Aeration Sewage Treatment


When used to measure the dissolved oxygen in an aeration tank, sensors tend to quickly become contaminated and need frequent cleaning. A cost-effective solution to this problem has finally been found with the development of the Yokogawa DO402 Dissolved Oxygen Converter system. With this system, the sensor is mounted in a float ball holder that protects it from contamination and enables continuous maintenance-free use for extended periods.

Sewerage Treatment Procedure


Float HoldersSewage that flows into a treatment plant is sent to a primary sedimentation tank to remove the garbage and sludge. Thereafter, it is routed to an aeration tank where activated sludge (sludge containing bacteria, protozoa, and other microorganisms) is added and air is blown into the mixture to agitate it. The microorganisms in the activated sludge thrive on the oxygen and cause the organic substances in the sludge to proliferate and the generated solids to be precipitated.

A shortage of dissolved oxygen (DO) will kill the microorganisms, so the DO concentration in the aeration tank must be properly controlled. A DO analyzer is used to continuously measure the DO concentration.

The spherical float stays relatively clean because contaminants are washed off by the surface-level flow of water. The sensor diaphragm is kept relatively free of contamination as it is positioned at the same height as the top portion of the float.

  • Continuously and stably measures dissolved oxygen concentration
  • Reduces operating costs
  • Eliminates the need for manual cleaning

Product Recommendations

Detector: DO30
Float holders: FD30, PB30
Converter: DO202 DO402

Field Data

DO Readings Data

DO Readings Data

No effects of contamination after four months of continuous operation

We conducted a test with two DO30G sensors that were equipped with the PB350G Float Ball Holder. During the test, no maintenance was performed on one of the DO30G sensors, while the other DO30G sensor was cleaned every two weeks and calibrated monthly. Over the entire duration of the test, the DO30G sensor that did not receive cleaning showed minimal contamination. Furthermore, its measurements did not deviate appreciably from those of the sensor that was regularly maintained.


  • The measuring point must be at a location where air bubbles are not a frequent occurrence.
  • To prevent the sensor diaphragm from being damaged by solids in the sample liquid, the arm of an angled float holder should be pointed in the downstream direction.
  • For more information contact your local Yokogawa Analytical Marketing Department.


Related Products & Solutions

2-Wire 24VDC Transmitter / Analyzer DO202

This loop-powered analzyer is designed for both ppm and ppb dissolved oxygen measurements, suitable for both Pharmaceutical and Power Generation applications. HART, Foundation Fieldbus, and Profibus versions are available.

4-Wire Analyzer DO402G

Flexibility, reliability and low maintenance are among the benefits provided by the EXA DO402G dissolved oxygen converter.

Measuring Sensor DO30G

The DO30G sensor for dissolved oxygen is designed for use in water treatment plants such as sewage treatment works, effluent activated sludge process, and potable water treatment. It is also effective in river monitoring, intake protection, fish farming, and other fields where water quality is important.


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