Re: When producing ethanol, can salt water from the ocean be used?

Just to make sure you aren't confused... the ethanol production process does not actually "consume" much water. I believe that the majority of the water used by an ethanol plant goes into the fermentation "broth"; this broth consists of water, corn grits, yeast, and some trace nutrients to help the yeast grow. The growth of the yeast and the transformation of corn starch into ethanol both make some water temporarily unavailable, but I think this a small proportion of the overall volume of the fermenter. At the end of the fermentation, the rest of the broth water is processed to separate the ethanol and water. This water will leave the plant as steam or as wastewater. The waste water gets treated at some point and returned to the environment.

Now to the question of using seawater in this process... This would present a couple problems. I think it is very likely that the yeast used to produce ethanol would be inhibited by water as salty as seawater. It is possible, however, that a salt-tolerant, ethanol-producing microorganism could be found. The second problem I see comes in the step were the ethanol is separated from the fermentation broth. I think that this is accomplished by either distillation or membrane separation, and the salt could foul these up. These are technical problems that could be solved readily, I think; whether they would add significant expense to the process, I don't know.

So, I think that seawater could technically be used in a specially designed ethanol plant.

An ethanol plant adds to the burden on the water supply, but I am not sure ethanol production is particullarly "water-intensive", relative to other types of processes. A meat processing plant, for example, uses scads of water.