The significance of large scale seawater desalination in achieving urban water security

Posted on 29 June 2012

by Neil Palmer, CEO

Following a protracted drought, seawater desalination has become a strong component of bulk water supplies for the five Australian mainland state capitals. On aggregate, seawater desalination can now provide up to 35% of current average annual water demand. After the drought break in 2010, extensive flooding occurred in the eastern states and there has been public criticism of the decision to build the desalination plants. However, construction of desalination capacity should be considered in the long term (50 years) during which time population growth will increase demand and droughts and possibly climate change will put existing conventional supplies under stress.

Introduction

It has become popular for some in the media with short memories to knock desalination. “Knee jerk reaction, political decision, why not build a cheap dam, expensive, energy guzzling, built to feed the profits of private water companies, destroys the marine environment, should only be turned on as a last resort” are just some of the epithets that have circulated about desalination since the end of the Millennium Drought.

With 37 years as a professional engineer in the water industry in Australia – 20 years in Government, 15 years in the private sector and the last two leading the National Centre of Excellence in Desalination Australia – I have been in the industry long enough to remember when water security was the key objective of State Government water utilities and massive expenditure on water infrastructure was expected and celebrated by the voting public.

This changed during the 1970s when, under the influence of economic rationalism, State Governments learnt about demand management, reduced spending on new water supplies and increased rates, turning water utilities into “cash cows”. It was this era in which “water efficiency” (restrictions) became fashionable. This all worked tolerably well with increasing population and concomitant demand, provided rain kept falling regularly. The Millennium Drought (1997 – 2009) changed all this, and despite draconian compulsory water restrictions, many Australian cities came close to running out of water. As a result, six large seawater desalination plants have been built to serve Perth, Gold Coast, Sydney, Adelaide and Melbourne.

Common Desalination Myths

A number of myths have developed about desalination. Let’s look at some of them.

Myth 1 – The “knee jerk” reaction

No responsible Government of a sophisticated economy can sit and do nothing when their water supply is about to run out. The proposition that the decision to build the Sydney Desalination Plant was a “knee jerk political decision” is nonsense. Governments are guided by their water utilities on infrastructure investments and decisions to spend nearly $2 billion on new water supply infrastructure (the Sydney Desalination Plant) are never taken lightly. Indeed, the expenditure could be considered as “catch up” given the woefully inadequate investment in new water supplies since the 1970s.

Myth 2 – A dam would be cheaper and better

Dams take a long time to build and fill. Warragamba Dam, NSW, was approved in 1946 and was completed 14 years later in 1960. Thomson Dam in Victoria was approved in 1975 and completed eight years later in 1984. As a comparison, approval to build the Sydney Desalination Plant was given in November 2006 and it was opened just over three years later in January 2010. In 2010, plans to build dams at Traveston Crossing in Queensland and Tillegra in the Hunter Valley, NSW, were cancelled because of their potential impact on the environment. Dams are no longer seen as election winners. It would be extremely difficult under current circumstances to build large dams near populated areas, given the extent of public opposition.

Myth 3 – Desalination is energy guzzling

Energy needed to produce water at the Sydney Desalination Plant is around 3.5 kWh/kL. The average household uses about 200 kL per year. Thus if all the water for a household came from desalination, the energy required is about the same as that required to run the normal household refrigerator. The smallest ducted household reverse cycle air conditioner runs at about 8 kW. Thus, if all the water for the household came from desalination, the energy required is about the same as running the ducted reverse cycle air conditioning system for 15 minutes. One feature of all the big Australia desalination plants is that they all purchase renewable energy from wind farms to offset all energy used in the desalination process. Their operational carbon footprint is very low.

Myth 4 – Desalination is expensive

To cover the cost of desalination, naturally water rates must increase. In the case of Adelaide’s desalination plant, which will be capable of supplying up to half Adelaide’s current water demand, the rates have steadily increased since 2008. For an average household using 190 kL/y, the average weekly increase between 2008 and 2012 is $7.80. Now this also includes increases for such things as inflation, so the whole $7.80 is not attributable to the cost of the desalination plant. But let’s put this in perspective – $7.80 is about what you pay for a glass of beer from a bar. So for the modest charge which is equivalent to less than the cost of just one glass of beer per week per household, Adelaide consumers have water security and do not ever have to face water restrictions again. That’s a good deal.

Myth 5 – Desalination plants are built to feed the profits of the private water companies

Most of the big desalination plants in Australia have been built with some form of partnership between the water utilities and world leading desalination companies. In most cases, the construction was undertaken by Australian companies, but the process design was undertaken by experienced international desalination companies. The process has been guaranteed by the international desalination companies. There is much that could go wrong in such big and fast moving projects, so the modest profits need to be understood in terms of the large losses that can rapidly accrue if any part of the process fails. In all cases, the projects were tendered competitively with oversight and auditing as is normal for execution of a Government project.

Myth 6 – Desalination plants destroy the marine environment

Australia’s first major seawater desalination plant is at Kwinana, just south of Perth, on Cockburn Sound. Commissioned in November 2006, it has operated at 100% capacity (140 ML/d) continually since then – more than five years. Cockburn Sound has been a confined body of water since the construction of a causeway to HMAS Stirling on Garden Island in 1970. If ever there was going to be a problem with environmental impact of reverse osmosis concentrate, this would be the place. However, the experience of Perth’s first desalination plant provides confidence that no environmental harm results from well designed and maintained return concentrate diffuser systems.

Myth 7 – Desalination plants should only be turned on as a last resort

Water restrictions (using less) means reservoirs fall less quickly. As the levels drop further, restrictions become more severe, until ultimately the most extreme restrictions apply and even then without rain, the reservoirs will empty. Now there is an alternative to restrictions to slow the rate of reservoir depletion – running the desalination plants. The amount by which a water utility might run a desalination plant depends on the security of supply. If restrictions are to be avoided, then the desalination plant needs to run as a base load plant most of the time, with the reservoirs providing the peak load supply. The only time it really needs to be turned off is when the reservoirs are spilling.

Conclusion

The five Australian mainland capital cities have invested in desalination capacity up to 35% of their average demand. These climate resilient new water sources provide water security at an affordable price. Provided the desalination plants operate as base load plants, it means that water restrictions are likely to be a thing of the past. Energy consumption for desalination is much less than for other common household appliances (for example reverse cycle air conditioning), and the cost, if all household water came from desalination, is less than the cost of one glass of beer per week from a pub. Lastly, five years experience at 100% flow at Perth’s Seawater Desalination Plant, which discharges concentrate through a well designed diffuser into the confined Cockburn Sound, has not caused any detectable environmental harm. In fact, the diffuser pipework is covered in marine life and resembles an artificial reef.

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