Effect of the deposition of Ca2+on the Fe-based catalyst in the catalytic ozonation of high-salinity wastewater

Fe-based catalysts used for catalytic ozonation process (COP) were widely investigated. However, there was almost no research on engineering application of Fe-based catalyst for advanced treatment of high-salinity pharmaceutical wastewater. In this study, Fe shavings were used to form Fe-based monolithic catalyst packing, which was effectively applied to a pharmaceutical factory. It was found that chemical oxygen demand (COD) removal decreased by ∼ 20% after more than three years of operations. Regression analysis showed that ozone (O3) dosage and hydraulic residence time (HRT) had significant impact on the catalytic performance. The characterization results of Fe-based catalyst demonstrated that calcium carbonate (CaCO3) was deposited on the surface of the Fe-based catalyst inside the packing, and partial γ-FeOOH were converted into α-FeOOH. These phenomena impaired the catalytic capacity of Fe-based catalyst and further reduced the production of hydroxyl radicals (OH). Besides, the increase in bulk density of Fe-based monolithic catalyst packing indicated that the packing has collapsed. By comparing the surface film properties of Fe-based catalyst in wastewater with different salinity, it was concluded that high-salinity wastewater would accelerate the corrosion of Fe-based catalyst. This study can provide a reference for the engineering application of catalytic ozonation technology in high-salinity wastewater.