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

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 differ-ence 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 capil-lary suction time values of pre-THP-AD and post-THP-AD increased by 58% and 59%, respectively, and the propor-tion 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 de-clined, and the mechanically bound moisture transformed into free moisture. Additionally, the intensity of hydro-philic 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 mat -ter; additionally, this will provide a reference for optimised moisture-sludge separation processes and guidance for the optimisation of engineering operation parameters. (c) 2018 Published by Elsevier B.V.

Automated summary

The thermal hydrolysis and anaerobic digestion process improves sludge dewaterability by increasing capillary suction time values and free moisture content, converting organic matter into dissolved form. The interaction between moisture and organic matter declines, leading to enhanced sludge dewaterability.