16. o2
o2 o2 o2
Vertical flow subsurface wetland
Influent
Main filter filled with graded gravel and sand
Effluent
Collection and drainage pipe
17. Common problems in soil filters
1. Overloading (suspended solids, high
BOD, water)
2. Uneven distribution (over surface, over
clay)
3. Failure in drainage (waterlogging, roots)
4. Wrong choice of sand and gravel (texture,
mineral particle shape)
1
2
4
3
18. Improved distribution using controlled clogging
Geotextile
unit Pre- treatment in
sedimentation tank
0.6 m
in sand
3 m in silt
10 m