Dissolved oxygen: Why it matters and how we measure it

If you want to cite this blog post use: Sahaljanova, N. (2026). Dissolved oxygen: Why it matters and how we measure it. [online] redox.me Available at: https://redox.me/blogs/good-measurement-practices/dissolved-oxygen-why-it-matters-and-how-we-measure-it [Accessed Date Accessed].

What is dissolved oxygen? Have you ever wondered what fish actually breathe? They certainly do not split water to obtain oxygen. Instead, oxygen is present in water as dissolved molecules, which fish extract through their gills.

But it is not only the presence of dissolved oxygen that matters, it is its concentration that matters even more. Too much or too little? Both can cause trouble. In aquatic systems, it leads to physiological stress. For researchers, it means unreliable data. For industry, compromised production and unexpected costs.

Now that we know it is important, let’s look at some real-world examples where dissolved oxygen concentration plays a major role.

The real-world importance of dissolved oxygen

Dissolved oxygen is a key factor in many research areas. It is a small molecule that has an impressive ability to influence the experimental results. Whether it is a desired reactant or an unwanted interference, it tends to affect our work more often than we would wish for.

But dissolved oxygen does not stop at the laboratory door. Outside the lab, it becomes critical in a wide range of applications, some of them perhaps more relatable than one might expect (see Figure 1).

Figure 1. Infographics of dissolved oxygen importance (Illustration generated using LLM)

The most familiar examples include:

1. Environmental systems and Aquaculture
Returning to fish and other aquatic organisms, whether in natural waters or controlled aquaculture systems, maintaining oxygen balance is essential. Organisms thrive only within a specific dissolved oxygen range, and survival depends directly on it. 
Dissolved oxygen is also a primary indicator of water quality. In natural ecosystems, oxygen depletion may occur due to pollution, eutrophication, or rising temperatures. Changes in dissolved oxygen concentration can therefore reveal ecological imbalances and provide insight into the impact of climate change.

2. Food and fermentation processes
You may not realize it, but many foods and beverages rely on fermentation processes. Yeasts and bacteria shape the final product, from bread and yogurt to beer or wine. 
Microbial metabolism depends strongly on oxygen levels. Because there are many types with different oxygen requirements, precise control is essential for correct cell growth and biomass formation. Oxygen directly influences flavor development, food texture, or the overall production efficiency. Since industrial fermentation operates in batches or continuous mode, unexpected fluctuations can reduce yield and cause significant economic losses.

3. Wastewater treatment
Wastewater treatment also relies on living organisms. Aerobic bacteria are used to degrade organic pollutants in water, and their activity depends directly on the availability of dissolved oxygen. To sustain these biological processes, continuous aeration is needed. 
If oxygen levels fall below the required threshold, treatment efficiency decreases and water may not be sufficiently purified. Since aeration is one of the largest expenses in wastewater treatment plants, dissolved oxygen concentration has a direct impact on both process performance and cost. 

4. Industrial processes
Dissolved oxygen also plays a crucial role in countless industrial processes. In chemical manufacturing, oxygen can influence reaction pathways and product stability. In cooling water systems and process water circuits, oxygen levels affect operational efficiency and material durability. In oil and gas infrastructure, even small amounts of dissolved oxygen can accelerate material degradation. 
Across many industrial environments, oxygen becomes a performance-defining parameter. It is a key factor in corrosion processes, affecting infrastructure lifetime and maintenance costs.

5. Central heating systems and corrosion
And where does oxygen-driven corrosion affect us more directly than we might expect? In the central heating systems we rely on every day. Few people associate dissolved oxygen with their radiators, yet it plays a decisive role in the durability of the entire system. 
When dissolved oxygen is present in circulating water, it reacts with metallic components inside pipes, radiators and boilers, initiating corrosion processes. Over time, this leads to material degradation, reduced heat transfer efficiency, and can cause pipe failure and water leaks. This results in service interruptions and costly repairs. Replacing the damaged infrastructure is disruptive not only for residents but also for facility operators. 

How is dissolved oxygen measured in real life?

