Remediation of lead-contaminated soil using dissolved organic carbon solutions prepared by wine-processing waste sludge

• Higher DOC concentration, temperature, and liquid/soil ratio encourage the removal of Pb.
• About 95% of Pb was removed from the surface soil (5340 mg Pb kg-1) by the enhanced DOC washing.
• The enhanced DOC treatment enabled maintenance of soil fertility after washing.
• The presence of Ca2+ and Mg2+ encouraging the Pb removal was observed in this study.

Wine-processing waste sludge and alkaline substances, including KOH, NaOH, Ca(OH)2, and Mg(OH)2, were employed to prepare various dissolved organic carbon (DOC) solutions for remediating a Pb-contaminated cropland by soil washing. The Pb concentrations were 5340 and 4920 mg kg− 1 in the topsoil and subsoil, respectively. Aqueous solution treatment, general DOC treatment, and enhanced DOC treatment were proposed as treatments for the reclamation and determination of the factors affecting the removal of Pb, such as pH, initial concentration of the DOC solution, temperature, and washing frequency. The aqueous solution treatment could not remove sufficient Pb and therefore failed in the reclamation. Approximately 86.5% Pb was removed from the topsoil at pH 2.0 by the general DOC treatment undergoing two wash cycles. However, over 90% Pb was removed from the subsoil under the same conditions; only the final Pb concentration in the subsoil met the control standard, 500 mg kg− 1. About 93% Pb in the topsoil could be removed at pH 3.0 by the enhanced DOC treatment, which was performed using a 2500 mg L− 1 DOC solution containing abundant Ca2 + and Mg2 + at an 80:1 liquid/soil ratio (v/v) at 40 °C for 60 min. Meanwhile, organic matter, cation exchange capacity, NH4+-N, as well as exchangeable K, Ca, and Mg contents increased by 125%, 22.6%, 107%, 577%, 55.3%, and 306%, respectively, and the pH in the topsoil decreased to 3.7. The use of Ca(OH)2 and Mg(OH)2 not only prevented washing losses of the exchangeable Ca and Mg but also increased Pb removal by 20%. However, its use decreased the availability of P in the soil.