| dc.description.abstract | In anaerobic digestion, organic wastes are decomposed in the absence of oxygen primarily to produce biogas, which consists of methane and carbon dioxide. The methane content in biogas can be optimized by reducing carbon dioxide to obtain biomethane, which can be used as an alternative to natural gas. In this thesis, it is then of interest to study ways to enhance methane production from biogas. One of the approaches to increase the methane content is by facilitating the electron transfer mechanism, using conductive materials, between the electron-donating bacteria and electron-accepting methanogens.
The investigation was more focused on the potential of conductive materials such as Anthraquinone-2,6-Disulphonate (AQDS) and activated carbon to enhance the production of biogas and, consequently, methane. A biomethane potential (BMP) test was carried out in the laboratory under mesophilic conditions, to determine the methane production capacity of the samples inside a bioreactor that contains the conductive materials. The pressure developed inside the bioreactors was monitored regularly, and the volume of the biogas was calculated using ideal gas equations.
Our initial focus was to use AQDS as the conductive material in order to enhance methane production. However, the use of AQDS did not yield a substantial amount of methane. In addition, with the use of AQDS, excess nitrogen was produced. The possible reasons for the excess nitrogen and the much lower methane productions could be aged inoculum contaminated with nitrogenous compounds, incomplete biodegradation of the substrate (ethanol), and the impact of AQDS on the nitrogen level.
On the other hand, the use of activated carbon at 15 g/L as a conductive material had a significant positive impact on biogas and methane production, while at concentrations beyond 15 g/L, methane production decreased. However, the methane production at 60 g/L was surprisingly higher than 30 g/L and 45 g/L. Various reasons are outlined for the unexpected production of biogas and methane at 60 g/L, viz., microbially favourable conditions, higher adsorptive capacity, and a larger surface area and porosity of the activated carbon.
Furthermore, in this thesis, we have also reused the activated carbon from the first batch experiment to conduct another batch experiment. In that subsequent experiment, the reuse of activated carbon resulted in a decrease in biogas production. This could be because of a decline in the electron transfer effectiveness of the activated carbon caused by the adsorption of organic pollutants on its surface. Additionally, the study also examined biofilm formation on the surface of the activated carbon by using Scanning Electron Microscopy (SEM) to assess the attachment of microorganisms. | |
