Simultaneous removal of ammonium, phosphate, and phenol via self-assembled biochar composites CBCZrOFe₃O₄ and its utilization as soil acidity amelioration

High concentrations of ammonium, phosphate, and phenol are recognized as water pollutants that contribute to the degradation of soil acidity. In contrast, small quantities of these nutrients are essential for soil nutrient cycling and plant growth. Here, we reported composite materials comprising biochar, chitosan, ZrO, and Fe₃O₄, which were employed to mitigate ammonium, phosphate, and phenol contamination in water and to lessen soil acidity. Batch adsorption experiments were conducted to assess the efficacy of the adsorbents. Initially, comparative studies on the simultaneous removal of NH₄, PO₄, and phenol using CB (biochar), CBC (biochar + chitosan), CBCZrO (biochar + chitosan + ZrO), and CBCZrOFe₃O₄ (biochar + chitosan + ZrO + Fe₃O₄) were conducted. The results discovered that CBCZrOFe₃O₄ exhibited the highest removal percentage among the adsorbents (P < 0.05). Adsorption data for CBCZrOFe₃O₄ were well fitted to the second-order kinetic and Freundlich isotherm models, with maximum adsorption capacities of 112.65 mg/g for NH₄, 94.68 mg/g for PO₄ and 112.63 mg/g for phenol. Subsequently, the effect of CBCZrOFe₃O₄-loaded NH₄, PO₄, and phenol (CBCZrOFe₃O₄-APP) on soil acidity was studied over a 60-day incubation period. The findings showed no significant changes (P < 0.05) in soil exchangeable acidity, H⁺, Mg, K, and Na. However, there was a substantial increase in the soil pH, EC, available P, CEC, N-NH₄, and N-NO₃. A significant reduction was also observed in the available soil exchangeable Al and Fe (P < 0.05). This technique demonstrated multi-functionality in remediating water pollutants and enhancing soil acidity.