What does physical straining refer to in soil treatment?

Physical straining in the context of soil treatment refers to the ability of soil to filter out particles based on their size. This process is crucial for the effective treatment of wastewater in on-site sewage facilities. When discussing the size of bacteria relative to soil pore openings, the relevant aspect is that bacteria can be substantially smaller than these pore openings.

For the correct answer, the key point is that bacteria are typically larger than the soil pore openings. This means that as wastewater passes through the soil, the bacteria are unable to move through the spaces in the soil effectively, resulting in their removal from the wastewater. This physical straining is significant because it helps to reduce the overall bacterial load in the effluent before it is further treated or reaches the groundwater.

In this context, physical straining is a critical component of how soil functions to treat and filter wastewater, while other listed concepts may address different processes involved in water treatment and pathogen elimination.