Electrochemical enzyme-based biosensor array for monitoring of organic acids and ethanol in biogas processes
In light of steadily increasing energy demand and irreversible exhaustion of fossil fuels, further expansion of renewable energy sources is continually gaining importance. Utilization of biomass, as a widely available energy carrier, is capable of providing great contribution to sustainable energy s...
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|Summary:||In light of steadily increasing energy demand and irreversible exhaustion of fossil fuels, further expansion of renewable energy sources is continually gaining importance. Utilization of biomass, as a widely available energy carrier, is capable of providing great contribution to sustainable energy supply. The efficient production of biogas, however, calls for an improved biomass supply chain. Economic operation of biogas plants depends in particular on reliable process monitoring. Often, process disturbances are accompanied by fluctuations in the concentration profile of some intermediates produced during the anaerobic fermentation process. Nowadays, the focus has mainly been set on volatile fatty acids (such as acetate and propionate) as an indicator for imbalanced process conditions and only little account has been taken to the relevance of other organic acids and alcohols, like lactate, formate and ethanol.
In this work, an electrochemical enzyme-based biosensor array for simultaneous determination of D-lactate, L-lactate, formate and ethanol is developed. The amperometric sensing principle is based on two enzymes in each case: an analyte-specific NAD+-dependent dehydrogenase combined with a diaphorase from Clostridium kluyveri. The latter converts its substrate Fe(CN)63- to Fe(CN)64-, which generates a concentration-dependent current by oxidation at an polarized electrode. Enzymes were immobilized by chemical cross-linking with glutaraldehyde on platinum thin-film electrodes. The optimization of the biosensor performance has been investigated in regard to enzyme loading, glutaraldehyde concentration, cofactor concentration (NAD+ and Fe(CN)63-), pH value and temperature. The potential for repeated and long-term application has been proven by evaluation of operational and storage stability. Typically, enzyme-based
biosensors are characterized by a high specificity due to the remarkable properties of enzymes as biological recognition element. Measurements in real samples, however, are prone to interfering effects by other electroactive species in the sample solution. The specificity of the biosensing system is determined in response to various interfering compounds and results reveal no cross-talk effects during simultaneous measurement of the four different analytes of interest. Successful practical performance for rapid and on-site analysis, has been demonstrated by quantification of D-lactate, L-lactate, formate and ethanol in various feedstocks (maize- and sugar cane silage) and spiked fermentation samples from three industrial biogas plants. Good correlation is obtained for results determined by the biosensor array in comparison to conventional commercial analytical methods applied (photometry and gas chromatography). In contrast to these techniques, the biosensor array offers the advantages of facile on-site application with a portable measurement set-up, rapid analysis time by simultaneous operation and
application in untreated samples. The measuring system has also been applied for long-term monitoring of a lab-scale biogas reactor (0.01 m3) for a period of two months. Regular analysis of alcohol- and organic acid levels provides a beneficial supplementation to standard monitoring parameters, like biogas production, methane yield, pH and temperature. This additional information can help to identify changes in the microbial methane formation and potentially indicate upcoming imbalances at an early stage.
For improved practical implementation of the developed biosensor array, the required cofactors have been co-immobilized on the sensor surface of screen-printed carbon electrodes. Modification with graphene oxide enables the establishment of a reagent-free biosensing system. Such biosensors can be manufactured economically by thick-film technology and used as disposable test strips for simplified on-site monitoring of several key intermediates in the biogas fermentation medium.|
|Physical Description:||160 Pages|