Influence of Tabriz Petrochemical Sludge on Preferential Flow and Bromide Transport Parameters in a Calcareous Loamy Soil

Preferential flow pathways cause leaching of significant amount of nutrient elements from the root zone. The objectives of this study were to evaluate the influence of petrochemical sludge on preferential flow and transport parameters of bromide in convection-dispersion equation (CDE) and mobile-immobile models in a calcareous loam soil. The soil was taken from the research farm of University of Mohaghegh Ardabili. The sludge was prepared from the Tabriz Petrochemical Company. The used rates of fresh sludge were: 0, 25, 50, 75, and 100 t ha-1. After air drying, the sludge was mixed with the air-dried soil and filled in PVC tube (25 cm height and 15 cm diameter) and kept in greenhouse at the temperature of 22 ± 4 ˚C and moisture of 70 to 80 percent of field capacity for 6 months. The experiment was conducted as completely randomized blocks design with 5 sludge rates at 3 replications. Saturated hydraulic conductivity (Ks) and bromide breakthrough curves (BTCs) were measured in soil columns at the end of the sixth month. Dispersivity (λ) at the CDE and MIM models, immobile water (θim) and solute exchange coefficient (α) at the MIM model were estimated by fitting measured BTCs data (time and relative concentration of bromide) to these models using HYDRUS-1D software. All sludge rates significantly decreased Ks by 55% to 67% and increased bromide breakthrough time by 60.29% to 63.19% compared to the control. Dispersivity at both CDE and MIM models significantly increased only for the 50 t ha-1 of sludge compared with the control. The sludge did not significantly affect θim and α parameters. The results showed that petrochemical sludge controlled preferential flow of bromide in the studied soil from semiarid region.