Regulation of phenol oxidation into polymeric derivatives ready for flocculation using polyaluminum chloride

Phenol, a toxic compound commonly found in wastewater, can be removed using the iron-tetraamidomacrocyclic ligand (Fe-TAML) and H₂O₂. However, it incurs high costs for Fe-TAML and H₂O₂, while treated water retains high chemical oxygen demand (COD) and CO₂ emissions. To address these challenges, this study proposes converting phenol into polymeric derivatives followed by flocculation. Mass spectrometry (MS) reveals that phenol polymerization precedes polyphenol oxidation in the reaction, with slower reactions favoring phenol polymerization over polyphenol oxidation. It further demonstrates that reducing Fe-TAML dosage can slow down the reaction, thereby increasing the formation of polymeric derivatives at pH 10. Subsequent flocculation with polyaluminum chloride (PAC) effectively precipitates these products. When phenol concentration increases from 100 to 2500 ppm (mass ratio of H₂O₂ : phenol : PAC = 10 : 10 : 1), COD rises from 10% to 19%, while CO₂ emissions decrease by over 45%. Meanwhile, the cost is reduced from 4.616 to 3.416 $ per kg phenol, as the Fe-TAML/phenol mass ratio decreases from 0.08% to 0.056%. Overall, this strategy is more cost-effective than conventional methods, requiring less Fe-TAML and H₂O₂ while significantly reducing COD and CO₂ emissions.