# Application of Iron-Modified Activated Carbon for Phosphate Removal in Aqueous Systems
## 4 Conclusions  
The current research has explored the applicability of surface-modified activated carbon to prevent phosphorus leaching from river beds as well as testing for the potential for river bed remediation. Novel approaches were taken to simulate the leaching characteristics under stirred batch simulations. Additionally, the removal of phosphate from sediment layers was also observed under hydraulic stress. The results showed high degrees of phosphorous sorption under various hydraulic stresses, indicating a promising method for algae prevention and river bed remediation. The individual results derived from the study are summarized below:  
* Adsorption experiments comparing activated carbon (AC) and ferric chloride-modified activated carbon (SMAC) were conducted to evaluate phosphate removal efficiency. SMAC exhibited significantly enhanced anionic removal capacity due to surface modification, and its adsorption behavior followed the Freundlich isotherm model. The phosphate removal efficiency was positively correlated with the amount of cationic iron bound to the AC surface; however, it was found that metal-modified activated carbon exhibits an optimal modification point for maximizing adsorption efficiency, which in this study was achieved with a ferric chloride concentration of 0.2 M. The adsorption behavior of SMAC followed the Freundlich isotherm model, indicating a heterogeneous surface and multilayer adsorption mechanism. * Applications of SMAC to river bed conditions were tested to prevent phosphate leaching. For this, field conditions were simulated to verify the effects of hydraulic flow at the soil of Chudong water area. In this study, we used stirred batch simulations to represent the turbulent flow conditions during applications. Under static conditions without hydraulic flow, SMAC exhibited approximately twice the phosphate removal efficiency compared to normal AC. Moreover, as hydraulic flow intensity increased, the effectiveness of SMAC in preventing phosphate leaching became even more pronounced, indicating its superior performance under dynamic water conditions. * Long-term experiments were conducted to assess phosphate removal within the soil layer under hydraulic stress conditions. Phosphate concentrations in pore water were found to decrease exponentially with depth, consistent with hyperheic exchange processes enhanced by flow conditions. Additionally, the application of SMAC consistently reduced phosphate leaching over time and contributed to soil remediation, regardless of hydraulic stress. Due to its stable performance under both static and dynamic hydraulic conditions, along with its ease of synthesis and field application, SMAC shows strong potential as a versatile material for sediment contamination control in diverse aquatic environments such as river beds, lake beds, and coastal areas. * To advance the applicability of SMAC in environmental remediation, further research is required to address several limitations of the current study. The present work did not assess competitive adsorption effects in the presence of coexisting anions such as sulfate (SO4\({}^{2-}\)), nitrate (NO3\({}_{-}\)), and bicarbonate (HCO3\({}_{-}\)) under realistic water chemistry conditions. Additionally, long-term stability, reusability, and regeneration potential remain unexplored, which are essential for field deployment. Moreover, large-scale validation under diverse environmental conditions--such as variations in salinity, pH, and dissolved oxygen--is necessary to optimize SMAC's performance for practical applications. Addressing these research needs will help establish SMAC as a reliable and robust material for sediment contamination control and water quality management. Conceptualization, W.-H.S. and S.C.; Investigation, W.-H.S., G.-E.K. and J.-Y.L. ; Writing--original draft, W.-H.S. ; Writing--review & editing, W.-H.S. and S.C.; Visualization, W.-H.S. ; Project administration, S.C.; Funding acquisition, S.C. All authors have read and agreed to the published version of the manuscript.