Thesis Defence: Ozone pretreatment of hydrothermal liquefaction aqueous stream from municipal sludge for enhanced biological degradation
November 29 at 9:30 am - 1:30 pm
Anmol Parajuli, supervised by Dr. Cigdem Eskicioglu, will defend their thesis titled “Ozone pretreatment of hydrothermal liquefaction aqueous stream from municipal sludge for enhanced biological degradation” in partial fulfillment of the requirements for the degree of Master of Applied Science in Civil Engineering.
An abstract for Anmol Parajuli’s thesis is included below.
Defences 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 defence.
ABSTRACT
Wastewater treatment plants (WWTPs) face challenges in managing mixed sludge due to its high volume and range of organic and inorganic contaminants. Hydrothermal liquefaction (HTL) emerges as a promising alternative of commonly adopted anaerobic digestion (AD), offering resource recovery and the potential to convert sludge into biocrude oil. However, HTL technology for sludge management is hindered by the generation of HTL aqueous which constitutes of complex soluble compounds that are inhibitory for biological treatment within WWTPs. This necessitates pretreatment of HTL aqueous for onsite biological treatment. This study explores the efficacy of ozone pretreatment of HTL aqueous in enhancing its biodegradability.
This study evaluated the effects of ozonation on HTL aqueous phase derived from dewatered mixed sludge, employing dissolved ozone doses ranging from 0.03 to 0.18 g ozone/g chemical oxygen demand (COD) of HTL aqueous phase. The HTL process was conducted at 350°C with a 15-minute residence time, and the resulting aqueous phase was diluted tenfold prior to ozone pretreatment. At the maximum ozone dose, substantial reductions of 43%, 69%, and 72% in COD, nitrogen heterocyclic compounds (both 2-Methylpyridine and 2,6-Lutidine), and total phenolics of HTL aqueous were observed, respectively. Concurrently, total volatile fatty acids exhibited an increase, plateauing at doses between 0.14 and 0.18 g ozone/g COD. The pH stabilized at 5.3 for doses ranging from 0.12 to 0.18 g ozone/g COD from an initial value of 8.0 in HTL aqueous.
Subsequent biodegradability assessments for pretreated HTL aqueous by mesophilic and thermophilic biochemical methane potential assays revealed enhancements of 98% and 89%, compared to non-pretreated (control) samples, in specific cumulative methane yields, respectively, at an optimal dose of 0.14 g ozone/g COD. The ultimate biodegradability index (UBOD/COD), at 28 days, increased from 0.54 to 0.95 at the highest ozone dose of 0.18 g ozone/g COD. Statistical analyses confirmed the significant positive impact of ozonation on both aerobic and anaerobic biodegradability of HTL aqueous. These findings demonstrate the efficacy of ozonation as a pretreatment strategy for enhancing the biological treatability of HTL aqueous, potentially facilitating more efficient downstream biological processes in WWTPs.
