21 Deep Sand

The Deep Sand is a passive biological filter that can reduce nitrate and a little phosphate.

The sand bed consists of fine sand and has a layer height of at least 10 cm. Over time, organic matter and bacteria penetrate the soil layer. The bacteria break down the organic matter using oxygen, so that anaerobic conditions develop in deeper layers. Here, bacteria can also break down organic matter, but due to a lack of oxygen, they consume nitrate.

If the organic matter load rises too high, zones with hydrogen sulphide formation can develop (sulphate respiration). This absolutely undesirable and hardly controllable process should be avoided and this is the critical point of this method. Also the strong mixing of the soil layer by digging animals disturbs the denitrifying biology. These disadvantages can be avoided by the extended JAUBERT method.