Bacteria survival experiment for assessment of wastewater reuse in agriculture

Growth and survival of a strain of E. coli were investigated in laboratory-scale soil columns under essentially static conditions in three Egyptian agricultural soils. One pore volume of a buffer solution of known cell concentration was applied to a set of identical columns at time zero, and individual columns were analyzed for viable E. coli colony forming units at times ranging from 1 hr to 7 d and at various soil depths. The resulting concentration-depth profiles yielded information that can promote proper application of wastewater reuse in agriculture and the assessment of associated health and environmental risks. Biomass growth in soil occurred over the first 2 to 3 days after application, achieving biomass production 40–70 times the number of cells applied depending on the soil. Culturable populations declined to only a few viable cells at the end of 7 days. E. coli growth rate and total biomass production were well correlated to the soil organic content. Indoor conditions resulted in slower but more prolonged E. coli growth than in outdoor experiments, verifying the determinative roles of climatic factors and soil moisture.