Dissolved Oxygen Sensors

Dissolved oxygen (DO) tells an operator whether the bacteria in an aeration basin have enough oxygen to digest the organic load, and every cubic metre of air blown into that basin is paid for in electricity. Continuous DO measurement with automatic blower control typically saves a quarter of a treatment plant's energy, which is why the DO sensor is the most important analytical instrument on a wastewater site.

The sensors measure 0 to 20 ppm (mg/L) of oxygen with temperature compensation, using an amperometric membrane cell or an optical luminescence element depending on model; the optical type needs no membrane or electrolyte and drifts less between calibrations. Process conditions are 0 to 50 °C and up to 4.5 bar, with a 1" NPT male connection for immersion on a handrail-mounted pipe in the basin, or for mounting in a side-stream flow cell on a sample line. Automatic air-blast or wiper cleaning options keep the membrane clear of biofilm.

The transmitter provides 4–20 mA, HART or FOUNDATION Fieldbus, and can also display oxygen in percent saturation and provide salinity and barometric compensation.

Applications are aeration basins, wastewater treatment, biological processes, fish farming and side-stream DO measurement in municipal and industrial wastewater, environmental monitoring and biological treatment processes.