Wednesday, January 11, 2012

Re-using water

If you ever learned anything about water in the natural world, you've probably learned about the water cycle. You know, water evaporates from the oceans (or lakes, or rivers, or anywhere, really, but it's usually depicted as the oceans, since this is where most evaporation occurs in the world), condensates to form clouds, and then precipitates (either as rain or snow) to fall upon the land, where it is either intercepted by plants or finds its way to the ground, and then into rivers or the groundwater, to eventually flow back (ultimately) to the oceans. True, there are parts of this that are complicated by the presence of other things that use the water - like animals drinking it and excreting it as sweat or waste - but the water that ends up in the oceans is the water that started in the ocean, and so it continues...

But let's focus on that little interruption: the "like animals drinking it and exreting it" part. We humans do a great job of collecting, concentrating, and treating (to a degree) water we use for drinking. We humans also do a great job of collecting, concentrating, and treating (to a degree) water we have urinated or defecated into. Such treated waste water invariably ends up in a water body, and if we are not next to the ocean, that waterbody tends to be the nearest one around (usually a river or a lake), and after a stretch of several tens of miles, there is a place where water is withdrawn (usually from a river or a lake, but also often from groundwater) for use as drinking water without people having an *ick* reaction.

If you were one of the people who remembers the bru-ha-ha that happened in June 2011, when Portland emptied an 8-million gallon reservoir after a man urinated in it, then you will likely think that what more scientists and planners propose in the future is going to be gawdawful: reuse municipal wastewater to augment drinking water supplies. If you're gagging in your coffee right now, then let me first say a few things about the Portland incident:
  • the human bladder can contain between 200-800 mL of urine (0.05-0.21 gallon).
  • rounding 0.25 gallon of urine (let's assume the Portland guy had a really big bladder that was completely full), the concentration of urine was 0.25 gallons urine/7800000 water = 0.000000032 gallons urine/gallon water (and that's assuming that the water in the reservoir was pure water, and the urine was pure urine).
In other words, as Dave Zetland said at the time (which is also relevant here):
They are basically implying that the reservoirs are full of Evian when they are full of water that's going to be treated anyway. They claimed that people in the area "may" have thrown objects in the water, but those people were questioned. Seems like they were more interested in finding an excuse to drain the water.

The pity is that people are NOW going to think their reservoirs are super clean (not!) and that water recycling is way too gross (not!).
And water recycling (if done correctly) is not gross. It is - after all - what astronauts have done for a long time, and what the city of Singapore has been doing for over a decade now. Further (to use points from the post at PhysOrg):
Potable water reuse projects account for only a small fraction of the volume of water currently being reused. However, many drinking water treatment plants draw water from a source that contains wastewater discharged by a community located upstream; this practice is not officially acknowledged as potable reuse.

The concentrations of chemicals and microbial contaminants in reuse projects designed to augment drinking water supplies can be comparable to or lower than those commonly present in many drinking water supplies.

Water reuse projects tend to be more expensive than most water conservation options and less expensive than seawater desalination and other new supply alternatives. Although the costs of reclaimed water are often higher than current water sources, the report urges water authorities to consider other costs and benefits in addition to monetary expenditures when assessing reuse projects. For example, water reuse systems used in conjunction with a water conservation program could be effective in reducing seasonal peak demands on the drinking water system. Depending on the specific designs and pumping requirements, reuse projects could also have a larger or smaller carbon footprint than existing supply alternatives or reduce water flows to downstream users and ecosystems.
If you are still gagging a little to think about these sorts of things, then the next point might not give you too much peace of mind about the current state of affairs with regard to governance:
Water reuse regulations differ by state and are not based on risk-assessment methods, the report says. Adjustments to the federal regulatory framework could help ensure a high level of public health protection, provide a consistent minimum level of protection across the nation, and increase public confidence in potable and non-potable water reuse.

No comments: