Abstract
Anaerobic digestion (AD) is an established organic waste management technology, producing biogas and organic fertiliser as end-products. Despite being an established technology, AD still faces key challenges, including substrate-induced instability and the requirements for the removal of carbon dioxide (CO2) from biogas. Carbon-based materials have been recently employed as stabilising agent and as adsorbent to manage some of these limitations. Biochar, a by-product from biomass pyrolysis, has been identified as a sustainable alternative material to commercial grade carbon-based adsorbent in AD. However, research on the use of biochar has mostly focused on thermophilic batch AD, without considering the biochar production conditions and how they interact with the AD process at mesophilic conditions. The microbial communities in thermophilic AD are very sensitive to any slight fluctuation in process conditions, hence, the preference for mesophilic digestion is well known.
This research investigated the impact of biochar on a mesophilic operated AD process stability and the potential to produce biogas with increased concentrations of methane (CH4) in-situ towards approaching a state of biomethane. The biochar employed was derived from the slow pyrolysis of bamboo, a phytoremediation biomass, and corn stover, the agricultural residue after a harvest of corn. Based on reviewed literature, properties of biochar that favour AD stability, and increased CH4 concentration in biogas were identified and the range of the identified optimal properties were implemented in a design of experiment (DoE). A batch biochemical methane potential test was implemented within the framework of a Taguchi-based DoE. The Taguchi DoE was coupled with grey relational and principal component analyses, in order to objectively identify the optimal combination of parameters that support the aim of this research. Optimal conditions determined from the batch test were replicated in a semi-continuous two-stage experiment by using a control digester and a biochar amended digester...
D.Phil. (Mechanical Engineering)