What type of impurities do anthracite cap layers in water filters help to remove?

Anthracite cap layers in water filters are particularly effective in removing iron impurities from water. Anthracite is a type of coal that is characterized by its hardness, high carbon content, and porous nature. When used in filtration systems, the physical structure of anthracite allows it to effectively trap and filter out various particulates, including dissolved and suspended iron, which can be present in groundwater and surface water sources.

The effectiveness of anthracite in removing iron is rooted in its ability to provide a large surface area for adsorption and filtration. As water flows through the anthracite layer, the iron particles are captured, reducing their concentration in the treated water. This is especially important because elevated levels of iron can lead to coloration and staining in water, as well as unpleasant tastes and odors.

The other options—oxygen, pH, and hydrogen—do not represent impurities that anthracite specifically targets. Oxygen is a dissolved gas, pH is a measure of acidity or alkalinity, and hydrogen is a part of water itself. Therefore, these elements are not effectively removed by a filtration medium like anthracite in the same way that iron is.