Hybrid use of coal slag and calcined ferralsol as wetland substrate for improving phosphorus removal from wastewater

Abstract

In this study, natural ferralsol (NF) was calcined to enhance its phosphorus (P) adsorption. The NF and calcined ferralsol at the selected temperature (CF500) were characterized by SEM, FTIR, XRD, XRF and other experiments to elucidate changes in morphology and physicochemical properties. CF500 and coal slag (CS) were examined as wetland media individually and combinedly. The applicability of CF500 and CS as the hybrid media in the lab–scale horizontal sub–surface flow constructed wetlands (HSSF–CWs) was evaluated. It was found that 500 °C was the best calcination temperature of NF for P adsorption. The maximum P adsorption capacity of CF500 (19.4 mg/g) was 60.4 ± 2.2 % greater than that of NF. While isotherm data of P sorption by CF500 were fitted both Langmuir and Freundlich models, the kinetic data was better described by Pseudo-second-order model. Thermodynamic parameters revealed the endothermic and spontaneous nature of the P sorption by CF500. The combination of CF500 and CS leveraged the merits of individual substrates while mitigated their demerits. The optimal mixing ratio of CF500 to CS was 1.25:1 by volume. The hybrid CF500–CS substrate HSSF–CWs demonstrated satisfactory P removal efficiency (99.44% ± 0.1) and effluent P concentration (0.08 ± 0.01 mg/L). Application of the mixed substrate in the HSSF–CWs resulted in negligible side effects on their effluent quality. Due to abundant availability of raw materials, simplicity of preparation, as well as efficiency and safety of application, a mixture of CF500 and CS is a promising hybrid substrate in HSSF–CWs for P–rich wastewater decontamination.