Dissolved Oxygen Meters

Dissolved Oxygen Meters

Water quality measurement is performed in different ways across industries and measuring dissolved oxygen is one of them.

Dissolved oxygen is an indicator of the health of the ecosystem. When more organisms die and bacterial growth in water will spike. This will consume the dissolved oxygen causing the formation of dead zones, thereby killing aquatic plants and animals.

A low level of dissolved oxygen may also indicate high levels of pollution. The dissolved oxygen levels in water is measured using special types of devices known as dissolved oxygen meters. These meters are used in water and wastewater treatment applications and have been successfully tested for their desired performance.

Why is Dissolved Oxygen Measurement Important for Wastewater Treatment?

Solid and liquid waste is separate as a part of wastewater treatment. This separation is completed through two stages – primary and secondary treatment. In the primary treatment, large solids are removed from wastewater and dissolved and suspended solids are removed during the secondary treatment. Sewage microorganisms are introduced to the wastewater in the secondary treatment.

This process is usually accomplished using an aeration tank or the trickling filter. Sewage microorganisms are introduced to sludge and mixed with air. This air activates microorganisms and help them convert organic wastes into inorganic byproducts. Dissolved oxygen (DO) is used for this purpose. If DO concentration is low then these microorganisms may be dead and do not perform as required. Thus, DO concentration in water is tested regularly in wastewater treatment plants using dissolved oxygen sensor.

Factors That May Affect DO Concentration in Water

The DO concentration in water may be affected by the following factors.

  • Temperature: DO in water may be affected by temperature variations. The DO concentration may get low at high temperatures and vice-versa.  
  • Salinity: Many solid wastes produced during processes may contain high level of salt. This salt carries charge, which may be attracted to water molecules in the solution 
  • Pressure: Dissolved oxygen is affected by atmospheric pressure. When the atmospheric pressure increases the partial pressure of oxygen increases and vice-versa.  
  • Humidity: DO level in water may be affected by water vapor or humidity. The partial pressure of oxygen increases with increasing humidity, and vice versa. 

Methods of Measuring Dissolved Oxygen in Water and Wastewater Plants

Dissolved oxygen is measured in various ways, including iodometry, colorimetry, and electroanalytical methods. In this, iodometry and colorimetry are often performed in lab settings, and are one-time measurement techniques, with limited possibilities. However, most process owners rely on electroanalytical methods for oxygen measurement. They feature polarographic and galvanic oxygen probes. These oxygen probes work on the principle of oxidation and reduction.

These probes are attached to dissolved oxygen meters. There are two types of meters used – portable meters and benchtop meters. Among these, portable meters are compact sized and can be used anywhere. These meters vary in testing method, function, and design. Our selection features portable dissolved oxygen sensors, which have been extensively used in water and wastewater treatment plants.

How Do Dissolved Oxygen Meters Work?

The dissolved oxygen meters feature a probe or sensor and permeable or semipermeable membrane. The amount of oxygen diffuses across a membrane into a sensor or probe. When the oxygen reaches the sensor, a reduction reaction occurs, and an electrical signal is produced. This signal produces a readable measurement on a meter.

How to Choose the Right Dissolved Oxygen Meter for Your Application

Choosing the right DO meter can be a daunting task. The following tips will be helpful in this context.

  • Application Requirements: Where do you plan to perform the dissolved oxygen measurement –in the lab or the field? How much water volume will be measured? You considerations would depend on these answers.
  • Ease of Use: Although all DO meters are designed to measure the dissolved oxygen, they may not be easy to use. Some may require specialized training and need to be handled only by experts, so, ensure to focus on the ease of use whenever choosing the model.
  • Data Accuracy: Dissolved oxygen measurements will help users to decide upon the course of water treatment. So, you need to check on the data accuracy prospect. You can do some online research and read the technical information carefully to see the movement of DO meter required to make accurate measurements.
  • Total Cost of Ownership: This consideration would involve the acquisition price and cost of maintenance.

Maintenance Tips for Dissolved Oxygen Meters

Although designed for challenging work environments, these dissolved oxygen meters must be maintained properly to ensure their lasting performance. The following are some maintenance tips that would help maintain the dissolved oxygen meter for water treatment in good condition. 

