So How Does OMEGA Clean the Water?
The OMEGA photo-bioreactors float in seawater, and are filled with waste water, which is basically freshwater, and means that there is a salt gradient between the waste water inside the OMEGA and the surrounding seawater. We use this gradient to clean the waste water. Here’s how:
There are special water permeable membranes that selectively let water through and keep back almost everything else. This gives them some really interesting uses. For example, if we put one of these membranes between the two sides of a U-shaped tube, and we put salt in one side of the tube to form a concentrated salt solution called brine, the brine, which cannot pass through the membrane, forms a chemical gradient that pulls the water on the left side of the U-tube through the membrane into the brine on the right side of the tube. This process is called forward osmosis (or just osmosis).
It’s amazing. It balances osmotic pressure against hydrostatic pressure. There is no added energy. The water is pulled through the membrane by the salt gradient until the water on the right side balances the osmotic force pulling it through by hydrostatic force pushing it back.
What if we put wastewater and algae on one side of the membrane and brine or just seawater on the other?
The salt gradient pulls only water through the membrane from the wastewater, leaving behind algae and wastewater contaminants. This concentrates the algae, making them easier to harvest, and cleans the water passing through the membrane, forming clean saltwater.
The same process will work for the OMEGA photo-bioreactors filled with wastewater, which is freshwater, floating in seawater, which is 3.5% salt, an adequate gradient for forward osmosis to help us harvest the algae and clean the water released into the sea.
But what about the water? Why should we release freshwater into the sea? 97.5% of the water on Earth is seawater, and a map of freshwater scarcity shows in red that there are already large areas with limited water supplies, and even in places with water one in eight people lack access to clean drinking water, and 1.5 million children die each year from water-borne diseases.
We talked about forward osmosis (FO) cleaning wastewater without adding energy, but making it salty. Could we use this same membrane and run the system backwards and make freshwater from saltwater? Or rather seawater? You bet we can!
But it takes a lot of energy. We have to put pressure on the seawater side to force the water through the membrane. It’s like pumping water uphill. It works, but it takes energy. The process is called, you guessed it, reverse osmosis, the opposite of forward osmosis, and it’s used all over the world to make seawater into drinking water, but it also makes brine.
Well, let’s think about this. We can use seawater, which is 97.5 percent of all the water in the world, and make it into freshwater using reverse osmosis, but it takes a lot of energy, and it makes brine as a toxic byproduct…
Hold on! We know that forward osmosis uses brine and no added energy to clean wastewater although it makes it salty. And reverse osmosis uses saltwater, and a lot of energy, to make drinking water and brine.
Okay, let’s combine the two systems, and use the brine produced by reverse osmosis to pull wastewater through the forward osmosis membrane, which gives us concentrated algae and clean but salty wastewater, or rather, brine diluted with clean wastewater. And then we use this clean diluted brine for reverse osmosis that produces really clean water and brine. Back to the forward osmosis and around we go!
We put wastewater in and get FO/RO clean water out. Likewise, in the OMEGA system, we use brine from reverse osmosis to pull the wastewater through the forward osmosis membrane to clean the wastewater and make clean diluted brine which we use for reverse osmosis to get freshwater. And of course we get the brine back.
Think about it. This not only uses and detoxifies the brine, but it saves two thirds of the energy used to make seawater into freshwater, and we get really clean freshwater, in this case from wastewater. At the same time, we produce algae from the nutrients in the wastewater that eliminate wastewater discharge, capture carbon, and produce biofuels, fertilizer, biochar and other products.
An undergraduate engineering student on the OMEGA team, Matt Klaxton, built a prototype of this system. He investigated the impact on wastewater of the algae growing in it, the electocoagulation harvesting process, forward osmosis, reverse osmosis, and after all that, if anything was left in the water. The good news: it was cleaner than most drinking water.
And that’s what OMEGA does about the water.