BlueInGreen NEWSWIRE
SDOX Technology by Scott Osborn
One of the most common questions I get from people when I make technical presentations about our SDOXâ technology is, “If you inject water that is supersatured with dissolved oxygen or ozone, won’t it degas after it is released into the water?”
This question is based on the fact that BlueInGreen’s SDOX technology takes a sidestream of water and dissolves gaseous oxygen into the water to concentrations near 350 mg/L and then injects this high DO water into the water being treated. A dissolved oxygen concentration, or DO, of 350 mg/L is very, very high when compared to normal DO values measured in water in open systems such as a stream, wastewater treatment plant or lake. The highest DO typically measured in a fully oxygenated stream open to the atmosphere would be around 11 mg/L, as this is near the DO when the water is totally saturated with oxygen molecules dissolved in the water. The stream will not hold any more than 11 mg/L dissolved oxygen if it is saturated.
It stands to reason that if water at normal pressure exposed to the atmosphere will not hold any more dissolved oxygen than 11 mg/L, then water exiting the SDOX with a DO of 350 mg/L should try and revert back to original conditions and not hold more than 11 mg/L. Therefore, 350-11 = 339 mg/L of oxygen should leave the water by forming bubbles and rising up out of the water. That’s a lot of degassed oxygen.
(A word about saturation and the SDOX…the SDOX works by dissolving oxygen into water under high pressure. The reason for this is that if you increase the concentration and pressure of the oxygen gas that is interacting with the water, the water will hold more oxygen and the saturation value goes from 11 mg/L at normal pressure contacting air to 350 mg/L at high pressure contacting oxygen. This can be explained by imagining a closed box with a volume of one cubic foot filled with air at normal atmospheric pressure. Inside the box there is a specific number of oxygen molecules for that cubic foot of air. This number is known as the concentration of oxygen. When this air comes into contact with water, the oxygen molecules will enter the water until the concentration of oxygen molecules in the air is in equilibrium with the concentration of oxygen molecules in the water. As the concentration of oxygen in the gas increases, the concentration of oxygen in the water increases as well. Now, if you replace the air in the box with oxygen, the number of oxygen molecules increases by more than four-fold. This is because air is just over 20% oxygen. The oxygen concentration in the gas is increased and so is the amount of oxygen the water will hold that is in contact with the gas. To increase the pressure of the oxygen gas, you must compress the cubic foot to a much smaller volume. The high-pressure oxygen has the same number of molecules as it did when it was at atmospheric pressure, but the volume is much less. Therefore, the oxygen molecules are much closer together and more concentrated. This increased concentration in the gas because of increased pressure, creates water with a much greater concentration of oxygen. This is how the SDOX is able to reach extremely high DO levels in the water stream being injected into the treated water. Now, back to the question…)
Anyone can observe the degassing phenomenon by opening a can of your favorite carbonated beverage and pouring it into a glass. Bubbles form in the drink and rise to the surface creating a foam layer on top. The drink is under pressure inside the can and when you open the can, the pressure is released which decreases the concentration of CO2 that the drink can hold. Therefore, the dissolved CO2 leaves the drink as bubbles. Another place to observe this phenomenon that helps me answer the question about the SDOX, is at the tap in your kitchen. Have you noticed that when you turn on the cold water and fill a clear glass, the water remains clear? But when you turn on the hot water and fill a clear glass with it, the water is cloudy and full of bubbles. The reason for this is that as the temperature of water increases, the amount of dissolved gas the water can hold decreases. As an example, saturated DO for water at 10°C is 11 mg/L but at 70 °C (temperature of hot water) the most dissolved oxygen water will hold is 4.3 mg/L. When your tap water starts out in a river, lake or groundwater, it is about 80% full of dissolved air. When it is heated, the water can only hold about a third of the dissolved air that it could before being heated. As the hot water is stored in the heater and pipes, it is at a fairly high pressure, so the dissolved air won’t come out of solution. But once the hot water exits the tap and loses pressure, the amount of dissolved air that it can hold is far less than what it contains. Much of the air that was dissolved cannot stay dissolved and forms bubbles in the glass.
What does this have to do with the SDOX?
