The release of sludge-born bacteria and their further subsurface transport was studied. The migration of bacteria was investigated in column experiments which were carried out under the conditions corresponding to naturally occurring extreme rainfall. Coal fly ash as well as coarse and medium grained sand, whose properties are similar to the soils present in degraded areas, were used as column beds. Sewage sludge was applied on the top of column beds in the quantity corresponding to the best land-reclamation practice. Clostridium perfringens and fecal coliforms were used as bio-tracers of fecal pollution. The obtained results showed the dynamic of bacterial cells' leaching from the sludge matrix, and the dynamic of their infiltration through the column beds to the effluents. The bacterial breakthrough curves obtained for the fly ash and for the sandy media differ significantly, reflecting the differences in transport processes and in the survival of bacterial cells. It has been found that the fly ash layer, whose thickness equals 0.80 m, can be regarded as an effective filter, which limits bacterial migration. When sludge is applied to the sandy soils, about 0.02% of the initial number of sludge bacteria can migrate downwards the sandy layer and can cause contamination of potentially shallow aquifers.
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