Operator concept
What is dissolved oxygen?
Dissolved oxygen, or DO, is the amount of oxygen gas dissolved in water, measured in mg/L. It matters most in wastewater, where the microorganisms that break down waste need enough oxygen to live and work. In rivers and lakes, fish and other aquatic life depend on it too.
Why dissolved oxygen matters
The microbes that do the work in activated sludge are aerobic, which means they need oxygen to eat the dissolved waste. Keep the dissolved oxygen where it should be and they stay healthy and the effluent comes out clean. Let it drop and the useful microbes slow down or die, while the organisms that thrive without oxygen take over and produce odors. Out in a river, the same thing happens on a larger scale: too much waste uses up the oxygen and fish cannot survive.
How operators measure and control it
A dissolved oxygen meter with a probe reads the level right in the water. In an activated sludge plant, blowers push air into the aeration basin to hold the dissolved oxygen the microbes need, and the operator raises or lowers the air to keep it in range. Too little starves the process; far too much just wastes power on the blowers, so good operators dial it in.
Common questions
- What is dissolved oxygen?
- The amount of oxygen gas dissolved in water, measured in mg/L. It is what aquatic life and treatment microbes rely on to breathe.
- Why is dissolved oxygen important in wastewater?
- The microorganisms in activated sludge are aerobic, so they need dissolved oxygen to break down the waste. Too little and treatment fails and odors start.
- How is dissolved oxygen measured?
- With a DO meter or probe placed in the water. In a plant, operators track it in the aeration basin and adjust the air to hold it in range.
- What happens if dissolved oxygen is too low?
- The good microbes slow down or die, treatment drops off, and odor-causing organisms can take over. In a natural water body, low DO can kill fish.