Author: ronnie

Polarographic dissolved oxygen (DO) sensors are essential tools in various fields, including biotechnology, environmental monitoring, and water treatment. These sensors measure the concentration of dissolved oxygen in liquids, providing critical data for process control and quality assurance. Proper handling and maintenance of polarographic DO sensors are crucial for accurate and reliable measurements. This article outlines key steps and best practices for managing these sensors effectively.

Understanding Polarographic DO Sensors

Polarographic DO sensors operate on the principle of electrochemistry. They consist of a cathode (usually made of platinum or gold) and an anode (often silver or silver chloride) immersed in an electrolyte solution and separated from the sample by a gas-permeable membrane. When a voltage is applied, oxygen diffuses through the membrane and is reduced at the cathode, generating a current proportional to the oxygen concentration.

Steps for Effective Handling of Polarographic DO Sensors

1. Initial Setup and Polarization
   • Sensor Connection: Connect the DO sensor to the appropriate controller or meter according to the manufacturer’s instructions. Ensure all connections are secure to avoid signal interference.
   • Polarization: Before using a new sensor or after prolonged storage, it must undergo polarization. This process involves applying a voltage to the sensor, allowing it to stabilize. Typically, polarization can take between 6 to 24 hours. Follow the manufacturer’s guidelines for the specific polarization time required.
2. Calibration
   • Zero Calibration (0% Oxygen): Perform this calibration in an oxygen-free environment. This can be achieved by using a zero-oxygen solution or nitrogen gas. Ensure the sensor reads close to zero nA, indicating no oxygen presence.
   • Span Calibration (100% Oxygen): Calibrate the sensor in an environment with known oxygen concentration, usually air (20.9% oxygen). The sensor should provide a stable reading, typically in the range of 40 nA to 100 nA, depending on the sensor model and conditions.
3. Maintenance
   • Regular Calibration: Regularly calibrate the sensor to ensure accurate measurements. Frequency depends on usage conditions but should generally be done before each measurement series or at least once a week.
   • Membrane and Electrolyte Replacement: Periodically inspect and replace the membrane and electrolyte solution. A damaged membrane or depleted electrolyte can lead to erroneous readings.
   • Cleaning: Clean the sensor regularly to remove any biofouling or debris. Use appropriate cleaning solutions recommended by the manufacturer to avoid damaging the sensor components.
4. Operational Tips
   • Temperature Compensation: Ensure the sensor is equipped with temperature compensation, as oxygen solubility varies with temperature. Many modern sensors include automatic temperature compensation.
   • Sample Handling: Avoid bubbles in the sample, as they can cause fluctuations in oxygen readings. Stir or mix the sample gently to ensure homogeneity.
   • Storage: When not in use, store the sensor in a protective cap filled with a storage solution or in an appropriate dry place. Follow the manufacturer’s recommendations for long-term storage.
5. Troubleshooting
   • Unstable Readings: If the sensor provides unstable or fluctuating readings, check for air bubbles under the membrane, proper sensor polarization, and adequate calibration.
   • Low or No Signal: Ensure the sensor is properly polarized and connected. Check the membrane and electrolyte for any signs of damage or depletion.
   • Slow Response Time: A slow sensor response can indicate membrane fouling or aging. Cleaning or replacing the membrane can resolve this issue.

Conclusion

Handling polarographic DO sensors with care and precision is essential for obtaining reliable data in any application involving dissolved oxygen measurement. By following proper setup, calibration, maintenance, and troubleshooting steps, you can ensure that your polarographic DO sensor provides accurate and consistent results. Regular attention to these details will extend the life of your sensor and enhance the quality of your measurements, ultimately contributing to the success of your operations.

For further information or specific guidelines, always refer to the manufacturer’s manual and support resources.

In the realm of bioprocessing, the volumetric mass transfer coefficient, or kLa, is a critical parameter that measures how effectively oxygen is transferred from the gas phase to the liquid phase in bioreactors. This coefficient is vital for ensuring that cultured cells receive the oxygen necessary for optimal growth and productivity. Here’s a closer look at what kLa entails and how it can be optimized to boost bioprocess efficiency.

Understanding kLa

kLa stands for volumetric mass transfer coefficient, where:

• k is the mass transfer rate at the gas-liquid interface,
• L indicates the transfer is occurring in the liquid phase,
• a represents the surface area available for gas exchange.

