An analysis of the transport of bacteria from biosolids through the unsaturated profiles of three different soils

Stabilized sewage biosolids are commonly used as a soil amendment, but transport through soil of any microbial pathogens present is poorly understood. Soils differ fundamentally in texture and structure; those containing greater amounts of finer particles tend to form more stable structures that allow water to percolate but bypass the soil matrix. Undisturbed soil monoliths were collected from three representative Ontario soils.{09}Transport of microorganisms through these monoliths was investigated under controlled conditions, using bacteria present in liquid and dewatered stabilized sewage biosolids ( Escherichia coli, Salmonella spp., fecal streptococci and Clostridium perfringens) and two tracers (Geobacillus stearothermophilus and fluorescent polystyrene microspheres). Transport of bacteria was mainly associated with preferential flow. More microorganisms were transported through finer-textured soils than coarser-textured materials, and more were transported following the application of liquid biosolids than after dewatered material. E. coli and fecal streptococci were good indicators for transport of vegetative pathogens and microspheres, but not of spore-forming bacteria.