Abstract
The conversion of C1 gas feedstock, such as carbon monoxide (CO), to useful platform chemicals has attracted considerable interest in industrial biotechnology. One conversion method is electrode-based electron transfer to microorganisms using bioelectrochemical systems (BESs). In this BES system, acetate is the predominant component of various volatile fatty acids (VFAs). To appropriately separate and concentrate the acetate produced, a BES-type electrodialysis cell with an anion exchange membrane was constructed and evaluated under various operational conditions, such as applied external current, acetate concentration, and pH. A high acetate flux of 23.9 mmol/m2∙h was observed under a −15 mA current in an electrodialysis-based bioelectrochemical system. In addition, the initial acetate concentration affected the separation efficiency and transportation rate. The maximum flux appeared at 48.6 mmol/m2∙h when the acetate concentration was 100 mM, whereas the effects of the initial pH of the anolyte were negligible. The acetate flux was 14.9 mmol/m2∙h when actual fermentation broth from BES-based CO fermentation was used as a catholyte. A comparison of the synthetic broth with the actual fermentation broth suggests that unknown substances and metabolites produced from the previous bioconversion process interfere with electrodialysis. These results provide information on the optimal conditions for the separation of VFAs produced by C1 gas fermentation through electrodialysis and a combination of a BES and electrodialysis.
Highlights
The biological conversion of industrial waste gases containing carbon dioxide and carbon monoxide are being highlighted to reduce the emissions of greenhouse gases and simultaneously produce the building blocks of fuel and more useful commodity chemicals [1,2]
The changes in acetate concentration in both the anode and cathode chambers were examined while various currents (−5 to −15 mA) were applied to the cell (Figure 2)
The results show that approximately 20% less acetate in the fermentation broth (i.e., effluent from the results show that approximately 20% less acetate in the fermentation broth is transported to the anode chamber than the synthetic solution, former electrosynthesis process) is transported to the anode chamber than the synthetic solution, even when the particulates were removed by centrifugation (Figure 5B)
Summary
The biological conversion of industrial waste gases containing carbon dioxide and carbon monoxide are being highlighted to reduce the emissions of greenhouse gases and simultaneously produce the building blocks of fuel and more useful commodity chemicals [1,2]. Im et al (2018) reported that a bioelectrochemical system (BES) could compensate for the limitation of natural biological CO conversion and enhance the production of volatile fatty acids [3]. The applied potential of the BES supplies reducing power for autotrophic microorganisms and improves the yield of C1 gas conversion and cell growth [4,5,6,7,8]. The metabolites produced from BES-based C1 fermentation may contain acetate as well as various volatile fatty acids (VFAs) and alcohols [9,10]. Additional separation processes are needed to Energies 2018, 11, 2770; doi:10.3390/en11102770 www.mdpi.com/journal/energies
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