ENVIRONMENTAL PERFORMANCE OF THE ADELAIDE DESALINATION PLANT
Tim Kildea 1, Vanesa Ayala 2, Milind Kumar 1, Guillermo Hijos 2, Javier Artal 2
1. South Australian Water Corporation, Adelaide, SA
2. AdelaideAqua, Adelaide, SA
ABSTRACT
Desalination has come to the fore in Australia as a
means of “water proofing” Australian coastal cities
against drought. The construction of large
desalination plants along the coast has generated
considerable public debate. Assurance was
provided to the community that the care for the
local terrestrial and marine environment remained a
core value in the development of the project.
Marine monitoring studies undertaken for the
Adelaide Desalination Project have shown that the
saline waste stream discharged to the marine
environment rapidly disperses and dissolved
oxygen concentrations adjacent to the outfall are
conducive for maintaining a healthy aquatic
ecosystem. The project has been an outstanding
success in terms of meeting its operational and
environmental commitments.
INTRODUCTION
years. At handover, the ADP had already delivered
in excess of 17 GL of high quality drinking water
into SA Water’s distribution system.
The ADP incorporates a high level of operational
flexibility, with nominal daily production rates from
30 to 300 ML/d, in 15 ML/d increments. This
flexibility was necessary due to the multiple sources
of drinking water for Adelaide (catchment, River
Murray, desalination) and the need to ensure
optimum usage of lower cost, climate dependent
water sources.
At maximum plant production rate of 100 GL per
year, ADP can produce approximately 50 % of
Adelaide’s current drinking water needs, providing
the only climate independent source of water for the
city. Although this provides some water security for
Adelaide, the ADP is only one of a number of
strategies that the State is incorporating to meet
city’s growing water needs.
The South Australian Water Corporation (SA
Water) is a government-owned utility which
provides water and wastewater services to more
than 1.5 million people in South Australia. In
December 2007, following years of severe drought
conditions, the State Government announced the
Adelaide Desalination Project as part of a major
investment in securing water supplies for the State.
The building of the 100 gigalitres
Adelaide Desalination Plant (ADP)
early 2009. The plant was was
constructed by AdelaideAqua,
consisting of McConnell Dowell,
ACCIONA Agua.
(GL) per year
commenced in
designed and
a consortium
Abigroup and
The ADP is the largest and most complex water
infrastructure project ever delivered by SA Water.
The $1.824 billion project was delivered on time
and within budget; an outstanding achievement for
SA Water and the AdelaideAqua consortium.
The ADP (Fig. 1) was officially handed over to the
Operator, AdelaideAqua Pty. Ltd. (AAPL), on 12
December 2012. AAPL are a partnership between
ACCIONA Agua and TRILITY, who have a contract
to operate and maintain the plant over the next 20
Figure 1 Adelaide Desalination Plant
Environmentally, the ADP has one of the lowest
carbon footprints of any desalination plant in the
world. A contract with AGL has ensured that the
ADP is powered by GreenPower accredited energy
over the next 20 years.
The energy consumption of the total plant has been
optimised through sustainable design and by
recovering residual energy by using outfall turbines.
Ultra Filtration pre-treatment (with washwater
recovery) coupled with patented high recovery
Reverse Osmosis membranes (48.5%) minimises
seawater abstraction requirements to achieve
optimum energy consumption. The above
processes have contributed to a specific energy
consumption of approximately 3.7 kWh/kL.
There were number of key environmental drivers
for the project other than reducing the carbon
footprint. During the environmental assessment
process a number of committments were made to
the community in regards to the care of the local
terrestrial and marine environment, in the region of
the ADP.
Over 250,000 native plants of local providence
were planted around the ADP, which also included
the development of an extensive wetland
ecosystem for the management of stormwater on
site.
During the construction phase, initiatives such as
marine tunnelling for the intake and outfall
pipework, using large tunnel boring machines,
protected sensitive nearby habitats including
coastal cliffs and offshore reefs.
