Biological filter systems

Biological filter systems


Typical schematic of a biological filter system.

Biological filter systems use air to assist microorganisms, worms and beetles to break up organic material in wastewater with very little or no odour. Typical systems use a single chamber and two pumps, one for wastewater and one for air.

Wastewater passes through several layers of organisms on finely structured humus, coco peat and geotextile fabric. Clarified wastewater settles at the bottom of the chamber where it is pumped out of the tank.

Biological filters treat wastewater close to a secondary standard (a higher standard than septic tanks but not as high as aerated wastewater treatment systems). Effluent must be disposed of under the soil (i.e at least 300 millimetres deep) using either a covered soil absorption system or as subsurface irrigation on a paddock.

Common problems with biological filter systems are:

  • unanchored tanks rising out of the ground after rainfall
  • power disruptions can cause pump burn out and system failure
  • stormwater accessing the tank because the tank is too low or run-off is not diverted
  • no service agreement with a qualified service provider for regular inspections.

Effluent (treated wastewater) from biological filter systems may be released onto your property through:

  • amended soil mounds
  • sand mounds
  • absorption trenches and beds
  • evapotranspiration absorption beds
  • subsoil irrigation.


Saturday 02 July
2,529,499 ML
2,618,706 ML
8,828 ML
1,262 ML
5,351 ML
Saturday 02 July