Types of Desal

Growing up in Hong Kong and Minnesota, where rain water is plentiful blinded me from the reality of fresh water scarcity. It was not until I lived in Southern California where I learned not to take fresh water availability for granted.

Only 2.5% of Earth's water being fresh water and 2/3 of that being frozen and the remaining is liquid surface water (Nat Geo April, 2010), the remaining 97.5% obviously is the ocean. As human population continues to increase exponentially, the supply of freshwater is increasing and we are depleting our groundwater supply at a much higher rate than they are being recharged. Soon enough we will experience that there is just not enough freshwater to sustain the Earth's population.

Desalination will be the answer to solve this problem, and there are three kinds:

1. Forward Osmosis. Water molecules (from salt water) will diffuse through a membrane into a even more concentrated "draw solution". The "draw solution" will contain special salts that will evaporate by a low-grade heat after the water molecules have diffused through the membrane. This method requires no energy input.

2. Carbon Nanotubes. Electrically charged nanotubes will be attached to the membrane and salt ions will be repelled by the charge and the uncharged water molecules will slide through the membrane.

3. Biomimetic. The membrane will be covered wth proteins that conduct water in and out of living cells. The positive charge in the channels will repel salt ions thus only allowing water molecule to pass through. This method is similiar to the way potassium channels function in our cells.

(Nat Geo April, 2010)

What do you think is the best method?

I'd like to say that forward osmosis would be the best because it does not require energy input, however I will need more information on the "draw solution" (what is it made of, are there any side effects) in order to make an informed decision. Plus, whatever happened to reverse osmosis? It was not mentioned in the issue.

Desal is such an expensive technology, currently only wealthy countries can afford this process...cost also poses as a problem to the availability of the technology in the future.