Luongo, Vincenzo (2017) Anaerobic processes for waste biomass treatment: applications and mathematical modeling. [Tesi di dottorato]

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The increasing global energy demand and depletion of fossil fuels are driving international policies to promote the use of alternative energy sources, leading to the mitigation of global warming and greenhouse gas (GHG) emissions. In this context, the sustainable valorisation via biological anaerobic processes of organic waste biomasses represents a promising technology for producing renewable energy and value added chemicals in a biorefinery concept. Anaerobic Digestion (AD) and Dark Fermentation (DF) are the most explored biological routes to produce renewable energy in the form of methane and hydrogen gas, respectively. Due to its high flexibility and applicability to a wide range of organic substrates, AD has been largely adopted in full scale applications, with increasing interest from both academia and industries. Conversely, low biohydrogen yields and incomplete biomass conversion limit DF scaled-up applications as a self-standing biotechnology for energy production. Moreover, the combination of different anaerobic processes, such as DF-AD or DF-Photo-Fermentation (PF), might be adopted to overcome the main drawbacks deriving from the application of DF processes. A significant example is represented by the use of DF by-products, such as organic acids and alcohols, for H2 production via PF. The combined DF-PF process results in the increase of the total hydrogen yield (usually evaluated in terms of mol H2 mol C6H12O6-1) and the production of poly-β-hydroxybutyrate (PHB), which are stored by Purple Non-Sulphur Bacteria, performing the PF step, as a carbon reserve available under nutrient starvation. In this thesis, different anaerobic technologies have been applied to achieve higher biogas yields and/or by-products valorisation in a biorefinery concept. In particular, the enhancement of AD performances, in terms of biogas productivity, has been addressed by optimizing the crucial start-up phase of an anaerobic fluidized bed reactor. The stability of DF and enhancement of biohydrogen yields have been obtained by optimizing the operative conditions of a DF reactor continuously fed with cheese whey in thermophilic regimen, and by adopting a combined DF-PF configuration for the energetic valorisation of the organic fraction of municipal solid wastes, respectively. Contextually, the valorisation of Dark Fermentation effluents (DFE) was achieved by i) producing PHB via PF, ii) extracting value added acids with anionic resins or iii) using DFE as a complex media for the dissolution of recalcitrant materials. Furthermore, a 1-D mathematical model has been presented to analyse and predict the microbial colonization of anaerobic multispecies biofilms.

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