Treatment of real benzene dye intermediates wastewater by the Fenton method: characteristics and multi-response optimization

Benzene dye intermediates (BDI) wastewater has caused major environmental concern due to its potential carcinogenic, teratogenic, and mutagenic effects. Treatability reports dealing with the advanced chemical oxidation of BDI are limited. In this work, the Fenton method was applied to treat the real BDI wastewater to provide a deep insight into single as well as combinative effects of the main process variables influencing the treatment performance. First, we evaluated the effects of the reaction time, initial pH, initial [H2O2] concentration, and initial [Fe2+] concentration on the Fenton oxidation efficiency of real BDI wastewater. Furthermore, based on the Box-Behnken response surface methodology (RSM), an empirical mathematical model between response values, namely the chemical oxygen demand (COD), total organic carbon (TOC), color removal efficiency, sludge iron mass ration (SIMR), and influence factors were established to evaluate the interaction effects and optimize the experimental conditions. All of the proposed models were adequate with an R-2 range from 0.9561 to 0.9880. In addition, three of these factors had different effects on four studied response values. By overlaying the responses, the optimum conditions were obtained at an initial pH of 4.13, an initial [H2O2] concentration of 1.0 M, and an initial [Fe2+] concentration of 0.36 M. Verification experiments were conducted at the optimum conditions, which led to a COD removal efficiency of 85.29%, a TOC removal efficiency of 75.23%, a color removal efficiency of 99.99%, and a SIMR response of 0.39, respectively, and the results were in good agreement with the values predicted by the model. In addition, the BOD5/COD ratio was observed to increase from 0.08 to 0.49, indicating an improvement in biodegradability.