Hydrothermal pretreatment of press mud: Characterization and potential application of hydrochar and process water

In the present study, press mud (PM), a major waste by-product from sugar industries, was subjected to hydrothermal pretreatment (HTP) to create resource recovery opportunities. The HTP process was performed with the PM samples in a laboratory scale high pressure batch reactor (capacity = 0.7 L) at 160 °C and 200 °C temperatures (solids content = 5 % and 30 %). The pretreatment resulted in separation of solid and liquid phases which are termed as solid hydrochar (HC) and process water (PW), respectively. High heating value (HHV) of HC was ∼14-18 MJ kg^-1, slightly higher than that of PM (14 MJ kg^-1). The thermogravimetric analysis showed about 1.5-1.7 times higher heat release from HC burning compared to that observed from combustion of PM. Apart from this, the HC and PM showed no phytotoxicity during germination of mung bean (Vigna radiata). Moreover, the biochemical methane potential test on the PW showed a generation of 167-245 mL biogas per gram of chemical oxygen demand added. Hence, the HTP offers several resource recovery opportunities from PM which may also reduce the risks of environmental degradation.