No abstract

The sorption, desorption, and speciation of cadmium (Cd), nickel (Ni), and iron (Fe) in four calcareous soils were investigated at the pH range of 2-9. The results indicated that sorption of Fe by four soils was higher than 80 % at pH 2, while in the case of Cd and Ni was less than 30 %. The most common sequence of metal sorption at pH 2-9 for four soils was in the order of Fe ≫ Ni > Cd. Cadmium and Ni sorption as a function of pH showed the predictable trend of increasing metal sorption with increase in equilibrium pH, while the Fe sorption trend was different and characterized by three phases. With regard to the order of Cd, Ni, and Fe sorption on soils, Cd and Ni showed high affinity for organic matter (OM), whereas Fe had high tendency for calcium carbonate (CaCO3). Results of metal desorption using 0.01 M NaCl demonstrated that metal sorption on soils containing high amounts of CaCO3 was less reversible in comparison to soils containing high OM. In general, Cd and Ni desorption curves were characterized by three phases; (1) the greatest desorption at pH 2, (2) the low desorption at pH 3-7, and (3) the least desorption at pH > 7. The MINTEQ speciation solubility program showed that the percentage of free metals declined markedly with increase of pH, while the percentage of carbonate and hydroxyl species increased. Furthermore, MINTEQ predicted that saturation index (SI) of metals increased with increasing pH.

Biochar production via pyrolysis is a promising option to be used for sewage sludge treatment. Here we investigated the uptake of potentially toxic elements (PTEs) from sewage sludge and its biochar (450°C) into cherry tomato plants and its fruits in pot experiments (2, 5 and 10%) to assess the health risks associated with fruit consumption. We further studied the ability of the PTE-rich amendments to immobilize PTEs already present in soil through spiking of soil (pH 7.4) with Cd, Cu and Zn. Our ndings suggest that tomato consumption is not a human health risk when grown in soil amended with sewage sludge and its biochar; in most treatments PTE uptake into fruits was similar to the control. Vegetative plant growth was highest in sewage sludge-amended soils.Yet 5 and 10% biochar-amended soils signi cantly increased tomato fruit yield compared to untreated sewage sludge application (400-500% higher than 10% sewage sludge-amended soil) and signi cantly decreased fruit uptake of Cu and Zn. Importantly, biochar also signi cantly immobilized PTEs present in contaminated (spiked) soil. As expected, available (DTPA-extractable) PTE contents were typically lower in biochar-amended soil and sequential extraction indicated that the PTEs were predominantly bound in more recalcitrant soil fractions (organic matter associated and Fe-Mn oxides-bound). We conclude that pyrolysis can be a key technology for sewage sludge treatment and subsequent use of the biochar in urban, and potentially even contaminated, horticultural sites. Statement Of NoveltyThere are some studies on the sewage sludge and its biochar effect on potentially toxic elements (PTEs) behavior in soil-plant system. Yet, less well investigated is the uptake of PTEs into reproductive plant organs, which is of paramount importance for assessing the health risk associated with consumption of plant seeds and fruits. Also, little is known about the potential for immobilization of PTEs by biochar that already contains elevated levels of PTEs. The other novelty of this manuscript is to compare the bioavailability and fractionation of PTEs in spiked soil with non-spiked soils as in uenced by sewage sludge and its biochar addition.

Biochar production via pyrolysis is a promising option to be used for sewage sludge treatment. Here we investigated the uptake of potentially toxic elements (PTEs) from sewage sludge and its biochar (450°C) into cherry tomato plants and its fruits in pot experiments (2, 5 and 10%) to assess the health risks associated with fruit consumption. We further studied the ability of the PTE-rich amendments to immobilize PTEs already present in soil through spiking of soil (pH 7.4) with Cd, Cu and Zn. Our findings suggest that tomato consumption is not a human health risk when grown in soil amended with sewage sludge and its biochar; in most treatments PTE uptake into fruits was similar to the control. Vegetative plant growth was highest in sewage sludge-amended soils. Yet 5 and 10% biochar-amended soils significantly increased tomato fruit yield compared to untreated sewage sludge application (400–500% higher than 10% sewage sludge-amended soil) and significantly decreased fruit uptake of Cu and Zn. Importantly, biochar also significantly immobilized PTEs present in contaminated (spiked) soil. As expected, available (DTPA-extractable) PTE contents were typically lower in biochar-amended soil and sequential extraction indicated that the PTEs were predominantly bound in more recalcitrant soil fractions (organic matter associated and Fe-Mn oxides-bound). We conclude that pyrolysis can be a key technology for sewage sludge treatment and subsequent use of the biochar in urban, and potentially even contaminated, horticultural sites.