Mechanistic insights into melanoidins-induced hydrophilicity of thermal hydrolyzed sludge and its impact on dewaterability

Although thermal hydrolysis pretreatment enhances disposal efficiency of sludge, it inevitably leads to melanoidins formation, which will negatively impact the subsequent wastewater treatment processes. However, their effect on the dewaterability of thermal hydrolyzed sludge (THS) remains poorly understood. This study aimed to uncover the underlying mechanisms of how melanoidins affecting dewaterability of THS. Using resin-adsorption method to reduce melanoidins content by 50% led to 21% and 6% decreases in capillary suction time and specific resistance to filtration, respectively, and a 14% increase in sludge cake solid content. Conversely, accumulating melanoidins to 200% worsened THS dewaterability, altering surface morphology and reducing floc stability, which increased the content of bound water by 9%. Additionally, a higher melanoidins level increased the hydrophilic components in extracellular polymeric substances while reducing hydrophobic sites and structures. These findings indicate that melanoidins impair THS dewaterability by altering flocs spatial properties and increasing hydrophilic structures and components.