Catalytic ozonation of organic contaminants in petrochemical wastewater with iron-nickel foam as catalyst

This work investigated the removal of organic contaminants in actual petrochemical wastewater by catalytic ozonation with iron-nickel foam as catalyst. Under different conditions, the DOC removal percentages ranged from 40% to 61%, the sCOD removals were from 73% to 96% in the reaction time of 120 min. Two thirds of the 66 detected organic compounds disappeared in the treated wastewater. The biodegradability of the petrochemical wastewater was greatly improved after catalytic ozonation. TP, TN, NO3-N, Cl- and some heavy metals in the petrochemical wastewater were also removed to some extent. The influence of pH and initial organic matter concentration on the performance of catalytic ozonation was limited. Increase of aqueous ozone concentration and catalyst dosage was advantageous for organic contaminants removal. The probable mechanism of catalytic ozonation was proposed as that the iron-nickel foam was oxidized by ozone into the mixture of oxides, hydroxides, and hydroxyoxides. On one hand, the hydroxyl groups on the catalyst surface motivated the formation of (OH)-O-center dot. On the other hand, the electrons transferred among different valences of transition metals facilitated the decomposition of ozone. The generated (OH)-O-center dot diffused into bulk solution, working together with ozone to degrade the organic contaminants. From theoretical modeling, the residue ozone in the off gas can be reduced from 98% to 11% by using iron-nickel foam as the catalyst.