Which filtration method uses porous membranes with defined pore sizes to remove microorganisms primarily by physical screening?

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The main idea is removing microorganisms through a barrier that has uniform, defined pore sizes so particles larger than the pores are physically blocked. This approach uses a thin membrane that acts like a sieve: water passes through, while bacteria and other microbes are retained because they are bigger than the membrane’s pores. By selecting different pore sizes (for example, microfiltration or ultrafiltration ranges), you can target specific microorganisms and achieve a physical screening effect.

This is different from sand filtration, where filtration happens through a packed bed of granular media and the mechanism isn’t defined by precise pore sizes—coagulation, sedimentation, and straining contribute, but the pores aren’t uniform or controlled in the way a membrane is. Activated carbon filters rely mainly on adsorption to remove contaminants, not on size-based screening of microbes. Distillation removes microbes by separating water from contaminants through evaporation and condensation, not by filtering them through a pore-defined barrier.

So, the described method—porous membranes with defined pore sizes that physically screen out microorganisms—matches membrane filtration.