Optimization of a zeolite-packed denitrifying biofilter treating mixed textile wastewater and secondary effluent via response surface methodology

In this study, the performance of a zeolite-packed denitrifying biofilter treating a mixture of textile wastewater and secondary effluent was optimized using response surface methodology (RSM). The effects of textile wastewater ratio (TWR), hydraulic retention time (HRT) and pH on chemical oxygen demand (COD), total organic carbon (TOC), color and nitrate removal efficiencies were systematically investigated. Quadratic models showed good predictive ability and significant agreement between experimental and predicted results (p < 0.0001). The results indicated that pH was the most influential factor for COD, TOC and nitrate removal, while TWR had the strongest effect on color removal. Increasing pH and HRT enhanced overall treatment performance, whereas higher TWR levels negatively affected most responses due to increased refractory organic and dye compound loading. Multi-response optimization identified the optimum conditions as 24.05% TWR, 14.38 h HRT and pH 7.59. Under these conditions, the predicted removal efficiencies were 80.93% for COD, 76.26% for TOC, 47.50% for color and 67.36% for NO 3 - -N, which were successfully validated experimentally with removal efficiencies of 81.20%, 76.70%, 47.90% and 67.80%, respectively. The zeolite-packed denitrifying biofilter demonstrated effective simultaneous removal of organic matter, color, and nitrate, combining adsorption and biofilm-based denitrification in a single treatment system.