Septic Tank

A correctly-sized septic tank is an effective method of wastewater treatment where there is sufficient suitable land area available for disposal, where further treatment occurs within the soil in aerobic conditions (inside the tank the processes are anaerobic).

Septic tank

Septic tank

Benefits

  • Proven technology with a wide range of suppliers
  • Low or no power consumption
  • Inexpensive
  • Three-yearly pump-outs only

Drawbacks

  • Council may be resistant, especially on smaller sections and the system relies upon the soil for completion of treatment
  • Require sufficient land area and larger setbacks from ground and surface water
  • Dependent on the (sustained) treatment capacity of the soil

Aerated Wastewater Treatment System

An AWTS incorporates a septic tank, but also has a chamber where pumps are used to generate air bubbles. This chamber replaces the aerobic treatment which occurs in the soil in the standard septic tank system, meaning that the effluent produced is already of a higher standard. Whilst primary treated (septic tank) effluent cannot be irrigated using dripper lines, secondary treated effluent, such as from an AWTS, can be irrigated through drippers (note: several other systems also produce secondary, or advanced secondary, treated effluent).

Aerated Wastewater Treatment System

Aerated Wastewater Treatment System

Benefits

  • Wide range of off-the-peg systems
  • ‘All-in-one’ packaged plants
  • Relatively economical to purchase
  • When operating well can produce a high quality effluent
  • Well accepted by council

Drawbacks

  • Significant power consumption, expensive operation
  • Can be noisy
  • Maintenance can be costly (replacement pumps, etc)
  • Cope poorly with fluctuations in input (whether up or down) so less well suited to holiday homes, etc

Media filters/reactors

These systems use a media filter chamber to contain the aerobic treatment process. The media can include sand/gravel, peat and textiles amongst other things. These systems achieve secondary or advanced secondary treatment and are well suited to tertiary treatment if required or desired (additional disinfection by chlorine or UV).

Media filter 1

Media filter 1

Media filter 2

Media filter 2

Benefits

  • Some off-the-peg systems available
  • Cope better with fluctuations in input
  • Produce a high quality effluent
  • Some well accepted by council

Drawbacks

  • Can be more expensive
  • Construction can be tricky
  • Can under some configurations (eg recirculating) achieve high levels of nutrient reduction (important for sensitive receiving environments like waterways)
  • If they fail it can be expensive and difficult to replace the media
  • Council may require extensive monitoring of some designs (eg peat beds)

Vermicomposting Units/Humus Ecology Filters

These systems act a little like compost heaps where solid wastes collect and are degraded by the resident worm population whilst the liquids filter through to a collection area below. Generally the level of treatment is of a high primary standard, but some systems achieve a secondary level of treatment.

Vermicomposting system

Vermicomposting system

Benefits

  • Some systems well accepted by council (other systems may not be)
  • Probably cope better than other systems with a garbage grinder and even some chemical use
  • Produce a reasonable quality effluent
  • Low (or even no) power consumption
  • Can be quite compact units
  • Can be used with drip irrigation (some systems)

Drawbacks

  • Poor nutrient reduction (nitrogen/phosphorous) (may be OK or even a benefit if water is used appropriately in a low-sensitivity receiving environment)