What type of filter removes solids through gravity rather than applied pressure?

Slow sand filters are designed to remove solids from water primarily through the force of gravity rather than the application of pressure. This type of filtration relies on a relatively slow rate of water flow through a bed of sand, allowing the natural processes of sedimentation and biological activity to take place.

In a slow sand filter, water enters the filter from above and percolates down through layers of sand. As it does so, larger particles settle to the bottom over time, and smaller particles are captured by the sand grain surface along with microbial biofilms that develop on the sand. This results in effective removal of suspended solids, bacteria, and other impurities without the need for external pressure to push the water through the filter media.

The efficiency and simplicity of slow sand filters make them a cost-effective solution for water treatment, particularly in small-scale or decentralized systems. They require minimal energy input and have low maintenance needs, making them advantageous in certain contexts.