For 100000 inhabitants, Qm is given by:

3.5 ■ 130 ■ 100000 ■ 10-3 + 6000 L inh. d m3 d 31 ,

Vm 24 inh. d h d h while the average daily flow rate Qd (dry-weather flow) is:

The required permeate flow rate of a membrane module has to equal the maximum volume rate Qm; and the required membrane surface area Am can be determined from permeate flux of common membrane modules. At 8°C, a flux of Jp8 = 25 L m-2 h-1 is given. For higher temperatures (here 10 °C) the flux is about 15% higher than at 8°C (MUNLV 2003), resulting in:

According to Eq. (12.5), the required membrane surface area AM follows:

For maintenance cleaning twice a year, the complete membrane area is taken out of operation. Each cleaning procedure lasts about 1 day; the effective membrane area is in operation, therefore, only 363 days year-1 or about 99% of the time. To realize the required flux, the total membrane surface area At must be 101% of AM.

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