Phenol contaminated municipal wastewater treatment using date palm frond biochar: Optimization using response surface methodology

Abstract

Phenol is classified as an emerging contaminant which can be very toxic even at low concentrations and should be removed from wastewaters before reaching the environment. In this study date palm frond and leaf were pyrolyzed at different temperatures to identify the best adsorbent (feedstock) and pyrolysis temperature to remove phenol from aqueous solutions. Date palm frond pyrolyzed at 600 °C, termed DPF600, achieved the highest phenol removal rates of 64% and adsorption capacity of 15.93 mg/g. Response surface methodology approach using Box-Behnken design was implemented to obtain the optimal pH (6), contact time (20 h) and dosage (0.1 g) for the maximum phenol adsorption. A predicted adsorption capacity was found as 16.62 mg/g which was in close agreement with the experimental adsorption capacity of 17.38 mg/g. Isotherm and kinetic models in both linear and non-linear forms indicated that Freundlich model (R2 = 0.99, χ2 = 0.02, RMSE = 1.09) and pseudo-second order model (R2 = 0.99, χ2 = 0.85, RMSE = 5.41) fit best the obtained experimental data. Thermodynamics calculations affirmed that the adsorption of phenol onto DPF600 biochar was endothermic and spontaneous. The point of zero charge was found to be at 6.5 for DPF600 biochar. Scanning electron microscopy coupled with energy dispersive X-ray, Fourier transform infrared spectroscopy and X-ray diffraction confirmed adsorption of phenol onto DPF600 biochar. Application of DPF600 biochar to remove phenol from synthetic primary and secondary treated wastewater samples achieved 60 and 85% removal rates and 241 mg/g and 22.28 mg/g adsorption capacities, respectively. Regeneration studies showed promising adsorption capacities indicating the efficacy of DPF600 for the removal of phenol from wastewater.