Now try another experiment. Find a large clear pitcher and fill it ¾ full with cold water. Now, run the water until it is hot. Instead of filling an empty clear glass, this time run the hot water into the pitcher with the cold water. Notice that the water in the pitcher is not cloudy with bubbles. The reason there are no bubbles is supersatured hot water was quickly mixed with cold water that had the capacity to hold the excess dissolved air that the hot water was trying to get rid of. Since the supersatured water was distributed with water that could hold its excess air, the air remained dissolved and no bubbles formed. Also, if there were any bubbles formed, they were very small (since when gas comes out of solution, bubbles start to form at the molecular level) and quickly re-dissolved into the larger body of water in the pitcher. As long as there is enough capacity of the cold water in the pitcher to hold the excess air in the hot water trying to come out of solution, no bubbles will form. If you start off with the pitcher being only ¼ full of cold water and run hot water until the pitcher is full, there will be bubbles since the hot water has exceeded the cold waters capacity to hold the dissolved gas.
OK, now I am finally going to get around to trying to answer the question about the SDOX. The SDOX process that prevents the supersaturated water from degassing oxygen is the same process as adding hot water to the pitcher ¾ full of cold water. The SDOX adds supersatured water to a larger body of water being treated to reach an overall DO value that is less than saturation and usually much less (6 mg/L for example), so there is plenty of capacity in the water being treated to hold the extra dissolved oxygen from the SDOX water. There is no reason to treat water with dissolved oxygen that’s already full of dissolved oxygen. Therefore, every application of the SDOX will involve treating water with a high capacity to hold dissolved oxygen. The trick is to properly mix and distribute the supersaturated stream injected into the water being treated in such a way that the DO of the entire body of water being treated remains below saturation and the supersaturated water is distributed through mixing faster than the oxygen gas exits the solution. The process of liquid-to-liquid mixing is relatively much faster than the process for excess dissolved oxygen to form a molecular level bubble and then conglomerate with other molecular bubbles to form a bubble large enough to begin to float to the top of the water being treated. Even if some bubbles do form, they are very small and will quickly re-dissolve as they are mixed into water with subsaturated DO.
If a large body of water requires treatment to a DO of 6 mg/L, then only a small amount of the side stream containing water at 350 mg/L needs to be injected to reach the target level. As an illustrative example, say you have a water stream of 1 million gallons per day (MGD) that is initially at a DO of 3 mg/L. The required DO after SDOX treatment is 6 mg/L. The side stream water flow rate of 350 mg/L water required is ((6 mg/L – 3 mg/L)*1,000,000 gal/day*3.79 L/gal)/350 mg/L = 32,486 L/day of SDOX water = 8571 gal/day = .008571 MGD which is 1/117 of your treated water flow rate of 1 MGD. This is the equivalent of adding 1 tablespoon of hot water to 1.8 quarts of cold water in the pitcher experiment discussed earlier. This relatively very small amount of supersaturated water is very easy to distribute without allowing degassing. Because of the high concentration of dissolved oxygen in the stream exiting the SDOX, only a small amount of water needs to be added to the water being treated to provide the required oxygen. This results in a relatively small footprint, pump size, and pipe size for the SDOX.
Proper mixing of the supersaturated water stream exiting the SDOX into the water being treated is part of the specialized design of the injection nozzle. The injection nozzle can be configured to properly distribute the supersaturated water in flowing basins, streams or large, still bodies of water such as lakes or storage lagoons. The mixing energy is provided from the pressure inside the SDOX used to supersaturate the side stream of water. The mixing and distribution energy is a result of recovering much of the energy consumed by the pump and compressed gas components of the SDOX.
In conclusion, the SDOX is able to add side streams of water that are highly supersaturated with dissolved oxygen into water being treated without degassing because of the design of the mixing nozzle. The energy required to distribute the supersaturated water to prevent degassing is recovered from the pump and compressed gas pressure that creates the supersaturation process. This nearly closed loop, energy process helps minimize the energy footprint of the SDOX, as well as provide operating cost savings over conventional technologies.
I had my house repiped and after the fact my hot water is coming out of the tap and it appears to be super saturated. It is only the hot water not cold? Plumbers say it’s my hot water tank but there is no water around my tank.