Effect of Wastewater and Compost on Transport of Some Heavy Metals in Soil Profile

In order to investigate the effect of wastewater and compost on transport of heavy metals in a soil column, a factorial experiment based on completely randomized design with three replication was conducted. The variables included three types of water: fresh water (W₁), treated wastewater (W₂) and a composition of 50% raw wastewater and 50% fresh water (W₃). Besides, four levels of compost were also studied: the control without compost: 0 (C₁), 40 (C₂), 80 (C₃) and 120 (C₄) t/ha. Soil sampling was done at three depths: 10 (D₁), 40 (D₂) and 85 cm (D₃). Based on these factors: 12 W_iC_j treatments, 12 W_iD_j treatments and 9 C_iD_j treatments were studied. In this regard, 36 volumetric metal lysimeters (30×30×126 cm) were designed. Soil in the lysimeter had three layers: upper (clay), middle layer (clay loam) and bottom layer (sandy clay loam), respectively. After the preparation of lysimeters, basil was planted in them. After harvesting the basil, soil samples were taken from 10, 40 and 85 cm and amounts of Ni, Pb, Cd, Fe, Cu, Zn and Mn were measured. The results showed that the effects of type of water, level of compost, and soil depth on all of the elements were significant (p< 0.05). The dual and trial interactions effects of the factors (except type of water*compost and depth*water type*compost) were significant (p< 0.05) for all elements. The highest concentration of the elements were observed in the W₃ C₄ D₁. In the W₃C₄ treatment, rates of Pb (474%), Cd (508%), Cu (550%), Zn (463%) and Fe (411%), and in the C₄W₂ treatment, rate of Ni (563%) and Mn (570%), were increased compared to the control. Based on the results, to reduce risks of long-term environmental impacts of heavy metals from wastewater and compost application, continuous monitoring of soil and water resources is necessary.