In order to determine the amount of dissolved oxygen in water, measurements are made by authorized laboratories to determine the dissolved oxygen level. Dissolved oxygen levels in natural waters and wastewaters depend mainly on physical, chemical and biochemical activities found in water. Dissolved oxygen analysis is always applied in water pollution measurements, water quality control activities and wastewater treatment plants.

Accreditation laboratories generally use two different methods for the determination of dissolved oxygen:

• Winkler or iodometric method and its modifications
• Electrometric method using membrane electrodes

The Winkler method is based on the oxidizing property of dissolved oxygen. In contrast, the membrane electrode method is based on the rate at which molecular oxygen spreads across the membrane. Which method will be applied depends on the level of sensitivity expected, the existing interventions and the facilities of the laboratories.

Dissolved oxygen measurements are important for the following reasons:

• Indication of water aerobic or anaerobic
• Indicator of the continuity of living life in natural waters
• Biochemical oxygen demand (BOD) measurements
• Efficiency of ventilation systems in aerobic treatment plants
• Causing Korozyana

Oxygen concentration in activated sludge tanks used in biological wastewater applications is very important and needs to be measured continuously. The oxygen concentration determines the quality of the tanks and the speed of the treatment process. In these measurements, conventional electrochemical measurement methods, polarographic or galvanic measurement, are applied. Both measurement methods are based on depletion of electrolytes and degradation of anodes during measurement.

Dissolved oxygen concentration in wastewater treatment plants for almost 40 years by competent laboratories has been determined using electrochemical methods. In recent years, great efforts have been made in terms of advanced technological developments and optimization of electrochemical measurement techniques.

In addition, laboratories accredited by national and international accreditation organizations, measurement activities, TS EN ISO / IEC 17025 standard in accordance with their activities.