Enhancement of sludge dewaterability via the thermal hydrolysis anaerobic digestion mechanism based on moisture and organic matter interactions

Abstract

It is known that sludge dewaterability improves during the thermal hydrolysis process (THP); however, the effect of thermal hydrolysis and anaerobic digestion (THP-AD) on sludge dewaterability is unclear. Further, the difference between thermal hydrolysis as pre-treatment for anaerobic digestion (pre-THP-AD) and as post-treatment (post-THP-AD) is also unclear. Based on the evolution of the interaction between organic matter and moisture, the mechanism of pre-THP-AD and post-THP-AD improving the sludge dewaterability was explored. The capillary suction time values of pre-THP-AD and post-THP-AD increased by 58% and 59%, respectively, and the proportion of free moisture increased by 10.44% and 10.59%, respectively, compared with the conventional anaerobic digestion (CAD) process. The cell structure was destroyed and most organic matter was converted into dissolved form through THP, organic matter degraded during AD, the interaction between moisture and organic matter declined, and the mechanically bound moisture transformed into free moisture. Additionally, the intensity of hydrophilic functional groups, such as amide I decreased and amide II disappeared after (pre- and post-) THP-AD. The surface hydrophobicity of sludge samples was enhanced and sludge dewaterability improved. The mechanism of pre-/post-THP-AD enhanced sludge dewaterability based on the interaction between moisture and organic matter; additionally, this will provide a reference for optimised moisture-sludge separation processes and guidance for the optimisation of engineering operation parameters.