2nd International Salinity Forum

Salinity, water and society–global issues, local action 1

Seawater desalination in Australia and the Perth experience—a sustainable 

solution

Gary Crisp1

1

Desalination Technical Leader, GHD Pty Ltd, Brisbane.

Abstract

In the face of the driest winter on record, the Perth Seawater Desalination Plant (PSDP) 

commenced delivering an annual capacity of 45 GL of much needed drinking water into the 

Integrated Water Supply Scheme (IWSS) in November 2006.

The PSDP, located at Kwinana, 30 kilometres south of Perth, Western Australia, has been 

heralded as a landmark in the development of the Australian water industry. It is a strong and 

worthy contender to be regarded as a world-leading model for future sustainable seawater 

desalination plants globally. At a peak capacity of 144 MLD, the $387 million plant (which 

includes $64 million of integration assets), is the largest operating seawater desalination plant 

outside of the Middle East, and Australia’s first large-scale desalination facility for public 

water consumption.

The PSDP is also the largest seawater desalination plant in the southern and eastern 

hemispheres and looks likely to maintain this status into the foreseeable future. At full 

capacity, it is the biggest single water source feeding into the IWSS, providing some 17 per 

cent of Perth’s water needs.

Construction commenced in June 2005 after a unique tendering process which involved a 

design competition between two short listed finalists from eleven original submissions. The 

plant was built on an extremely tight time schedule and budget and this came with its own set 

of challenges. Some key environmental challenges included; approvals and regulations, 

energy, concentrate management, marine monitoring, aesthetics and community involvement.

The desalination plant was built by the Multiplex-Degremont Joint Venture, in alliance with 

the Water Corporation. The joint venture is registered as the proAlliance (Perth Reverse 

Osmosis Alliance). The plant will be operated for 25 years by Degremont in alliance with the 

Water Corporation.

A recently completed 82 MW wind farm supplies over 272 GWhr of energy per year to 

Perth’s electricity grid. The PSDP will consume 185 GWhr of energy per year from the grid 

making it the world largest desalination plant using renewable energy. Coupling this energy 

source with the low specific energy consumption achieved from the plants novel design, 

incorporating isobaric energy recovery devices (PX) from ®ERI, ensures that it is the world’s 

most energy conscious plant.

Considering the plants partial two pass system which produces a permeate at less than 100 

mg/L TDS, from a feedwater salinity of 35,000 mg/L, the achievement of a specific energy 

consumption of less than 3.9 kWh/m3 is remarkable.

Other unique aspects of the plant include the partial second pass which has been included to 

ensure a bromide content of less than 0.1 mg/L in the product water and Degremont’s 

proprietary Densadeg sludge thicker to ensure dewatered sludge can be safely transported and 

disposed of to landfill. Although inert and the fact that PSDP is located along an industrial 

zone, Water Corporation committed to prohibit the return of ferric sulphate sludge to the 

ocean to ensure that there were no aesthetic impacts on the white sandy coastline.

Further, in order to meet the strict environmental conditions, the seawater concentrate is 

returned 470 metres into the ocean via a 40-port diffuser, with nozzles spaced at five metre 

intervals, to ensure total mixing of seawater concentrate within 50 metres of each side of the 

last 200 metres of pipeline. Therefore, the discharge is effectively no different from the 

naturally occurring seawater in terms of its salinity and meets the Environmental Protection 
2nd International Salinity Forum

Salinity, water and society–global issues, local action 2

Authority’s stringent criteria. Extensive real-time monitoring in Cockburn Sound will 

continue together with annual marine habitat mapping to ensure long term impacts of the 

project continue to be managed.

The additional cost for the average residential customer is AU$40 per annum, less than 

AU$0.70 per week, as stated by the (then) Premier of Western Australia on announcement of 

the project in July 2004 has come to fruition as originally estimated.

Taking all the above factors into account and considering the plants small physical footprint 

(on land and in the sea), this plant is one of the most sustainable water sources in Australia, 

and the only water source in Australia that wholly caters for the triple bottom line, economic, 

social and environmental factors. All other sources only cater for the double bottom line, 

economic and social factors.

This paper will describe the contracting, design, operational and environmental 

characteristics of the Perth Seawater Desalination Plant and demonstrate why this project 

is leading the world in terms of sustainable desalination. Further, the paper will touch on 

future sustainable practices such as gleaning energy from osmotic pressure in combination 

with other renewable energy sources and how, with this in mind, future desalination sites 

will be strategically set aside for future generations.

