A comparative study on the effects of NaOH and CaCl2 additives on dewatering properties and product characteristics of oily scum via hydrothermal treatment

•NaOH and CaCl2 improved the dewatering properties of oily scum.•Compared with NaOH, CaCl2 had a stronger dewatering ability.•The chemical compounds in the liquid product from oily scum HT were obtained.•The combustion behaviors of the obtained hydrochars were evaluated. Hydrothermal treatment (HT) is used to upgrade oily scum for its disposal and utilization. The effects of sodium hydroxide (NaOH) and calcium chloride (CaCl2) on the dewatering properties and product characteristics of oily scum via HT were investigated in this study. Results showed that NaOH and CaCl2 proved effective in terms of increasing the liquid product and decreasing the moisture content in hydrochars. Compared with NaOH, CaCl2 resulted in a higher liquid product and a greater moisture removal capacity after HT of oily scum. The addition and adding concentrations of NaOH or CaCl2 had significant influences on combustion behaviors of hydrochars. The combustion kinetic parameters of hydrochars derived from HT of oily scum with NaOH or CaCl2 were obtained. The results can provide valuable reference for enhancing the dewaterability and resource utilization of oily scum.