UpcyclingResidual Carbon in Hydrothermal ProcessingWastewater to Cultivate Gluconobacter oxydans

Hydrothermal carbonization and liquefaction (HTC, HTL) are wet biomass valorization techniques that produce biofuels and a recalcitrant, carbon-laden aqueous phase (AP) containing phenolics, furans, and organic acids. Gluconobacter oxydans is an acetic acid bacterium whose incomplete citric acid cycle gives it applications in fermentation and biomining. The goal of this study was to determine if G. oxydans could utilize the carbon present in AP for growth and, if so, which compound groups. Using AP from HTC/HTL of model food waste as a supplement to conventional yeast peptone mannitol (YPM) media, we found that APs produced at higher temperatures contain fewer phenolics and cyclic aldehydes. At lower concentrations, AP aids bacterial growth. As-carbonized AP produced at any temperature increases G. oxydans growth at 5% supplementation of YPM (by volume); AP produced at 310 °C improves growth at up to 25% AP. Dichloromethane extraction of AP either improves or does not change growth for every process temperature and AP concentration tested. COD decreases slightly following bacterial digestion, with the 5-hydroxymethylfurfural concentration decreasing by over 90%. Through this study, we demonstrate G. oxydans growth on high-concentration HTC/HTL AP, partially treating AP and decreasing the need for conventional media.