Enhancing wastewater denitrification performance through a sequentially integrated electrocoagulation–sand filtration system: Multi-objective optimization by RSM-CCD analysis
摘要
In this research, a three-stage continuous reactor involving an electrocoagulation (EC) unit and dual-step simultaneous horizontal sand filtration (SF) was designed to achieve the maximum potential of the EC-flocculation method for the denitrification process. The system employs a hybrid electrode arrangement with Fe cathodes and Al anodes, operating at a head difference of 1.5 cm. A set of 30 experiments according to the central composite design (CCD)-based response surface methodology (RSM) was designed to optimize the effects of the main parameters, including initial nitrate concentration (90-450 mg/l), process time (10-130 min), initial pH (2-10) and current intensity (1-3.8 A) on the EC-SF system performance. Moreover, the ANOVA results confirmed a satisfactory agreement between the experimental and predicted data for removal efficiency, energy consumption and flow rate of the process, with R2 values of 0.96, 0.98, and 0.75, respectively. Notably, employing sand filtration as a post-treatment improved the flocculation efficiency (>90%) of destabilized nitrate ions through capturing unsaturated aluminum hydroxide particles within the sand media. The optimum conditions with an initial nitrate concentration of 187.2 mg/l, current intensity of 1.7 A, 100 minutes reaction time and pH 5 resulted in 93.52% nitrate elimination efficiency with a flow rate of 10 ml/min and energy consumption of 4.29 kWh/