Abstract: 1. Introduction and Motivation Considering the global climate change, the efficient use of clean and renewable sources of energy is one of the key research areas. In this context, the biological production of methane and other combustible biogas produced by anaerobic fermentation of organic wastes is gaining growing importance. These fermentation processes attract more and more interest mainly due to the possibility to use different types of residues like food waste, dairy wastes and many other organic wastes as feeding substrates. However, efficient biomass conversion to biogas is only possible if the process parameters taking direct influence on the fermentation process are continuously and reliably monitored. This allows efficient process control. One of such key process parameters are the volatile fatty acids (acetic, propionic, butanoic) formed during the biomass conversion process. The reliable monitoring of such organic acids and other volatile organic compounds (VOCs) gives valuable information and their analysis even at low concentrations ( 〈 2000 ppm) allows to model the actual microbial state and to adapt the feeding to keep their concentration and their inhibiting influence on the fermentation process low. Conventionally, the analysis of the organic acid composition in anaerobic fermentation processes is done by sophisticated methods like gas chromatography [1], infrared spectroscopy [2] , and high pressure liquid chromatography (HPLC) [3]. However, the major disadvantages of these methods are their complicated and time consuming sample pre-treatment routines and high costs. In this paper, an automated measuring system developed by combining a silicon rubber membrane based carrier gas probe (Fig. 1) with a thermo-cyclically operated metal oxide gas sensor array [4] is introduced. This automated system might enable in-situ monitoring of different VOCs developing during the bio-fermentation processes in time periods of about one hour. 1. Method of VOC monitoring Metal oxide gas sensors (MOGs) are well established as gas sensing devices for monitoring of VOCs and oxidizable gases like CO, H 2 and CH 4 . Thus, before measurement of dissolved VOCs, CH 4 and other to cross-sensitivity contributing gas components present in the biogas fermentation sample must be driven out. In a first step, a small amount of the fermentation liquid (about one liter) is extracted from the main reactor and its pH is shifted to an alkaline value by dosage of potassium hydroxide. This allows transformation of the dissolved organic acids to the dissociated state and enables purging out CH 4 , H 2 and all other non-acidic, physically dissolved gas components contributing to the sensor signal, by a high flow of N 2 . Then, pH is shifted to a value near or even lower than the pKa value of the organic acids by dosage of phosphorous acid. Now the dissolved organic acids are in the undissociated molecular state and equilibrate with the gas state (Henry´s law). This enables the uptake of molecular dissolved organic acids from the liquid state into the constant flow of synthetic air (carrier gas: 5ml/min) by permeation through the gas permeable silicon rubber membrane of the gas carrier probe. By the help of the carrier gas the organic acids are transported to the metal oxide gas sensor array (Fig 1a) for analysis. 1. Results and Discussion Several SnO 2 /additive gas sensing composites have been prepared and the most interesting candidates with respect to their remarkably high sensitivity and most characteristic conductance vs. time profile (CTP) shapes when operated in thermocyclic mode [4,5] will be reported. When the carrier gas probe is immersed in acetic acid/deionized water admixtures some metal oxides show characteristic CTP-shapes (Fig. 1b) representing the individual surface reaction processes with acetic acid. In addition, some first experiments with real fermentation liquids resulted in some unexpected gas developments with pH and time well indicated by characteristic CTP-changes, which will highlight the presentation. 1. Conclusions and outlook By some extended in-situ monitoring experiments of acetic acid in deionized water as a model substance using a gas carrier probe combined with a 4-fold metal oxide sensor array, several metal oxide materials could be identified as good candidates for monitoring of organic acids in biogas fermentation processes. Monitoring experiments in real fermentation samples and analysis of the CTPs yielded gas formation changing with pH and time. These gas formation processes have to be referenced by simultaneous Gas Chromatograph-Mass Spectrometry (GC-MS) analysis and the results will be reported as well in context with the MOG sensitivity data. 1. Acknowledgement This work is part of the EBIPREP collaboration project (www.ebiprep.eu/). It is financed by the EU International Programme INTERREG V Oberrhein 2017-2020. References [1] V. Diamantis, P. Melidis, A. Aivasidis; Continuous determination of volatile products in anaerobic fermenters by on-line capillary gas chromatography, Analytica Chimica Acta 573-574(2006)189-194 [2] H.M. Falk, P. Reichling, C. Andersen, R. Benz; Online monitoring of concentration and dynamics of volatile fatty acids in anaerobic digestion processes with mid-infrared spectroscopy, Bioprocess Biosyst Eng (2015) 38:237-249 [3] P.v. Zumbusch, T. Meyer-Jens, G. Brunner, H. Märkl; On-line monitoring of organic substances with high-pressure liquid chromatography (HPLC) during the anaerobic fermentation of waste-water, Appl Microbiol Biotechnol (1994)42:140-146 [4] K. Frank, V. Magapu, V. Schindler (†), H. Kohler, H.B. Keller, R. Seifert; Chemical analysis with tin oxide gas sensors: choice of additives, method of operation and analysis of numeric signal, 7th East Asian Conference on Chemical Sensors, Dec. 3-5, 2007, Singapore, SENSOR LETTERS 6 (2008) 908-911. [5] Navas Illyaskutty, Jens Knoblauch, Matthias Schwotzer, Heinz Kohler; Thermally modulated multi sensor arrays of SnO2/additive/electrode combinations for enhanced gas identification, Sensors and Actuators B 217 (2015) 2-12 Figure 1

