Ammonium nitrogen (NH4+-N) recovery from synthetic wastewater using biosolids-derived biochar

The nutrient removal in the wastewater treatment plant is a critical step before the treated water is either recycled or discharged into natural water bodies. The current work provides a low-cost and environmentally sustainable nitrogen recovery approach from wastewater using biosolids-derived biochar. The biochar, produced from the pyrolysis of biosolids, was tested for NH4+-N adsorption from a synthetic wastewater sample via a batch adsorption experiment and compared with biomass-derived biochar, cation exchange resin, zeolite, and activated carbon. The adsorption capacity of biochar produced at 500 °C was around 1.8 mg g−1 for an initial NH4+-N concentration of 50 mg L−1, which was half of the cation exchange resin and zeolite given the presence of sulfonate (-SO3H) and -OH groups on their surface to exchange H+ ion with NH4+-N ion. The external surface layer and intra-particle diffusion were the rate-controlling steps of the adsorption process, as reflected in the kinetic modelling results, where a pseudo first-order model could best describe the evolution of adsorption. The presence of active sites with varied affinities towards NH4+-N adsorption on the heterogeneous surface of the adsorbent and the occurrence of multilayer adsorption were implied by the acceptable fitting of isotherm experimental data to Freundlich and Temkin models, respectively. Biosolids-derived biochar may be an attractive adsorbent for ammonium recovery from wastewater in a circular economy concept.