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Enhanced biodegradation of model lignocellulosic wastes in laboratory-scale bioreactors and landfills

Muaaz-Us-Salam, Syed 2020. Enhanced biodegradation of model lignocellulosic wastes in laboratory-scale bioreactors and landfills. PhD Thesis, Cardiff University.
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In municipal solid waste (MSW) landfills, lignocellulosic wastes degrade slowly and cause the slow and prolonged release of biogas into the atmosphere. This release is adding to anthropogenic climate change, which is arguably the biggest challenge humankind faces today and requires immediate attention. As a solution to this problem, the overall aim of this study was to enhance biodelignification in landfills. This aim was supported by two research questions - To what extent can enzymatic & bacterial biodelignification systems breakdown lignocellulose in realistic lignin wastes, with the prospect of enhanced biogas recovery? What is the impact of flow & heterogeneity on bacterial biodelignification systems in model lignocellulose-containing bioreactor landfills? Two representative lignocellulosic wastes found largely undegraded in old landfills, i.e. newspaper and softwood, were used. Lignin peroxidase enzyme and a recently isolated lignin-degrading bacterial strain (Agrobacterium sp.) were used in tests conducted in stirred bioreactors with methanogens from sewage sludge. Lignin peroxidase resulted in ~20% enhancement in cumulative methane produced in newspaper reactors. It had a negative effect on wood (~10% decrease in total methane generated compared to controls, possibly due to simultaneous depolymerisation and repolymerisation of lignin on the surface of the wood preventing further depolymerisation). Agrobacterium sp. strain enhanced biodegradation of both wood (~20% higher release of soluble organic carbon and enhanced breakdown) and newspaper (~2-fold biogas yield). Furthermore, homogeneous and heterogeneous pore-structure configurations containing newspaper and sand were prepared to mimic old landfills. In the homogeneous case, 2-fold enhancement of biogas yield occurs, which is consistent with soluble organic carbon (sOC)/pH profiles. In the heterogeneous case, there is no significant enhancement. This is likely due to the much lower hydraulic conductivity of the newspaper/sand mixture compared to the outer sand zone, resulting in preferential flow paths through the sand. This paired with very low pH and very high sOC in the column impacts the microbial communities and their activity adversely. Overall, this thesis has surveyed the literature and identified the problem of slowly degrading newspaper and woody wastes in landfills. It has formulated research questions addressing this problem by studying accelerated degradation of these wastes, and the application of this technology to conditions close to reallife field-scale conditions (flow, heterogeneity). Enzymatic and bacterial biodelignification systems show promise under stirred-bioreactor conditions, as well as homogeneous lab-scale landfills. However, under heterogeneous conditions, the biodegradation process is more complicated.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Lignocellulose; Bioreactor; Landfill; Biogas; Delignification; Methane.
Date of First Compliant Deposit: 29 January 2021
Last Modified: 29 Jan 2021 09:28

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