Recycled Water Irrigation in Australia - Environmental Sustainability: Role of Green Technologies - page 39

sector and the reuse water consumption as a
percentage of total water use for each enterprise
type. Whilst beef, sheep and grain production use
the largest volume of reuse water, it amounts to
only 1 % of this industries' total water use (ABS
2010b ). Horticulture and fl oriculture use the
greatest amount as a proportion of total water use
(10 %), followed by vegetable and mushroom
production (4 %). This may be a refl ection of the
relative proximity of these industries to major
wastewater treatment plants which supply the
majority of reuse water and are located in prox-
imity to densely populated urban areas.

Sedimentation also removes a proportion of the
heavy metal(loid)s which, being mainly cations,
bind to negatively charged organic matter and
clay particles. In secondary processes, bacteria
remove soluble and colloidal wastes by assimilat-
ing organic matter to form new microbial biomass
and by producing gas through the use of organic
matter for endogenous respiration. Tertiary pro-
cesses such as nutrient removal, fi ltration and dis-
infection are employed as an additional step to
achieve suffi cient removal of coliforms, parasites,
salts, trace organics and heavy metal(loid)s to
make the water suitable for unrestricted irrigation
of food crops. These steps can be carried out con-
comitantly with earlier processes and include
nutrient removal through precipitation (as in the
case of phosphorus-P) and gaseous emission (as
in the case of nitrogen-N though denitrifi cation),
and disinfection by UV light, chlorine or ozone
reduces the number of pathogens present in the
waste stream by inactivation.

2 Wastewater Treatment

and Public Health

2.1 Wastewater Treatment

Untreated wastewater originates from domestic
households, commercial premises and industrial
activities. It does not include storm water which is
the rainfall run-off from sealed surfaces including
roofs and roads. It typically consists of 99.9 %
water and 0.1 % impurities which include:
dissolved and suspended organics, pathogens,
nutrients, trace elements, salts, refractory organ-
ics, priority pollutants and heavy metal(loid)s.
Varying degrees of treatment can be applied to
remove or reduce these contaminants in wastewa-
ter. The aim of wastewater treatment is to produce
water which is fi t for purpose, i.e. when used as
intended will not threaten human health or
degrade the receiving environment. The extent of
treatment required is usually regulated by Public
Health or Environmental Protection Authorities.
Wastewater reclamation processes are tradi-
tionally grouped into preliminary, primary, sec-
ondary and tertiary treatment processes though it
is possible to fi nd signifi cant overlap at wastewa-
ter treatment plants. At the preliminary stage,
large debris and fi ner abrasive material are
removed to prevent damage to downstream equip-
ment. In the primary processes, sedimentation is
used to remove approximately 65 % of the solid
content of raw sewage and approximately 35 % of
the biochemical oxygen demand (BOD).

2.2 Governance and Quality

Requirements of Reclaimed
Water Use

Regulations governing the use of reclaimed water
are not uniform throughout Australia; each state
and territory has responsibility for managing nat-
ural resources and public health in their jurisdic-
tion. Legislation for wastewater reuse is covered
by acts relating to food safety, public health and/
or environmental protection. As such the state
Public Health Authority and/or Environmental
Protection Agency have responsibility for polic-
ing reclaimed water reuse.
Many states require enterprises which irrigate
with reclaimed wastewater or supply reclaimed
wastewater for the purpose of irrigation to pro-
duce and adhere to environmental (irrigation)
management plans and/or user agreements. The
plans should include a study of the irrigation site
characteristics and justify how the wastewater
will be applied so that its use will not threaten
human health or adversely impact on the receiv-
ing environment. The need for user agreements to
ensure wastewater is being utilised in the