if yes then how can we kept it constant because membrane fouling increases with the time.
Hi Adnan,
In FOMBR, HRT is determined by FO permeate flow rate, QFO (+Q sludge wastage ). When membrane area is fixed, QFO is directly related to the water flux of the FO membrane. The FO water flux is determined by the transmembrane osmotic pressure difference and is affected by membrane fouling. If you want to kept the HRT, i.e. FO water flux constant. There is a few parameters to be taken into account: 1. the DS concentration should be maintained constant. 2. the concentration factor (CF, if you use sludge wastage as a control of the salinity buildup then CF= (QFO+Qwastage)/Qwastage) and the influent salt concentration should be constant, since these 2 factors determins the steady-state mixed liquor salt concentration. Once the DS concentration and the mixed liquor salt concentration are fixed, the transmembrane osmotic drive force will be fixed. As for the membrane fouling, if an constant HRT is really crucial to your experiment and membrane fouling is not one of your focus, You may consider to use low FO water flux (i.e. low DS concentration) + high coarse bubble aeration intensity to minimize the membrane fouling. Fouling is an flux related phenomenon, low flux will typical result in low fouling.
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