What is membrane flux and how does fouling affect it?

Membrane flux (J) is the volume of permeate passing through the membrane per unit area per unit time (L/m2/h). Initial flux depends on pressure, temperature, and membrane properties. Fouling - the accumulation of rejected materials on the membrane surface or within pores - progressively reduces flux. Types include particulate fouling, biofouling, organic fouling, and scaling. Control methods: pretreatment, regular cleaning, crossflow operation, and flux control.