Filtration is an effective physical method for controlling microbial growth by utilizing filters with extremely small pores that can physically remove microbes from liquids or air. The size of these pores is significantly smaller than the microbes themselves, preventing the microbes from passing through while allowing the liquid or air to flow freely. This process is particularly useful for sterilizing heat-sensitive liquids when heat treatment is not feasible.

One specific type of filter, known as a High Efficiency Particulate Air (HEPA) filter, is designed to eliminate airborne particles and microbes from the air. HEPA filters are commonly employed in various settings, including airplanes, to ensure that the air is free from harmful microorganisms.

In liquid filtration, a typical setup involves a vacuum pump and a flask, where contaminated liquid containing microbes is placed above a filter. As the vacuum creates suction, the liquid passes through the filter, while the larger microbes are trapped, resulting in sterile liquid. For instance, bacteria such as Micrococcus luteus and even larger cells like sperm can be effectively filtered out due to their size relative to the filter's pores.

In air filtration, HEPA filters work similarly by capturing airborne microbes and particles, ensuring cleaner air in environments where air quality is critical. This method of filtration is a vital component in various applications aimed at controlling microbial contamination.

Overall, filtration serves as a crucial technique in microbiology and public health, allowing for the effective separation of microbes from liquids and air, thereby contributing to safer environments.