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Azarmina, Negin

University of British Columbia

To curb carbon emissions from rising fossil fuel consumption, emerging technologies prioritize biomass as a renewable energy source. Hydrothermal liquefaction (HTL) is a hightemperature and high-pressure process converting 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, the feasibility of 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 by a wide range of parameters. Digesters with HTL aqueous contributing 12.0%, 23.1%, and 43.3% of the total COD load were fully inhibited after 42, 29, and 15 days, respectively. Even at a 4.89% COD contribution from HTL, inhibition occurred after 95 days of operation. HTL-4.89% experienced complete inhibition for 42 days, followed by 218 days of 76% steady-state inhibition before eventually recovering fully. The inhibition of the digesters was confirmed by a significant reduction in biogas production, decreased organic consumption, and the accumulation of volatile fatty acids within the digesters. The operation of HTL-1.21% and HTL-2.74% for over 180 days without any signs of inhibition confirmed the practicality of biogas production with a COD contribution as high as 2.74% from HTL aqueous. Nitrogen heterocyclic compounds appear to exert inhibitory effects on the thermophilic anaerobic co-digestion of HTL aqueous feedstocks, as digesters with higher HTL aqueous ratios exhibited correspondingly increased levels of these compounds.

Text

2023-11-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86655

Civil Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/