Keywords: desalination, seawater concentrate management, energy use, ecological footprint,

sustainable water source

Introduction

In the face of the driest winter on record, the Perth Seawater Desalination Plant (PSDP) 

commenced delivering an annual capacity of 45 GL of much needed drinking water into the 

Integrated Water Supply Scheme (IWSS) in November 2006.

The PSDP, located at Kwinana, 30 kilometres south of Perth, Western Australia, has been 

heralded as a landmark in the development of the Australian water industry. It is a strong and 

worthy contender to be regarded as a world-leading model for future sustainable seawater 

desalination plants globally. At a peak capacity of 144 MLD, the $387 million plant (which 

includes $64 million of integration assets), is the largest operating seawater desalination plant 

outside of the Middle East, and Australia’s first large-scale desalination facility for public 

water consumption.

The PSDP is also the largest seawater desalination plant in the southern and eastern 

hemispheres and looks likely to maintain this status into the foreseeable future. At full 

capacity, it is the biggest single water source feeding into the IWSS, providing some 17 per 

cent of Perth’s water needs.

Construction commenced in June 2005 after a unique tendering process which involved a 

design competition between two short listed finalists from eleven original submissions. The 

plant was built on an extremely tight time schedule and budget and this came with its own set 

of challenges. Some key environmental challenges included; approvals and regulations, 

energy, concentrate management, marine monitoring, aesthetics and community involvement.

The desalination plant was built by the Multiplex-Degremont Joint Venture, in alliance with 

the Water Corporation. The joint venture is registered as the proAlliance (Perth Reverse 

Osmosis Alliance). The plant will be operated for 25 years by Degremont in alliance with the 

Water Corporation.

A recently completed 82 MW wind farm supplies over 272 GWhr of energy per year to 

Perth’s electricity grid. The PSDP will consume 185 GWhr of energy per year from the grid 

making it the world largest desalination plant using renewable energy. Coupling this energy 

source with the low specific energy consumption achieved from the plants novel design, 

incorporating isobaric energy recovery devices (PX) from ®ERI, ensures that it is the world’s 

most energy conscious plant.
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Salinity, water and society–global issues, local action 3

Considering the plants partial two pass system which produces a permeate at less than 100 

mg/L TDS, from a feedwater salinity of 35,000 mg/L, the achievement of a specific energy 

consumption of less than 3.9 kWh/m3 is remarkable.

Other unique aspects of the plant include the partial second pass which has been included to 

ensure a bromide content of less than 0.1 mg/L in the product water and Degremont’s 

proprietary Densadeg sludge thicker to ensure dewatered sludge can be safely transported and 

disposed of to landfill. Although inert and the fact that PSDP is located along an industrial 

zone, Water Corporation committed to prohibit the return of ferric sulphate sludge to the 

ocean to ensure that there were no aesthetic impacts on the white sandy coastline.

Further, in order to meet the strict environmental conditions, the seawater concentrate is 

returned 470 metres into the ocean via a 40-port diffuser, with nozzles spaced at five metre 

intervals, to ensure total mixing of seawater concentrate within 50 metres of each side of the 

last 200 metres of pipeline. Therefore, the discharge is effectively no different from the 

naturally occurring seawater in terms of its salinity and meets the Environmental Protection 

Authority’s stringent criteria. Extensive real-time monitoring in Cockburn Sound will 

continue together with annual marine habitat mapping to ensure long term impacts of the 

project continue to be managed.

The additional cost for the average residential customer is AU$40 per annum, less than 

AU$0.70 per week, as stated by the (then) Premier of Western Australia on announcement of 

the project in July 2004 has come to fruition as originally estimated.

Taking all the above factors into account and considering the plants small physical footprint 

(on land and in the sea), this plant is one of the most sustainable water sources in Australia, 

and the only water source in Australia that wholly caters for the triple bottom line, economic, 

social and environmental factors. All other sources only cater for the double bottom line, 

economic and social factors.

Perth Seawater Desalination Plant description

Perth Seawater Desalination Plant (PSDP) is located in Kwinana, an industrial area 

approximately 25 km to the south of Perth. The plant draws water from the ocean via an open 

intake catchment, located in Cockburn Sound approximately 200 metres offshore in 11 metres 

of water 6 metres below sea level.

