Effect of biological sewage sludge and its derived biochar on accumulation of potentially toxic elements by corn (Zea mays L.).

The land application of sewage sludge can cause different environmental problems due to the high content of potentially toxic elements (PTEs). The objective of this study was to compare the effect of urban biological sewage sludge (i.e. the waste of activated sludge process) and its derived biochar as the soil amendments on the bioavailability of PTEs and their bioaccumulation by corn (Zea mays L.) under two months of greenhouse conditions. The soil was treated by adding biochar samples at 0 (control), 1, 3, 5% w/w. The diethylenetriamine pentaacetic acid (DTPA)-extractable concentrations of PTEs including Zn, Pb, Cd, Cr, Ni, Fe, and Cu in soil and their accumulation by plant shoot and root were measured. Conversion of the biological sewage sludge into the biochar led to decrease the PTEs bioavailability and consequently decreased their contents in plant tissues. The DTPA extractable metal concentrations of produced biochar in comparison to the biological sewage sludge reduced 75% (Cd), 65% (Cr), 79% (Ni and Pb), 76% (Zn), 91% (Cu) and 88% (Fe). Therefore, the content of Ni, Fe, Zn and Cd in corn shoot was decreased 61, 32, 18 and 17% respectively in application of 5% biochar than of raw sewage sludge. Furthermore, the application of 5% biochar enhanced the physiological parameters of the plants including shoot dry weight (twice) and wet weight (2.25 times), stem diameter (1.70 times), chlorophyll content (1.03 times) in comparison to using 5% raw sewage sludge. The results of the study highlight that application of the biochar derived from urban biological sewage sludge in soil could decrease the risk of PTEs to the plant.

Pretreatment of lignocellulosic waste as a precursor for synthesis of high porous activated carbon and its application for Pb (II) and Cr (VI) adsorption from aqueous solutions.

Effects of Elm tree sawdust pretreatments using alkali and alkaline earth metals (NaCl, KCl, CaCl2, MgCl2 and Elm tree ash) and deashing solutions (water, HCl, HNO3 and aqua regia) before the carbonization process on the porosity of produced activated carbons and Pb (II) and Cr (VI) adsorption were studied. The activated carbons were characterized by pore size distribution, surface area, FTIR, and SEM-EDX analysies. Based on the results, HCl leaching pretreatment of the biomass increased the activated carbon adsorption capacity of Cr (VI) from 114 to 190 mg g-1. The treatment of biomass with alkali and alkali earth metal salts, especially MgCl2, remarkably increased the activated carbon adsorption capacity of Pb (II) from 233 to 1430 mg g-1. The results indicated that Pb (II) adsorption was attributed to both the mesoporous structure of activated carbon and the abundance of Mg on the activated carbon's surface. On the other hand, the micropores played a major role in Cr (VI) adsorption capacity. The development of the micro- or mesoporous structure of activated carbons through pretreatment of lignocellulosic precursor could be an approach for providing high performance activated carbons for Pb (II) and Cr (VI) removal from aqueous solutions.