• An extended sand layer (about 30 cm in thickness) above the
gravel layers improves significantly the performance of the system,
while a total bed thickness of 80 cm proved to be adequate
(Type III design).
• The presence of plants increases the efficiency. No significant differences
were observed among the two different plant species
tested.
• The use of special porous media (zeolite–bauxite) as substrate
materials did not enhance significantly the performance of the
system. These materials are proposed to be placed in special filters
treating the effluent of the CWs.
• The presence of aeration tubes is important for the aeration of
the bed. The aeration tubes cannot be substituted by plants.