The complete process (which takes about half an hour, sea to storage) includes the following 

steps:

• an open intake,

• screening to protect the feed pumps and dual media filters,

• single stage dual-media filtration,

• cartridge filters for polishing and security,

• a two-pass reverse osmosis process,

• potabilisation treatment (including remineralisation, fluoride injection, disinfection).

Plant optimisation

The PSDP design has been optimized in relation to the following factors:

• availability,

• redundancy,

• flexibility of operation.

The plant consists of two 50%-capacity streams and adequate redundancy has been catered 

for in relation to major equipment (pumps, blowers and air compressors, filters, electrical 

transformers). Plant operation is automated and flexible to cater for diverse seawater feed 
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Salinity, water and society–global issues, local action 4

variations (temperature, TDS), and to give a variable flow according to different operation 

options (recovery, permeate flow, number of racks in operation, demand and membrane age).

Intake structure

Intake screening at the intake structure consists of course barred screens offshore and 

automatically cleaned travelling band screens onshore.

Seawater forwarding pumps

The PSDP seawater forwarding pumping station is based on wet well /dry well design. The 

hydraulic conditions in the intake structure were monitored using computerised fluid 

dynamics. The study confirmed the initial choice in terms of tank design including the pump 

inlet arrangement.

Pre-treatment design

The pre-treatment design was based on the results of a pilot study performed during the 

summer and winter of 2004 and the winter of 2005 as discussed below. Filtration velocity, 

media type and effective size and water conditioning were optimised for high and low 

temperatures and varying water qualities. The seawater is fed by gravity to the seawater 

pumps. The raw water is pumped and water conditioning is performed in-line using static 

mixers. The treatment line dosing includes pH correction using sulphuric acid and 

coagulation using ferric sulphate and a coagulant aid.

Filtration is performed by 24 pressurised dual media filters using anthracite and sand as filter 

media. Based on an acceptable filtration velocity established in the pilot plant trials, the 

nominal flow can be achieved from 20 filters. The filtration is based on a 24 hour filtration

cycle, each filter being periodically backwashed with air and water which takes one hour. The 

backwash water can be either filtered water or brine.

Pilot test

The pilot tests were conducted for pre-treatment only, while the RO design was based on the

membrane supplier’s software and Degrémont knowledge on membrane performances and 

rack hydraulics. The desalination plant pre-treatment design was based on a 4-month pilot test 

performed during the preliminary engineering phase. The main objectives of this study were 

to select the number of filtration stages, the type of filtering media and the coagulation 

conditions.

Pilot test were performed during two periods, one in the summer of 2004 and the other in the 

winter of 2005. The water quality remained relatively stable over the two periods of tests. The 

level of particles, characterized by turbidity and SDI values were relatively high for an open 

seawater intake.

The pilot unit used for this study comprised of 4 transparent columns, each equipped with a 

feed pump and able to operate under gravity or pressure. Coagulation was performed in-line 

using ferric chloride and coagulant aid. The pH of coagulation was adjusted using sulphuric 

acid. Different media were evaluated, including pumice, anthracite and sand, with different 

particle size according to the number of filter stages: single or double stage filtration.

The seawater was monitored for temperature, turbidity, conductivity and pH on a continuous 

basis, and for SDI, UV absorbance, TOC and salinity on grab samples. The filtered water was 

monitored for turbidity on-line, and for iron, pH, salinity, UV absorbance on grab samples. 

Periodical evaluation of algae count was also performed, as well as bacteria counts.

The first part of the pilot test performed in summer 2004 was dedicated to the comparison of 

single stage filtration versus double stage filtration, rather than to the comparison of different 

media in a single filtration stage configuration. The comparison was made on filtered water 

quality and filter clogging velocity.

In all the configurations, the filtered water turbidity and SDI remained below 0.1 NTU and 4 

%/min respectively. The optimization of the water conditioning and the use of a ripening 

phase allowed for the achievement of filtered water SDI’s consistently below 3.5%/min 
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Salinity, water and society–global issues, local action 5

(average 3%/min) on a reliable basis. Based on these results, a single stage filtration process 

was selected to pre-treat the seawater from an open seawater intake.

