This study evaluates the effects of levulinic acid addition and different operating conditions on the physicochemical and structural properties of the resultant OPT hydrochar as well as on the liquid phase composition to identify its potential reaction pathway during wet torrefaction. The addition of levulinic acid enhances the solid yield and HHV of the hydrochar and promote repolymerisation and condensation reactions for the formation of secondary char with high HHV. The highest energy yield of 66.47 was attained from the OPT hydrochar wet torrefied at 220 °C for 24 h with 1.0 M of levulinic acid. Increasing the levulinic acid concentration promoted secondary chars to agglomerate. Liquid phase analyses showed that wet torrefaction of OPT in the presence of levulinic acid promotes the hydrolysis of hemicellulose and cellulose to glucose at mild operating conditions and enhances the rehydration of 5-HMF to levulinic acid. © 2023 The Authors