Dissolved Oxygen Theory Guide

Oxygen is the third most common element in the universe and the most common in the Earth’s crust (49%). However, because oxygen is highly reactive, most of it is bound to other elements to form chemical compounds. Elementary oxygen in its two allotropes O₂ and O₃ (ozone) only exists in relevant concentrations on our planet. That is because it stems from biological processes that pertain to Earth (mainly photosynthesis).

Thus, elementary oxygen and its occurrence are linked to life and its chemical activities. Due to its reactive nature, it also contributes to less desirable processes, such as corrosion or fire hazards.

Measuring concentrations of oxygen dissolved in water can be very important for monitoring habitats (such as lakes, oceans or aquariums), production processes (such as beer or cheese fermentation), treatment of wastewater, or corrosion-sensitive processes.

O₂ is a highly reactive molecule, so reactive in fact that it only exists in our atmosphere because it is continuously produced by photosynthesis. It reacts as an oxidizing agent—i.e. in a chemical reaction it receives electrons. Most Dissolved Oxygen sensors utilize this property of electrochemical reactions for measuring oxygen concentrations. These types of sensors are well established as conventional methods for measurement. They can be categorized as galvanic or polarographic sensors. Optical sensors constitute a modern alternative to these electrochemical methods.

This chapter summarizes some hints and recommendations of the daily use of Dissolved Oxygen sensors. They are based on generally accepted handling and operational rules.

One important analysis to assess water quality is determining the BOD (Biochemical Oxygen Demand). BOD is an indicator of the amount of organic matter present in freshwater. High BOD levels may indicate that water is contaminated with coliform bacteria, other pathogens and organic compounds and therefore unfit for human consumption.