Evaluation and optimization of a pilot-scale catalytic ozonation–persulfate oxidation integrated process for the pretreatment of dry-spun acrylic fiber wastewater

An integrated process of catalytic ozonation–persulfate oxidation was developed for the pretreatment of dry-spun acrylic fiber (DAF) wastewater on a pilot scale. Box–Behnken design and response surface methodology (RSM) were used for the design and optimization of the integrated process. A second-order polynomial regression equation was established to describe the chemical oxygen demand (COD) and total nitrogen (TN) removal efficiency of the integrated process and was validated by the analysis of variance and residual techniques. The interaction effects of operational parameters were investigated using response surface analysis. Results showed that the maximum COD and TN removal efficiency of 42.36% and 28.51% were achieved for DAF wastewater when the reaction time, reaction temperature, addition of ozone and addition of persulfate were 4.44 h, 61.82 °C, 40 g h −1 and 1.3 kg t −1 , respectively. Furthermore, the biodegradability of raw and treated DAF wastewater was compared, and the (BOD 5 )/COD (B/C) ratio increased from 0.078 to 0.315, indicating a significant biodegradability improvement. The comparison of N composition before and after the integrated process indicated that organonitrogen was converted into ammonia nitrogen, nitrate nitrogen, and nitrogen, which resulted in the removal TN. This result confirmed that the integrated process of catalytic ozonation–persulfate oxidation was effective in improving the biodegradability of DAF wastewater and was promising for pretreatment prior to biological treatment.