Available at: https://digitalcommons.calpoly.edu/theses/3249
Date of Award
3-2026
Degree Name
MS in Civil and Environmental Engineering
Department/Program
Civil and Environmental Engineering
College
College of Engineering
Advisor
Tryg Lundquist
Advisor Department
Civil and Environmental Engineering
Advisor College
College of Engineering
Abstract
Hydrothermal liquefaction (HTL) converts wet biomass into a biocrude oil that presents opportunities for sewage sludge management. However, it also generates a secondary wastewater (HTL aqueous phase; HTL-AP) that can inhibit nitrification (by an average of 60% in this study), meaning it cannot be disposed of in a biological treatment plant. Instead, it must be pretreated to reduce nitrification inhibition. One proposed pretreatment method is wet air oxidation (WAO), which this study found to reduce inhibition to by an average of 29% compared to HTL-AP. The goal of this study was to evaluate the relationship between certain WAO reactor operational conditions (oxygen partial pressure, oxygen feed, residence time, and temperature) and the reduction in nitrification inhibition, as determined by the ISO 9509 bioassay. Duplicate nitrification inhibition bioassays were conducted on 8 WAO-treated samples. Oxygen partial pressure had a moderate inverse relationship with inhibition removal, oxygen feed had a weak relationship, and residence time and temperature had no defensible relationship with inhibition reduction. The concentrations of chemical compounds in the WAO treated samples was also investigated, but only weak relationships were found. In all bioassays, WAO treated samples were less inhibitory than untreated HTL-AP samples, demonstrating inhibition reduction with WAO regardless of treatment conditions within the ranges.