Greywater Treatment Plants

Grey water for this purpose is defined as all wastewater originating from a household with the exception of toilet wastes.

Grey water, whilst containing organic, dissolved and particulate matter, pathogens and the like, maintains only a minor percentage of such constituents when compared to that of total household wastewater (black and grey water combined).

Grey water has typically 20 - 30% of the pollutant load contained in the total household waste stream, the approximate strengths are as follows:-

Suspended Solids
Faecal coliform
TD Salts

50 - 150 mg/litre
40 - 180 mg/litre
0 - 10,000+/100 ml
30 - 250
1 - 30 mg/litre
5 - 15 mg/litre
6.5 - 8.5
50 - 5000 mg/litre

Faecal coliform numbers are difficult to quantify, as in some cases the figure will be zero.

However, depending upon household practices, numbers can be large (7 log), and these instances are usually associated with laundry waters (washing nappies etc).

The OHW designed and built 'Droughtmaster' range of domestic greywater treatment plants are currently under test for NSW Department of Health accreditation, and are expected to gain full approval mid 2006.

The Plant will be available in 2 models, the first capable of producing tertiary treated effluent suitable for re-use within the household; and the second, capable of producing secondary treated effluent suitable for garden irrigation only.

The Droughtmaster plants are designed to handle 800+ litres of grey water per day, undergoing primary settling and anaerobic digestion, extended aeration, clarification, tertiary filtration (if used for internal reuse) and disinfection or sterilisation prior to discharge.

Droughtmaster GR.

This Plant is designed to treat effluent to a level fit for watering the landscaped areas of a property.  Whilst the aeration and clarification chambers are standard, this Plant has as its base design a contact chlorinator to provide disinfection prior to discharge, such discharge carried out via a submersible pump or gravity.

The Plant has a bypass to the reticulated sewerage network (if available), so that in times of wet weather the treated grey water can be directed away from land.

In situations where mains sewer is not available, a 'limiting factor' study will probably be required to establish the appropriate size for the irrigation area.  The contact chlorinator contains sufficient chlorine stocks to last for 6 months, so it is recommended that service visits take place at these intervals.

There is a visual and audible alarm unit to alert the householder in the event of equipment failure.

Droughtmaster IR.

The second and more sophisticated of the two Plants produces tertiary treated effluent for internal re-use in washing machines and for toilet flushing.  This unit incorporates a passive multi-media filter capable of enhanced filtration and Phosphorous reduction (if desired).

From the filter, effluent flows to a small storage reservoir awaiting household demand.   When the capacity reaches a predetermined level, a valve automatically opens to allow excess liquid to be pumped to the landscaped areas, though always keeping enough in reserve to satisfy potential internal demand.

The effluent for both internal re-use and garden irrigation is subject to UV sterilisation prior reaching its destination.

The Plant has a by-pass to the reticulated sewerage network (if available), so that in times of wet weather the treated greywater can be directed away from the land, but is still available for internal re-use.

The IR model uses state of the art technology to monitor all working parts.  If a fault is detected in any of these, the Plant will automatically telephone the service & maintenance provider to alert them to the problem.

Effluent Quality

It is expected the treated effluent will fall within the following parameters:-

Droughtmaster GR

  Suspended Solids
  Faecal coliform

< 10mg/litre
< 10mg/litre

Droughtmaster IR

  Suspended Solids
  Faecal coliform

< 5
< 5
< 2

Operation & Maintence

Both Plants are designed to be simple in both operation and maintenance.  The GR has two working parts and the IR the same + a UV unit.  Maintenance should be carried out on a 6 monthly basis if using contact chlorination in order to replenish tablet stocks. However, the householder could do this if allowed by Council.

If the Plant has back to base telemetry and UV sterilisation, maintenance should only be required annually, but this will ultimately depend on the NSW Dept of Health.


Very little data is available on nutrient component strength levels in treated greywater. It is assumed there will be reasonable levels of Phosphorous present, derived in the main from detergents and the like.  Nitrogen concentrations will be quite low, and those present are probably generated from degradation of Ammonia-N.  However, a major source of Nitrogen normally found in wastewater, Urea, does not factor significantly in Greywater, although this will vary depending on household and individual practices.


  • The GR model can be fitted with UV sterilisation rather than contact chlorination if required.

  • The GR model can be fitted with back to base telephone monitoring.

  • It is recommended that a low sudsing washing powder be used in washing machines.
    e.g Omomatic or similar.


Droughtmaster GR          $5,360.00 + GST + delivery & installation
Droughtmaster IR           $8,500.00 + GST + delivery & installation

BASIX & Greywater re-use

If the Model IR were to be installed in an average 4 bedroom home on a 600 sq metre block of land, with the treated effluent used for the laundry, toilet and garden, in most circumstances this would be sufficient to meet the BASIX criteria for water savings.

Commercial or Large Scale Plants

Until recently, there has been little demand for greywater treatment plants on a commercial scale. OHW has been involved in the design and construction of only one plant, a caravan park with small motel in Tweed Shire.