(681f) Hydrothermal Liquefaction of Municipal Sludge: Biochar, Biocrude, and Aqueous Co-Product Transformations with the Addition of Carbonate and Hydroxide Alkali Metals.

The hydrothermal liquefaction (HTL) of municipal sludge presents a promising avenue for sustainable waste management and biofuels production. Alkali metal catalysts have been shown to be promising for enhancing biocrude generation through waste-to-energy technologies by promoting depolymerization, deoxygenation, denitrogenation, and other reactions. Municipal sludge composition can vary substantially based on the types of treatment processes performed in a wastewater treatment plant. For example, some plants require supplemental alkalinity for nitrification which can impact the calcium concentration in the sludge and the resulting product distribution and characteristics. In this study, we have investigated the transformative effects of carbonate and hydroxide compounds on the three main HTL products: biochar, biocrude, and aqueous co-product (ACP). Municipal sludge was collected from the Wakarusa Wastewater Treatment Plant, located in Lawrence, KS. HTL was performed to determine the impact of the addition of calcium carbonate, calcium hydroxide, and sodium carbonate on the organic elemental composition, nutrient recovery, and product yields. Preliminary results suggest that the addition of Na₂CO₃ has the highest biocrude yield at 46.21 ± 1.23 (afdw%). The highest biochar yield was found to be 22.61 ± 0.64 (afdw%) with the addition of Ca(OH)₂. GC-MS results showed substantial change in biocrude composition depending on which chemical was added to the reaction. When no chemical was added, biocrude structure seems to have followed an acid pathway to mainly generate long chain alkanes and olefins. However, when carbonate and hydroxide alkali metals were added to the reactor, the reaction pathway changed towards the formation of amides. The addition of calcium carbonate and calcium hydroxide did not impact the CHNO composition of the biocrude with average values of 74.72% carbon, 9.7% hydrogen, 6.6% nitrogen, and 8.98% oxygen (by difference). However, the addition of sodium carbonate resulted in a lower biocrude carbon content of 71.97% and consequently higher concentration of oxygen in its composition at 13.6%. Further analysis of the biocrude properties, as well as the impact of the addition of calcium carbonate, calcium hydroxide, and sodium carbonate on the ACP and biochar properties, will also be discussed.