Slow Sand Filters

02/23/26

“How can we slowly filter water through sand?”

Sand Filters come in all different shapes and sizes. The earliest sand filters were slow-operating mechanisms. Water would slowly trickle over a large, contained sand bed. Over the course of a few weeks, the sand bed will develop a Schmutzdecke, or thin biofilm derived from the accumulation of suspended organic particles and microorganisms from the water. The schmutzdecke will break down organic contaminants as water passes through it. The sand will then adsorb and retain particles from the water as it passes through. The slow process allows for the creation and operation of the schmutzdecke. These Slow Sand Filters are an electricity and chemical-free way to biologically and physically treat water. Slow sand filters usually have a loading rate of 200 – 400 liters of water per square meter per hour, forcing them to take up large amounts of space for municipal usage.

Image credit: http://www.waterandwastewater.com