Bacteria Transport and Deposition in Calcareous Soils Under Unsaturated Flow Conditions

Abstract Microbial contaminants transport to groundwater is a serious environmental problem that can result in large outbreaks of waterborne diseases. Some of bacteria can travel from vadose zone and cause contamination of groundwater resources. Thus, an accurate prediction of transport and fate of pathogenic microorganisms in unsaturated soil is needed to protect groundwater resources. The main objectives of this research were quantitative study of bacterial transport and deposition under unsaturated conditions in calcareous soils. A series of column leaching experiment with well-controlled suction and flow rate was conducted. Breakthrough curves (BTCs) of Pseudomonas fluorescens and Cl were measured. After the leaching experiment the bacteria was measured in difference layers of the soil columns. The HYDRUS-1D kinetic attachment-detachment model (AD) was used to evaluate the transport and deposition of bacteria in soil columns. The breakthrough curves in soils were described well by attachment-detachment model. Whereas the model fit underestimate the amount of bacteria retention in the soil columns. The detachment rate was less than 0.001 of the attachment rate, indicating irreversible attachment of bacteria. Most of the cells were retained close to the soil column inlet, and the rate of deposition decreased with depth. Microbial reduction rate for the soil was 10.18-13.34 log m-1. High reduction rate of bacteria was attributed to soil calcium carbonate that has favorable attachment site for bacteria.