The current installations of sensors in the liquid phase in digesters are usually not sufficient for the fast detection of disturbances. Thus, the application of strategies for process control is restricted. In this paper, multiparameter (micro-) sensors as novel process analytical tools are introduced, which are coupled with wireless data transmission and are designed for an easy integration into digesters. Furthermore, the combination with a lance-based sampling system, which enables sampling in the core of the liquid phase, is described. The monitoring and sampling devices allow for the measurement at various positions in the liquid phase for the purpose of the identification of gradients. Three case studies were performed: (i) at an open hydrolysis basin, (ii) a mid-sized biogas plant with a concrete roof, and (iii) a larger biogas plant equipped with a flexible roof. Online measurements of the redox potential and offline analysis of the dry matter, ammonia, and acetic acid concentrations indicate plant-specific gradients, which appear in the liquid phase. Thus, the concept is not only suitable to improve the monitoring in digestion processes but also to identify the most suitable locations for installing sensors and sampling ports for a fast detection of process disturbances.

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.

This work describes the development and application of different lance-based monitoring systems coupled to an integrated multiparameter sensor probe for the spatial investigation of the liquid phase in biotechnological processes. Miniaturized electrochemical sensors are integrated into a housing, which is fixed at the head of a lance, both made of stainless steel. It can be moved inside a reactor in horizontal direction by the lance itself and in vertical direction by a flexible rope, which is connected to the sensor probe. Inserting the sensor unit directly into the liquid phase of a fermenter, e.g. in laminar processes like biogas and beer production, coupled with multiposition measurements allows to obtain space and time resolved data. The monitored parameters are the pH value, the redox potential, the temperature, and the concentration of dissolved carbon dioxide. Wireless data transfer is realized by means of radio technology with the virtual control center RAMOC (Radio Aided Monitoring) of the company innotas GmbH. Results of the

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