Modeling and Optimizing of NH₄⁺ Removal from Stormwater by Coal-Based Granular Activated Carbon Using RSM and ANN Coupled with GA

• Main Authors: Aixin Yu, Yuankun Liu, Xing Li, Yanling Yang, Zhiwei Zhou, Hongrun Liu
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Water
• Subjects: response surface methodology (RSM); back-propagation artificial neural network (BP-ANN); genetic algorithm (GA); coal-based granular activated carbon (CB-GAC); stormwater
• Online Access: https://www.mdpi.com/2073-4441/13/5/608

As a key parameter in the adsorption process, removal rate is not available under most operating conditions due to the time and cost of experimental testing. To address this issue, evaluation of the efficiency of NH₄⁺ removal from stormwater by coal-based granular activated carbon (CB-GAC), a novel approach, the response surface methodology (RSM), back-propagation artificial neural network (BP-ANN) coupled with genetic algorithm (GA), has been applied in this research. The sorption process was modeled based on Box-Behnben design (BBD) RSM method for independent variables: Contact time, initial concentration, temperature, and pH; suggesting a quadratic polynomial model with <i>p</i>-value < 0.001, R² = 0.9762. The BP-ANN with a structure of 4-8-1 gave the best performance. Compared with the BBD-RSM model, the BP-ANN model indicated better prediction of the response with R² = 0.9959. The weights derived from BP-ANN was further analyzed by Garson equation, and the results showed that the order of the variables’ effectiveness is as follow: Contact time (31.23%) > pH (24.68%) > temperature (22.93%) > initial concentration (21.16%). The process parameters were optimized via RSM optimization tools and GA. The results of validation experiments showed that the optimization results of GA-ANN are more accurate than BBD-RSM, with contact time = 899.41 min, initial concentration = 17.35 mg/L, temperature = 15 °C, pH = 6.98, NH₄⁺ removal rate = 63.74%, and relative error = 0.87%. Furthermore, the CB-GAC has been characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET). The isotherm and kinetic studies of the adsorption process illustrated that adsorption of NH₄⁺ onto CB-GAC corresponded Langmuir isotherm and pseudo-second-order kinetic models. The calculated maximum adsorption capacity was 0.2821 mg/g.