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Thesis Defence: Anaerobic Co-Digestion of Hydrothermal Liquefaction Aqueous Phase with Municipal Sludge
October 24, 2023 at 9:15 am - 12:15 pm
Negin Azarmina, supervised by Dr. Cigdem Eskicioglu, will defend their dissertation titled “Anaerobic Co-Digestion of Hydrothermal Liquefaction Aqueous Phase with Municipal Sludge” in partial fulfillment of the requirements for the degree of Master of Applied Science in Civil Engineering.
An abstract for Negin Azarmina’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
To curb carbon emissions from rising fossil fuel consumption, emerging technologies prioritize biomass as a renewable energy source. Hydrothermal liquefaction (HTL) is a high temperature and high-pressure process to convert waste biomass into renewable biofuels. Due to the extensive substrate processing capabilities of the HTL process, relatively low operating temperatures, and no requirements for pre-drying to process the biomass, it has been receiving much attention from industries and researchers. Biocrude oil and hydrochar are the main products of this process. In addition, the liquid by-product, HTL aqueous, contains high concentrations of organics, nitrogen, and phosphorus compounds. There is a knowledge gap for treatment of HTL aqueous within the vicinity of wastewater treatment plant, particularly as a substrate for downstream anaerobic digestion, when HTL utilizes municipal sludge as feedstock.
In this study, thermophilic anaerobic co-digestion of HTL aqueous, mixed sludge, and dewatering centrate of mixed sludge has been investigated. Seven bench-scale digesters were semi-continuously fed for a total of 420 days. In these digesters, HTL aqueous chemical oxygen demand (COD) contribution to digester’s total COD load were 0, 1.21, 2.74, 4.89, 12.0, 23.1 and 43.3%. To monitor digesters’ performance, influent and effluent streams have been characterized for a wide range of parameters.
Digesters with HTL aqueous contribution to total COD load of 12.0%, 23.1% and 43.3% were fully inhibited after 42, 29, and 15 days, respectively. Digester with 4.89% COD √contribution by HTL was also inhibited after 95 days of operation. HTL-4.89% was fully inhibited for 42 days followed by 218 days of 76% steady-state inhibition prior to complete recovery. Digesters’ inhibition was confirmed by significant reduction of their biogas production, along with their organic consumption and accumulation of volatile fatty acids in the digesters. Operation of HTL-1.21% and HTL-2.74% for over 180 days with no signs of inhibition, confirmed the practicality of biogas production with COD contribution as high as 2.74% by HTL aqueous. Nitrogen heterocyclic compounds appear to exert inhibitory effects on the thermophilic anaerobic co-digestion of HTL aqueous feedstocks, as digesters with elevated HTL aqueous ratios exhibiting correspondingly increased levels of these compounds.
