Adsorption and desorption of lead in Iranian acid and alkaline soils amended with sewage sludge-derived biochar

The effective management of sewage sludge materials in an environmentally and economically acceptable way is through the pyrolytic conversion of the sludge to biochar and its use for agricultural purposes. The aims of this work were: (1) to assess the effect of biochar prepared from sewage sludge at two different temperatures (350 oC and 650 oC) on the adsorption/desorption capacity of Pb (II) in two different Iranian soils (acidic and alkaline soils), and (2) to investigate the adsorption/desorption isotherm. The results indicated that with increasing pyrolysis temperature, the soil pH, ash content, aromaticity, BET, and total heavy metal concentration increased. On the other hand, the pyrolysis yield, percentages of H, N and O, atomic ratios, CEC and polarity of biochar decreased. The adsorption and desorption of Pb was more accurately described by the Langmuir isotherm than the Freundlich isotherm The maximum adsorption capacity of biochars increased for alkaline and acidic soils when pyrolysis temperatures increased, suggesting that high temperature pyrolysis led to the biochars having high Pb adsorption capacity. The desorption of pre-adsorbed Pb (II) by NaNO3 decreased in soils incorporated with biochars.