What materials can be used as media in wastewater treatment processes?

The choice indicating that rock, concrete, or plastic can be used as media in wastewater treatment processes aligns with standard practices in the field. In wastewater treatment, media serve as a substrate for biological growth, help in filtration, and promote the settlement of solids during different stages of treatment.

Rock and concrete are often used in the construction of various treatment units, such as trickling filters and biofilters, where they provide a large surface area for microorganisms to attach and grow, facilitating the breakdown of organic materials. Plastic media, such as plastic biofilm carriers, are also widely used because they are lightweight, resistant to corrosion, and can be designed in various shapes to optimize surface area for biological activity.

Using these materials improves the efficiency and effectiveness of the treatment process by enhancing aeration, promoting microbial growth, and improving the physical structure of the treatment system. In contrast, the other materials listed in the options are not commonly utilized in wastewater treatment applications, making this choice the most suitable answer.