Degradation of pulp mill wastewater by a heterogeneous Fenton-like catalyst Fe/Mn supported on zeolite

A novel heterogeneous catalyst, Fe/Mn supported on NaY zeolite, was effectively applied for treating pulp mill effluents. The results of the wastewater quality analysis showed that aromatic structures were present in raw pulp mill effluents, which indicated the difficulty for biodegradation treatments. Two different catalysts were prepared by impregnation (Fe-Mn/NaYim) and sol-gel (Fe-Mn/NaYsg) methods, respectively. The Fe-Mn/NaYsg catalyst demonstrated higher COD removal efficiency and was more stable than the Fe-Mn/NaYim catalyst. The synergistic effects were found between Fe and Mn for COD removal. The highest COD removal efficiency (75.2%) was yielded with the Fe-Mn/NaYsg catalyst (Fe/Mn molar ratio of 2) with 4 mmol/dm³ of H₂O₂ and 1.2 g/dm³ of catalyst addition. A constant COD removal over time was obtained; the COD removal efficiency amounted to 45% after the Fe-Mn/NaYsg catalyst repeatedly degrading pulp mill effluents for five times. The distribution and transformation of the polarity and molecular weight (MW) of dissolved organic carbon (DOC) in the heterogeneous Fenton process were also studied. Experiments showed that the hydrophobic fraction comprised the largest fraction of DOC (60%) in raw wastewater and high MW molecules were transformed into low MW molecules after the heterogeneous Fenton process. This study broadened the application of the Fenton technology.