Towards high carbon conversion efficiency by using a tailored electrodialysis process for in-situ carboxylic acids recovery

Production of carboxylic acids from anaerobic fermentation has gained increasing attention. However, acidogenic fermentation is still facing challenges such as low yield of carboxylic acids and difficulties in product recovery and purification. The emission of acidogenic off-gas CO2 leads to a reduced carbon recovery (∼70%) and also increases the carbon footprint of the anaerobic treatment process. In this study, a tailored electrodialysis stack was integrated with a fermenter to recover the products and hence to improve quantity and quality of the produced carboxylic acids. Three levels of currents, i.e., 0.4, 1, and 4 A (T1, T2, and T3), were applied during electrodialytic separation of carboxylic acids and 12 cycles of electrodialysis were carried out to evaluate the performance of the integrated system. Results showed that different degrees of carboxylic acids removal led to varied impacts on the yield of carboxylic acids, economic viability, and the instability of microbial community. Compared with the case without coupling electrodialysis process, the carbon conversion rate increased by 28.04% in T3, which was due to the reuse of inorganic carbon introduced by a tailored electrodialysis process. After 12 cycles of fermentation, the percentage of Clostridiales finally increased from 0.11% (inoculum) to 31.15% in T3, which also confirmed the possible autotrophic acidogenesis by using inorganic carbon. This work would provide a promising solution to improve the recovery of carboxylic acids from organic wastes and achieve minimum carbon footprint in the organic waste management process.