Pistia stratiotes L. Biochar for Sorptive Removal of Aqueous Inorganic Nitrogen

Biochar has proven effective in the remediation of excess nitrogen from soil and water. Excess nitrogen from agricultural fields ends up in aquatic systems and leads to reduced water quality and the proliferation of invasive species. This study aimed to assess the efficiency of chemically surface-modified biochar produced from invasive Pistia stratiotes L. for the adsorption of inorganic nitrogen (NH₄⁺ and NO₃^-). Biochar structure was investigated using scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and inductively coupled plasma mass spectrometry. The results from adsorption experiments indicate that NH₄⁺ removal was optimal (0.8-1.3 mg N g^-1) at near-neutral pH levels (6.0-7.5), while NO₃^- removal was optimal (0.4-0.8 mg N g^-1) under acidic pH conditions (4.8-6.5) using the modified biochar. These findings highlight the significance of solution pH, biochar morphology, and surface chemistry in influencing the adsorption of NH₄⁺ and NO₃^-. However, further studies are necessary to assess the potential oxidative transformation of NH₄⁺ to NO₃^- by biochar, which might have contributed to the reduction in NH₄⁺ in the aqueous phase.