The second period of tests was carried out during winter from June-July 2005. During these 

tests, the program focused on single stage filtration. Several types of media from local 

suppliers were tested to select the suppliers for the plant under construction.

Reverse osmosis

A single pipeline conveys pre-treated seawater via 5 micron cartridge filters to the HP pumps 

and energy recovery devices. The first pass has twelve seawater reverse osmosis (SWRO) 

racks, each with a production capacity of 13,350 kL/d, or a total of 160 ML/d. Each rack uses 

1,134 FilmtecTM model SW3OHRLE400 membrane elements housed in ProtecTM 7M sideport pressure vessels.

The product water, depending on variables such as seawater salinity, membrane age and 

temperature, ranges from 150 to 300 mg/L, at about 45% recovery. The RO trains are fed 

with six Weir split-case centrifugal HP pumps, each with a capacity of 1,144 kL/h at 620m of 

differential head, driven by 2,600 kW Siemens Motors. The best efficiency point of these 

pumps is approximately 86%. The reject stream from the RO modules is passed to twelve 

arrays of sixteen ®ERI model PX-220 energy recovery devices, each array with a capacity of 

800 kL/h, where the pressure is transferred to an equal volume of seawater. This pressure is 

boosted by about 5% and circulated into the RO modules by twelve Union® vertical booster 

pumps, each with a capacity of 661 kL/h at 39 m of differential head, driven by 112 kW 

motors controlled by VFDs. The plant is arranged with six SWRO trains on each side of a 

central pump aisle. Three HP pumps feed a high-pressure manifold or "pressure centre" which 

in turn feeds a bank of six SWRO racks. Flow from the manifold to each train goes through a 

high-pressure control valve which allows fine adjustment of the membrane feed pressure. 

Each rack has a dedicated PX-device array and booster pump. The PX device arrays are

situated between the membrane-vessel racks.

To further reduce salinity of the product water to 10-50 mg/L and reduce bromide to 0.1 mg/L 

the first-pass permeate goes to a second pass consisting of six low-pressure 'brackish water' 

reverse osmosis racks, with further product water extracted from the reject stream of the first 

stage, giving a recovery of 90%. Post-treatment chemicals include hydrated lime, gaseous 

chlorine and carbon dioxide. Product potable water flows through a four-hour buffer tank 

before being pumped approximately 13 kilometres to the fresh water reservoir that supplies 

the city of Perth with drinking water. Reject brine, after use as backwash for the dual-media 

filters, is pumped 0.5 km out to a diffuser field in Cockburn Sound.

Energy recovery devices

In a SWRO system equipped with PX (Pressure Exchanger) energy recovery devices, the 

membrane reject is directed to the membrane feed. The transfer of pressure from the reject 

stream to the seawater is performed by direct contact of the two streams inside the ducts of 

the PX rotor. The rotor contains no intervening pistons or valves. A small diameter rotor duct, 

in essence a 'tube' full of low pressure seawater is connected to the high pressure reject, which 

forces the seawater out at high pressure. Immediately afterwards, the tube, now nearly full of 

low pressure reject, is released to ‘drain’ and the reject pushed out by incoming seawater at 

feed pump pressure. There is virtually no interfacial mixing because:

• the tubes are small diameter,

• each operation is performed in around 0.05 seconds.

This is accomplished by mounting a bundle of tubes in a rotor which presents each tube to the

appropriate ports in the end casings. The rotor spins freely, driven by the flow at a rotation 

rate proportional to the flow rate, usually around 1,000 rpm.

The concept was devised by Mr Leif Hauge in a prototype initially fabricated in stainless 

steel. The commercial breakthrough came when the rotors and casings were fabricated in 
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Salinity, water and society–global issues, local action 6

precision ceramics, which are immune to corrosion and highly resistant to wear. A small 

amount of water flows from high to low pressure through the narrow end gaps and the narrow 

annulus that surrounds the PX device rotor, creating a nearly frictionless seawater-lubricated 

hydrodynamic bearing. There is no shaft or shaft seal. Each PX device is limited in size to 

220mm diameter, but unlimited capacity is achieved by arraying multiple devices in parallel.

In practice, the lubrication flow through the PX devices is approximately 1% of the brine flow 

to the array and together with the transient mixing in the passages leads to an increase in 

salinity of the seawater fed to the membranes of about 2.5%

A total energy transfer efficiency of up to 98% is possible, and efficiency is nearly constant 

over a wide range of flow and pressure variations.

