Absorption trenches and beds

Absorption trenches and beds

Absorption trenches diagram

Septic tank, dosing siphon and trench set-up.

Absorption trenches or beds are used to release effluent below the surface through narrow and deep trenches, or wide and shallow beds. Effluent flows by gravity or is pumped along the length of the trench or bed through distribution pipes, and is then filtered through gravel or sand to the underlying soil.

Septic tanks are the most common treatment system used with absorption trenches and beds, but they may also be combined with composting toilets, biological filters, and aerated wastewater treatment systems (standard or with membrane filtration).

Common problems with absorption trenches and beds are:

  • trenches are constructed in a series (end to end) rather than adjacent to each other
  • no fences or barriers are put in place to stop vehicles or animals collapsing the trenches
  • uneven distribution of effluent caused by gravity trickle feeding, instead of using pressure dosing mechanism or a pump
  • trenches or beds too small for amount of effluent (hydraulic load).


Thursday 20 June
1,353,979 ML
2,581,850 ML
9,240 ML
1,320 ML
-7,624 ML
Thursday 20 June