Membrane structural characteristics mainly refer to membrane pore size, surface roughness, symmetry, etc. These characteristics are closely related to membrane fouling. When the membrane pore size is larger than the solute molecule diameter, although the membrane water production is high in the initial stage of operation, the solute quickly blocks the pores causing a rapid decline in flux. The larger the pore size, the greater the degree of flux decline over time. When the membrane pore size is smaller than the solute molecule diameter, the decline in water flux is no longer due to pore blockage by solute, but mainly caused by concentration polarization on the membrane surface and the formation of an EPS gel layer.

It is generally believed that membranes with smooth surfaces are less susceptible to fouling by solutes, while membranes with rough surfaces easily adsorb pollutants and are fouled more quickly. Roughness increases the contact area between the pollutant and the membrane, and can also generate certain frictional resistance that inhibits the suspensionof particles on the membrane surface.

The Dow membrane structure consists of three layers: (1) Polyester reinforced non-woven fabric, approximately 120 μm thick. (2) Polysulfone porous intermediate support layer, approximately 40 μm thick. (3) Polyamide ultra-thin separation layer, approximately 20 μm thick. This membrane has a hard, smooth surface with no loose fibers, uses a porous intermediate support structure, with a surface pore size of about 150 Å. The above membrane structure determines its fouling resistance and biodegradability.