# Effect of Pyrolysis Conditions on Removal of Pb(II) from Aqueous Solution by Biochar Derived from Anaerobically Digested Sewage Sludge Pretreated with nZVI

## TL;DR

This study shows how biochar made from sewage sludge and treated with iron can effectively remove lead from water, with optimal results at 700°C.

## Contribution

The novel use of nZVI pretreatment in anaerobically digested sewage sludge biochar for enhanced Pb(II) removal is demonstrated.

## Key findings

- nZVI pretreatment significantly improved Pb(II) removal efficiency.
- Biochar at 700°C with aluminum foil wrapping achieved 99.4% Pb(II) removal.
- Adsorption mechanisms included surface precipitation, ion exchange, and complexation.

## Abstract

This study investigated the ability of anaerobically digested sewage sludge biochar (ADSSBC), pretreated with nanoscale zero-valent iron (nZVI) prior to anaerobic digestion (AD), to remove lead (Pb(II)) ions from aqueous solutions. Batch adsorption experiments were conducted to evaluate the effects of various parameters, including nZVI dosage, O2-exclusion method (aluminum foil wrapping or N2 purging), pyrolysis temperature (300–800 °C), adsorbent dosage, pH, coexisting ions, contact time, and initial Pb(II) concentration. Experimental data were fitted to adsorption kinetic and isotherm models. The characteristics of nZVI30-ADSSBC-700 before and after Pb(II) adsorption were analyzed using FTIR, SEM–EDS, XPS, and XRD to identify the adsorption mechanisms. The results showed that nZVI addition at 30 mg/g-TS prior to AD significantly enhanced Pb(II) removal efficiency compared with the control. Among the investigated pyrolysis temperatures and O2-exclusion methods, the biochar produced at 700 °C using aluminum foil wrapping exhibited the highest Pb(II) removal efficiency (99.4%) at an initial Pb(II) concentration of 200 mg/L. The maximum Langmuir adsorption capacity obtained for this biochar was 139.3 mg/g. The pseudo-second-order kinetic model best described the Pb(II) adsorption kinetics. The investigated models and the results of physicochemical analyses indicated the involvement of both physical and chemical adsorption mechanisms, including surface precipitation, ion exchange, pore filling, and, to some extent, complexation.