Evaluating the Water Quality Impacts of Hydrothermal Liquefaction Assessment of Carbon, Nitrogen, and Energy Recovery

This research evaluates possible water impacts arising from creation of potent wastewaters during hydrothermal liquefaction (HTL) of organic wastes. Aqueous co-products (ACPs) arising from HTL of eight feedstocks contained very high concentrations of traditional wastewater pollutants: 100–3300 mg/L total nitrogen (N), 45–3600 mg/L total phosphorus (P), and 16,000–234,000 mg/L chemical oxygen demand (COD). pH was 4.4–8.8. These characteristics render ACP more noxious than relevant benchmark wastewaters. Adjustment of published energy ratio metrics to account for ACP treatment reveals that energy yield is moderately decreased, and energy consumption for COD, TN, and TP removal is of the same order of magnitude as liquefaction. Recovery of valuable nutrients (i.e., N and P) from ACP via precipitation could reduce the energy intensity of ACP management and mitigate its impact on energy recovery. In particular, precipitation-based nutrient recovery could enhance HTL's appeal as means to valorize waste into renewable energy and valuable scarce materials.