Potabilisation

The potabilisation treatments includes remineralisation using CO2 injection and lime 

(saturated lime water), and injection of fluoride and chlorine to meet the Water Corporation 

requirements.

Concentrate discharge

The PSDP treatment line includes a full backwash water facility based on 

clarification/thickening and sludge dewatering using centrifugation. The clarified backwash 

water is mixed with the reverse osmosis brine before discharge. The brine discharge was 

subject to a specific design, based on a scale model testing study performed by the Water 

Research Laboratory (School of Civil and Environmental Engineering Technical, University 

of New South Wales) under the direction of Worley Parsons specialist engineers.

To ensure that the environment is protected, a series of marine monitoring studies were 

commissioned prior to and as part of the environmental approvals. These included; Whole 

Effluent Toxicity testing on simulated brine and actual seawater concentrate at 

commissioning and 12 months after commissioning, sediment oxygen demand tests, 

international literature review of dissolved oxygen levels, ecological investigations, cause 

effect models, and an intensive baseline investigation commissioned to document water 

quality and macrobenthic fauna present prior to operations.

Before and during operations a real time monitoring system, located at three points within 

Cockburn Sound feeds data back to the plant constantly. At one-minute intervals, temperature 

and conductivity is being recorded at 1-2m intervals through the water column, and dissolved 

oxygen is recorded at the bottom of each monitoring buoy and at mid-depth. Management 

responses have been agreed with the regulator in the event agreed trigger levels are reached.

Baseline water quality monitoring and testing in the discharge area as discussed above was

undertaken many months before plant commissioning. This baseline monitoring included the

following parameters:

• light intensity,

• salinity depth profile,

• temperature depth profile,

• dissolved oxygen depth profile,

• turbidity,

• Secchi depth,

• nutrients concentration (phosphorus, nitrogen, ammonium, nitrates and nitrites),

• metals,

• phytoplankton.

Western Australia’s environmental regulator, the Environmental Protection Authority (EPA) 

set strict criteria for the concentrate discharge, requiring the salinity within 50 meters of the 
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Salinity, water and society–global issues, local action 7

discharge point to be within 1.2 ppt of background levels. By the time the discharge is one 

kilometre offshore, salinity must be within 0.8 ppt of background levels. Extensive modelling 

revealed that salinity represents the most constraining water quality parameter.

The plant’s true environmental standing was confirmed by field campaigns which, included 

tracing an environmentally benign dye added to the plant discharge, which showed that the 

desalination discharge rapidly mixes with the surrounding waters. Stratification in the sound 

is mostly drive through temperature, not salinity gradients.

As the plant is fully automated specific care has been taken in relation to instrumentation to 

ensure reliable and safe operation of the plant. Analytical panels assess information from 

sensors installed at the intake, pre-treatment, first pass RO feed second pass RO and potable 

water systems. These incorporate hydrocarbon monitors, turbidimeters, pH meters, ORP, online SDI, conductivity and temperature as required. Residual chlorine and fluoride are also 

monitored for the drinking water. Parameters such as dissolved oxygen and ORP are also 

monitored in the discharge water back to the sea to ensure that strict environmental guidelines 

are adhered to.

Plant commissioning

Seawater first flowed through the plant intake in October 2006. Product water from the plant 

began flowing into Perth's municipal water supply on November 7. By December, the first six 

first-pass racks were running. By the end of February 2007, the entire plant was in operation.

During the construction period, the supply of filtration media and chemicals were finalized. 

Some pilot tests were performed to verify the quality of the inorganic coagulant as well as the 

coagulant aid. Ferric sulphate was finally selected and implemented on the full-scale plant. 

During the commissioning, Degrémont standard quality control was applied to the filter 

media loading and commissioning and during the filter start-up, allowing fine-tuning of the 

backwash and maturation phases, and of the water conditioning.

The SWRO trains were commissioned and started up two at a time with the corresponding HP 

pump isolated on the high-pressure manifold. Start-up followed a thorough flushing of each 

train with pretreated seawater at design flow rates to remove any residual construction debris. 

