Estimate the working principle of the water treatment tanks shown in the image.

The tank on the left is labeled "砂滤器" (shā lǜ qì), which translates to a sand filter. The tank on the right is labeled "炭滤器" (tàn lǜ qì), which translates to a carbon filter.

A sand filter is a type of depth filter commonly used in water treatment. It removes suspended solids, turbidity, sediment, and other larger particles from water by trapping them within a bed of sand or other granular media. This process is a crucial first step in many water purification systems.

A carbon filter, also known as an activated carbon filter, uses a bed of activated carbon to remove contaminants from water. It is highly effective at adsorbing chlorine, chloramines, volatile organic compounds (VOCs), pesticides, herbicides, and other chemicals that can cause bad tastes and odors in water. It often follows a sand filter in a multi-stage filtration system.