Saturday, August 18, 2007

Reverse Osmosis at the WCRWP

The Queensland State Government is currently busy with the construction of the Western Corridor Recycled Water Project (WCRWP). We took a brief overview of the scheme on this blog back in May. However, as I mentioned at the time, the WCRWP is a mega-project and we’d only just skimmed the surface.

Many readers of this blog seem to be particularly interested in reverse osmosis (RO) as an important treatment process of the WCRWP. We’ve previously discussed the important mechanisms by which RO membranes work, the variable rejection that can be expected for various contaminants, the reasons behind why RO is a relatively energy-intensive process, issues associated with membrane biofouling and even the potential alternative process of forward osmosis (FO).

However, I thought it would be useful to take a quick look at some of the actual RO membranes intended to be used at the WCRWP advanced water treatment plants and their modular configuration. I gathered most of this information (and the photograph) from a recent conference paper prepared by Troy Walker from Veolia Water Australia [1].

The WCRWP consists of three advanced water treatment plants treating effluents from six sewage treatment plants in Brisbane and Ipswich. Two of the advanced water treatment plants are located in the Brisbane area (Luggage Point and Gibson Island) and one just outside Ipswich at Bundamba.

The Bundamba plant is being built in two stages by the ‘Bundamba Alliance’ of Thiess and Black&Veatch. It will have an initial capacity of 20 million litres per day, which will then be delivered for use by Swanbank Power Station. This stage is due to be completed this month so we can probably expect an announcement fairly soon. The plant will then be expanded to deliver an additional 30 million litres per day available for Tarong Power Station by mid next year.

The Gibson Island advanced water treatment plant is being delivered by the ‘Gibson Island Alliance’ of Montgomery Watson Harza, Burns and Roe Worley, Balderstone Hornibrook and United Group Infrastructure. The Luggage Point plant is being delivered by the ‘Luggage Point Alliance’ of CH2MHill and Laing O’Rourke. These two plants will have a combined capacity of 116 million litres per day, which will be used to supplement the supplies of Wivenhoe Dam, -Brisbane’s main drinking water reservoir.

RO membranes are typically manufactured such that they are wrapped spirally around a porous tube. A further casing is then placed around the membrane to keep it in place and this unit is called a ‘membrane element’. This means that instead of membranes appearing as large flat sheets (which is what they are inside the element), they appear as a solid round tube. This tube is then placed inside a high-pressure vessel so that it can be pressurised to push water through it.

All three advanced water treatment plants will be using RO units with membranes known as ‘thin film composite polyamide membranes’. However, the membranes are expected to be sourced from different suppliers between the three plants. The different suppliers would have been selected based largely on commercial considerations of the various construction alliances, but also reflect variable feedwater characteristics such as nutrient and salt concentrations.

The vast majority of commercial RO membrane elements (for this type of application) are a standard 200 mm (8”) diameter and 1 m long. However, the Bundamba Alliance has designed that plant to use new generation 450 mm (18”) diameter, 1.5 m long membrane elements. These much larger membrane elements are manufactured by Koch Membrane Systems with the tradename ‘Megamagnum’. This element size is relatively new to the market and the Bundamba plant will be the largest installation of these membranes in the world.

Megamagnum RO membranes at Bundamba [1]

The larger membrane system results in a smaller number of membranes and pressure vessels on each RO unit itself, with 65 membranes used instead of what would be an equivalent of more than 450 smaller sized elements.

However, these membrane elements do present some additional challenges compared to standard 200 mm diameter elements. For one, they are much heavier (113 kg compared with 20 kg for new membranes), which has required the construction of a unique mechanical loading device.

While the membrane material itself is commonly used by many suppliers, the unique diameter of the element is only provided by Koch Membrane Systems. This carries an ongoing risk that if this membrane fails to meet treated water quality targets, or suffers from an unacceptable fouling rate, replacement membranes cannot be employed from an alternative supplier. One consideration under review is the possibility of installing smaller membranes into the 200 mm pressure vessels by means of a modified brine seal and sleeving.

The RO units at each plant will be arranged in a three-stage array. That means that the concentrated rejected stream from one membrane then moves on to a second, and then third, membrane where it is further concentrated each time. This arrangement is used to maximise the proportion of water that can be recovered as product water. The three plants are designed to achieve approximately 85% of feed volume as product water. The remaining 15% becomes the membrane ‘concentrate’, which will undergo further treatment prior to discharge to the Brisbane River and Moreton Bay.

Once recycled water starts being produced and delivered to Swanbank Power Station, I will –needless to say- be most interested to see some early performance data. Hopefully we will see some detailed data on contaminant rejection as well as achieved water recovery and energy consumption. When can we take a tour of the plant?

[1] Walker, T., Roux, A. and Owens, E. (2007) Western Corridor Recycled Water Project - The largest recycled water scheme in the southern hemisphere. In: Water Reuse and Recycling (Eds, Khan, S. J., Stuetz, R. M. and Anderson, J. M.) UNSW Publishing, Sydney, 498-511.


Anonymous said...

I was reading your profile Favorite Books. I know TKAMB and C22, but what are the others??

Stuart Khan said...

Ha! I’m not going to tell you. They’re all classics and you can work them out. Only the last one is somewhat Australian-specific.

mborchar said...

Hi Stuart
I find your Blog really informative, and I would like to be a regular reader - exchange info etc.
I am the Australian Correspondent for Global Water Intelligence, I am based in Brisbane, but have a national interest. I a good news research journalist - not interested in gossip - just the good stuff that people are doing in the water industry - and how the govt is managing (mismanaging) what is going on.
I enjoy your commentary.

Stuart Khan said...

Thanks for your note mborchar,

I appreciate the positive feedback. I expect that you must be quite occupied as the Australian correspondent for GWI since there is so much going on here at the moment! I hope you find something useful from this blog and I’d appreciate any insights that you are able to offer us.


Stuart Khan said...

As anticipated...

Qld's first recycled water produced
Roberta Mancuso
The Brisbane Times
August 23, 2007

Queensland's deputy premier has boasted about the progress of the state's new water grid, presenting its first bottle of purified recycled water to parliament - but refused to drink it.

Deputy Premier Anna Bligh today held up a bottle of recycled water in state parliament, declaring: "This is south-east Queensland's first recycled water."

Opposition MPs urged her to drink it, chanting "down, down, down" - which she was reluctant to do given it had been treated to only an industrial standard.

"This is the first step of a project that we should all be very proud of," Ms Bligh said. "We ought to be singing it from the rooftops."

Opposition Leader Jeff Seeney described Ms Bligh's water bottle stunt as "pointless".

"It was recycled water that she wasn't even prepared to drink and can't be safely drunk," he said.

He also criticised the amount of water the advanced treatment plant would be able to convert.

"It's a tiny fraction of the water that's needed to make any difference to the crisis in Brisbane," Mr Seeney said.

Premier Peter Beattie said water was now flowing through the Bundamba advanced water treatment plant, and within days, would help drought proof south-east Queensland.

"While many said it couldn't be done, purified recycled water will be delivered to Swanbank power station by the end of the month as promised," Mr Beattie told parliament.

The advanced water treatment plant will accept wastewater from Goodna and Bundamba water treatment plants and convert it into purified recycled water.

It will then be transported by a 7.3km pipeline from Bundamba to Swanbank near Ipswich.

"When this stage of the water grid comes online at the end of the month, up to 15 megalitres a day of drinking water will be freed up for south-east Queenslanders, the equivalent daily supply of a community the size of Ipswich or Logan," Mr Beattie said.

Anonymous said...

Mismanaging is right

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