What are the different types of DO sensors?

The monitoring of the dissolved oxygen content in water, is an important aspect of water quality management. Oxygen levels have a direct impact on aquatic organisms' survival, treatment efficiency, and ecosystem health.

It is not possible to measure oxygen by simply dipping a thermometer in a pond. DO sensor are required. Here's the problem: Not all DO sensors work the same.

You may have asked yourself the following questions:

• "What does dissolved oxygen mean in water?"

• "How does DO work?"

• "Which DO sensor should I select for my application?"

Then this guide is just for you.

This comprehensive article will cover:

1. What does dissolved oxygen actually mean?

2. Why it is important to monitor your system.

3. How the three main types DO sensors work.

4. Compare the advantages and disadvantages of each side by side.

5. How to choose the best DO sensor for you.

You'll know by the end which DO sensor best suits your application.

What is dissolved oxygen in water?

The term dissolved oxygen (DO) is used to describe the amount of oxygen in water that has been dissolved. Aquatic life is dependent on dissolved oxygen for survival, just as humans are.

Why is dissolved Oxygen so Important?

• Aquatic life: Fishes, shrimp, and the majority of microorganisms require oxygen to perform their essential biological functions. They suffocate without enough DO.

• Microbes are dependent on oxygen to break down organic material in wastewater. If DO falls too low, treatment will slow down or fail.

• For natural eco-systems: DO (dissolved oxygen) is an important indicator of water quality. Low oxygen levels are often a sign of pollution, algal growth, or ecosystem stress.

Healthy levels of DO

• Clean, aerated Water: 5-14 mg/L

• Stress zone: 3-5 mg/L (fish become stressed, growth slows)

• Danger zone: less than 3 mg/L

• Hypersaturation: > 14 mg/L

You can't effectively manage dissolved oxygen without a DO Sensor.

Why do we need DO sensors?

It's not practical to measure oxygen manually. You can't "see" dissolved oxygen, unlike temperature or pH. DO sensor is essential.

The DO sensor is used for:

• Enhance aquaculture productivity by keeping shrimp and fish alive and healthy.

• Optimize wastewater Treatment – Preventing energy waste in aeration tank.

• Protect Ecosystems- Tracking hypoxia zones on lakes and rivers

• Support industrial processes - ensuring oxygen levels meet production requirements.

There are many types of DO sensors, all designed to suit specific requirements.

Types of DO sensors

There are three types of DO sensors.

1. Electrochemical Do sensors (Clark type)

2. Galvanic DO sensors

3. Optical Do sensors (fluorescence based)

Explore each one in detail.

1. Electrochemical DO Sensors

Principle:

• The Clark-type sensor is the oldest and the most widely used. It was developed in the 1950s.

• These consist of a cathode and anode, covered by a thin membrane that allows oxygen to pass through.

• When a voltage applied, oxygen molecules diffuse across the membrane, and are reduced at cathode. This creates a current that is proportional to DO concentration.

Pros:

• Widely available and well established.

• Purchases are relatively inexpensive.

• Ideal for controlled laboratory and industrial applications.

Cons:

• Regular calibration is required.

• Water flow is a factor. Results may not be accurate if the water is still.

• Membranes, electrolytes and other components need to be replaced over time.

• Sensors with older technology have a slower response time.

Applications:

• Research laboratories.

• Basic industrial monitoring

• Cost is more important than stability.

2. Galvanic DO sensors

Principle:

• Galvanic sensors are similar to Clark-type but use dissimilar metals, (anode & cathode), that create their unique potential difference.

• They generate currents naturally, without the need for an external source of power.

• The amount of oxygen that diffuses through the membrane is proportional to how much current is generated.

Pros:

• Self-powered: No external polarization is required.

• Electrochemical sensors have a faster response time.

• They are suitable for portable devices because of their lower power consumption.

Cons:

• Membranes and electrolytes are still essential.

• Maintenance is required (cleaning and replacing membranes).

• Sensors with a shorter lifespan than optical sensors

Applications:

• Portable water quality meters

• Field studies and sampling on site

• Environments in educational and laboratory settings

3. Sensors Optical DO (Fluorescence Based)

Principle:

• Uses the phenomenon known as fluorescence quenching.

• Blue LED lights are used to excite a special luminescent dye.

• The sensor measures fluorescence intensity and lifetime in the presence of oxygen.

• The concentration of DO directly correlates with the amount of quenching.

Pros:

• No membranes, no electrolyte solution -- minimal maintenance.

• High accuracy and stability of readings.

• Water flow and stirring will not affect the sand.

• Long life, reduces long-term operating costs.

