Date

2022-12-22

Author

Ghaderikia, Amin

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Bioelectrochemical methane production, known as electromethanogenesis, provides an emerging technology for carbon recycling via the conversion of carbon dioxide to methane with the additional benefit of simultaneous organic waste reduction. Bioelectrochemical conversion reactions in an electromethanogenic microbial electrolysis cell (MEC) are catalyzed by electro-active biofilm on the electrodes; hence, biofilm formation has a key role in system performance. In this study, the objective was to evaluate the impacts of different start-up strategies on the performance of methane production from a complex waste, cattle manure in bioelectrochemical reactors. At first, the focus was on the performance of an electromethanogenic MEC and designed experiments for providing a comparative analysis of the impact of biofilm formation upon feeding a simple substrate, acetate (ACE), and a complex waste, cattle manure (CM). To this purpose, single chamber MECs were operated with an applied voltage of 0.7 V on a fed-batch mode. Upon biofilm formation on the sole carbon source (ACE or CM), a selected number of MECs (ACE_CM and CM_ACE) were subjected to cross-feeding during the test period. Even though the difference in the current production rate between the ACE_CM and CM_CM reactors was 20% in favour of the ACE_CM, cross-feeding lowered methane production. The results showed that there was around 20% higher methane production rate (131.6 ± 2 mL/L-d) when CM was used as the sole feed. Evidently, microbial community analysis showed that the primary substrate shapes the community of the bioelectrodes and cross-feeding does not have a significant impact on the microbial community. Based on this knowledge, the second set of experiments was designed to investigate the impact of the use of biofilm attached electrodes formed via CM addition, and the amendment of a carbon-based conductive material, granular activated carbon (GAC), on the integrated system of anaerobic digestion – microbial electrolysis cell (AD-MEC). AD-MEC systems are a combination of MECs and conventional AD reactors and have recently been used for enhanced methane production from waste materials, however, there is limited information on the start-up procedures. Further, the choice of reactor medium (buffer) is significant in the performance of bioelectrochemical systems; therefore, in this work, the performance of AD-MEC reactors fed with CM using two different buffer solutions, 100 mM phosphate-buffered saline (PBS) solution and a salt media without phosphate has been compared. Using the salt buffer solution in the AD reactor resulted in a 4 times higher net methane yield and 5.8 times lower lag time than the same reactor with 100 mM PBS media. The highest methane production rate of 12.03±0.01 mL/d and methane yield of 318.1±1.4 mLCH4/g volatile solids added (VSadded) were attained in the presence of salt medium with the amendment of biofilm-attached GAC, named, BioGAC when bare electrodes were used in AD-MEC. The yield attained in AD-MECs was around 25% higher than conventional AD.

Subject Keywords

Anaerobic Digestion (AD), Microbial Electrolysis Cell (MEC), AD-MEC, Biofilm Formation, Bioelectrode

URI

https://hdl.handle.net/11511/101933

Collections

Graduate School of Natural and Applied Sciences, Thesis