This comprehensive work has advanced the optimization of VFA production, PHA synthesis, nutrient recovery, and environmental sustainability:
Characterization and Pretreatment: 14 residues from the pulp and paper industry, along with slaughterhouse waste, glycerol, and dairy sludge, were characterized. Physical and chemical pretreatments were tested, with alkaline pH (10) yielding higher volatile fatty acid (VFA) concentrations. Codigestion trials demonstrated optimal VFA production at a 4:1 substrate-to-inoculum ratio, achieving up to 20 g/L of VFAs.
Fermentation and Process Optimization: Semi-continuous processes showed improved VFA production. Fe(0) nanoparticles did not significantly impact results. VFA concentration was improved using membrane filtration and reverse osmosis.
Reactor Operations: A 1 m³ reactor and pilot systems were successfully operated, with VFA concentrations of 5–6 g/L achieved.
Bacterial Strain Screening: Two strains were identified as optimal for polyhydroxyalkanoate (PHA) production, showing robustness and high productivity in bioreactors. Biopolymers produced complied with specifications for further applications.
Innovative Fertilizers and Algal Cultivation: PHAs were used in fertilizer coatings with tunable release kinetics. A hybrid microalgae cultivation system achieved significant nutrient recovery and biomass production, making algal biomass suitable for agricultural applications.
Digestate Treatment and Nutrient Recovery: Digestate was processed via mechanical separation, ultrafiltration, and reverse osmosis, optimizing nutrient recovery and reducing energy consumption. Ammonium sulfate was recovered and utilized in trials.
Process Modelling and Life Cycle Assessment (LCA): Process modelling for VFA production was conducted, analyzing cost, energy use, and environmental impact. LCA identified electricity consumption as the primary contributor to environmental impacts. Social LCA highlighted tailored stakeholder engagement strategies.