The efficiency of oxygen transfer, as indicated by kLa, influences cell health and productivity directly. Insufficient oxygen transfer can lead to reduced cell growth and lower product yields, making kLa optimization a crucial aspect of bioprocess engineering.

Strategies to Optimize kLa in Bioreactors

Improving kLa involves enhancing the conditions and equipment used in the oxygen transfer process. Here are several effective approaches:

1. Increase Agitation Speed

Boosting the agitation speed in bioreactors enhances the mixing and increases the turbulence within the culture medium. This results in a larger surface area for oxygen to dissolve into the liquid, thus increasing kLa.

2. Enhance Aeration

Increasing the aeration rate by pumping more air or pure oxygen into the bioreactor raises the oxygen’s partial pressure, enhancing its solubility and transfer efficiency into the medium.

3. Utilize Pure Oxygen

Switching from air to pure oxygen can dramatically increase the oxygen concentration gradient between the gas phase and the liquid phase, enhancing mass transfer rates.

4. Optimize Impeller Design

Using impellers that are specifically designed for better gas dispersion can increase the effective surface area for mass transfer. Different types and configurations of impellers may be experimented with to find the most effective option for specific bioprocess requirements.

Check out bbi-biotech’s impeller designs in our bioprocess shop.

5. Reduce Liquid Viscosity

A lower viscosity in the liquid medium facilitates better mixing and enhances the dispersion of gas bubbles throughout the liquid. This can be achieved by adjusting the composition of the medium or its temperature.

6. Optimize Bubble Size

Smaller bubbles create a larger surface area relative to their volume, enhancing oxygen transfer. Spargers or diffusers that produce a fine bubble size can significantly improve kLa.

bbi-biotech offers micro spargers with various pore sizes and ring sparger with various hole sizes.

7. Control Environmental Conditions

Factors like temperature and pH can affect the solubility of oxygen in the liquid medium. Maintaining these within optimal ranges ensures higher solubility and better diffusion rates, thus improving the efficiency of oxygen transfer.

Conclusion

Optimizing kLa is essential for maximizing the efficiency of bioreactors by ensuring adequate oxygen transfer to support cell growth and productivity. By applying the strategies outlined above, bioprocess professionals can enhance the performance of their bioreactors, leading to improved outcomes and yields. This focus on efficient oxygen transfer is fundamental to the success and scalability of biotechnological applications.

At bbi-iotech, we are constantly striving to bring innovations and improvements to our bioreactor technologies that elevate operational efficiency and reliability for our valued customers. It’s with great enthusiasm that we announce a significant upgrade in our bioreactor designs, focusing on a key component that is pivotal for sterile operations and overall system performance: the mechanical seal in our bioreactor stirrer shafts.

Introducing Advanced Seal Technology

After a period of thorough evaluation and rigorous testing, we are integrating a state-of-the-art mechanical seal into our bioreactor stirrer shafts. This new seal technology is distinguished by its fully encapsulated design, marking a leap forward in seal solutions.

Key Features and Benefits

• Enhanced Sterile Operations: The seal technology we’ve chosen is specifically designed for sterile applications. It guarantees the highest standards of hygiene and contamination control, which are paramount in bioprocessing and pharmaceutical manufacturing.
• Minimized Cleaning and Maintenance: Thanks to its encapsulated design, the seal greatly reduces the need for regular cleaning and maintenance. This not only cuts down operational costs but also significantly lowers downtime, boosting productivity.
• Durability and Reliable Performance: Engineered for durability, the seal comes with advanced coating options that ensure it withstands the demanding conditions of bioreactor operations. This translates to consistent performance and reliability over time.
• Seamless Compatibility: We have conducted extensive compatibility tests with our bioreactor systems to ensure that these new mechanical seals integrate flawlessly. Stirrer shafts equipped with the new seals can be directly exchanged with older models, eliminating the need for any modifications.

Encapsulated Design: A Game Changer

The hallmark of this new mechanical seal is its encapsulated design, which shields the spring mechanism from direct contact with the process media. This innovative approach significantly diminishes the risk of fouling and accumulation of materials, a common challenge in bioreactors handling media with solids or high viscosity.

We are excited about the potential of this upgrade to set new standards in bioreactor technology and operational excellence. For more information or to discuss how these developments can benefit your operations, please don’t hesitate to get in touch.

At bbi-biotech, we are more than just a supplier; we are your partner in innovation, dedicated to advancing the field of biotechnology together.

Stay tuned for more updates as we continue to innovate and enhance our technologies for your success.