Pseudomonas Fluorescens Adsorption Affected by ‌Calcium Carbonate and Calcium Sulfate under Unsaturated Flow Conditions

Soil is a suitable medium for the growth and transport of different microorganisms. Recently, an increasing interest has been shown in the transport and fate of microorganisms in porous media due to the concern for potential outbreaks of diseases caused by surface and groundwater contamination. Soils in arid and semi-arid regions as in Iran contain considerable amounts of sulfates and carbonates which may influence the adsorption and filtration of bacteria. This research was carried out to determine the adsorption and filtration of Pseudomonas fluorescens through sand columns mixed with different amounts of calcium carbonate and calcium sulfate under unsaturated flow conditions. Four levels of calcium carbonate: 0, 5, 10, and 20 %w/w and three levels of gypsum: 0, 5, and 10 %w/w were mixed with sand and the treatments were arranged in a (completely randomized) factorial design with three replicates. The prepared mixtures were poured homogenously into Pyrex pyrex cylinders with height of 20 cm and internal diameter of 7 cm. A constant concentration (106 CFU m-1) of cylinders 20 cm high and 7 cm in internal diameter. A constant concentration (106 CFU m-1) of bacteria suspensions was supplied at the upper boundary limit of the columns in a steady state flow and was followed for five pore volumes (PV). The bacteria concentration was measured at 0-5, 5-10, 10-15, and 15-20 cm sections of the columns immediately after leaching. The results showed that calcium sulfate and calcium carbonate were able to significantly influence the filtration of bacteria in all measured sections. The combination of carbonate sulfate and calcium carbonate treatments also significantly increased the physical filtration of bacteria along the columns. The retained bacterial profiles and the filtration coefficient obviously showed that the bacteria were held mostly in the upper layers of the columns. Enhanced physical filteration, tortuosity, and reduced apparent pore water velocity are known to be important in bacterial filtration under unsaturated conditions along the column layers. Therefore, these results imply that soils with calcium carbonate and calcium sulfate may play an important role in bacterial filtration and, thereby, in reducing the pollution of water resources.