Harnessing Haloferax mediterranei for Bioplastic Production from Organic Waste
| dc.contributor.author | Zhang, Xueyao | en |
| dc.contributor.committeechair | Wang, Zhiwu | en |
| dc.contributor.committeemember | Zheng, Yi | en |
| dc.contributor.committeemember | Huang, Haibo | en |
| dc.contributor.committeemember | Liao, Jingqiu | en |
| dc.contributor.committeemember | Pruden-Bagchi, Amy Jill | en |
| dc.contributor.department | Civil and Environmental Engineering | en |
| dc.date.accessioned | 2025-12-17T09:00:46Z | en |
| dc.date.available | 2025-12-17T09:00:46Z | en |
| dc.date.issued | 2025-12-16 | en |
| dc.description.abstract | This dissertation investigated <i>Haloferax mediterranei</i> 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. | en |
| dc.description.abstractgeneral | This dissertation explored a new way to turn food waste into environmentally friendly plastics using a unique microorganism called Haloferax mediterranei. Unlike petroleum-based plastics, which persist in the environment, the plastics made in this study are biodegradable and can reduce both plastic pollution and waste disposal challenges. The research focused on feeding this salt-loving microbe with food waste, a material that normally costs money to throw away, turning a disposal problem into a valuable resource for making biodegradable plastics. Since microbes cannot directly digest food waste, it first needs to be broken down into smaller molecules called volatile fatty acids (VFAs). Usually, these VFAs must be cleaned before use, which is costly. This dissertation showed that H. mediterranei can directly use unpurified VFAs if steps are taken to reduce harmful byproducts, cutting down on expensive purification. In addition, electricity-assisted processes were tested to improve the quality of unpurified VFAs, which in turn made the resulting plastic softer, more flexible, and in turn more profitable in the market. This dissertation also demonstrated that the process is not only effective in short-term tests but can also run continuously for more than a year. Pilot-scale trials using large tanks proved that the method can be scaled up, combining food waste pretreatment, microbial fermentation, and chemical-free bioplastic recovery. Overall, this dissertation shows a practical pathway to recycle food waste into valuable bioplastics. By lowering production costs and improving material quality, the work brings biodegradable plastics closer to widespread use and supports the transition toward a more sustainable circular economy. | en |
| dc.description.degree | Doctor of Philosophy | en |
| dc.format.medium | ETD | en |
| dc.identifier.other | vt_gsexam:44748 | en |
| dc.identifier.uri | https://hdl.handle.net/10919/139936 | en |
| dc.language.iso | en | en |
| dc.publisher | Virginia Tech | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject | Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) | en |
| dc.subject | Food waste | en |
| dc.subject | Arrested anaerobic digestion | en |
| dc.subject | Volatile fatty acid (VFA) | en |
| dc.subject | Halophilic fermentation | en |
| dc.subject | Circular bioeconomy | en |
| dc.title | Harnessing <i>Haloferax mediterranei</i> for Bioplastic Production from Organic Waste | en |
| dc.type | Dissertation | en |
| thesis.degree.discipline | Civil Engineering | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |
Files
Original bundle
1 - 4 of 4
- Name:
- Zhang_X_D_2025_support_3.pdf
- Size:
- 698.45 KB
- Format:
- Adobe Portable Document Format
- Description:
- Supporting documents
- Name:
- Zhang_X_D_2025_support_4.pdf
- Size:
- 1.61 MB
- Format:
- Adobe Portable Document Format
- Description:
- Supporting documents
- Name:
- Zhang_X_D_2025_support_1.pdf
- Size:
- 487.79 KB
- Format:
- Adobe Portable Document Format
- Description:
- Supporting documents