Ozonation of acidic phenol wastewater with O3/Fe(II) in a rotating packed bed reactor: Optimization by response surface methodology

The relatively low gas–liquid mass transfer efficiency and the low activity of ozone in acidic solution limit the application of ozonation. In this work, ferrous-catalyzed homogeneous ozonation (FCHO) was adopted to treat acidic phenol wastewater in a rotating packed bed (RPB), and the operating conditions in this process were optimized by using a response surface method (RSM). The variables investigated included the rotation speed (300–1500 rpm), liquid flow rate (10–30 L/h), ferrous ion concentration (0–0.8 mM) and inlet ozone concentration (30–70 mg/L). Experiments were carried out on the basis of a central composite design approach. It was found that ferrous ion could effectively enhance the ozonation of phenol and the rotation speed affected both phenol degradation degree and ozonation efficiency greatly. Quadratic models were developed with phenol degradation degree and ozonation efficiency as the responses, and the model predictions were confirmed to fit well with the experimental data with a deviation less than 11%. The BOD/COD values increased from 0.2 to 0.56 at the maximum phenol removal rate in the validation experiment. It is concluded that the quadratic model is an effective tool to optimize the FCHO process of phenol in the RPB.

► Fe(II) as the catalyst to improve ozonation efficiency of phenol. ► A rotating packed bed as the liquid–gas contactor. ► A response surface method (RSM) was used to optimize ozone concentration. ► Model predictions fit well with the experimental data with a deviation less than 11%. ► A phenol removal rate of 70% and a BOD/COD value of 0.56 was reached.