What characterizes the media used in intermittent sand filter systems?

In intermittent sand filter systems, the media plays a crucial role in the treatment process, particularly in the filtration and biological treatment of wastewater. The correct choice indicates that the media can be mineral sand or equivalently sized crushed glass, which aligns with the standards for effective filtration.

Mineral sands are typically granular materials that facilitate both the physical filtration of pathogens and solids, as well as the biological degradation of organic matter through the growth of microorganisms on the surface of the sand grains. Crushed glass can serve a similar purpose, offering a durable and chemically stable medium that provides desirable filtration characteristics while allowing for proper drainage and aeration.

The quality of the filter media is essential; it needs to allow water to pass through while retaining particles and supporting beneficial microbial activity. This option stands out as it provides flexibility in materials, ensuring that systems can utilize either mineral sand or crushed glass, depending on availability and suitability for local conditions.

In contrast, the other choices are less applicable. Organic materials would not provide the necessary structural integrity and filtration capabilities required in this context. The restriction to natural stones would limit options and overlook effective synthetic alternatives. Lastly, a media of varying sizes might not be optimal as consistent particle size is generally preferred to maintain uniform flow and effective treatment through the