Attachment K - HSTP Design

Greywater Characteristics

The definition of greywater in the AS/NZS 1547:2012 Onsite Domestic-wastewater
Management is: “The domestic wastes from a bath, shower, basin, laundry and
kitchen but excluding toilet and urinal waste”.

The characteristics of greywater generated by a household will vary also according to

the dynamics of the household and is again influenced by the number of occupants,

the age distribution of the occupants, their lifestyle characteristics and water usage
patterns. Wastewater may have become contaminated in three ways

e by microorganisms, many of which may be pathogenic, i.e. cause disease;

e chemically by dissolved salts such as sodium, nitrogen, phosphates and chloride
or by organic chemicals such as oils, fats, milk, soap and detergents which may
provide food for micro-organisms and plant growth; and

e physically polluted by particles of dirt, food, lint and sand etc.

Greywater contains many impurities, including nutrients such as nitrogen and
phosphorus, which may harm the environment and the soil in particular. There are
some chemicals, which are not capable of being treated or degraded in the soil.
Therefore the soil ecosystem must be capable of adsorbing, absorbing, assimilating or
treating the chemical impurities and nutrients without medium and long-term
degradation of the soil of the environment. Domestic greywater treatment systems are
designed primarily to treat organic matter and are not normally designed to remove
chemical salts such as sodium, nitrates and phosphates that may be found in
greywater.

If a member of the house is ill or is carrying a subclinical infection, greywater may
carry infectious bacteria or viruses. However, in order for the greywater to make
another person ill it would be necessary for that person to drink or otherwise consume
the contaminated greywater inhale aerosols, touch or consume items, which have
come in contact with contaminated water. The objectives of the standards are to avoid
human contact with greywater. When greywater is being used follow these rules:

e don’t drink or play in greywater.

e don’t allow anything that may be eaten to come in contact with greywater.

e don’t allow greywater to pond on the surface or run off the property.

e don’t wash domestic pets in greywater or allow these pets to drink the greywater.

e wash your hands after contacting greywater or otherwise dealing with greywater.

Storage of Greywater

All forms of wastewater when stored will turn septic unless the wastewater is treated
to a high standard. Similarly, when greywater is stored it will also turn septic giving
rise to offensive odours and provide conditions for microorganisms to multiply.
Significant levels of pathogens have been found in stored greywater after eight days.
Should the stored septic greywater be surface irrigated it will give rise to extremely
offensive odours, provide conditions conducive to disease transmission and attract
insect and rodent vectors. Greywater must not be stored, other than temporarily,
unless adequately treated.

 

Unearthed Geotechnical P/L. 17 Design Report 023-038