• Ideal for long-term and continuous monitoring.

Cons:

• Purchase cost is higher.

Applications:

• Aquaculture : Continuous Monitoring of DO in Fish and Shrimp Ponds

• Wastewater Treatment: Precise control of oxygen in aeration tank.

• Monitoring of the environment: Reservoirs, lakes, rivers and wetlands.

• Industrial Water Systems: Beer breweries, food processing and high purity water applications.

This is the gold standard of DO measurement. optical fluorescent DO sensors are the best choice if you're looking for accuracy, stability and low maintenance.

Compare DO Sensor Types

Sensor Type	Principle	Pros	You can also find out more about Cons	Best Applications
Electrochemical(Clark).	Polarized electrode + membrane	Widely used and low cost	Membrane replacement is flow-dependent and requires calibration	Labs controlled environments
Galvanic	Natural current via dissimilar metals	Self-powered, portable-friendly	Membrane still requires maintenance but shorter lifespan	Portable DO Meters for Field Work
Optical Fluorescence	Fluorescence quenching color	Long-term, accurate, stable and low-maintenance monitoring	Initial cost is higher	Environmental monitoring, aquaculture, wastewater and industry

How to Select the Right DO Sensor

The right sensor for your application depends on the environment, budget , and .

Consider these factors:

1. Environment -- Is this a lab under controlled conditions or an outdoor environment with harsh elements?

2. Maintenance -- Do you have a staff that can perform frequent calibrations?

3. Accuracy - Do you need precise, stable data over time?

4. Budget -- Do you prefer low-cost upfront costs or low-cost long-term costs?

Quick recommendations:

• Lab Research – Electrochemical Sensors

• Field use – Galvanic sensors.

• Long term monitoring (aquaculture wastewater, environment- Optical sensor.

Applications of DO Sensors in Real World

1. Aquaculture

For healthy growth, fish and shrimp need specific DO levels. Low oxygen levels can cause massive losses in commercial fish farming. Aquaculture tanks and ponds are increasingly using optical DO sensors to monitor oxygen levels and reduce stress.

2. Wastewater Treatment

Aeration tanks in wastewater treatment plants must maintain sufficient DO for microbes digest organic pollutants. Under-aeration can reduce efficiency and waste energy. DO sensors give real-time feedback for optimizing energy usage and treatment performance.

3. Environmental Monitoring

Water health is monitored by government agencies and research institutions that deploy DO sensors to lakes, rivers and reservoirs. Continuous monitoring of DO helps detect hypoxia and pollution events.

4. Industrial Applications

For industries such as food processing and pharmaceuticals, DO monitoring is essential to ensuring product quality. Too much oxygen can ruin the taste of beer, while oxygen levels in bioreactors must be controlled to prevent microbial growth.

The Future of DO Sensing

The technology is changing rapidly. The next generation of DO monitoring includes

• IoT sensors for DO: Wireless transmission of data in real-time.

• AI-driven analysis: Predicting oxygen depletion before it happens.

• Integrated Water Quality Platforms: Combining pH, EC and turbidity with DO for holistic monitoring.

The trend for anyone who manages the dissolved oxygen content in water is clear: optical fluorescent DO sensors offer accurate, low maintenance, and intelligent monitoring solutions.

The conclusion of the article is:

Understanding dissolved oxygen is water, is the first step to protecting aquatic life and improving wastewater treatment. To manage oxygen efficiently, selecting the right DO sensor can be critical.

• Electrochemical Sensors are inexpensive but require constant calibration.

• Galvanic Sensors are portable, self-powered and still require maintenance.

• Fluorescence (optical) sensors are the most popular choice in modern applications due to their unmatched accuracy and stability.

The right DO Sensor can make a huge difference, whether you are running a fishery, managing a wastewater treatment plant, or monitoring an artificial lake.

Q1: What is dissolved oxygen in water?
Dissolved oxygen refers to oxygen molecules present in water that are available for aquatic organisms to use.

Q2: Why is measuring dissolved oxygen important?
Because oxygen levels directly impact aquatic life, wastewater treatment efficiency, and overall water quality.

Q3: Which type of DO sensor is best for aquaculture?
Optical DO sensors are best, as they are accurate, stable, and require minimal maintenance.

Q4: How do I calibrate a DO sensor?
Electrochemical and galvanic sensors require regular calibration with air-saturated water or standard solutions, while optical sensors often need much less frequent calibration.

Our fluorescence-based DO sensors, the BGT-WDO(K) and BGT-WDO(K2), with a measuring range of 0–20 mg/L, suitable for most applications.

For more details and pricing, please contact us.