The intake of large volumes of seawater by
desalination plants is often a focus of community
concern, in particular protecting local marine
wildlife. The ADP intake structure was designed to
minimise entrapement and entrainment of marine
organisms by setting a maximum seawater intake
velocity of 0.15 m/s, which is equivalent to the
average current veloicty in the region. The structure
was also located in deep water away from local
reefs and far from nursery fish grounds.
Finally, duckbill valves were incorporated into the
diffuser design to assist in the rapid dispersion of
the saline concentrate waste generated from the
desalination process, into the marine environment.
A novel engineering solution which has increased
the effectiveness of the diffuser when operating at
low flow rates.
In Australia, detailed monitoring studies have been
developed by the plant operators and owners to
assess the environmental performance of seawater
reverse osmosis (SWRO) desalination plants.
These studies have provided a substantial volume
of information which shows the positive outcomes
of good planning and engineering in minimising
potential impacts to the environment.
This paper aims to present some of the water
quality data collected for the Adelaide Desalination
Project, in particular salinity and dissolved oxygen
concentrations. The results focus on the
performance of the ADP in dispersing saline
concentrate waste into the marine environment.
Salinty concentrations adjacent to the diffuser are
compared to results obtained from ecotoxicological
studies conducted as part of the environmental
impact assessment process. The comparisons aim
to provide an appraisal of how well the plant
performs in meeting its enviromental commitments.
METHOD
The data presented in this paper are based on
three separate studies. These studies are:
Water Quality Characterisation Study
In order to estimate the temporal and spatial
dispersion of the saline concentrate from the ADP
diffusers, monthly oceanographic surveys are
undertaken in the region of the outfall.
Water column profiling is undertaken at sites 100
m, 500 m and 5 km north and south of the Adelaide
Desalination Plant outfall, at a water depth of 5 m,
10 m, 15 m, 20 m and 25 m. Three reference sites,
located approximately 10 km offshore, are included
in the study, which encompasses a total survey
area of 100 km2.
At each site, vertical distribution of specific
conductivity (uS/cm), dissolved oxygen (mg/L), pH,
turbidity (NTU), water temperature (degrees
Celsius) and depth was obtained using a YSI 6600
series V4 sonde.
Depth profiles were undertaken by lowering the
instrument through the water column at a rate of
approximately 0.2 metres per second. Data, which
included the instruments position (longitude and
latitude) and depth (metres) in the water column,
were logged and stored every two seconds.
Diffuser performance
A study was undertaken to assess the intensity and
dispersion of the saline concentrate from the ADP
diffuser under a “worst case” scenario of low tidal
currents and a maximum production rate of 300
ML/d.
The survey was undertaken on 4th June 2013,
coinciding with a local period of minimal tidal
movement (termed a “dodge tide”), low wind (< 10
knots) and calm seas (<0.5m).
Specific conductivity, dissolved oxygen, water
temperature and depth were recorded at the
seafloor at over 70 sites, covering an area over 100
km2 around the ADP outfall.
Spatial plots were derived using the grid-based
graphic program Surfer 8 (Golden Software Inc.),
which interpolates irregularly spaced XYZ data into
a regularly spaced grid. The grid was then used to
produce an image map to show how concentrations
(salinity and DO) changed across a defined area.
The data are interpolated using the “Natural
Neighbour” algorithm, which is a geostatistical
gridding method used to express the spatial trends
that occur for each of the different parameters.
Ecotoxicology
Work carried out for the Environmental Impact
assessment of the Adelaide Desalination Project
(SA Water 2009) utilised ecotoxicology testing in
order to assess the potential biological impacts that
saline concentrate may have upon marine
organisms.
The study utilised, where possible, South Australian
species. Five species from four taxonomic levels
(polychaete,
crustacean,
plant,
fish
and
phytoplankton) were utilised in the ecotoxicological
experiments to derive an ecological trigger value
that represented the dilution required for the safe
disposal of saline concentrate into the marine
environment.
