Applicability of Multivariate Pretreatments of Municipal Solid Waste within the Framework of the Circular Economy to Enhance Resource Recovery via Dark Fermentation and Anaerobic Digestion

<p dir="ltr">Anaerobic digestion (AD) traditionally stabilizes biowaste from various sources efficiently. Today, it's recognized as a versatile process aligning with the zero-discharge biowaste concept. AD not only treats waste streams but also generates bioenergy, reduces greenhouse gas (GHG) emissions, and enables nutrient recycling via organic biofertilizers. Additionally, AD holds the potential to produce valuable materials like volatile fatty acids (VFAs), which can replace petroleum-derived sources in biodegradable bioplastics. This positions AD as a cornerstone of the circular economy, optimizing resource usage, extending the lifespan of natural resources, and reducing raw material consumption. </p><p dir="ltr">Incorporating hydrothermal pretreatment (HTP) significantly enhanced the semi-continuous AD process. Under HTP conditions (170 °C, 3 bars, 30 min), sewage sludge experienced a 41% increase in the solubilization of macromolecular organic compounds. This improved biodegradability led to a 50% reduction in chemical oxygen demand (COD) and a 63% improvement in volatile solids (VS) destruction, while methane yields soared by 52%, reaching 176 ml/g TCODadded. Additionally, HTP doubled the digestate dewaterability. Furthermore, when HTP was coupled with AD, the microbial community exhibited greater resilience in adapting to and mitigating emerging pollutants like per- and polyfluoroalkyl substances (PFAS) without disrupting the AD process. </p><p dir="ltr">This dissertation also investigated Ydro Process® biotechnology from Tradeworks Environmental Inc. as a bioaugmentation method in batch and semi-continuous AD. In batch mode, it boosted the VFAs yield to 103.5 mgVFAs/gVSSadded, while in the semi-continuous system, it increased the methane yield by up to 87%. Additionally, Ydro bioaugmentation enhanced sludge stability and improved dewaterability by 10%.</p><p dir="ltr">Iron additives' effectiveness varied based on size, dose, and experimental factors, such as inoculum and feedstock type. Nano iron improved fermentation, but microscale zero-valent iron (mZVI) had an antagonistic effect. When directly added to digesters, nanoscale zero-valent iron (nZVI)’s impact was limited. However, coupling it with ultrasonication as a pretreatment led to significant improvements in VFAs production and biomethanation. </p><p dir="ltr">Keywords: Anaerobic Digestion, Circular Economy, Energy Recovery, Value-added Byproduct, Fermentation, Wastewater Sludge, Hydrothermal Pretreatment, Bioaugmentation, Additives, Microbial Community, Dewaterability, Anaerobically Digested Sludge, Per - and polyfluoroalkyl Substances (PFAS)</p>