... , manganese, rust, colloid material, mechanical impurities, suspended solids and other particles in the above 20UM of substances hazardous to ... effectively prevent the reverse osmosis membrane fouling. System can automatically recoil, and so is red. 1.4 Fourth stage pretreatment ( ... remove very small colloidal particles in the water, so that the turbidity reached 1 degree, but still per milliliter ...