Microbial electrochemical monitoring of volatile fatty acids during anaerobic digestion

Volatile fatty acid (VFA) concentration is known as an important indicator to control and optimize anaerobic digestion (AD) process. In this study, an innovative VFA biosensor was developed based on the principle of a microbial desalination cell. The correlation between current densities and VFA concentrations was first evaluated with synthetic digestate. Two linear relationships were observed between current densities and VFA levels from 1 to 30 mM (0.04 to 8.50 mA/m², <i>R</i>² = 0.97) and then from 30 to 200 mM (8.50 to 10.80 mA/m², <i>R</i>² = 0.95). The detection range was much broader than that of other existing VFA biosensors. The biosensor had no response to protein and lipid which are frequently found along with VFAs in organic waste streams from AD, suggesting the selective detection of VFAs. The current displayed different responses to VFA levels when different ionic strengths and external resistances were applied, though linear relationships were always observed. Finally, the biosensor was further explored with real AD effluents and the results did not show significance differences with those measured by GC. The simple and efficient biosensor showed promising potential for online, inexpensive, and reliable measurement of VFA levels during AD and other anaerobic processes

Microbial electrolytic capture, separation and regeneration of CO₂ for biogas upgrading

Biogas upgrading to natural gas quality is essential for the efficient use of biogas in various applications. Carbon dioxide (CO₂) which constitutes a major part of the biogas is generally removed by physicochemical methods. However, most of the methods are expensive and often present environmental challenges. In this study, an innovative microbial electrolytic system was developed to capture, separate and regenerate CO₂ for biogas upgrading without external supply of chemicals, and potentially to treat wastewater. The new system was operated at varied biogas flow rates and external applied voltages. CO₂ was effectively separated from the raw biogas and the CH₄ content in the outlet reached as high as 97.0 ± 0.2% at the external voltage of 1.2 V and gas flow rate of 19.6 mL/h. Regeneration of CO₂ was also achieved in the regeneration chamber with low pH (1.34 ± 0.04). The relatively low electric energy consumption (≤0.15 kWh/m³ biogas) along with the H₂ production which can contribute to the energy input makes the overall energy need of the system low, and thereby makes the technology promising. This work provides the first attempt for development of a sustainable biogas upgrading technology and potentially expands the application of microbial electrochemical technologies