Abstract. For the investigation and characterisation of liquid media with microorganisms, electrochemical sensors are typically used. Usually the microorganisms are part of the process or cannot be excluded for different reasons. This paper describes the application of various electrodes, which are partly miniaturised and combined with multi-sensor systems for several applications in processes containing microorganisms. The application in industrial bioprocesses like beer brewing and biogas production, and in paper manufacturing, is described. The performance of the multi-sensor systems, and thus their suitability for a contribution to improved process monitoring, is evaluated. The multi-sensor systems represent an interesting tool to enhance monitoring capacities at installed systems without the necessity for huge port installations and offer the possibility to monitor the spatial distribution of gradients. The developed systems presented here allow location-independent measurements in process plants with a variable positioning of the sensors in the industrial reactors.