Sustainable recovery of melanoidins from thermal hydrolyzed sludge by macroporous resin and properties characterization.

Melanoidins, the dark-color recalcitrant Maillard reaction by-products in thermal hydrolyzed sludge (THS), cause significant adverse effects on wastewater treatment. This study aimed to develop an efficient adsorption method for recovering melanoidins from THS by macroporous resin. The adsorptive characteristics of six macroporous resins (XAD761, XAD8, XAD16HP, FPX66, HPD-600 and IRA958Cl) showed that XAD761, not yet reported for melanoidins extraction, was the most appropriate with the highest recovery ratio. The adsorption kinetics followed pseudo-second-order model, and the adsorption process was confirmed to be physical, spontaneous, and exothermic, without changing the structure of the adsorbed melanoidins. In the dynamic adsorption, the breakthrough point increased with a decreasing flow rate. After five consecutive regeneration cycles, XAD761 resin maintained stable adsorption efficiency and thus had a good potential for reuse. Furthermore, the physicochemical properties of the extracted THS melanoidins were compared with model melanoidins to lay the foundation for their management, in terms of morphology, molecular weight (MW), and spectrophotometric properties. These results demonstrate that XAD761 resin extraction is a promising sustainable method for practical application in the recovery of melanoidins from THS.