Effect of Cow Manure’s Particle Size on Bacterial Contamination Transport in Soil using Attachment-Detachment Model under Saturation Condition

Livestock manures are a source of pathogenic microorganisms that cause contamination of water surface and groundwater. The aim of this study was to simulate the effect of cow manure granulation on the transmission coefficients of Escherichia coli in a column of sand under saturated flow. Cow manure with particle sizes of 0.25, 0.5, 1 and 2 mm equivalent to 30 (ton/hec) in terms of dry weight was used. The effect of fertilizer treatments on the transmission of Escherichia coli in the soil was investigated by measuring the number of bacteria and chloride detector in the drainage water, up to 20 cm3 of pore volume. In order to determine chloride, Levenberg-Marquardt algorithm and nonlinear optimization were used, and to determine bacterial retention and transfer, a two-site kinetic Attachment-Detachment equation and inverse solution were used. The results showed that the bacterial transfer simulation was performed well for all fertilizer treatments by HYDRUS-1D using a two-site kinetic model (average of mean deviation and coefficient of determination was 0.056 and 0.905 respectively). The 0.25 mm treatment had the best agreement with the simulation results. The highest concentration of wastewater bacteria was obtained in the fertilizer treatment of 2 mm, which is due to the coarseness of fertilizer particles and faster and earlier removal of bacteria from its particles. The lowest attachment coefficient rate, was obtained in the fertilizer treatment of 2 mm (5.59*10-6 s-1) due to the release of more bacteria in this fertilizer treatment and as a result of increasing the rate of detachment coefficient (3.61*10-1 s-1). Also, with increasing soil depth, the amount of bacterial retention increased, which is probably due to the accumulation of bacteria on the surface of soil particles at lower depths.