Biohythane production of post-hydrothermal liquefaction wastewater: A comparison of two-stage fermentation and catalytic hydrothermal gasification

Developing efficient methods to recover energy from post-hydrothermal liquefaction wastewater (PHW) is critical for scaling up hydrothermal liquefaction (HTL) technology. Here we evaluated two-stage fermentation (TF) and catalytic hydrothermal gasification (CHG) for biohythane production using PHW. A hydrogen yield of 29 mL·g⁻¹ COD and methane yield of 254 mL·g⁻¹ COD were achieved via TF. In comparison, a higher hydrogen yield (116 mL·g⁻¹ COD) and lower methane yield (65 mL·g⁻¹ COD) were achieved during CHG. Further, a techno-economic and sensitivity analysis was conducted. The capital cost and operating cost for TF varied with the different reactor systems. TF with high-rate reactors suggested its promising commercialized application as it had a lower minimum selling price (−0.71 to 2.59 USD per gallon of gasoline equivalent) compared with conventional fossil fuels under both the best and reference market conditions. Compared with TF, CHG was only likely to be profitable under the best case conditions.