What is Dissolved oxygen?

Dissolved oxygen is a reference for the amount of free oxygen found in water. Dissolved oxygen is a very important parameter when looking at water quality as it can have a large influence on the organisms living in a body of water. Typically, dissolved oxygen provides a good indication of the condition of water, therefore understanding these levels can help a good deal when looking to improve or maintain good water quality.

How does dissolved oxygen enter the water?

The dissolved oxygen enters the water through the surrounding air, or as a result of plant life via photosynthesis. Air carrying oxygen can enter across the water surface, or can be introduced by processes such as aeration (occurring naturally or via man made solutions). Dissolved oxygen can also be introduced as a waste product from the process of photosynthesis from plant life such as algae, sea weed and other aquatic plants.

How can I measure dissolved oxygen

For the measurement of dissolved oxygen you will typically require a sensor and in most cases a meter or controller to interpret the information provided by the sensor. A dissolved oxygen sensor commonly comprises one of the following technologies –

♦ Clark electrode
♦ Optical dissolved oxygen sensor

Deciding which sensor is best will depend on the budget you have available and the time you have to undertake maintenance and calibration. In recent time’s optical dissolved oxygen sensors have been favoured over the traditional Clark electrode technology. The main reason for this change is due to the low maintenance / low drift characteristics of the optical sensor. This makes the sensor ideal for use on long term applications and those where reducing costs associated with maintenance is key. Optical dissolved oxygen sensors have no dependence on flow, therefore they are also ideal for applications where “still” water is present. A Clark electrode in comparison will require maintenance to ensure it provides accurate and reliable data, as the filling solution within the sensors can dry out over time. They are also dependent on flow to perform correctly, so will require some form of stirring or flow depending on the application.

What type of dissolved oxygen meters are available and which is best for me?

Typically dissolved oxygen meters are found in 3 products types –

♦ Sensor only, with an analogue or digital output
♦ Sensor with handheld display / data logger
♦ Sensor with a permanent controller

Your selection will be decided by your application. If for example you already have an existing SCADA or data collection system you may decide that you can integrate a dissolved oxygen sensor into your system directly. This will of course mean that to perform calibration on the sensor you will most likely need a handheld device or PC software with communication cable. If however you would like a permanent display for readings / data logging or calibration then a permanent controller may be your best option. If a portable meter is needed for spot measurement or for carrying out short term monitoring or deployments, then use with a battery powered display or data logger may be the best option available to you.

To ensure you select the appropriate device for your application please feel free to contact us mail@bellenviro.co.uk or call our technical sales team 01280 817304