Influence of pH and Ionic Composition on Activated Carbon Transport and Retention in Saturated Porous Media

Activated carbon mobility in saturated porous media depends on aqueous conditions that influence particle passage and retention. This study investigated how pH and electrolyte composition affect activated carbon transport and retention in saturated porous media. The effects of pH (4.0–9.0) and three electrolytes (NaCl, CaCl₂ and NaHCO₃) at concentrations of 1 and 10 mmol/L were evaluated using relative effluent concentrations (C/C₀) measured at 1, 3 and 5 pore volumes (PV). Deionised water served as the reference treatment. Activated carbon breakthrough increased with pH, with C/C₀ at 5 PV rising from 0.385 at pH 4.0 to 0.840 at pH 9.0. In contrast, increasing electrolyte concentration reduced breakthrough. At 5 PV, C/C₀ decreased from 0.702 to 0.594 under NaCl, from 0.547 to 0.418 under CaCl₂, and from 0.735 to 0.651 under NaHCO₃ as concentration increased from 1 to 10 mmol/L. CaCl₂ produced the lowest effluent concentrations among the electrolyte treatments, indicating the greatest retention under the tested conditions, whereas NaHCO₃ produced comparatively higher breakthrough. Compared with deionised water (C/C₀ = 0.786 at 5 PV), all electrolyte treatments reduced activated carbon breakthrough. Mass balance analysis showed that 65 mg of the 100 mg injected was recovered in the effluent, while 25 mg was independently measured as retained material, giving a total mass recovery of 90%. The findings demonstrate that activated carbon transport through saturated porous media varied substantially with pH, electrolyte concentration and electrolyte composition. These results highlight the importance of aqueous chemical conditions in evaluating activated carbon mobility and retention in porous systems.