Plant start-up went according to schedule despite several unplanned incidents which could be 

considered normal in the context of a large plant start-up. Perhaps the most worrying was that 

most of the PX devices in the plant were exposed to excess high flow at least once, including 

one incident where flows rose to 81 kL/h in each PX device (62% higher than the maximum 

rated capacity) for six hours. These events occurred while the plants automated control 

systems and many of the process alarms were suppressed.

In addition, fibreglass construction debris stopped the rotors of several PX devices. However, 

the devices suffered negligible damage. The general comment of the commissioning team 

was that the start up of the SWRO trains with the PX devices was very easy and the devices

are quite flexible and robust.

For the first stage RO, with 97% energy recovery, the specific energy consumption (SEC) of 

the HP pump and the booster pumps is 2.4 kWh/kL with the high pressure flow rate being 

trimmed by a highpressure control valve. The specific energy consumption (SEC) for the 

second reverse osmosis pass, and post-treatment can be as much as 1.4 kWh/kL, depending 

on full or partial second pass operation. The seawater supply pump and reject brine discharge 

consume about 0.3 kWh/kL. Currently, with new membranes and operating at nominal 

capacity with an overall water recovery rate of 42%, the plant itself consumes less than 3.9 

kWh/kL including pre-treatment, both RO passes, post-treatment, and all electrical losses. 

This is a remarkably low SEC for a seawater desalination plant.

While the pre-treatment was partially commissioned, reverse osmosis first pass and second 

pass were gradually started, as well as the potabilisation treatment, allowing the first drinking 

water production to start in November 2006. In terms on energy recovery, the ®ERI installed 

on the first pass reverse osmosis performs in the design value: the first energy recovery 
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Salinity, water and society–global issues, local action 8

figures are within the 94% energy recovery guaranteed on this plant.

Major environmental issues

Energy

Desalination is an energy intensive process. Reverse osmosis requires significantly less 

energy than that of thermal distillation. The energy often comes from fossil fuels, so as well 

as the expense, there is the disadvantage of CO2 emissions. Critics say desalination could 

worsen climate change, by adding to greenhouse gases, and contribute to water shortage. 

Ironically it is what will solve water shortage.

As SWRO technology improves, energy inputs and hence CO2 emissions will decline, 

particularly in relation to large-scale desalination plants. The use of reverse osmosis 

membrane technology (essentially filtering water through a membrane under pressure) rather 

than distillation (boiling and condensation) lessens the energy requirement because the water 

does not need to change state from liquid to vapour.

High energy use and consequent high greenhouse gas emissions are an aspect of desalination 

that needs to be addressed from an environmental perspective. A plant similar to Perth’s, even 

with energy recovery devices (ERD) connected, will consume about 24 megawatts of 

electricity to produce about 45 GL of water per year. This represents about 185 GWh/year 

(which is 21.1 MW average) of energy per year which equals the amount of electricity needed 

by about 30,000 households. The opportunity to use renewable energy arose for PSDP and 

this plants energy is supplemented with energy injected into the grid from a new wind farm 

constructed north of the city.

Proposing offsets such as carbon offsets (tree planting) can be expensive and can lock up 

water reserves if not planted in carefully chosen locations (e.g. catchment thinning proposals). 

The nuclear energy debate and solar-thermal technologies in Australia continue to develop. 

However, as the ongoing need for large-scale water sources increase, energy sources will 

continue to be key part of the desalination equation, and must be thought through carefully 

during planning.

The energy required to permanently produce 17% of Perth’s water supply, i.e. enough water 

for over 300,000 people and their homes and gardens, is about the third of the energy of one 

Boeing Jumbo Jet flying continuously. A Jumbo uses 80 MW of power for take-off and 65 

MW of power to cruise as apposed to 21 MW of power for PSDP.

Backwash material

The PSDP discharge products that have been carefully managed include; the seawater intake 

screen washings, clarified backwash effluent from the media filtration plant, reverse osmosis 

plant seawater concentrate stream, neutralised reverse osmosis plant chemical clean 

wastewater and reverse osmosis plant flushing water. The PSDP has been engineered to 

ensure that backwash materials (solids) are disposed to landfill. This decision was made due 

to the presence of ferric sulphate and poly DADMAC (an organic coagulant) added to 

coagulate particulate and colloidal material from the influent seawater, and concerns about 

possible discolouration of the white sandy beaches, should this backwash be discharged at 

sea. Solid wastes from the intake screens, media filters and lime system are captured in the 

wastewater treatment clarifier. The sludge from the clarifier is dewatered by centrifugation to 

a spadeable cake for disposal to landfill. Offsite environmental management considerations 

include the salt content of the sludge; the quantity of the sludge; and handling quality of the 

sludge.

