Clear water as a colloidal suspension - interesting demonstration of zeta potentials in water. And, how it ties into dissolved oxygen in wastewater treatment
Water is an interesting polar solvent. Remembering back to my high school chemistry class - it was often called the universal solvent. Water's hydrogen bonding can make a solution with a multitude of compounds. However, oxygen is not very soluble in water at atmospheric pressures. In wastewater systems, we use fine bubble diffusers, jet aerators, and any number of strategies - yet most air (roughly about 19% oxygen) pushed into the water does not become "dissolved oxygen".
Lately, I have been able to work with some newer technology for enhancing gas transfers into wastewater. Developed by BlueInGreen, the systems uses advanced high pressure adsorption technology to supersaturate water. As I am interested in getting oxygen into wastewater, I wanted to see that if supersaturating water could improve oxygen transfer. In most cases adding oxygen to wastewater in pure form results in most of the oxygen flashing off to the atmosphere due to low solubility in the water. The oxygen bubble coalesce and rise to the surface - thereby leaving the water with minimal transfer efficiency into D.O.
Using BlueInGreen technology, we were seeking to avoid this waste and transfer much high levels of D.O. into solution (and for the wastewater bacteria). Instead of using air, the SDOX system uses pure oxygen. And, this is a big difference maker. Instead of a gas with 19% O2, we have 100% O2. But without advanced injection/adsorption system, it would be similar to past pure oxygen systems where we could get only temporary high DO levels before the bubbles coalesced. The difference is the pressure system and other bits of advanced engineering allowing for the production of nano-bubbles. Moving from micro to nano bubbles takes advantage of Zeta Potentials - with nano sized pure oxygen bubbles, you can create a stable colloidal solution of oxygen in water. The electrical charge of the nano-bubbles repels the individual oxygen bubbles. This results in D.O. levels above 30 mg/L with stability over 24 hours in wastewater.
To show the impact of zeta potential forces in water, we added India Ink to a normal tap water (control) and tap water after SDOX treatment (creating a oxygen colloidal suspension). In the Control the India Ink drops to the bottom as expected. In the SDOX beaker, the ink particles have to navigate through the matrix of oxygen bubbles and are diffused into the solution. This action reveals how Zeta Potentials keep the nano oxygen bubbles stable in solution.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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