Fate of biodegradable disposables in high-solids anaerobic digestion followed by hydrothermal liquefaction

• Author / Creator

  Niknejad, Parisa

• To address the growing concern of environmental sustainability and waste management,
  recent research efforts have been dedicated to investigating innovative methods for the
  treatment and conversion of biodegradable disposables and bioplastics. These studies delve into
  the potential of high solid anaerobic digestion (HSAD) followed by hydrothermal liquefaction
  (HTL) as integrated processes to facilitate the transformation of these materials. However,
  several fundamental and engineering bottlenecks are associated with their practical application.
  To date, limited information is available on the fate of bioplastics during HSAD and HTL
  process. Thus, this thesis aims to address these research gaps by investigating the degradability
  of bioplastics during HSAD and their subsequent degradation during HTL under various
  operating conditions.
  First, the biodegradability and transformation of biodegradable disposables through an
  integrated process of HSAD followed by HTL was investigated. During the HSAD phase, the
  paper-based disposables demonstrated efficient degradation. Conversely, compostable plastic
  bags and utensils showed resistance to degradation, leading to a reduction of 29.5% and 8.99%,
  respectively, in methane yield compared to the control group. However, the HTL process
  exhibited promising results, as it was able to completely convert the undegraded plastic bags
  and utensils present in the HSAD digestate into biocrude. This transformation significantly
  lowered the potential environmental risks associated with bioplastic pollution from digestate
  application on land. Furthermore, by increasing the HTL temperature from 280 to 350˚C, the
  yield and quality of biocrude, particularly in terms of heavy oil content, were improved.
  Second, the co-digestion of bioplastics and source-separated organic waste (SSO) using
  an integrated approach involving HSAD and followed by HTL under various operating
  conditions at 280 °C, 330 °C, and 370 °C was explored. During the HSAD process, bioplastics
  underwent fragmentation, resulting in a notable reduction in methane recovery. Nonetheless,
  the HTL process proved to be highly effective in completely converting bioplastics, thereby
  mitigating the potential environmental risks associated with bioplastic pollution. Experimental
  observations indicated that an increase in temperature from 280 to 330 °C led to a higher weight
  percentage of biocrude. However, when the temperature was further increased from 330 to
  370 °C, both the weight percentage of biocrude and hydrochar decreased, while the weight
  percentage of total gas showed a peak rise. At a temperature of 330 °C, the maximum higher
  heating value for bioplastics was achieved, surpassing that of the control group.

• Subjects / Keywords

  • Bioplastics
  • High solid anaerobic digestion
  • Hydrothermal liquefaction
  • Biomethane
  • Biocrude

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-5rqa-qz24

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.