15 August 2008

From Potty to Potable

A very good article in the New York Times about the system which reintroduces treated waste water into California's drinking water supply. The sewage is collected and put through a multi-step process that renders it nearly pure. It is then pumped into a man-made reservoir where it mixes with naturally-collected drinking water, percolates through several hundred feet of sand and gravel, and replenishes the aquifer. About 18 months later, it's pumped back above-ground where it's chlorinated and is brought back into the drinking supply

In addition to the technical specifications, there are several interesting observations, the first being how the issue is typically framed:

If you like the idea, you call it indirect potable reuse. If the idea revolts you, you call it toilet to tap.
Also interesting is the range of possible fresh water to waste water ratios in various systems around the world (think of it as the supply of tolerance relative to the demand for water):
Singapore mixes 1 percent treated wastewater with 99 percent fresh water in its reservoirs. (In Orange County, the final product will contain 17 percent recycled water.) Residents of Windhoek, Namibia, one of the driest places on earth, drink 100 percent treated wastewater.
There is a reminder of the many hidden uses of energy, noting that "about a fifth of California’s energy is used to move water from north to south".

Finally, an example of the technical absurdity that the human psyche makes necessary:
It’s one of the many pardoxes of indirect potable reuse that the water leaving the plant in Fountain Valley is far cleaner than the water that it mingles with. Yes, the water entering the sewage-treatment plant in Fountain Valley is 100 percent wastewater and has a T.D.S. — a measure of water purity, T.D.S. stands for total dissolved solids and refers to the amount of trace elements in the water — of 1,000 parts per million. But after microfiltration and reverse osmosis, the T.D.S. is down to 30. (Poland Spring water has a T.D.S. of between 35 and 46.) By contrast, the “raw” water in the Anaheim basins has a T.D.S. of 600.

If everything in the Fountain Valley plant is in perfect working order, its finished water will contain no detectable levels of bacteria, pharmaceuticals or agricultural and industrial chemicals. The same can be said of very few water sources in this country. But once the Fountain Valley water mingles with the county’s other sources, its purity goes downhill. Filtering it through sand and gravel removes some contaminants, but it also adds bacteria (not necessarily harmful, and local utilities will eventually knock them out them with chlorine) and possibly pharmaceuticals.
The main message is, of course, that rising demand pressures on available resources and the consequences of consumption mean that it is becoming economically and morally necessary to look to the waste stream as a potential resource stream. Thankfully, this is an arena in which technology can play a large role (indeed, that is the subject of this article). I tend to have greater faith in our potential to create new technologies rather than our ability to curb our consumption. That's not to say that I think that this reality is morally defensible, only that it's historical trend which appears very difficult to change. Call it realenvironment.

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