Dissertation Defence: Insights into the Inhibition of Anaerobic Digestion by Hydrothermal Liquefaction Aqueous Phase derived from Municipal Sludge
February 27 at 10:00 am - 2:00 pm
Ronald Kizza, supervised by Dr. Cigdem Eskicioglu, will defend their dissertation titled “Insights into the Inhibition of Anaerobic Digestion by Hydrothermal Liquefaction Aqueous Phase derived from Municipal Sludge” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering.
An abstract for Ronald Kizza’s dissertation is included below.
Examinations are open to all members of the campus community as well as the general public. Please email cigdem.eskicioglu@ubc.ca to receive the Zoom link for this exam.
Abstract
Hydrothermal liquefaction has emerged as a promising thermochemical technology for converting municipal sludge into biocrude oil, providing an alternative energy source and a more space-efficient option than conventional sludge treatment methods such as composting. However, the large-scale implementation of this technology faces a significant challenge due to the substantial volume of aqueous byproduct, referred to as the hydrothermal liquefaction aqueous phase, which it produces, requiring effective management solutions. Anaerobic digestion has been proposed as a sustainable treatment method for the aqueous phase, with the potential to recover additional energy as methane. However, the aqueous phase contains toxic compounds that inhibit anaerobic digestion, thereby limiting its effectiveness. The exact cause and mechanism of this inhibition remain unclear, highlighting the need for comprehensive research to better understand and mitigate these challenges.
In this dissertation, various approaches were utilized to develop a deeper understanding of the aqueous phase’s inhibitory compounds and their impacts on downstream anaerobic biodegradation processes. First, it employed ultrafiltration fractionation and biochemical methane potential assays to understand the molecular weight distribution of the organics in the aqueous phase and their impact on biodegradability. Then, batch anaerobic toxicity assays were performed to quantify and compare the relative toxicities of model potential inhibitory compounds commonly found in sludge-derived aqueous phase, thereby screening out the most inhibitory compounds. Finally, modelling was employed to predict the inhibition of sludge-derived aqueous phase based on the abundance of individual inhibitory compounds.
Results showed that the molecular weight distribution significantly affected the rate of anaerobic biodegradability, with the lowest molecular weight fraction (<1 kDa) achieving the highest rate. However, the specific cumulative methane produced from different molecular weight fractions was not significantly different. Based on anaerobic toxicity assays, compounds such as 3-methylcyclopentanone, indole, pyridine, 2-ethylpyridine, 3-aminopyridine, phenol, and 2-aminophenol were identified as the most toxic to both mesophilic and thermophilic anaerobic digestion, while pyrazines and δ-valerolactam exhibited minimal inhibition. Modeling using Generalized Additive Models revealed that the inhibition of the aqueous phase during anaerobic digestion can be predicted with reasonable precision based on the concentration of 15 selected constituent compounds. These findings contribute to a deeper understanding of the inhibition of anaerobic digestion by aqueous by-products from hydrothermal liquefaction and inform strategies to optimize methane production from such waste streams.