Abstract: This work aims to provide a detailed understanding of the challenges related to the computation of the relative static permittivity and electrolytic conductivity of a sample medium from its impedance response recorded with interdigitated electrode (IDE) geometries. Within the scope of the study, impedance data has been measured and evaluated for a total of nine sample media using two distinct IDE geometries. Particular emphasis is laid upon the compensation of parasitic influences affecting the impedance response. With the raw data supporting this study fully disclosed, the reader is offered the opportunity to comprehensively retrace the evaluation procedure proposed in the text.

Abstract: We demonstrate a novel impedimetric approach providing unprecedented insight into characteristic properties of dielectric thin films covering electrode surfaces. The concept is based on the joint interpretation of electrochemical impedance spectroscopy (EIS) together with dielectrometry (DEM) whose informative value is mutually interconnected. The advantage lies in the synergistic compensation of individual shortcomings adversely affecting conventional impedimetric analysis strategies relying exclusively on either DEM or the traditional EIS approach, which in turn allows a reliable determination of thickness and permittivity values. The versatility of the method proposed is showcased by an in‐situ growth‐monitoring of a nanoporous, crystalline thin film (HKUST‐1) on an interdigitated electrode geometry.

Abstract: 1. Introduction and Motivation Considering the global climate change, the efficient use of clean renewable energy source is one of the key research areas. In this context, the biological production of methane and other biogas produced by anaerobic fermentation of organic wastes is gaining importance. These fermentation processes attract more interest mainly due to the possibility to use different organic wastes as feeding substrates. However, efficient biomass conversion to biogas is only possible if the process parameters taking direct influence on the fermentation process are continuously and reliably monitored. This allows efficient process control. Some of key process parameters are the volatile fatty acids (VFAs) like acetic, propionic, butanoic acids formed during the biomass conversion process. The reliable monitoring of VFAs and other volatile organic compounds (VOCs) gives valuable information and their analysis at low concentrations ( 〈 2000 ppm) allows to model the actual microbial state and to adapt the feeding to keep their concentration and their inhibiting influence on the fermentation process low. Conventionally, the analysis of the VFAs in anaerobic fermentation processes is done by sophisticated methods like gas chromatography [1], infrared spectroscopy [2] , and high pressure liquid chromatography (HPLC) [3]. However, the major disadvantages of these methods are their complicated and time consuming sample pre-treatment routines and high costs. In this paper, an automated measuring system developed by combining a silicon rubber membrane-based carrier gas probe (Fig. 1) with a thermo-cyclically operated metal oxide gas sensor array [4] is introduced. This automated system might enable in-situ monitoring of different VOCs developed during the bio-fermentation processes in time periods of about one hour. 2. Method of VOC monitoring Metal oxide gas sensors (MOGs) are well established as gas sensing devices for monitoring of VOCs and oxidizable gases like CO, H 2 and CH 4 . Thus, before measurement of dissolved VOCs, CH 4, H 2 and other cross-sensitivity contributing gas components present in the biogas fermentation sample must be driven out. In a first step, a small amount of the fermentation liquid (about one liter) is extracted from the main reactor and its pH is shifted to an alkaline value by dosage of KOH. This allows transformation of the dissolved VFAs to the dissociated state and enables purging out CH 4 , H 2 and all other non-acidic, physically dissolved gas components, by a high flow of N 2 . Then, pH is shifted to a value near or even lower than the pKa value of the VFAs by dosage of H 3 PO 4 . Now the dissolved VFAs are in the undissociated molecular state and equilibrate with the gas state (Henry´s law). This enables the uptake of molecular dissolved VFAs from the liquid state into the constant flow of synthetic air (carrier gas: 5ml/min) by permeation through the gas permeable silicon rubber membrane of the gas carrier probe. By the help of the carrier gas the VFAs are transported to the metal oxide gas sensor array (Fig 1a) for analysis. 3. Results and Discussion In a screening process several additive/SnO 2 gas sensing composites have been prepared and the most interesting candidates with respect to their remarkably high sensitivity and most characteristic conductance vs. time profile (CTP) shapes when operated in thermocyclic mode [4,5] will be reported. When the carrier gas probe is immersed in acetic acid/deionized water admixtures some metal oxides show characteristic CTP-shapes (Fig. 1b) representing the individual surface reaction processes with acetic acid. 4. Conclusions and outlook By some extended in-situ monitoring experiments of acetic acid in deionized water as a model substance using a gas carrier probe combined with a 4-fold metal oxide sensor array, several additive/SnO 2 materials could be identified as good candidates for monitoring of organic acids in biogas fermentation processes. Monitoring experiments in real fermentation samples and analysis of the CTPs yielded gas formation changing with pH and time. Some CTPs sampled at real fermentation liquid (pH 3) and referenced by the CTPs at pH 8 allowed the conclusion that the VFAs formed by the fermentation process can be really detected by the metal oxide sensor array. But to rule out any doubts, these gas formation processes have to be referenced by simultaneous Gas Chromatograph-Mass Spectrometry (GC-MS) analysis and these results will be reported as well in context with the MOG sensitivity data. 5. Acknowledgement This work is part of the EBIPREP collaboration project (www.ebiprep.eu/). It is financed by the EU International Programme INTERREG V Oberrhein 2017-2020 References [1] V. Diamantis, P. Melidis, A. Aivasidis; Continuous determination of volatile products in anaerobic fermenters by on-line capillary gas chromatography, Analytica Chimica Acta 573-574(2006)189-194 [2] H.M. Falk, P. Reichling, C. Andersen, R. Benz; Online monitoring of concentration and dynamics of volatile fatty acids in anaerobic digestion processes with mid-infrared spectroscopy, Bioprocess Biosyst Eng (2015) 38:237-249 [3] P.v. Zumbusch, T. Meyer-Jens, G. Brunner, H. Märkl; On-line monitoring of organic substances with high-pressure liquid chromatography (HPLC) during the anaerobic fermentation of waste-water, Appl Microbiol Biotechnol (1994)42:140-146 [4] K. Frank, V. Magapu, V. Schindler, H. Kohler, H.B. Keller, R. Seifert; Chemical analysis with tin oxide gas sensors: choice of additives, method of operation and analysis of numeric signal, 7th East Asian Conference on Chemical Sensors, Dec. 3-5, 2007, Singapore, SENSOR LETTERS 6 (2008) 908-911. [5] Navas Illyaskutty, Jens Knoblauch, Matthias Schwotzer, Heinz Kohler; Thermally modulated multi sensor arrays of SnO2/additive/electrode combinations for enhanced gas identification, Sensors and Actuators B 217 (2015) 2-12 Figure 1

