The effect of excess water on the hydrothermal carbonization of anise waste from ouzo production on Lesvos island

Beverage and food production industries are playing a major role in the local economy of Lesvos Island, with ouzo production being - by far-the most prominent one. In the framework of this present study, anise waste from ouzo production were sampled and valorized by means of hydrothermal carbonization (HTC) for the production of hydrochars. The novelty of this study is the examination of the products quality for different excess water percentages in the hydrothermal reactor. In addition, the hydrothermal treatment of anise waste is a novel and unique application. On the one hand, the analysis included the assessment of the chemical oxygen demand (COD), the total phenolic content (TPC), the pH and the conductivity of the HTC liquors. On the other hand, the higher heating value (HHV), the mass yield and the phytotoxicity were assessed for the produced hydrochars. The COD and TPC fluctuated for moderating conditions of temperature and excess water. On the one hand, reduced excess of water increased the mass yield and the HHV, while it reduced the pH values of hydrochars. On the other hand, all hydrochars had low germination index values, which is an indicator that the use of hydrochar as soil amendment is problematic and should be further investigated.