NH4-N-loaded biochars are suitable candidates for soil amendment and fertilization. Sewage sludge-based biochar and biochar from the invasive species black wattle were used as sorbents for the adsorption of ammonia from a concentrated solution to mimic the wastewater treatment plant reject water stream. To increase ammonium recovery efficiency, two post-pyrolysis activation techniques were compared: steam activation and hydrogen peroxide treatment. It was found that the success of the treatment options was material dependent; therefore, post-pyrolysis treatments will require optimization for different applications based on feedstock. A simplified version of an adsorption process simulated in Aspen Tech predicts that NH4-N may be recovered at an energy cost lower than that of the Haber-Bosch process for black wattle biochar yields of below 19.5%. The biooil and syngas produced during pyrolysis can be used to lessen the energy requirements of the process, so that the solid portion may be utilized as an adsorbent and soil fertilizer. The energy-based sustainability of this technology warrants a more in-depth investigation for evaluation of the techno-economic feasibility for this class of loaded sorbents, and whether this method of nitrogen capture from wastewater is a suitable replacement of the costly Haber-Bosch process.