Abstract: Fully exploiting the potential of enzymes in cell‐free biocatalysis requires stabilization of the catalytically active proteins and their integration into efficient reactor systems. Although in recent years initial steps towards the immobilization of such biomolecules in metal–organic frameworks (MOFs) have been taken, these demonstrations have been limited to batch experiments and to aqueous conditions. Here we demonstrate a MOF‐based continuous flow enzyme reactor system, with high productivity and stability, which is also suitable for organic solvents. Under aqueous conditions, the stability of the enzyme was increased 30‐fold, and the space–time yield exceeded that obtained with other enzyme immobilization strategies by an order of magnitude. Importantly, the infiltration of the proteins into the MOF did not require additional functionalization, thus allowing for time‐ and cost‐efficient fabrication of the biocatalysts using label‐free enzymes.

Abstract: In recent years, 3D printers developed rapidly from an expensive niche product used mainly by architects and designers into a versatile tool for engineers helping them to quickly realize and test new ideas. While most of the reported examples still focus on the use of 3D‐printed parts as mechanical but chemically inert tools, we developed a 3D‐printed modular reactor system which allows the fast implementation and testing of enzyme cascades. 3D printing offers several advantages in this context, as complex fluidic structures that cannot be fabricated by other methods can be generated, and the printed reactors are easily scalable in order to adjust their size to specific reaction parameters. Using a so‐called PolyJet technique, highly porous monolithic enzyme carriers were printed and directly UV‐cured from acrylate monomers, allowing simple immobilization of enzymes in a subsequent step. The enzyme immobilisates were fixed in a 3D‐printed housing with integrated fluid distributors forming a compact module to conduct a biotransformation step. Several of such modules can be connected in series to a pumping and analyzing system. A model cascade connecting two enzyme transformation modules, the first containing Glucose Oxidase and the second containing Horseradish Peroxidase, was operated using a commercial FPLC system for flow control and UV–Vis detection of the generated product. In order to adjust the temperature, a Peltier‐based tempering jacket for the enzyme transformation modules was designed. In addition, a flow‐through pH regulation module was developed, based on an electrochemical principle which allows unidirectional pH changes without the need for membranes or discharge of partial fluid streams. Except for the electrodes, also the pH regulation module was fabricated by 3D printing.