Regional Information- Desalination

The Central Coast does not currently have a desalination plant although a desalination plant located at Toukley sewage treatment plant is a future option in the WaterPlan 2050 strategy and has been granted conditional approval by the NSW Government.  The plans for the plant have been approved but this is part of Gosford City and Wyong Shire Councils’ long term planning.  The construction of the plant has not commenced and is not planned to commence any time in the near future.  It is simply a future option at this stage.

If the plant was to be constructed it would deliver 20 ML (1ML = 1 million litres) a day to Central Coast residents and is considered to be an important back up, should water conditions worsen.  The plan not to go ahead with the plant at this time is due to the high costs of both constructing and running the plant and because there is not the current need for the additional water supply to justify the costs.  The two Councils simply want a future alternative that is not dependant on the weather.

The discharge from the plant, should it ever be built, would be released through the ocean outfall at Norah Head.  This is the same ocean outfall used by Wyong Shire for treated effluent discharge.  As the treated effluent is fresh water it is expected that by discharging the saline water with the fresh water effluent the impact of the current low salinity water in the ocean outfall will be amended.  It will bring the salinity of the water being discharged closer to that of the sea water.

Should the plant ever be built both Councils have committed themselves to using green power sources to power it in order to reduce green house gas emissions from the plant.  The State approval for the pant also specifies a number of conditions relating to the plant which target protecting the environment both during the construction and operation of the plant.  Both Councils are in full support of these conditions and are committed to ensuring the environment is protected from any adverse impacts.

Temporary desalination plants were also considered but both Councils consider this to be an absolute last resort option and the earliest that this may happen is 2012.  At this point though it is not even being considered and is very unlikely to happen at all in the foreseeable future of the Central Coast.

How does desalination work?

One of the processes more commonly used for desalination is called reverse osmosis (RO). It is a membrane separation process in which the water from a pressurised saline solution is separated from its dissolved material by flowing through a membrane.  No heating is required for this separation.  The major energy required for desalination is for pressurising the water being fed into the membrane; typically up to 62 atmospheres for seawater (the pressure at sea level is one atmosphere therefore 62 atmospheres would be like being almost 1000m underwater).  The saline water is pumped into a closed vessel where it is pressurised to overcome the osmotic pressure of the solution before being diffused through the membrane. As a portion of the water passes through the membrane, the remaining feed water increases in salt content.  This portion of this feed water is then discharged without passing through the membrane.

A distinct advantage of desalination of seawater is that it is climate proof and can continue to produce at full capacity even if declining rainfall means dam storages and rivers are dwindling and groundwater aquifers shrinking.  However, seawater desalination demands tough marine environment management.  Catchment protection measures need to be in place to maintain the quality of seawater being processed.

These measures are already in place on the Central Coast should a desalination plant ever be constructed.  The treated effluent outfall points in the ocean are independently monitored by The University of Newcastle (Ourimbah Campus) and have been for the at least the last seven years (started in approximately1998).  This would provide a means of on-going monitoring for the outfall sites with both pre- and post desalination data.