Anaerobic digestion (AD) has widely been deployed in the bioenergy industry. However, continuous improvement of AD technology is needed for an enhanced energy recovery, therefore, this research investigates strategies for enhancing energy recovery in AD technology. To achieve this, a lab-scale integrated system consisting of an upflow Anaerobic Sludge Blanket (UASB) reactor and Microbial Fuel Cell (MFC) device was operated over four feeding cycles, at high alkaline pH level, using synthetic sewage water as feed. In the first feeding phase, an Organic Loading Rate (OLR) of 8.0 g COD/L/day was set for the UASB feeding, which was reduced to 5.0 g COD/L/day in the subsequent feeding cycles. Whereas the effluent of the UASB served as feed for the MFC device. First and Second feeding cycles had average pH’s of between pH 7.8 and pH 8.2, with up to 90.0% COD removal and 95.0% biomethane quality recorded, whilst the MFC produced an average of 5mV. Whereas in the Third feeding cycle, pH level of the UASB was increased to an average of pH 9.4, causing an increased purity of biomethane to 99.0%, and doubling the MFC output, whilst COD consumption reduced by approximately 75.0%, with up to 85.0% of total biogas volume lost. In the Fourth cycle, the UASB pH was maintained at pH 8.0, resulting in the MFC output increasing by six-fold, whilst 61.0% of the lost COD consumption capacity and 87.0% of biogas volume, were recovered. Outcome of this experiment demonstrates the influence of pH in alternating energy output of a UASB/MFC system between biogas and bioelectricity. Metagenomics and metatranscriptomics analyses revealed the presence of different microbes in the UASB digester, with Synergistales and Clostridiales dominating the hydrolytic bacterial group, whilst Methanomicrobiales and Methanosarcinales dominated the methanogenic archaea. Varying population and metabolic activities of the microorganisms was observed with change in pH of the UASB digester. Additionally, Lignocellulose biomass, including rice husk, sugarcane bagasse, straw and wood shavings, were pre-treated with alkaline under anaerobic condition to produce cellulose degradation products (CDP) that were tested for biomethane potential (BMP). At the end of the analysis, rice husk CDP had the highest biomethane volume followed by sugarcane bagasse CDP, with 84.0% and 92.0% COD removal respectively. Straw and wood shavings CDPs had nearly the same volume of biomethane, with approximately 88.0% and 75.0% COD removal respectively. The results showed that all the produced CDPs were biodegradable with different methane potential, making them suitable as AD substrate.
|Date of Award
|2 May 2023
|Paul Humphreys (Main Supervisor) & Simon Rout (Co-Supervisor)