Now, when we have seen how dissolved oxygen plays a crucial role across biological, industrial, and infrastructure systems, an important question arises: how can it be measured reliably?

Accurate and real-time determination of dissolved oxygen concentration is essential to ensure that levels remain within the required range for each process. When deviations are detected early enough, corrective action can be taken before they develop into technical failures, product losses, or infrastructure damage.

There are three common techniques used across industries to determine dissolved oxygen concentration. The oldest of these is the Winkler titration method. When performed correctly, it provides highly accurate results and is often considered a reference method.

The main trade-off? It does not allow real time or continuous measurement. This procedure includes multiple steps and careful sample handling, which makes it time-consuming and labor-intensive (see Figure 2). For this reason, the Winkler method is primarily used for calibration, verification, or certification purposes, rather than for ongoing process control.

Figure 2. Simplified multistep Winkler titration procedure (Illustration generated using LLM)

If the Winkler method is too slow for modern processes, what alternatives allow real-time oxygen monitoring? Luckily, we no longer need to rely on someone running to the lab with a sample bottle. Instead, dissolved oxygen sensors offer a far more practical solution. 

Dissolved oxygen sensors
Sensors that enable continuous, real-time monitoring directly at the site of the process provide an effective approach. A sensor can remain installed in the operating line and continuously track dissolved oxygen levels, allowing immediate reaction if fluctuations occur. In other cases, it can be deployed temporarily, for example to assess water quality in lakes and other natural water sources, or during laboratory measurements.
In practice, dissolved oxygen is measured using two sensor technologies: optical and electrochemical. Each operates based on a different physical principle, and offers distinct advantages and limitations.

Optical sensors
These sensors operate based on the principle of luminescence quenching. Oxygen affects a light-emitting sensing layer, and the resulting change in signal allows determination of its concentration. This technique provides stable performance, does not consume oxygen during measurement, and requires less frequent calibration. 
In many cases, these sensors perform exceptionally well and may be the right choice. The trade-off, however, lies in their complexity. Light sources, photodetectors, and advanced electronics increase both cost and power consumption. While this may not be an issue in small-scale applications, systems requiring dozens or hundreds of sampling points can face significant cost challenges. 

Electrochemical sensors
This is where electrochemical sensors become particularly attractive. Instead of using light and optics, they rely on a much simpler approach, the electrochemical reduction of oxygen at an electrode surface. Electrochemical dissolved oxygen sensors are typically classified as either polarographic (Clark-type) or galvanic sensors, and both have been widely used for decades. 
Their construction is relatively simple and compact (see Figure 3), which makes them more affordable than optical systems. This makes them especially appealing in installations with multiple measurement points, where cost differences quickly become noticeable.

Figure 3. Working principle of electrochemical dissolved oxygen sensor

It might seem that after so many years of practical use, there is little room left for improvement. In reality, the opposite is true. Despite their long history, electrochemical sensors still involve limitations. Since these sensors consume oxygen either to a greater or lesser extent, depending on the electrode size, their performance depends on flow conditions. Membrane fouling, electrolyte changes, or gradual signal drift remain very real challenges affecting long-term stability. 
Of course, high-end electrochemical systems aim to reduce these limitations, but as you might expect, that improvement rarely comes for free. 
The real challenge is not simply developing a good sensor, but developing one that combines reliability with affordability. A sensor that is robust enough for demanding applications, yet inexpensive enough to be used wherever it is actually needed, not only where budget allows it. 
This challenge is not only theoretical. It is exactly the motivation behind our current development work (see Figure 4 for CAD design), creating an electrochemical dissolved oxygen sensor that stays reliable without becoming overly expensive, enabling broader use in applications where cost has so far limited monitoring (see Figure 5 for realistic electrode configuration picture).

 Figure 4. CAD design of our sensor prototype

Figure 5. Electrode system inside our sensor prototype

In the end

Dissolved oxygen is invisible, but its consequences are not. It shapes ecosystems, affects production processes, and influences the lifetime of infrastructure we rely on every day.

Measuring it accurately is essential, but making that measurement accessible is equally important. Bridging that gap is what drives ongoing efforts in sensor development.