Influence of soil type, moisture content and biosolids application on the fate of Escherichia coli in agricultural soil under controlled laboratory conditions

Aims: To determine the fate of the enteric indicator organism, Escherichia coli, in sewage sludge (biosolids)-amended agricultural soil in relation to soil type and moisture status under controlled conditions. Methods and Results: We enumerated Escherichia coli in soil by membrane filtration and most probable number techniques. The background concentration of E. coli was higher in sandy loam than in silty clay soil. E. coli numbers increased in soil following addition of dewatered, mesophilic anaerobically digested sludge. Escherichia coli declined to a small extent with time in both moist and air-dried unamended control soils, although decay was only highly significant (P < 0.001) in moist sandy loam (T-90 = 100 days). Removal rates were high in sludge-treated moist soil (T-90 = 20 days), but were significantly reduced in amended air-dried soil. Conclusion: Slow removal of E. coli in air-dried soil as against their rapid decay in moist soil after sludge application indicated that the soil biota are involved in pathogen reduction processes in sludge-amended soil. Significance and the Impact of the Study: Soil ecological mechanisms are implicated as having a critical role in the fate of enteric organisms introduced into temperate agricultural soil in sewage sludge.