Bimetallic Fe-Mn-impregnated activated carbon: One-step dry pyrolysis synthesis from hawthorn kernels for COD reduction and nitrate removal from industrial wastewater

Analysis of wastewater from industrial estate No. 3 in Yasouj showed high levels of COD and nitrate. This wastewater was treated using an adsorption process with Fe 3 O 4 /Mn 2 O 4 /Activated carbon made from hawthorn kernels (Fe:Mn:AC). The composite was produced through a one-step dry pyrolysis method. Characterization analyses using FTIR, XRD, SEM, EDX, BET, and VSM techniques were conducted, revealing a mesoporous structure (BET analysis) with various functional groups on the Fe:Mn:AC adsorbent (FTIR analysis). The effects of solution pH, adsorption time (kinetics), and initial contaminant concentration on equilibrium in batch adsorption were examined. The greatest reduction in COD and nitrate occurred in an acidic environment (pH = 3–4). Kinetic analysis with different models indicated that the data best fit the Elovich and pseudo-second-order models, highlighting the importance of external diffusion (film diffusion) during adsorption. The equilibrium data aligned well with the extended Langmuir isotherm, which predicted maximum adsorption capacities of 148.021 mg/g for COD and 136.463 mg/g for nitrate. Continuous flow experiments demonstrated that flow rate and bed height affected the removal of COD and nitrate, confirming the high adsorption capacity of the Fe:Mn:AC adsorbent.