Transport of Pseudomonas fluorescents through unsaturated sand columns: Influence of calcium carbonate and calcium sulfate

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Abstract

Transport of pathogenic bacteria has been recently considered a major source surface and subsurface water contaminations. Soil could affect transport or filtering of bacteria depending on its physical and chemical properties. Calcium carbonate and calcium sulfate are two important minerals of arid and semi-arid soils that their effect on bacteria transport has not been investigated, yet. In this study, the influences of calcium carbonate (0, 5, 10 and 20 %w/w) and calcium sulfate (0, 5 and 10 % w/w) in sand mixtures on Pseudomonas fluorescens transport were studied under unsaturated condition the experiment was in factorial arrangement adapted to a completely randomized design with three replicates. The mixtures were poured into pyrex cylinders with length of 20 cm and diameter of 7 cm and a steady unsaturated flow was established. Then, bacteria suspensions of 106 cfu cm-3 were applied as step input on the columns. The effluent concentration was measured during leaching up to 5 pore volumes (PV). The calcium carbonate and calcium sulfate could significantly affect the effluent concentration. The highest and lowest amounts of bacteria transfer were recorded for sand and 20% calcium carbonate treatments, respectively. Calcium carbonate application significantly reduced the effluent concentration. The effect was significant for 0.25 PV, 0.5 PV, 1 PV, 2.5PV and 5 PV. However, the influence of calcium sulfate was not significant in all of the effluent volumes. Breakthrough curves obviously demonstrated the filtering and adsorption of bacteria when calcium carbonate and calcium sulfate and carbonate minerals which might be used to reduce the bacteria transport and/or subsurface water contamination.

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