What type of filter uses sand and gravel to treat wastewater?

The type of filter that uses sand and gravel to treat wastewater is indeed the sand filter. Sand filters are a crucial part of wastewater treatment processes as they utilize layers of sand and gravel to remove impurities and suspended solids from the water.

In use, water is passed through these layers, where the larger gravel acts as a support for the finer sand above. The sand particles trap smaller particles, bacteria, and some organic materials as water flows downward due to gravity, effectively filtering out contaminants. Sand filters are valued for their relative simplicity, low cost, and effectiveness in both large-scale wastewater treatment plants and small, decentralized systems.

Understanding the application of sand filters is critical in various wastewater treatment scenarios, as they can be part of a larger treatment system, providing a fundamental step in ensuring cleaner effluent before it is released or subjected to further treatment processes.

Other options, such as gravity filters, carbon filters, and bag filters, serve different purposes and may employ various materials or mechanisms, but they do not specifically focus on the combination of sand and gravel to achieve the filtration required in wastewater treatment.