Development of a model framework for simultaneous synthesis and selection of Anaerobic Digester Structures
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Date
November, 2019
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Abstract
The anaerobic treatment process has increasingly been recognized as an efficient technology for sustainable nutrient recovery, renewable energy generation, and environmental sanitation due to its strong potential to mitigate current energy resource and climate change challenges. However, the success of industrial-scale anaerobic digestion is only possible if the following two prerequisite factors are met: availability of a sustainable supply of organic feedstock and design of optimal process configurations containing appropriate digester subunits that are well adapted to the characteristics of the feedstock of interest. A lot of combinations of the fundamental anaerobic digester types exist, which becomes impossible to test all the possibilities in order to determine the one with the absolute best performance. This study did not focus attention on devising new digesters with the aim of improving the performance of the system, but rather optimally arranged some combinations of plug flow reactors (PFRs) and continuous stirring tank reactor (CSTR) systems. The objective of study was to establish a framework based on multi-criteria decision analysis, for optimal selection of anaerobic digesters and practical implementation of digester networks, which is amendable to any substrate and digester configuration. Anaerobic treatability study was performed using pineapple waste, pig waste, abattoir waste and food waste to obtain cummulative biogas yield curves followed by development of the digester configurations using the attainable region technique. A hybrid Analytical Hierachy Process and Fuzzy Technique for Order Preference by Similarity to Ideal Solution was used in the selection of plug flow anaerobic digesters for the configurations. The following biogas volumes were obtained at the end of the 30 days retention period; for pig waste, for abattoir waste, for food waste and for pineapple waste. Quantity of feedstock used was 5kg per sample. A novel framework for the selection of multi stage anaerobic digesters has been presented. Optimal digester configurations obtained differ based on substrate used. The selected plug flow anaerobic digesters for subunit were Expanded Granular Sludge Bed for scenario 1, scenario 2 and scenario 3 were Anaerobic Baffled Reactor.
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A thesis submitted to the Department of Agricultural and Biosystems Engineering, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfillment of the requirements for the degree of Master of Philosophy in Agro Environmental Engineering,
Keywords
Analytical Hierarchy Process, Anaerobic Digestion, Attainable Region, Fuzzy Logic, TOPSIS, Scenario Planning