MASTER'S THESIS - SuSanA

4 Presentation of technologies for rural areas
4.3.5.2 Unplanted drying bed
An unplanted drying bed (see Figure 4.19) is a man-made drying bed with drainage layer and drainage pipe
at the bottom, that collects liquids through the drainage system. The purpose is the dewatering of the
sludge. The process reduces the sludge volume by 50 to 80 %. The sludge is not stabilised and needs further
treatment (as well as the drained water). For desinfection, co-composting is possible (Tilley et al. 2008).
Figure 4.19: Unplanted sludge drying bed (Tilley et al. 2008)
Unplanted sludge drying beds are appropriate for small to medium size communes. Large space is required
far away from the houses as odours and flies will occur. Advantages are that it is a low-cost treatment with
moderate construction cost and no electricity requirements (Tilley et al. 2008).
4.3.5.3 Planted drying bed
Planted drying beds are similar to unplanted drying beds, but they are constructed with plants and
ventilation pipes (see Figure 4.20). The appearance is therefore similar to vertical flow Cws. Roots facilitate
the water to get out of the sludge as roots are growing through the sludge. Sludge is applied into a
screening chamber, that is installed next to the drying bed. Purpose is the dewatering and stabilisation of
the sludge, but no desinfection. Therefore, planted drying beds should be combined with co-composting.
Sludge application can take place every three to seven days, sludge removal is necessary after two to three
years (Tilley et al. 2008).
Figure 4.20: Planted sludge drying bed (Tilley et al. 2008)
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