Seawater concentrate discharge

In order to meet the strict environmental conditions, the seawater concentrate is returned 470 

metres into the ocean via a 40-port diffuser, at a velocity of 4m/s through nozzles spaced at 

five metre intervals, to ensure total mixing of seawater concentrate within 50 metres of each 

side of the last 200 metres of pipeline.
2nd International Salinity Forum

Salinity, water and society–global issues, local action 9

Footprint

The Perth Seawater Desalination Plant is functionally laid out in an area of 6.5 hectares which 

can be regarded as its terrestrial footprint. Extensive computer modelling supported by a die 

test, as previously discussed, suggests that the diffuser with its 40 nozzles spaced at 4 metre 

intervals will ensure that the returning seawater concentrate is effectively mixed within an 

area of less than 2.5 hectares. It can then be argued that the spatial area of influence attributed 

to the plant on land and sea is only 9 hectares.

However to ensure that the total environmental affect of the plant is considered, we have to 

take into account the area attributed to the wind farm. The wind farm that has been 

constructed to inject the 185 GWh per year into the grid at Badgingarra, 200 km north of 

Perth and covers an area of 31 square kilometres, so with two thirds of its energy earmarked 

for the PSDP the terrestrial area attributed to power generation is 20 square kilometres. This 

area is still actively farmed as the only impact is the base of the 36 turbines (48 in total) 

which cannot be used for grazing. You will however find the farmers herds in lines in the 

shade of the turbines during the heat of the day.

Should we compare this plant to Perth’s largest surface water supply source namely, 

Serpentine Dam, which when constructed in 1961 had an assured yield of 51 GL /year at 98% 

reliability. This dam has a catchment area of some 664 square kilometres which cannot be 

used for any other land use. It is now mostly a dry dam basin of 1067 ha. There are no fish 

ladders and no in-stream flow releases. Since 1961 the reservoirs yield has been de-rated on 3 

occasions and the assured yield in 2005 was 15 GL /year at 98% reliability. In 2006 the 

reservoirs yield plummeted to 5 GL /year, almost a tenth of the PSDP yield at 100% 

reliability.

We can now also argue that Serpentine Dam and many other Western Australian and 

Australian dams have had other environmental impacts. In most cases fish ladders have not 

been provided to allow for migration of fish, inadequate or no in-steam flows occur which 

definitely has an affect on river ecology, both upstream and downstream. Further, there is an 

impoundment of silt and nutrients within the dam basin which once again affects river 

ecology upstream and downstream.

There is also the physical scar of the dam structure and the associated greenhouse gasses and 

carbon emissions that occurred during construction. When the total mass balance of all the 

environmental impacts are accounted for, a dam can have a massive environmental footprint.

It does not take much scientific deduction to work out which source has the largest 

environmental footprint. The one positive for the surface water source is that it has protected 

664 square kilometers of re-growth native forest, had in been old growth forest this would 

have been prized.

The bottom line is that the cost of water from the PSDP is the true triple bottom line cost of 

water as all the environmental, social and economic aspects have been taken into the 

equation.

Technological improvements for future

We are all well aware of the great strides made in the advancement of reverse osmosis, be it 

new materials, membranes including reverse osmosis and ultra-filtration pre-treatment 

membranes, antiscalant, energy recovery devices and efficient pumps and electric motors.

In years to come, with all the latest components, such as large diameter - high rejection 

membranes, the footprint attributed to seawater reverse osmosis plants will reduce, making 

them by far the least environmentally intrusive water sources in semi arid regions such as 

Australia, Spain and California to mention a few.

New technologies such as forward osmosis (reverse-reverse osmosis, entropy recovery –

osmotic power), may also become commercially viable. Forward osmosis utilises two sources 
2nd International Salinity Forum

Salinity, water and society–global issues, local action 10

of different salinity waters or liquids (e.g. seawater RO concentrate and wastewater) in 

combination with a semi permeable membrane, an energy recovery device (isobaric based), a 

booster pump and a Pelton impulse turbine. Utilising this equipment and the osmotic pressure 

that exists between these two liquids, energy can be recovered. This device has already been 

patented and prototypes constructed. A SWRO plant the size of PSDP located near a 

wastewater outfall can utilise the energy produced (5MW) from the osmotic pressure 

difference to power the associated desalination plant.

