Hydrothermal processing of biomass at temperatures of 180–350 °C under pressure in liquid water yields certain value-added products. However, besides the desired solid phase from hydrothermal carbonization or the desired biocrude oil from hydrothermal liquefaction, both processes also yield a process liquor as a mostly undesired by-product. Those hydrothermal liquid phases are rich in organic compounds and intermediates from the degradation of biomass under these conditions. Most common are organic acids, sugars, phenolic compounds, and furfural derivatives. Such a liquid phase can contain up to 30% of the initial carbon from the biomass. This underlines the necessity of treating those process liquors before releasing them to the environment or classical wastewater treatment plants. As these process liquors contain certain amounts of valuable carbon but simultaneously mostly do not contain certain chemicals feasible for a targeted reclamation, treatment of these process liquors combined with energy production to facilitate the hydrothermal process itself should be an interesting option. Anaerobic digestion (AD) is such an option that can degrade a huge variety of the compounds mentioned earlier turning it into valuable methane. However, AD has some limitations regarding long-chained or aromatic organic compounds. Therefore, wet oxidation (WO) is another interesting option degrading especially those compounds and turning them into short-chained fatty acids simultaneously producing excess heat. Both process could also be combined. This talk will present results from own experiments and literature regarding AD and WO. It will further discuss challenges and options for taking each of them or even a combination of both into account when treating hydrothermal process liquors in a somewhat beneficial fashion.

Treatment of process waters from hydrothermal processing of biomass: Anaerobic digestion, wet oxidation, or both

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