Abstract
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 p-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.
Highlights
In recent years, with the development of intensive urbanization, population growth, land use transformation, pollution, and changing climate patterns, fresh water availability has become one of the main issues facing humankind [1]
The ANOVA and response surface plots in response surface methodology (RSM) confirmed that contact time was the most significant parameter of NH4+ removal, and the relative influence order of the factors according to the coefficients of the code equation is as follows: Contact time > temperature > pH > initial concentration
The results of sensitivity analysis showed that the factors of NH4+ removal rate were in the order of: Contact time (31.23%) > pH (24.68%) > temperature (22.93%) > initial concentration (21.16%)
Summary
With the development of intensive urbanization, population growth, land use transformation, pollution, and changing climate patterns, fresh water availability has become one of the main issues facing humankind [1]. In this context, stormwater is being considered in water-stressed cities as an alternative water resource [2]. Despite its potential for augmenting water supplies and reducing runoff flood, urban stormwater contains contaminants that pose risks to human health and aquatic ecosystems. The high level of ammonia in water imparts taste and odor problems, can cause symptoms in aquatic organisms such as hypoxia, coma, and decreased immunity, resulting in slow growth and even a large numbers of deaths [8,9]
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