Exploring mechanism of five chemically treated biochars in adsorbing ammonium from wastewater: understanding role of physiochemical characteristics

Excess existence of ammonium in water bodies is a hazard to aquatic health. Recent studies demonstrated the use of pig manure biochar (PBC) as a potential adsorbent for ammonium removal. This study investigates alteration in the adsorption capability of modified PBCs to ammonium. Modifications were done by immersing PBC in different acid/alkaline mediums such as H₂SO₄ HCl, NaOH, KOH, and FeSO₄. Adsorption kinetics of modified PBC to ammonium was studied and compared. Also, physical characteristics of these modified biochars were analyzed using BET, SEM, XRD, and FTIR to explore the ammonium adsorption mechanism. The adsorption capacity of ammonia nitrogen was improved for PBC_KOH and PBC_HCl, whereas it was found to decrease for other modified biochars. The improvement is likely due to an increase in specific surface area and pore size as well as formation of active functional groups and ions during the modification process. While both pseudo-first-order kinetics (R² > 0. 9) and pseudo-second-order (R² > 0.9) kinetics could fit the adsorption kinetic data well, among modified biochars, PBC_FeSO4 and PBC_H2S04 fit better with pseudo-first-order model, while others fit pseudo-second-order model better. Both Langmuir and Freundlich model were in good agreement with the adsorption isotherm data for raw and modified biochars (R² > 0.9). Variation in the adsorption capacity of ammonia nitrogen by different modified PBC might be due to synthesis of both physical and chemical factors. This study will lay a theoretical foundation for the future exploration of modification treatments of pig manure biochar for adsorption of ammonia nitrogen from wastewater.