Valorization of hydrothermal liquefaction aqueous stream towards commercial viability of municipal sludge to biocrude oil conversion

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My overarching research program focuses on the development of advanced wastewater and sludge treatment technologies, and is motivated by many of the challenges my industrial collaborators/partners currently face. In particular, municipal wastewater treatment plants are increasingly stretched by ever growing volumes of hazardous materials in wastewater that become part of `municipal sludge.' This sludge is costly to process in order to effectively neutralize the pathogens, heavy metals, and a wide range of trace contaminants of emerging concern (TCECs) that it contains. My recent research has investigated several promising approaches to process this waste product, including thermochemical sludge conversion through hydrothermal liquefaction (HTL). HTL is a game-changing advancement, since it can convert sludge into biocrude that can be used as a fuel replacement. To date we have found that dewatered municipal sludge can be efficiently converted to biocrude oil and hydrochar at temperature and pressure of 350 C and 220 bar, respectively. Furthermore, at these elevated temperatures and pressures, many classes of TCECs (pharmaceuticals, hormones, antimicrobials) in municipal sludge are destroyed. Since this promising technology has the potential to sterilize the hazardous materials in municipal wastewater sludge by generating fuel that can be used in transportation, it has the double advantage of reducing costs associated with many other wastewater treatment solutions, and provides environmental benefits on several fronts. However, HTL creates a by-product, HTL aqueous, that without additional treatment, jeopardizes the future scale-up prospects of this technology at wastewater treatment plants. The pollutant levels in HTL aqueous significantly exceed discharge regulations to the environment and the risks of returning it to headworks is unknown. The HTL aqueous is also an untapped nutrient/bioenergy resource that holds revenue-generating potential for treatment plants due to its high concentration of organic acids. However, there are also many classes of organics, including furans, ketones, phenols, and N-heterocyclic compounds, reported to be inhibitory to key microbial cultures in biological treatment processes, in particular anaerobic digesters with bioenergy recovery potential. Therefore, bioenergy potential of HTL aqueous is unknown. To address these gaps, over the next 5 years, 3 graduate and 2 undergraduate students, mentored by an analytical chemist, will develop and evaluate the performance of various detoxification methods for HTL aqueous derived from municipal sludge to valorize high concentrations of organic acids to generate biogas in advanced anaerobic digesters. These objectives will bring us one step closer to incorporating HTL sludge conversion processes to wastewater treatment plants seamlessly. Through ongoing partnerships with municipalities throughout British Columbia, outcomes of this research are poised to have immediate impact.