Harnessing <i>Haloferax mediterranei</i> for Bioplastic Production from Organic Waste

Abstract

This dissertation investigated Haloferax mediterranei as a robust platform for converting food waste into high-value biodegradable bioplastics. The dissertation first reviewed current knowledge on the organism's physiology and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) synthesis metabolism of this halophilic archaeon, identifying key technical challenges such as waste variability, feedstock pretreatment, and the needs for efficient volatile fatty acid (VFA) generation. Then, ex-situ VFA recovery from digestate was experimentally evaluated using hydrophobic deep eutectic solvents with omniphobic membranes, and kinetic-affinity relationships guided the separation design. To bypass VFA purification needs, in-situ VFAs produced from arrested anaerobic digestion (aAD) were also tested, showing that H. mediterranei can efficiently convert unpurified VFAs into PHBV when dilution was applied to reduce inhibitory compounds. Incorporation of microbial electrolysis cells in aAD further enabled the control of VFA composition, allowing the subsequent fermentation of PHBV with greater 3-hydroxyvalerate fractions for achieving superior material properties. Transitioning from batch to continuous fermentation processes, long-term cultivation in sequencing batch reactors demonstrated stable PHBV production over 450 days, while also exposing substrate and product inhibition phenomena. Mechanistic analyses clarified the role of inhibitory effects and maintenance energy requirements, and practical mitigation strategies such as pH adjustment were developed for high-salinity glycerol waste fermentation. Finally, pilot-scale demonstrations integrating 100-liter aAD pretreatment, 50-liter halophilic fermentation, and chemical-free polymer recovery validated the scalability of this technology. Collectively, these findings provided a comprehensive framework to overcome technical and economic barriers, advancing circular, waste-to-bioplastic production.