Taking the giant leaps that are occurring in creating freshwater from seawater, I know where I 

would invest if I had to invest in water infrastructure.

It’s all about energy

The world’s current global warming crisis is totally centred on mankind’s insatiable appetite 

for energy. The world’s climate change, which has occurred mainly due to the production of 

energy, has resulted in areas experiencing drastic and unprecedented water shortages. 

Ironically, the only way to create water in these areas is to use energy intensive means to 

produce water, such as desalination. This only results in higher energy demands and so the 

whole situation snowballs further out of control.

The only way to counter this is to produce unlimited clean energy, no matter what the cost. 

This can not only be done using renewable energy, no matter how attractive this may seem. It 

is highly impractical and unachievable.

This is where nuclear fusion comes to the fore. This will become mankind’s saviour in the 

next 30 years. It is however this period where renewable energy and nuclear fission will reign 

supreme. The use of coal fired power stations has to be regarded as mankind’s ultimate 

environmental vandalism. Not only does the burning of coal contribute to most of the world’s 

carbon emissions, it also produces all of the mercury found in the oceans and to the acid rain 

that prevails. Wake up world.

Conclusions

• A clean unlimited energy supply is the key to most world problems, including water 

supply.

• The PSDP with a production of 143 700 cubic meters per day is currently the largest 

reverse osmosis plant in the Australasian region.

• During the commissioning period, the plant performances confirmed the design 

specifications:

• The pre-treatment composed of single stage dual media pressure filters is performing 

according to the pilot tests performed in 2004-2005,

• The reverse osmosis two pass design meets expected design parameters in terms of 

permeate salinity,

• The energy recovery device (PX) performances are within guaranteed values of the 

supplier and are operating at the highest efficiency ever reported for such devices at this 

scale.

• Plant performance is consistent with the design goals,

• the PSDP represents a significant milestone for the development of large-scale SWRO 

technology operating on renewable energy at a very low energy consumption level,

• The operators who commissioned the plant now operate the plant; this overlapping of 

functions has resulted in and increased level of operation ability and has allowed for a 

high level of optimisation of the plant operations for the 25-year operating Alliance 

contract,

• Desalination can have the smallest footprint of any source in Australia.
2nd International Salinity Forum

Salinity, water and society–global issues, local action 11

• A substantial component of Perth’s water supply needs will be met by water reuse and 

seawater desalination in the medium to long term (2nd SWRO Southern Seawater 

Desalination Plant is almost at Contracting Stage).

• The PSDP is the most sophisticated and sustainable SWRO plant in the world, utilising 

the most up-to-date components, it will be the world’s model plant and the only large 

plant using wind power.

• PSDP will be eclipsed by a more efficient plant, somewhere in the world within 3 years, 

but it may be many years before its wind power aspect is eclipsed.

• SWRO will still become more efficient with new High Rejection Membranes, Large 

Diameter Membranes and Membrane Pre-treatment.

• Forward Osmosis may become a new renewable Energy Source.

• State Governments are urged to undertake strategic forward planning in selecting SWRO

desalination and wastewater treatment plant sites and associated corridors now. This 

should be projected for 50 years ahead.

• Water reuse and desalination are sustainable water sources that will contribute to solving

Australia’s water resource issues.

• New technology will substantially improve the efficiency of SWRO.

• It’s all about energy.

References

G. Crisp and M. Rhodes, 2007, Perth Seawater Desalination Plant — Blazing a Sustainability 

Trail, Proceedings of the International. Desalination Association World Congress, Gran 

Canaria, Spain.

M. Sanz and R. Stover, 2007, Low Energy Consumption in the Perth Seawater Desalination 

Plant, Proceedings of the International Desalination Association World Congress, Gran 

Canaria, Spain.

M. Sanz, N Winsor and G Crisp, 2007, Perth Reverse Osmosis Project: Potable Water from 

Sea and Wind, Proceedings of the International Desalination Association World 

Congress, Gran Canaria, Spain.

Acknowledgments

The author acknowledges the Water Corporation for privilege to have worked there and to 

have been exposed to desalination in all its forms since 1996.