How is dissolved oxygen measured in water?

Dissolved oxygen (DO) measurement methods: Electrochemical/Polarographic (Clark electrode - O2 diffuses through membrane, generates current at cathode), Galvanic (similar principle, self-powered), and Optical/Luminescent (O2 quenches fluorescence of indicator - longer life, less maintenance). DO is expressed in mg/L or ppm, with saturation depending on temperature and pressure. Applications: wastewater aeration control, aquaculture, fermentation monitoring, and boiler feedwater. Proper DO levels ensure biological treatment effectiveness and aquatic life health.