4 ms·

Just to be clear, "brine" isn't "salty water." It mostly is, and the additional chemicals they mention are already in the sea water, not that were added someho

Just to be clear, "brine" isn't "salty water." It mostly is, and the additional chemicals they mention are already in the sea water, not that were added somehow in the process. It's just concentrated. That it's concentrated is a problem, obviously -- very high-saline water (e.g. brine) and concentrated toxins are a problem, and would cause environmental problems if just dumped. The most common way to deal with brine is simply diluting it before discharge, ensuring that the salt content isn't high enough that it sinks and forms a brine pool.

Jeff_Brown 8y ago
Diluting it with ... fresh water?
- endorphone 8y ago
  You churn it with a large volume of sea water and then discharge it when the salinity is only acceptably above the natural amount. I believe France limits it to 10% above the natural salinity. e.g. take 3 gallons of sea water and extract 1 gallon of fresh water. You have 2 gallons of +50% salinity brine. Churn it with 8 gallons of seawater and you're back to +10% salinity. Wash it out into the ocean.
mcv 8y ago
> the additional chemicals they mention are already in the sea water, not that were added somehow in the process. Are you sure? The article made it sound like they were added. If they're natural to sea water, simply diluting it with more sea water or possibly sewage that's headed for the ocean anyway, sounds like the obvious solution.
- dahfizz 8y ago
  Yup, desalination doesn't require adding "chemicals" to the water. It works using heat, electricity, and osmosis membranes[1]. I'm not sure why the article took the tone that it did. [1] http://large.stanford.edu/courses/2011/ph240/parise2/ http://large.stanford.edu/courses/2011/ph240/parise2/
  - alistairSH 8y ago
    Don't they add copper and other chemicals to prevent fouling of the pipes? Not strictly required for desalination, but required to keep the desalination plant running with minimum manual cleaning.
mirimir 8y ago
True. Basically, the brine is just sea water with some of the water removed. Based on the numbers in TFA, 2.5L of sea water becomes 1.0L of fresh water and 1.5L of brine. And so the brine is just 67% more salty than the sea water was. And it doesn't seem like diluting the brine with sea water before discharge would increase cost very much. From a 2010 presentation by Carlos Campos ("The Economics of Desalination for Various Uses") I get that seawater pumping and screening accounts for just 2-6% of the energy used in reverse osmosis.[0] 0) http://www.rac.es/ficheros/doc/00731.pdf http://www.rac.es/ficheros/doc/00731.pdf at p 24

Jeff_Brown 8y ago

Diluting it with ... fresh water?

endorphone 8y ago
You churn it with a large volume of sea water and then discharge it when the salinity is only acceptably above the natural amount. I believe France limits it to 10% above the natural salinity. e.g. take 3 gallons of sea water and extract 1 gallon of fresh water. You have 2 gallons of +50% salinity brine. Churn it with 8 gallons of seawater and you're back to +10% salinity. Wash it out into the ocean.

mcv 8y ago

> the additional chemicals they mention are already in the sea water, not that were added somehow in the process. Are you sure? The article made it sound like they were added. If they're natural to sea water, simply diluting it with more sea water or possibly sewage that's headed for the ocean anyway, sounds like the obvious solution.

dahfizz 8y ago
Yup, desalination doesn't require adding "chemicals" to the water. It works using heat, electricity, and osmosis membranes[1]. I'm not sure why the article took the tone that it did. [1] http://large.stanford.edu/courses/2011/ph240/parise2/ http://large.stanford.edu/courses/2011/ph240/parise2/
- alistairSH 8y ago
  Don't they add copper and other chemicals to prevent fouling of the pipes? Not strictly required for desalination, but required to keep the desalination plant running with minimum manual cleaning.

mirimir 8y ago

True. Basically, the brine is just sea water with some of the water removed. Based on the numbers in TFA, 2.5L of sea water becomes 1.0L of fresh water and 1.5L of brine. And so the brine is just 67% more salty than the sea water was. And it doesn't seem like diluting the brine with sea water before discharge would increase cost very much. From a 2010 presentation by Carlos Campos ("The Economics of Desalination for Various Uses") I get that seawater pumping and screening accounts for just 2-6% of the energy used in reverse osmosis.[0] 0) http://www.rac.es/ficheros/doc/00731.pdf http://www.rac.es/ficheros/doc/00731.pdf at p 24