Friday, September 07, 2007

Las Vegas Wash

Greetings from Las Vegas.

I came through Las Vegas primarily to visit the new Water Quality Laboratory and Applied Research & Development Center of the Southern Nevada Water Authority (SNWA).

This facility is practically ground-zero in the USA for research into emerging water quality issues such as the presence of pharmaceuticals and endocrine disrupting compounds (EDCs) in drinking water.

I was invited to visit Dr Shane Snyder, -an environmental toxicologist and Research & Development Project Manager at SNWA. Throughout the last decade Shane has conducted research focussing on water quality at Lake Mead on the Colorado River, -the home of Hoover Dam and one of the most important drinking water sources in the USA. Lake Mead is a vital water supply for Nevada, Arizona and California.

As Shane explained to me, Lake Mead and Hoover Dam are also an example of a planned indirect potable water recycling (IPR) scheme. All treated municipal effluent is recycled one way or another in Las Vegas. Much of it is used directly for irrigation, but a significant proportion is also returned to Lake Mead via a waterway known as the Las Vegas Wash.

The Las Vegas Wash is a flow of water that is comprised of urban runoff, shallow ground water, reclaimed water, and stormwater. As described on the website of the Las Vegas Wash Coordination Committee, reclaimed water (ie. recycled municipal effluent) is normally the largest contribution of water to The Wash.

Three municipalities (Las Vegas, Clark County and Henderson) discharge treated effluents into The Wash to give a combined total of more than 500 million litres per day. The discharged water is generally conventionally treated sewage effluent with nutrient removal. There are no advanced water treatment processes such as reverse osmosis or advanced oxidation prior to discharge. As a result, there have been a number of pollution concerns in Lake Mead. One of the major concerns has been salinity. Furthermore, Shane’s work over the last decade has shown that endocrine disrupting compounds (such as estrogenic hormones) have had a detrimental effect on fish in the lake.

Prior to human consumption, the water from Lake Mead (and Lake Las Vegas) is treated by processes including flocculation, ozonation, dual media (anthracite and sand) filtration and chlorination.

As the fastest growing population in the USA and being in the middle of the Mojave Desert, sufficient clean drinking water is not something that Las Vegas can afford to gamble. The city invests in water in a way that suggests that it truly recognises the value of its most precious resource. It maintains a comprehensive water quality analysis program and on-going research aimed at process optimisation and continual improvement.

The image below shows a pilot-scale ozonation reactor at one of the Las Vegas water treatment plants.

Here is Lake Mead showing dramatic evidence of the drought experienced during the last decade. This deck was built for fishing from. An almost identical picture appeared on the front page of the New York Times earlier this year.

This is another view of Lake Mead. In the distance you may be able to see some boats crowded into a receding marina. Well above the boats you can see a white band on the rocks behind. This is precipitated calcium carbonate (‘hardness’) from the lake water and reveals the previous water height. This image from the New York Times shows it even more dramatically.

The next two images are from Hoover Dam. Again, note the white scale on the rocks showing evidence of previous water height.

Finally, water from the lake is treated at a full scale Las Vegas water treatment plant, ready for distribution to customers.


Anonymous said...

We are constantly told that water recycling is a solution to the drought in Queensland. These pictures clearly show that water recycling has an insignificant impact since it is not a new water supply. Even with sewage going back into the reservoir, Lake Mead is a record low levels and recycled sewage can not prevent this. Only a fool would belive that you can keep recycling the same water around and around and never run out!

Stuart Khan said...

Thanks for your comment Anonymous,

Yes, it is true that water recycling is not an infinite resource, -only a proportion of water that is used by households is returned to the sewers and thus available for recycling. I haven’t seen anybody claiming anything different, but I would be grateful if you could point me to something that I may have overlooked.

Like most cities in the USA and Australia, Las Vegas has a licensed allocation of water that it can take from Lake Mead. The advantage of recycling treated effluent back into the lake is that the city is then re-credited for that volume and can thus extract a further equivalent volume of fresh water. So in fact, every drop that Las Vegas recycles represents a direct increase to the city’s available water supply.

Anonymous said...

"Only a fool would belive that you can keep recycling the same water around and around and never run out!"

The earth has been doing it successfully for millions of years.

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