What type of filtration system is described by a sub-micron filter?

A sub-micron filter is designed to effectively capture particles that are smaller than one micron in size, which includes a significant portion of bacteria and other microorganisms. This type of filtration is especially important in water purification systems used in hemodialysis to ensure that the water is safe and free from harmful pathogens. Reducing bacteria levels is crucial in maintaining patient safety during dialysis treatments.

The other options represent different types of filtration processes or system functions. For instance, while removing chlorine from water is typically accomplished through activated carbon filters, it is not the primary function of a sub-micron filter. Removing large sediments generally involves filters with larger micron ratings, not sub-micron ones, and increasing water pressure pertains more to system mechanics rather than filtration capabilities. Thus, a sub-micron filter's main role in the context provided is its ability to significantly reduce bacteria levels in the water supply.