Wednesday, December 06, 2006

A more appropriate argument

An argument is brewing over recycled water in Texas, USA.

The situation is a bit like Toowoomba in some ways: An inland city (in this case Dallas) has witnessed water resources being depleted over the last few years, while populations continue to rise. The city sits towards the top of an important river system (The Trinity River) and currently discharges treated effluent into that river. A plan has been developed to reduce that discharge and recycle the water for Dallas to use again.

There is growing disagreement about whether it is acceptable to recycle the water in Dallas or if it should be left to flow downstream as it currently does. However, this is where the comparisons with Toowoomba end. You see, downstream towns and cities on the Trinity River consider the “unplanned” recycled water that they receive to be a valuable resource. While some Australians refer to such schemes as “bad practice” [which, I notice has recently evolved to “bad science”], Texans are prepared to fight for it.

The city of Dallas operates two sewage treatment plants, -Central WWTP and South Side WWTP. Since 2003, Dallas Water Utilities has been developing a plan to upgrade the effluents from these plants and convey these back to city’s main storage reservoirs, Lewisville Lake and Lake Ray Hubbard.

The figure below was presented by Dallas Water Utilities personnel at a conference that I attended in 2005. It is not currently a formal plan of the agency, but shows in concept the types of ideas that are under consideration. Click for a larger image.

Dallas Assistant City Manager, Ramon Miguez, says that in the long term Dallas intends to supplement its supply with 60 million gallons of recycled water per day. However, there is now concern that newly developing legislation will prevent the city from keeping the water for its own use. Under this expected new legislation, the State of Texas could require the city to apply for a special permit to recycle the water instead of allowing it to flow downstream. In other words, the State could overrule any plans from Dallas that may reduce the volume of recycled water available for downstream communities.

The Trinity River supplies water to a number of very dry cities as it makes its way down to the Gulf of Mexico. Towards the bottom, the State’s largest city, Houston imports part of its supplies from the river to supplement its own diminishing groundwater supplies.

A lobbyist hired to represent Dallas’ interests was quoted this week as saying [be sure to read this with a Texan accent!] “if a powerful lobby of parched cities across Texas demands that Dallas send more water down the river, North Texas could see decades of deliberate planning flushed away”.

State Representative, Robert Puente, says the legislation will be based on science, not politics [-yes, I know its an unorthodox idea, but I can’t help thinking that it might have some merit]. He said “we need to make sure there’s enough water in our lakes and rivers to get all the way down to the Gulf of Mexico”. That seems like a very fair argument and I am certainly not suggesting that it is not an extremely important consideration.

There’s an argument brewing, to be sure. However, its strangely refreshing to see cities arguing for their right to practice (planned or “unplanned”) indirect potable water recycling. A truly bad practice –or bad science- is the failure to recognise a valuable resource when we see it. Perhaps we’ll work it out one day...


water consumer said...

The US has a much more developed concept of water rights than under Australian law.

Greg said...

You failed to mention one important similarity Stuart. Just like Toowoomba and indeed SE Queensland, Dallas and Texas is also suffering from the effects of a bad drought. In fact it is the worst drought since the 1950's there. Check it out here. Why is that everywhere there is drought a toilet to tap plan is mooted as a saviour?

Stuart Khan said...


During extended droughts, sometimes traditional water sources can become scarce. To address this problem, cities tend to first implement water conservation initiatives and then look for alternative supplies. This (at least partially) explains the correlation you have observed between droughts and interest in planned potable recycling.

Greg said...

Water consevation techniques should be an ongoing strategy used to offset a possible drought, not implemented several years into one. Dallas officials have waited until now to do so and it is one of the reasons there looking at planned potable recycling as you call it! They stuffed up just like Thorley and Beattie did here in QLD! If we were to have ongoing water conservation techniques and utilise recycled water for industry, parks and gardens, etc, it would go a long way to preventing a possible 'run out of water scenario' during an extended drought.
New dams are also required if we are to properly sustain population growth over many years and no amount of recycling water can prevent this and this is another area where all parties I mentioned stuffed up!

Stuart Khan said...


I agree with your comments regarding the need for water conservation to be ‘the norm’ in Australia, rather than a solution for ‘extreme situations’.

Here in NSW, we pump huge quantities of water from the Shoalhaven River, up a 600 m escarpment to Sydney, -at great cost in terms of both dollars and burning of fossil fuels to do it. We are probably going to start building an energy-guzzling desalination plant in the first half of next year. Sydney’s dams are at record low levels, and still, we have not even starting talking about moving beyond Level 3 water restrictions. You could be forgiven for thinking that water conservation is not a front-line in NSW.

desal boy said...

Why is it that desalination plants are automatically considered energy guzzling but recycling plants are not? NSW is proposing a somewhat environmentally friendly energy system for the deasalination plant. And if you look at the examples from Israel, desalination plants are becoming much more energy efficient. I know there is nothing worse than an argument between recyclers and desalinators but it's funny how desalination is automatically thought of as energy guzzling.

Stuart Khan said...

Hello ‘Desal Boy’ (nice name!),

Yes, I realise that it seems like municipal water recycling and seawater desalination should be of similar energy-intensiveness (since they tend to use the same technology). However, it really isn’t the case. By far the greatest energy requirement for reverse osmosis arises from the need to oppose the osmotic pressure of the saline water. Seawater is typically around 35 g/L salt, while secondary effluent is rarely more than a tenth of this. So in order to produce the same volume of treated water (to the same quality), seawater requires a much higher head pressure. Furthermore, for the same volume of treated water, there is a need to pump a greater volume of seawater past the membrane than is required for secondary effluent, -this has to do managing the process so as to minimise precipitation of salts onto the membrane (known as 'scaling').

You mentioned that "NSW is proposing a somewhat environmentally friendly energy system for the desalination plant". I’m afraid that I am completely ignorant of this and would be most grateful for any information that you can provide.

Desal boy said...

Saw it on a quick press report on the weekend. Although it may just be a political promise, I will try to track it down.

Greg said...

Clean wave energy and wind power could be utilised to significantly reduce the cost of Desalination. The one thing we must not forget about desal, the water is not effected by drought, recycled effluent is! If Algiers can do it so can Brisbane and Australia. Enough with the excuses Stuart!

Stuart Khan said...

Thanks Greg,

I like the sentiments expressed in your comment. I sincerely do hope that wind and wave power will someday (soon) be cheap sources energy in Australia. Currently, it is very difficult for them to compete with burning coal, but I share your optimism for a smarter future.

Also, I agree… anything Algiers can do, Brisbane should be able to do better!!

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