Water Purification Scheme

What is it?

ACTEW has been investigating and proposes to continue to examine proven advanced technology to treat used water to a standard safe for human consumption. The proposed Water Purification Plant would use suitable technology to treat water in a planned and controlled manner so the water complies with the national drinking water guidelines and other relevant standards.

Technology used

To provide a multi-barrier approach to water purification, ACTEW considered several treatment process options. The preferred combination of treatment processes is membrane filtration and reverse osmosis.

Membrane filtration uses hollow fibre membranes with fine pores to filter particles and micro-organisms. The membrane surface acts like a screen to retain the micro-organisms; similar to a screen door that retains insects. This step removes microscopic particles, contaminants and pathogens.

Reverse osmosis is the process of pushing water through a membrane or filter that traps almost all suspended and dissolved substances and micro-organisms to one side and allows water to come out the other side. The membranes have very small pores, so small that more than 99% of sodium and chloride ions are also removed. This step removes pollutants such as salts, organic compounds and viruses.

A further process is installed called ultra violet (UV) light/advanced oxidation. UV light is used to disinfect water and is effective at destroying micro-organisms such as Giardia and Cryptosporidium and other pathogens. Oxidation destroys chemical compounds. Strong oxidation agents such as hydrogen peroxide remove trace organic constituents.

The proposal would also take advantage of nature’s own water treatment process by letting the purified water flow into the natural environment before final treatment and distribution to consumers.

Responding to climate change and variability

All of the options outlined in ACTEW’s 2004-05 Future Water Options studies were based on some key assumptions. ACTEW identified that there had been a fundamental change in one of these assumptions; climate variability and climate change. Based upon work by CSIRO, it was predicted that by 2030, inflows into storages would decrease by 30%, on average. Between 2001 and 2006, however, inflows decreased by more than 60% and by nearly 90% in 2006 alone. This prompted ACTEW to review previous studies and look at further options to secure supply, including a Water Purification Scheme.

How much will it cost?

The cost of this option has decreased in recent years due to technological improvements and greater uptake around the world. The estimated capital cost for a 50ML/day plant is in the order of $220 million to $270 million, depending on the salt treatment technology. Operating costs would be in the order of $23 million per year. Whereas, the estimated capital cost for a 25ML/day plant are in the order of $180 million and operating costs about $10 million per year.

How long will it take?

This Scheme is expected to take 3 to 4 years to implement.