(400ap) Valorization of HTC-Derived Process Liquid from Dairy Manure for Deep Eutectic Solvent Synthesis

Dairy manure is a significant agricultural waste product, generated around 1.5 billion tons annually by the dairy industries. Effective management and treatment of dairy manure are crucial to mitigate environmental challenges, including water pollution, greenhouse gas emissions, and nutrient run-off. Hydrothermal Carbonization (HTC) has emerged as a promising technology for the conversion of dairy manure into valuable solid biochar, which can be used as a soil amendment or energy source. However, the process also generates a liquid by-product, often regarded as a waste stream. This process liquid contains organic compounds and nutrients that, if left untreated, can pose disposal challenges and environmental risks. Our research aims to valorize this HTC process liquid by utilizing it in the synthesis of efficient and hydrophobic Deep Eutectic Solvents (DES), turning a potential waste stream into a valuable product that will be capable of extracting methylene blue from aqueous solutions. The solvents were synthesized by adding trioctylphosphine oxide (TOPO) and DL-menthol to process liquid from HTC of dairy manure at three distinct temperatures 180°C, 220°C, and 260°C at a 1:1 volume ratio. The process liquid from HTC of dairy manure is rich in organic compounds, including carboxylic acids and amino acids, which can act as hydrogen bond donor (HBD), and the two mentioned components act as hydrogen bond acceptors, facilitating the creation of hydrogen bond networks within the two-phase mixture, and ultimately creating a separate hydrophobic phase that is identified as a DES. Through a comprehensive study, the surface characteristics of the solvents were studied utilizing Conductor-like Screening MOdel for Real Solvents (COSMO-RS), Fourier transform infrared (FTIR), and NMR. The physical properties of the solvents, such as density and viscosity were also evaluated. Finally, the solvent created was utilized for methylene blue removal, with the extraction experiments being conducted using ultraviolet-visible spectroscopy (UV-VIS).