Is desalination the answer to SD's water dilemma?
Heather Buschman
Saturday, 09 August 2008 18:21 UTC
The California Coastal Commission approved a plan this week that will allow a private company to build the country’s largest water desalination plan in Carlsbad. Yes, Southern California needs water desperately, but is this the best way to get it? From what I’ve read, the process of desalination – converting seawater to drinking water – is extremely inefficient. It takes 100 gallons of ocean water to make 15-50 gallons of tap water. Furthermore, the intake of water will kill millions of fish larvae and plankton a day, as well as several pounds of fish. Then, the output of salty waste, chemicals, and toxic metals will likely pollute local waters and disrupt habitats. A little bit of extra salt might not seem that bad considering the size of the Pacific Ocean, but this plant in Carlsbad is only the first of 20 others like it planned for the California coast.
I’d still be okay with desalination if that was our only option, but what about water reclamation? This “toilet-to-tap” method of recycling wastewater into drinking water might sound gross at first, but once you learn about how it actually works, it makes a lot of sense. In fact, there is already a wastewater reclamation plant in the South Bay and recycled water is used all over San Diego for irrigation. (I’m sure you’ve seen the signs in your apartment complex or place of work that tell you not to drink the water from the sprinklers.) Reclamation takes treated sewage, subjects it to an incredibly thorough purification process, and produces pure drinking water. The world’s best reclamation plant is just up the road in Orange County, where a fantastic public awareness program explained the science well enough to get people over the ‘ick’ factor, a point that has caused the failure of many other proposed reclamation projects, including one in San Diego. In O.C., they also take the purified water and send it back into the groundwater basin, to be mixed with regular water before being taken back up again. This last step is totally unnecessary, but has helped make the process sound a little more palatable. As this Union-Tribune article points out, however, there is a downside: current purification techniques might not get rid of the pharmaceutical wastes that find their way into our sewage water.
Is there a third (or fourth) alternative to solving Southern California’s water crisis? What do you think San Diego should do?
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Replies
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And strangely enough, the NY Times just came out with a timely article about the Orange County reclamation project, called A Tall, Cool Drink of…Sewage?. It emphasizes the point that the last step of sending the recycled water back into the ground water is purely for psychological reasons. Even a bit silly considering the “natural” water it then mingles with is far less pure.
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A typical Californian uses app. 70 gallons of water a day. Pretending, for the sake of argument, that there are 300 million Americans and that they use water like Californians, that’s about 21 × 10^9^ gallons per day. Meanwhile, the oceans have a volume 1.386×10^9^ km3 =
3.785 gal/L times 10^12^ L / km3 times 1.286×10^9^km3 = 4.87 × 10^21^ gallons
which means that even if every American got their water from desalination, we would be sipping
~ 4.31 × 10^-10^ % of the volume of the ocean per day. I think the ocean will survive.I remain sceptical about environmental problems related to desalination. And if there are problems, they are probably far outweighed by the environmental benefits of taking less water from our rivers and reservoirs.
But the big problem with desalination is that it takes a lot of power. It is also takes power to move the water up-hill to where it’s needed; in contrast, water taken from reservoirs moves downhill, generating electricity on the way. The environmental calculus for desalination is clearly negative if we have to burn a lot of coal to do it. Same goes for purification.
“Another good article”:
http://www.wired.com/science/planetearth/magazine/16-05/ff_peakwater -
Hi Erik – Thanks for bringing up these great points.
I do agree that there is probably no perfect solution to our need for water, so if the benefits outweigh the consequences we should do it.
A couple of things I forgot to mention about the recently approved Poseidon desalination plant in Carlsbad:
1) As part of the plan, Poseidon will be required to offset the damage to local marine habitats by spending $2.8 million to restore or create 37 acres of wetlands elsewhere.
2) As for the energy issue, Poseidon will be compensating for its estimated 90,000 tons of carbon emissions per year by purchasing offsets and spending $1 million on reforestation in the areas destroyed by the October 2007 wildfires. More importantly, they also plan to use solar power, though I don’t know how much of their total usage this will cover.
What’s your opinion on purchasing carbon offsets? Does it make a difference?
(the above numbers come from this Union-Tribune article)
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Hi, I totally agree with your concernces and disadvantages of conventional desalination plants.
But I would also like you to show a new technology using a kind of huge solar distille process to create clean drinking water. http://desalination.swan-i.de/en/
The plant is using only renewable energie sources, mainly the sun, but also wave and wind energy. The salt is remaining pure, because of the lack of any chemicals used during the process and is ready to be used/sold. We are still at the very beginning of this project, but I would like to hear your opinion. -
Sarah, the solar distilling sounds like a very interesting and good concept. I was wondering if this method also requires energy to transport the seawater, as Erik pointed out is a disadvantage to desalination? It sounds like for the solar desalination it would function well with water only being moved close by to large shallow areas. Would this be feasible in places like southern California, where oceanfront property is at a premium, or would the water have to be transported to places with more acreage available?
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San Antonio, Texas has taken the next step in ‘greening’ sewage. The San Antonio Water System will collect methane gas from the city’s 140,000 tons of biosolids per year and sell it to a company in Massachusetts to generate energy. This will complement San Antonio’s current practices of selling water reclaimed by the sewage treatment plant and using some biosolids for compost.
Does anyone know if San Diego captures methane gas? Come to think of it, how is methane gas converted to energy?
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“Come to think of it, how is methane gas converted to energy?”
I think they just burn it. Granted, this produces CO2, but methane is a much worse greenhouse gas, mol for mol. Net win.
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San Diego’s water problems cannot be solved by merely adding to the fresh water supply because that will only reinforce the bad habits that have gotten us (and the rest of the country) to this point. The addition will work for sometime, but will population growth, and the continued escalation of the average person’s water use, it will not be long before we are back to the same pressing shortage. Whatever is decided by the government and voters, water usage, pricing/rates and habits need to change for anything to be successful.
Also, it is not just the ‘water’ of the ocean that is of concern with desalination. The energy needed for the process is one thing, but the wildlife and ecosystems impacted and destroyed will not only harm sea-life, but the ecosystem goods and services we all depend on economically, socially and in order to continue to live at the same quality of life level. It may begin with a ‘small’ amount of little animals, plants and nutrients being sucked up or adversely impacted, but entire ecosystems depend on the filtration, sedimentation, food source, oxygen product, balancing of nutrients, etc., that those species and substances provide and contribute to. What will happen to the economy when dead zones begin to appear in tourism locations, when the fishing and sea-life viewing industries have to cut back, lower prices or shut down, etc? These industries will be affected but the rest of the economy will indirectly feel the impacts when income, indirect spending from tourists, tax income, state income from fishing and boating licenses, etc. begin to dwindle?
There are much greater issues here than “I cant water my lawn,” “the golf-course isn’t green,” “water bottling companies net more for supply,” “no more 30-60min showers or full pools on every corner,” etc. Look at indirect effects, and try to take the time to consider the long term, and all the possible consequences that make materialize.
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