What type of coal is used as filter media in water treatment?

Anthracite coal is the correct choice as filter media in water treatment because of its physical and chemical properties that make it ideal for this application. Anthracite is the highest rank of coal, known for its high carbon content, low volatile matter, and excellent hardness. These characteristics make it effective in the filtration process, where a porous medium is needed to remove impurities from water.

The hardness of anthracite allows it to maintain its integrity during the filtration process, while its low porosity helps control the flow of water, promoting effective filtration. Additionally, anthracite does not leach harmful pollutants into the water, ensuring that it serves as a safe and reliable medium for water treatment.

Other types of coal, such as bituminous, sub-bituminous, and lignite, are not typically used for filtration in water treatment. They contain higher levels of volatile materials and impurities that could compromise the quality of filtered water. Bituminous coal, for instance, is often used for energy production rather than filtration due to its higher pollution potential. Sub-bituminous and lignite coals, being of lower rank, also have properties that render them less effective for use in filtration systems.