Rates:Design of sewers means to find the diameter (size) and the slope (gradient) of sewers to carry the given amount of discharge providing self cleaning velocity.
The velocity in the sewers should be such that there is no silting of solids in the sewers. Generally, the velocity in sanitary sewers should not be less than 0.6 m/sec (2 ft/sec) and in the storm sewers it should not be less than 0.9 m/sec (3 ft/sec).
