Comparative Multi-Descriptor Structure-Performance Patterns in Silicon-Rich Sewage-Sludge-Derived Carbons for As(V) and Pb(II) Removal from Water

Municipal sewage sludge contains carbon and mineral constituents that can be recovered as water-treatment materials. This study compared four silicon-rich carbons prepared under different carbon dioxide activation and nitric-acid modification conditions to examine whether material properties ranked arsenic(V) and lead(II) removal consistently. Pre-contact characterisation combined spectroscopy, microscopy, elemental analysis, nitrogen sorption and surface-charge assessment. Separate model-groundwater solutions containing each contaminant were treated in triplicate at pH 6.0, 6.5 and 7.0. Mean removal ranged from 47.8 to 76.2% for As(V) and from 68.8 to 96.3% for Pb(II). Two-factor analyses detected no significant material, pH or interaction effects at the 5% level. Averaged across the three pH levels, M3 had the highest numerical As(V) removal (71.7%), whereas M1 had the highest numerical Pb(II) removal (92.2%). A separate low-concentration test with M3 reported final concentrations of 0.0080 ± 0.0006 mg L−1 As(V) and 0.0041 ± 0.0004 mg L−1 Pb(II). Fifth-cycle removal remained above 80% for both contaminants, with 88.2% dry sorbent mass recovery after five cycles. The different material rankings indicate that total surface area alone does not describe performance across both contaminants. Further analytical, leaching and natural-water assessments are needed before application to drinking-water treatment.