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  • Celecoxib Supplier Amongst these applications MFCs have gain

    2018-10-26

    Amongst these applications, MFCs have gained attention as a new technique for microbial biosensors, which are analytical devices that combine biological recognition components with physicochemical signal transducers to convert the response to the analyte into a measurable signal [5,37,41]. Unlike optical transducers, producing optical properties such as adsorption, fluorescence, luminescence or refractive index, the transductive Celecoxib Supplier of MFC biosensors converts biological responses to electrical signals [6]. MFC biosensors have competitive advantages including physical robustness, low cost, fast response, easy handling and portability [28,35]. So far, potential applications of MFC biosensors have focused mostly on environmental monitoring, which include BOD (biochemical oxygen demand) and VFA (volatile fatty acid) measurements, dissolved oxygen monitoring, and toxicity detection [1,4,7,21,39,47]. In an MFC, mono- or mixed species of microorganisms are attached to an anode in the form of biofilm (transducer) and the performance of an MFC biosensor greatly depends on the physiological state of the anodic biofilm, which is a dynamic system that changes its status upon the given conditions. Although many of the studies on MFC biosensors have employed single species due to their consistent response, using pure cultures is limited by the narrow range of utilisable substrates, which results in a rather narrow spectrum of substrate detection capacity in comparison with mixed cultures; this is in addition to the propensity of the mono-culture to get contaminated. It was reported that MFC biosensor produced lower maximum current (peak height) when real wastewater was tested compared to pure substrates such as acetate [9]. In this respect, using mixed cultures for MFC biosensors was suggested for the purpose of environmental monitoring [16]. Meanwhile, it is well understood that different substrates potentially have an impact on the structure and composition of the microbial community, which subsequently influences the MFC performance [14,20,22,30]. Furthermore and in addition to performance in terms of power generation and coulombic efficiency, the integral composition of the bacterial community enriched under a specific feedstock condition has a potential to acclimate to other substrates depending on the initial substrate type [3,48]. Therefore these various responses caused by different initial feedstock conditions could influence the selectivity, sensitivity and response time of an MFC biosensor. Further to these findings, it was successfully shown that a change of feedstock, after the initial maturing period with a starting feedstock, altered the MFC anode microbial composition [48]. However this particular study reported slow responses due to the relatively small anode electrode size (42cm2) compared to the working volume of the anode chamber (250mL) and batch feeding operation (10–17days for each feeding cycle). Continuous feeding operation could be a clearer and faster way to see the progress of the MFC anodic biofilm change. Continuous flow is also able to facilitate non-cumulative steady states as previously shown [27]. Bacterial cell metabolic adaptation would happen after repeated changes with exposure to a new substrate for prolonged periods, which could diminish the effect of initial carbon sources. A question still remains about how this transition would proceed in terms of biofilm metabolic activity and its power generating performance. Nevertheless, retaining a stable and reproducible response to analytes from anodic biofilms, is one of the key requirements when implementing the MFC technology to bio-sensing. The objective of this study was therefore to (1) understand the change of biofilm metabolic activity and power generating performance under different feedstock conditions, and (2) investigate the feasibility of obtaining stability and reliability of MFC anodic biofilms during the changes. For the current study, MFCs were fed continuously with two different substrates, acetate (carboxylic acid, monomer, non-fermentable) and casein (protein, polymer, hydrolysed into monomers). These two substrates were selected as exemplars of two completely different chemical compounds, in terms of their molecular structure, with one representing an accessible short-chain-sugar-based carbohydrate (acetate) and the other representing a more complex long-chain-sugar-based protein (casein).