Method for filtering

A method for filtrating, comprising:

• providing a filter structure for filtering a liquid containing solid particles having a diameter between 0.5 μm to 10 μm, the filter structure comprising:
• a first porous film having a plurality of first holes;
• a second porous film on the first porous film and having a plurality of second holes, wherein the second holes are smaller than the first holes;
• and
• a foam film capable of absorbing water disposed between the first porous film and the second porous film;
• wherein the diameters of the second holes are smaller than the diameters of solid particles in the liquid;
• and
• wherein the diameters of the first holes do not exceed 0.457 cm;
• drifting down a mixed solution onto a top surface of the second porous film of the filter structure to intercept residue larger than the second holes in the mixed solution, wherein a liquid in the mixed solution passes through the second holes and continues to flow downward;
• after the first porous film and the film capable of absorbing water absorbs the liquid, compressing the first porous film and the film capable of absorbing water by a compressing force to drain out the liquid and rinse the second porous film when the liquid flows back to the second porous film due to the compression to remove the residue blocking the second holes;
• and
• removing the compressing force so that the compressed first porous film and the compressed film capable of absorbing water springs back to an original shape.