Humification describes the process of sludge treatment in planted dewatering/drying beds. The sludge is loaded on the bed and dewatered by percolation in the filter and by evapotranspiration through the plants. The root system of the plants maintains the permeability of the sludge layer. The sludge is be added intermittently. Sludge has to be removed only once every 5 -10 years depending on design. The final product has is very well mineralized and has a soil-like structure. The long solids retention period and pathogen die-off and allows direct reuse of the solids in agriculture.