dissolved oxygen and nanobubbles

Introduction

Dissolved oxygen or DO refers to the level of free, non-compound oxygen present in water or other liquids. The DO value is important parameter for your water quality and the process where you use the water for. An ultrafine bubble or nanobubble is not dissolved oxygen a bubble is a gas cavity in water or another liquid. 

Conventionally aeration is a technology to increase the DO value in water. Now with the nanobubble technology we have two levels to increase the oxygen in water, the first levels is the dissolved oxygen and the second levels is via bubbles or gas cavities in water. For this reason we also call nanobubble generation an enhanced aeration technology.

The dissolved oxygen level is influenced by the following factors:

• Temperature of the water
• The salinity of the water
• The altitude of operation (atmospheric pressure)
• Biology in the water by respiration of fish and plants

The relationship between water temperature and DO is inverse: Cold water is able to hold more DO than warm water. The ultrafine bubble generators on this website pressurize gas and liquids and for that reason they are able to oversaturate the water. In nature under normal conditions a saturation level of 100% is the maximum. 

Air contains 20.95% oxygen. At standard barometric pressure (760 mmHg), the pressure or 'tension" of oxygen in air is 159 mmHG (760 x 0.2095). The pressure of oxygen in air drives oxygen into water until the pressure of oxygen in water is equal to the pressure of oxygen in the atmosphere. When pressure of oxygen in water and atmosphere are equal, net movement of oxygen molecules from atmosphere to water stops. The water is than in equilibrium or at saturation, with dissolved oxygen (DO) when the oxygen presssure in water equals the pressure of oxygen in the atmosphere.

PPM versus mg / L

We often get the question what the difference between DO ppm is versus DO mg/L. At first it looks two very different forms of measurement. They are both ratios, and to see how they align with each other, it’s easiest to start with ppm, or parts per million. As an example, let’s say you’re trying to determine the salinity of seawater, and you get a reading of 36,000 ppm; that simply means that for every million parts of water, there are 36,000 parts of salt.

What are parts? Parts can be any measure. Liters, buckets, or a drop of water (orange juice, gasoline, etc.). The size of the sample is irrelevant. It’s the RATIO of the tested parts (salt) to the total number of parts (seawater) that’s important. It’s easy to grasp ppm, but how about mg/L?

A liter of water (which is a metric measure of volume, or capacity) weighs 1 kilogram. That’s 1,000 grams. Now think about a milligram. It is 1/1000th of a gram, making it 1/1,000,000 th of a kilogram. Put another way, a liter of water weighs 1,000,000 milligrams. One million milligrams… see where this is going? For our purposes, 36,000 milligrams/Liter is the same measurement as 36,000 parts per million.* Both measurements tell us how many parts (milligrams) are present in every million parts (Liter).

In reality, for these measurements to be perfectly equal, they must be taken with pure water at standard temperature and pressure. Most testing instruments include an automatic temperature compensation feature (ATC) which corrects for this difference.

DO values table

Dissolved oxygen values saturation point and over saturated values

Links