Water, water everywhere and all we want to drink, shower in, swim in, grow food with, etc.

A Jim Bell Commentary

Many experts are projecting doom and gloom, scenarios of decreasing water supplies and increasing cost, yet the San Diego/Tijuana Region can easily become renewable water self-sufficient and even become a net water exporter.

Even if we assume the worst case scenario of zero precipitation and the complete cutoff of all imported water, the San Diego/Tijuana Region could completely replace all the freshwater it currently uses by installing PV panels over 4.3% of its roofs and parking lots. In 2015, 4.3% of our region’s roofs and parking lots will be about 9 sq. miles, or as shown in the graphic, 4.5 sq. miles on each side of the border.

The above statement is based on the following assumptions:

1. A yearly average of 5-hr. of sunlight per day,
2. 1,000 sq. feet of roof and parking lot per capita,
3. An average potable water consumption level of 180 gallons per capita per day,
4. A 2015 regional population of 6 million people,
5. That 70 gallons of freshwater can be extracted from seawater per kWh of electricity consumed through reverse osmosis (RO)
6. PV (photovoltaic) panels 15% efficient at converting sunlight into electricity, (Commercially available panels are already pushing efficiencies of 20% or better.

The electricity produced by this system would be used to power large scale reverse osmosis (RO) pumps to convert seawater into freshwater. The pumps push seawater through filters that let freshwater through while excluding salt, other minerals and contaminants in general.

The issue of sucking marine life into reverse osmosis system can be solved if seawater to be processed into freshwater is extracted from wells close to the ocean above high tide instead of direct ocean extraction. Since seawater coming into such wells would be sand filtered, marine organisms will be eliminated from the process.

Similarly, since “waste water” from the RO process will be twice as salty as seawater, it will have to be diluted by mixing it with seawater, also extracted from the near ocean wells, until the water to be returned to the ocean is no more than 20% saltier than seawater. Once diluted, its release into the ocean would be defused as an additional precaution against negative ecological consequences. Other sand filtering technologies have also been proposed.

Mining RO waste water for salt and other minerals opens up other local business and employment opportunities for the region and could potentially eliminate the need to return RO wastewater to the ocean at all.

The size of the “worst case scenario” RO system discussed above could be cut in half, if recycled sewage water was filtered and disinfected, then used for irrigation. Using graywater at home would also be a plus for efficient water use. This is because half of the potable water currently used in our region is used for irrigating landscaping and crops.

Water-use efficiency improvements could reduce the role of renewable-energy-powered RO as well.

Combining water recycling and efficient water use with better rainwater runoff collection and storage systems, our region would only need to install 15% efficient PV panels on 2% of its roofs and parking lots to provide equal or superior water use services in the future, compared with what we have today. Plus, if we want more freshwater, we can cover more roofs and parking lots with PV panels to power expanded RO capacity and create all the freshwater we want.

Additionally, all this can be funded through a water purchase agreement model that will pay for itself by redirecting the dollars we now export to pay for imported water into hiring local businesses and workers to make our region renewable water self-sufficient, with renewable energy powered RO being our back-up for water if all else fails.

The membrane configuration allows the process to be done at far less pressure (i.e. Depth) than is required for onshore.

Also, the DEMWAX is only pressurizing the product water which is significantly less energy than a traditional onshore plant which pressurizes the feedwater. This is a huge energy saver. Read the white paper on their website.

Great comments GoIllini, but I must address a couple things.

Regarding recovery rate: as you state, recovery rates can be the same onshore and off. You are right that an onshore plant can go to a 1% recovery to lower the osmotic pressure just like the DEMWAX system. However, the energy required will be far from the same as with the DEMWAX system. When an onshore plant goes to very low recovery, they must pump a whole lot of feedwater, even if it is at lower pressure. And because the best energy recovery devices are only about 91% efficient, that level of pumping will entail a substantial amount of extra energy (and costly energy recovery devices). The DEMWAX does not pump the feedwater at all so the ‘optimal’ recovery approaches zero. You will not find a shore based system that make any sense at that level of recovery.

As for the fouling, that is something that needs to be proven and is in testing. However, water at those ocean depths (and off the floor) is extremely clean. I think the maintenance economics will surprise people when they get their data in the ocean.

There’s this pesky thing called conservation of energy standing in the way. You’re either going to pump to this great feed pressure, or pump the same amount of pressure on the filtered water to get it back up to sea level. A “snorkel” is going to change this basic concept.

Cute though. Where does OCR find this stuff?

Your concerns are not correct. I have consulted with this company and can tell you…

With the DEMWAX, only the product water is pumped to surface whereas onshore plants pressurize feedwater (2 to 3 times more water), which requires significantly much more energy.

Furthermore, the pressure required for this system is near osmotic pressure. Onshore systems are about 2X osmotic pressure. The reason is somewhat technical, but has to do with recovery rates. Again, significantly more energy is required for the onshore system.

Finally, submersible pumps are well established as a technology. They have widespread use as every land well has one. They have long duty cycles with little maintenance. Also, the water hitting this pump is behind RO membranes and a whole lot cleaner than well water, reducing the impact on the pump.

Do you have any idea how big the ocean is? It covers nearly 75 % of the earths surface. Utilizing 12 acres of land under the ocean to prevent the depletion of fresh water on land is a hell of an improvement. In fact i would venture to say that it would be nearly impossible to build enough of these things.

The problem with you environmental “diva’s” is that nothing ever makes you happy. Except perhaps the thought that the world is going to hell and your complaining is going to save it.

At least Matt has the good sense to realize that the inhabitants of the 25 % of the earth which isnt covered in water (that leaves a lot of good 12 acre plots under the sea available for use) are violent, and thirsty. In your lifetime the population will have gone from 6 to 12 billion people. Since god has not seen fit to create any new lakes in the last few thousand years, i guess its up to us.

Don’t be an idiot, 12 acres is nothing, Its not even a big enough piece of land to raise a horse on, hell i wouldn’t even subject a dog to living on less than 50.

Yours truly,

Reality Check

Or you can use the approach from Ocean Motion Intl…that’s pure water from a clean, non-carbon system. I’d like to see this company get some of the publicity and support that these other “approaches” are seeing.

Maybe, someday when others realize that good money is being wasted and no real output is seen.

California, we need water. We can feed and save the smelt and then our farmers farm again!! Let’s take a look at all solutions and choose the best one’s (yes, plural! There are several viable, renewable and clean solutions out there!!)
Thanks for reading.