Qualitative Comparision of Optical and Electrochemical Sensors for Measuring Dissolved Oxygen in Bioreactors

• Main Author: Lindblom, Tomas
• Format: Others
• Language: English
• Published: Linköpings universitet, Teknisk biologi 2009
• Subjects: Biochemical process engineering; Biokemisk och bioteknisk processteknik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-17567

In this master thesis, optical dissolved oxygen (DO) sensors are compared to standard electrochemical DO-sensors. The optical sensors are also compared against each other. DO is an important parameter to measure and to control during microorganism fermentation.  A DO-sensor needs to fulfill certain criteria, such as; purposive response time, the ability to show accurate and stable readings without drift over time, have the capability to manage several sterilizations and exhibiting membrane fouling resistance. The reference used to test these parameters was an industrially accepted electrochemical sensor. By comparing the two technologies, optical sensors showed similar abilities to perform regarding response time and drift performance during the longer test runs. But the optical sensors showed a better performance during sterilizations, with less drift in raw value. When using electrochemical sensors as a reference, different brands of optical sensor gave different results when testing for accuracy at different concentration levels. Due to error in the method, tests for fouling were inconclusive. However, membranes from the two kinds of technologies showed an equal hydrophobic character. The two participating optical DO sensors, Mettler Toledo InPro 6990i and Hamilton Visiferm were compared regarding ability to manage sterilizations and generate accurate measuring values at different DO concentrations. The two sensor brands showed an equal behavior during the fifteen test sterilizations. The Mettler Toledo InPro 6990 had better abilities to follow the linear behavior of the electrochemical reference sensor. While the  Hamilton Visiferm sensor differed at most 3.5% units from the electrochemical reference values. Hamilton Visiferm was tested with analogue signal, which gave a noise problem. When using digital signal the noise disappeared. The goal of this study was to recommend a sensor, for Belach Bioteknik AB, and the recommendation would be Hamilton Visiferm, for being practical as well as reasonable priced without renounce of measuring quality.