Pristine biochar performance investigation to remove metals in primary and secondary treated municipal wastewater for groundwater recharge application

In this study, pristine biochar derived from date palm at 500℃ was used in batch reactors (simulating blending adsorbent in aeration tank) and fixed-bed columns (simulating holding adsorbent in fixed-bed reactors). The removal performance of the biochar was assessed toward single and mixed-metal solutions as well as synthetic primary and secondary treated wastewater for copper (Cu²⁺), iron (Fe²⁺), nickel (Ni²⁺) and zinc (Zn²⁺). The order of maximum adsorption capacities of the metal ions at pH 7 followed: Fe²⁺ (2.92/2.94 mg/g)>Cu^{2 +}(2.69/2.78 mg/g) >Zn²⁺(2.03/2.19 mg/g)>Ni²⁺(1.69/1.02 mg/g) in single/mixed-metal solutions and Zn²⁺(2.91/11.26 mg/g)>Fe²⁺(0.60/5.29 mg/g)>Cu²⁺(0.56/5.05 mg/g)>Ni²⁺(0.13/ 2.02 mg/g) in synthetic primary/secondary treated wastewater. Blending biochar in aeration tank reduced metal concentrations. The metal ion concentrations in the final effluent were below the World Health Organization drinking water limits (2, 0.3, 0.1 and 3 mg/L for Cu²⁺, Fe²⁺, Ni²⁺ and Zn²⁺, respectively) suggesting that treated secondary wastewater can be spread into potable aquifers following disinfection. The Freundlich and the Pseudo-second order models fit best the batch experimental data. Experimental data from column analysis fit well to the Thomas model. The adsorption of metal ions on the surface of biochar was confirmed by Scanning electron microscopy, Energy dispersive X-ray studies, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Desorption studies using different eluents demonstrated the reusability potential of the studied biochar.