(524b) Catalytic Hydrothermal Gasification of Post Hydrothermal Liquefaction Waste Water for Biogas Production

Hydrothermal liquefaction (HTL) of complex organic materials yields products including bio crude oil, post HTL wastewaster (PHWW). The PHWW contains approximately 100,000 mg/L COD of organics, which are mostly water soluble organic acids and nitrogen-containing aromatics. In order to further assimilate the residual energy and nutrients in PHWW, a sequential catalytic hydrothermal gasification (CHG) was used in this study to produce valuable biogas to maximize the energy recovery from HTL process, reuse the nutrients, and at the same time clean the PHWW. The effect of catalyst selection was investigated using ruthenium (Ru), sodium hydroxide (NaOH), and zeolite, which were used individually and in combination (e.g. Ru plus NaOH) to determine the optimal organic removal rate, gas yield, chemical compositions of gas products, and nutrient fate. Preliminary results demonstrated that a high gasification efficiency of 98% could be achieved in terms of COD removal. Hydrogen production was able to reach up to 28 mmol per g of organics in the PHWW, and methane (CH₄) production up to 21 mmol per g organics in the same condition. The concentration of water soluble short chain organic acids (C1-C4) increased, compared to PHWW feedstock, at lower temperature of 400°C but then decreased and was almost completely removed at higher temperature of 600°C. The concentration of ammonia-nitrogen was raised by 68% in the PHWW after CHG treatments, indicating that a significant denitrogenation of the nitrogen-containing aromatic compounds took place, thus better nutrient recovery was achieved.