  • Calibrate the Dissolved Oxygen Meter: This can be done using an appropriate calibration solution. Ensure to calibrate the device to the level of precision required for your application by following the recommendations made by the manufacturer.
  • Clean the Dissolved Oxygen Meter: The dissolved oxygen probe is inserted into the sample for testing. Hence, it must be cleaned with distilled water after every use. Do not use tap water or unfiltered water for cleaning because it can affect the performance of the electrode. If you observe any type of remnants or residues on the dissolved oxygen probe, then clean it using a brush or any other mild cleaning agent. Avoid using harsh cleaning agents or items that can scratch the sensor. 
  • Check the Levels of Electrolyte Solution: Check the level of electrolyte solution in the probe. If it has ended, it is advisable to refill it following the manufacturer's guidelines. Electrolyte levels may reduce due to evaporation or leakage, sometimes it may drop over time.
  • Store the Device Properly: Store the dissolved oxygen meter properly when not using it. Ensure to store the dissolved oxygen probe in electrolyte-filled storage cap or the manufacturer's recommended storage solution to prevent the sensor from drying out and losing accuracy.
  • Inspect the Membrane: An essential component of the DO probe is the membrane surrounding it. Check it frequently for any noticeable signs of wear, fouling, or damage. If you still notice any problems with the membrane, replace the membrane as directed by the manufacturer.
  • Check on Temperature Compensation: This is one of the vital features to ensure the accurate reading and reliable measurements of dissolved oxygen in water especially when there is a variation in the temperature of water. When there is variation in dissolved oxygen levels, it is important to ensure that the probe’s temperature compensation is functioning correctly. For precise readings, accurate compensation is necessary.
  • Replace Sensors: Sensors are prone to rupture or lose accuracy over time. The lifespan of several probes that have replaceable sensors should be taken into consideration, and the sensor must be replaced as needed.
  • Follow Manufacturers Guidelines: Always refer to the detailed routine maintenance guidelines your DO probe's manufacturer has provided. It's possible that different probes have particular needs and requirements.

Water treatment is essential to ensure the availability of pure water to a large population. This water treatment is performed at different levels. To ensure proper fulfillment, it must be performed using the right quality equipment. Being at the forefront of water treatment technologies for several years, we understand the importance of offering quality equipment. This is why we have carefully included only the best equipment in this category and across all categories of water treatment equipment.

These equipment are included after much careful consideration and proven to perform in their work environments.  With so many product options under this and each category, the selection of the right equipment can be overwhelming. Our experts will work closely with you and guide you through all phases of selection. Contact us today to discuss the product listed on this page or other categories. We would be happy to serve you.

Frequently Asked Questions

1. How do I calibrate a dissolved oxygen meter?

The sensor should be immersed in a calibration solution with a specific oxygen level during calibration. This solution should be at the same temperature as the sample you are going to evaluate and should not have any dissolved oxygen. The meter is thus modified to correspond to the expected value, guaranteeing accuracy in measurements. After being taken out of the span-point solution, the probe is rinsed with either distilled or deionized water.

2. What are the units of measurement for dissolved oxygen?

Milligrams per liter (mg/L), parts per million (ppm), and percent saturation (%) are the most popular units for dissolved oxygen measurements. The amount of oxygen present as a percentage of the maximum quantity of oxygen that can dissolve in the water at a specific temperature and pressure is known as percent saturation.

3. What are the common sources of measurement errors in dissolved oxygen meters?

Common sources of error include temperature variations, calibration errors, sensor contamination and fouling, electrode deterioration, air bubbles on the sensor membrane or in the sample, drifts, etc.

4. Can dissolved oxygen meters be used in both freshwater and saltwater environments?

Yes, dissolved oxygen meters can work in both freshwater and saltwater environments depending on the design and specifications. As long as the right equipment is used, proper maintenance and calibration are performed, and specific conditions of the environment are taken into consideration, this versatile tool is used in both saltwater and freshwater.

5. Can dissolved oxygen meters be used in both freshwater and saltwater environments?

Yes, dissolved oxygen meters can be used in both types of environments. However, the DO meter used in saltwater is made of materials with a coating that resist corrosion.

6. Can a turbulent application or bubbles affect DO reading?

Yes, bubbles can affect the reading and would probably fluctuate or settle on, the membrane itself.

7. What factors can affect the accuracy of DO readings?

There are various factors affecting the accuracy of dissolved oxygen in a sample, including salinity, pressure, temperature, and altitude. Cold water possesses more dissolved oxygen than hot water.

8. What is a BOD?

BOD is a measurement of how much oxygen is utilized by bacteria during the process of decomposition of organic waste components. For a standard test, DO measurements are typically taken at the start and finalization of a five-day incubation period.