The results from this study recommended a safe
dilution factor of 23:1 to protect 99% of typical
marine species.
RESULTS AND DISCUSSION
Average salinity concentrations
The main focus of desalination research,
worldwide, has been assessing how rapidly saline
concentrate waste streams disperse in the
receiving waters (Roberts et al. 2010). The results
from these studies have been highly variable and
have shown that dispersion occurs over a wide
distance range, extending from tens of metres to
several kilometres. The variation in dispersion has
been attributed to differences in plant capacities,
diffuser designs, local oceanographic features and
sampling methods (Roberts et al. 2010).
In the majority of cases the studies have shown that
the salinity concentration is usually no greater than
two parts per thousand (ppt) above the background
salinity within 20 m of the outfall. Thereafter the
saline concentrate plume rapidly disperses with
salinity concentrations only slightly greater than
background levels (< 0.5 ppt) within a couple of
hundred metres of the point of discharge (Roberts
et al. 2010). It should be noted that the majority of
these studies have been conducted in the
Mediterranean Sea, which is characterised as a
shallow, low-energy environment; conditions
considered to be sub-optimal for the rapid
dispersion of saline concentrate waste streams.
Results from the water quality monitoring of the
Adelaide Desalination Plant have shown that there
is a high degree of variation associated with the
dispersion of saline concentrate into the marine
environment
(Figure
2).
Average
salinity
concentration measured on the seafloor, 100
metres from the diffuser, at a depth between 15 m
and 20 m is represented by the red line. The blue
hashed line represents background salinity
concentration on the seafloor, approximately 10 km
from the ADP diffuser. Error bars represent
standard deviation.
Figure 2: Salinity concentrations on the seafloor
Monthly background salinity concentrations vary
from 35.6 ppt to 37 ppt, dependent on the time of
the year. This is natural for Gulf St Vincent (GSV)
and is a result of oceanic seawater mixing with the
seawater in the Gulf. Generally the GSV gets saltier
in summer from natural freshwater evaporation and
decreases in salinity during winter as freshwater
enters via seasonal rains. Density driven currents
develop in GSV over summer, and saltier water
from the upper parts of the Gulf moves past Port
Stanvac in late autumn/early winter. Hence average
background salinity concentrations in the Port
Stanvac region are highest around May/June.
Another feature is the movement of oceanic
seawater in response to the prevailing southerly
winds. The seawater moves into the Gulf and mixes
in the vacinity of Port Stanvac. Bye and Kämpf
(2008) noted that Port Stanvac lies at the junction
of two opposing gyres and this is reflected in the
large standard deviations observed for the average
salinity concentrations. Salinity concentrations are
highly variable not only monthly but weekly and
sometimes daily.
The majority of time the difference in salinity
concentration between background and 100 m from
the diffuser is less than 0.5 ppt. The largest averge
difference observed was 1 ppt during the month of
July (Figure 2). Based on the summary of results
outline in the Roberts et al. (2010) review on
desalination plant discharges, the ADP diffusers are
performing better than any other large plant
worldwide.
It should be noted that the results presented in
Figure 2 are based on a range of daily plant
production rates and oceanograpic mixing
conditions; variables which would influence the rate
of dispersion of the saline concentrate waste from
the diffusers.
Salinity contours
To effectively assess diffuser performance, a study
was required which incorporated “a worse case
scenario” of poor mixing conditions (dodge tide,
wind <10 knots and swell/seas < 0.5 m) at the
maximum plant production of 300 ML/d.
GSV is characterised by a phenomana called a
“dodge tide”. The “dodge tide” is an interplay
between semidiurnal lunar and solar tidal
constituents, which result in “significantly”
weakened tidal currents on a fortnightly basis
(Kämpf and Clarke 2012). It has been speculated
that during dodge tide events, “brine underflows”
would form consisting of a thin layer of hypersaline
water spreading along the seafloor, becoming
rapidly depleted in dissolved oxygen (Kampf and
Clarke 2012).
