Effects of different biochars on physicochemical properties and immobilization of potentially toxic elements in soil - A geostatistical approach

The impact of different biochars (BCs) on the physicochemical properties and immobilization of potentially toxic elements (PTEs) in contaminated soil irrigated with industrial wastewater for the last three decades was studied. Furthermore, the efficacy of applied BCs in reducing geostatistical risks was also evaluated. For this purpose, BCs were prepared from green waste (Cynodon dactylon L.) for the first time at different pyrolysis temperature (400 °C, 600 °C and 800 °C), and amended the contaminated soil in pots with two different ratios of 2% and 5% (w/w) under controlled conditions. The BCs amended soil samples were analyzed after five months (equivalent to the life span of a wheat crop). The physicochemical impacts of applied BCs on the soil showed that the acidic soil was changed to basic. A tremendous increase in water holding capacity, cation exchange capacity, dissolved organic carbon, carbon, phosphorus and potassium contents was observed. The PTEs concentrations and geostatistical risks were significantly (p ≤ 0.05) decreased by all the BCs. Among them, BC prepared at 800 °C and applied at a ratio of 5% was showed the best effects by reducing the bioavailable concentrations of Cd, Pb, Cr, Ni, Cu, Mn, Fe, As, Co and Zn in 88%, 87%, 78%, 76%, 69%, 65%, 64%, 63%, 46% and 21%, respectively. Similarly, significant (p ≤ 0.05) reductions in geoaccumulation index, enrichment factor, contamination factor, and ecological risk were recorded. Therefore, BC prepared at 800 °C and applied at a ratio of 5% is recommended for soil remediation.