During the purification of wastewater, coarse solids accrue frequently. They form sewage sludge. Before disposing or utilising the sludge, it hast to be desiccated. We rely on a natural process: The sewage sludge humification. Using this method, the fluid sludge is pumped onto beds and is spread and distributed over the surface. The water seeps into the earth (i.e. into a drainage layer), and the solid particles are collected on the surface and penetrated by plant roots. Reed (Phragmites communis) is particularly suitable for sewage sludge humification. Even if the sludge layer increases, it forms new stolons and spreads its rhizomes into higher substrate layers. Thus, the sludge is immobilised and decomposed into humus. After several years, the humus can be removed and used for horticulture.
The procedure is suited for wastewater treatment plants of every size. In the tropical and subtropical climate zones, we use different plant species which are comparable to reed.