The diffuser performance study was undertaken on
the 4th June, 2013, under optimal “worse case
scenario” conditions. A salinity contour map (Figure
8) was generated from over 70 sample points
covering an area of approximately 100 km 2. The
contours represent salinity concentrations (ppt) on
the seafloor, in the vicinity of the ADP diffuser
(yellow circle). The x and y axes represent eastings
and northings and provide a measurement in
metres of the size of the plume footprint.
The footprint is detectable over a distance of
approximately 6 km by 4 km. The maximum salinity
concentration
oberserved
was
38.1
ppt
approximately 100 m south of the ADP outfall
(Figure 3). At this point the plume is approximately
4 metres thick on the sea floor. Brine discharges
are often denser than seawater of natural salinities,
and therefore plumes tend to extend further along
the seafloor than at the surface (Roberts et al.
2010). As predicted, the data clearly shows that
elevated salinity concentrations are restricted to the
seafloor (Figure 3).
Salinity varies naturally with tidal cycles, particularly
due to the mixing of oceanic water and gulf water,
as observed in the variability of the ambient salinity
concentrations (Figure 2). Thus exposure to
elevated salinity concentrations is likely to vary both
spatially and temporally, particularly with changing
tides and weather patterns.
The footprint observed (Figure 8) is considered to
be the worst case scenario and therefore the
salinity concentrations at other times are likely to be
substantially lower. This is reflected in the average
salinity data obtained at other times of the year
while the plant has been operational (Figure 2).
Dissolved Oxygen
The question posed by Kämpf and Clarke (2012) on
whether dissolved oxygen becomes depleted as a
result of the denser saline water moving across the
seafloor is a simple one to answer. No.
In Figure 4, average ambient seafloor dissolved
oxygen concentrations throughout the year are
compared with dissoved oxygen concentrations
measured 100 metres from the diffuser, at a depth
between 15 m and 20 m. Error bars represent
standard deviation to the mean. When the two are
compared, there is no
significant difference
between the background dissolved oxygen (DO)
concentrations on the seafloor and those around
the ADP diffuser.
Figure 4: Seafloor oxygen concentrations
Figure 3: Salinity profile through the water column
Thereafter the plume quickly disperses to
concentrations approximately 0.6 ppt above
background salinity within 1 km of the outfall. It then
follows the depth gradient moving into deeper
water, reaching background concentrations of 37.3
ppt, approximately 4.5 km south of the outfall.
This is reiterated by the dissolved oxygen profile
through the water column, 100m north and south of
the ADP diffuser (Figure 5). These measurements
were taken during the diffuser performance study
and suggest that DO concentrations decrease
slightly from the surface to the bottom; an
observation that is expected due to normal surface
water oxygen supersaturation (>100%).
Dupavillion and Gillanders (2009) exposed
cuttlefish embryos (Sepia apama) to a range of
salinities until their hatch date. Their results showed
that there was no significant reduction in size and
weight of hatchlings until salinity concentrations
were greater than 42 ppt.
Beattie (2009) found that ascidians (Ascidiaceae)
and sea stars (Ophiuroidea) reacted in a similar
way when exposed to different concentrations of
saline concentrate. The results from this study
suggested that until salinity reached a threshold of
44 ppt, there was no impact on survival rates.
Figure 5: Dissolved oxygen profile through the
water column
On a regional scale there is no discernable
difference in DO concentrations on the seafloor
(Figure 9). The results presented are from a
diffusion performance study undertaken during a
dodge tide. Black crosses represent sampling
points and white crosses represent the exclusion
zone surrounding the ADP intake and outfall. The x
and y axes represent eastings and northings and
provide a measurement of distance in metres. DO
concentrations remain a consistent 7.5 mg/L across
the 100 km2 sampling region. This is somewhat
contradictory to Kämpf and Clarke (2012)
speculation on “brine underflows” depleting oxygen
on the seafloor.
