Microbial electrochemical systems applications

In this section, we discuss in detail how the selection of various experimental parameters affects each of these conditions. One of the first studies on EIS measurements in MXC applications by Strik et al. [29] covers some of these conditions very well, but we provide an expanded explanation here. While all these conditions are especially difficult to fulfill in a typical electrochemical cell, the conditions used in MXCs further exacerbate the problem. For example, it is known that polarization curves for microbial anodes exhibit nonlinear, Nernstian responses [30]. Thus, there are regions in the polarization curve where the system may not behave linearly even when small amplitudes are applied. The irreversibility of the enzymatic responses also leads to regions where finiteness is not met (Fig. 8.6). These cases would run also into difficulties in terms of the signal-to-noise ratio when small amplitudes are applied at potentials on the saturation region of the polarization curve. Similarly, as MXCs are biological reactors and can have changes in microbial responses due to small perturbations outside the conttol of researchers, conditions of both stability and causality are difficult to fulfill. 

Two other specific areas must be mentioned in this introduction the emerging fields of microbial fuel cells and microfluidic fuel cells. In some ways these two new fields can be considered embodiments of low-temperature fuel cells operating at the extreme size scales - microbial fuel cells have their genesis in the exploration of wastewater treatment in electrochemical and bioelectrochemical systems. These proposed applications are by their nature enormous in size, with reactor volumes measured in the tens of cubic meters (many orders of magnitude larger than the conventional low-temperature fuel cells). 

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