Attachment K - HSTP Design

Presence of Pathogenic Microorganisms

Greywater may be contaminated with microorganisms such as bacteria, viruses and
protozoa. It is these microorganisms, many of which may cause disease, that present
the greatest health concern associated with greywater recycling and disposal. While
many bacteria cannot survive in a hostile environment like soil, some bacteria and
viruses that cause disease are resilient and can often survive for long periods of time
in this environment. Disease transmission is principally through the faecal-oral route
where the greywater may be directly ingested through contaminated hands or
indirectly ingested through contact with contaminated items such as grass, soil, toys,
garden implements and treatment plants while they are being serviced. Transmission
may also occur through inhalation of irrigated spray, by penetration through broken
skin, and by insect vectors such as flies and cockroaches. Contaminated drinking
water aquifers may facilitate ingestion of pathogens.

Comparison with Raw Sewage and Blackwater

Raw sewage, blackwater and septic tank effluent are all forms of effluent that are
directly and grossly contaminated with human excrement and therefore represent a
public health threat. Sewage, blackwater and septic tank effluent are all managed by a
high level treatment before being released into the environment above ground level
and must at least be settled or filtered to remove solid particles before management by
sub-soil land application area. Raw sewage is usually directed, in metropolitan and
urban areas, to a centralised sewage treatment plant for treatment and utilisation or
disposal. Septic tank effluent is sewage that has been stored in a large vessel or tank
and has turned septic, i.e. all the oxygen in solution has been consumed by the
decaying process and the septic tank effluent becomes offensively smelly.

Laundry Greywater

Microbiological: variable thermotolerant coliform loads, depending on dwelling
occupancy i.e. family with children. Wash water has poorer microbial quality than
rinse water.

Chemical: sodium, phosphate, boron, surfactants, ammonia and nitrogen from soap
powders and soiled clothes.

Physical: high in suspended solids, lint and turbidity.

Biological: high in biochemical oxygen demand,

Laundry wastewater represents about 23% of household wastewater (35% of
greywater). The detergents used in clothes washing give rise to the presence of
phosphorus, ammonia, organic nitrogen and boron in varying amounts depending on
the product and suspended solids such as lint, hair and dirt. Many of these
contaminants are classified as nutrients and if transferred to waterways or
groundwater may lead to environmental damage.

 

Unearthed Geotechnical P/L. 18 Design Report 023-038