Electrolyte Impact on Methane Production in Anaerobic Digestion - Microbial Electrolysis Cell (AD-MEC) Integrated Systems

Date

2024-8

Author

Öden, Berkan

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The anaerobic digestion (AD) process is widely used to produce biogas rich in methane (CH4) that can significantly contribute to the replacement of non-renewable energy sources. However, conditions such as volatile fatty acid (VFA) accumulation and pH changes can reduce AD efficiency. Anaerobic digestion and microbial electrolysis cell (MEC) integrated systems (AD-MEC) is a promising technology, that can overcome these problems by improving electron transfer and stability of the methanogenesis process. In an AD-MEC, microorganisms utilize organic matter and convert it into CH4 while generating electric current by applying a small voltage. Electrolytes including phosphate-buffered saline (PBS) and carbonate buffer (CB) are used in AD-MEC systems for accelerated electron transfer and improved AD-MEC performance yet their impact on AD-MECs has not been evaluated previously. In this thesis, the effects of PBS and CB on AD-MEC integrated systems fed with cattle manure were investigated under 0.7 V and 0.9 V applied potential. In the experiments, single chamber MECs were used with carbon fiber brush (CFB) electrodes under mesophilic conditions and PBS concentration ranged from 10 to 50 mM while CB concentration was changed from 30 to 120 mM. The results showed that PBS and CB positively affected the current production of AD-MECs with current density production up to 0.23 ± 0.004 mA/cm2 at 0.9 V (50 mM PBS). Nevertheless, both electrolytes inhibited CH4 production. The no-buffer AD-MECs had the highest CH4 yield in both experimental sets up to 362.0 ± 1.0 mL CH4/g VSadded. However, the AD control reactors with the highest concentration of PBS (50 mM) exhibited the lowest CH4 yield (187.6 ± 17.9 mL CH4/g VSadded). Anaerobic toxicity assays showed the negative impact of increased buffer concentration on the AD microbial community and a reduction in CH4 production performance up to 50% (in 50 mM AD control reactor). Therefore, it is very important to optimize the selection and concentration of electrolytes for maximizing CH4 production in AD-MECs.

Subject Keywords

Anaerobic Digestion (AD), Microbial Electrolysis Cell (MEC), AD-MEC Integration, Electrolyte, Methane

URI

https://hdl.handle.net/11511/111422

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Graduate School of Natural and Applied Sciences, Thesis