The World Health Organisation (WHO) provided a
synthesis of all ectoxicological studies published in
peer review journals and suggested a more
conservative threshold of 10% above maximum
background salinity concentration (equating to 40.7
ppt for Port Stanvac).
Results to date from ADP suggest that salinity
concentrations recorded on seafloor, around the
diffuser are well below all these thresholds. A
comparison of threshold values are presented in
Figure 6.
Environment Protection Authority criteria for healthy
marine ecosystems stipulate a DO concentration
threshold of 6 mg/L. DO concentrations adjacent to
the diffuser have been measured at 7 mg/L or
greater throughout the year (Figure 4).
Ecotoxicology
The final question that could be asked is, “Is the
elevated salinty concentration observed around the
ADP outfall halmful to marine life?”.
The ecotoxicological studies undertaken as part of
the Environmental Impact assessment (SA Water
2009) recommended a safe dilution factor of 23:1 to
protect 99% of typical marine species. This equates
to 39 ppt based on maximum background salinity
concentration of 37.4 ppt. This is a conservative
estimate as most of the organisms tested did not
show signs of stress until salinity concentrations
reach 40 ppt or above.
The maximum salinity concentration recorded next
to the ADP diffuser was 38.1 ppt (Figure 2). All
things considered, these results suggest that there
should be minimal impact to the organisms living
around the ADP outfall. Other studies on the
toxicological effects of brine on local South
Australian marine species support this conclusion
(Dupavillion and Gillanders 2009, Beattie 2009).
Figure 6: Comparing salinity concentrations to
ecotoxicology results
CONCLUSION
Whilst studies have identified several potential
mechanisms by which desalination plants may
impact upon marine ecosystems many published
review articles and case studies cite little or no peer
reviewed literature and present little of no empirical
data to support statements regarding environmental
effects of desalination (Roberts et al. 2010). Hence
it is unclear whether the potential impacts of
desalination plants are assumed or have been
determined through rigorous ecological research.
Marine monitoring studies undertaken for the
Adelaide Desalination Project have shown that the
saline waste stream discharged to the marine
environment rapidly disperses and dissolved
oxygen concentrations adjacent to the outfall are
conducive for maintaining a healthy aquatic
ecosystem. The project has been an outstanding
success in terms of meeting its operational and
environmental commitments.
Figure 7: Marine life around the ADP outfall, April
2013
ACKNOWLEDGMENTS
Many thanks to:
Lorenzo Andreacchio and Dusty Rietveld for their
assistance in data analysis, figures and
introduction;and
Matt Blaikie, Carol Sims and Lorenzo for their
editorial red pen.
REFERENCES
Beattie K., 2009. Desalination Impacts on Marine
Invertebrates: Effluent Toxicity. Honours thesis.
Flinders University.
Bye, J and Kämpf, J. 2008. Physical
Oceanography. In Natural History of Gulf St
Vincent p56-70. Royal Society of South
Australia.
Dupavillon, J., and Gillanders, B. 2009. Impacts of
seawater desalination on the giant Australian
cuttlefish Sepia apama. Marine Environmental
Research 67, 207-218.
Kämpf, J. and Clarke, B. 2012. How robust is the
environmental impact assessment process in
South Australia? Behind the scenes of the
Adelaide seawater desalination project. Marine
Policy.
Roberts, D, Johnston, E. and Knott, N. 2010.
Impacts of desalination plant discharges on the
marine environment: A critical review of
published studies. Water Research 44, 51175128.
SA Water (2009) Proposed Adelaide Desalination
Plant
Environmental
Impact
Statement,
Government of South Australia.
World
Health
Organisation
(WHO)
2007.
Desalination for Safe Water Supply:Guidelines
for the Health and Environmental Aspects
Applicable to Desalination, Public Health and
the Environment World Health Organisation,
Geneva.
Figure 8: Salinity contours around the ADP diffuser
9
6118000
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Figure 9: Regional dissolved oxygen concentrations
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