Modelling the deactivation of Escherichia coli in Nigerian soils amended with differently treated manures.

AIM: This study aimed to simulate deactivation of Escherichia coli in soils amended with cattle manure after burning, anaerobic digestion, composting, or without treatment. METHOD AND RESULTS: The Weibull survival function was used to describe deactivation of E. coli. Parameters for each treatment were determined using E. coli measurements from manure-amended soils and evaluated against measurements at different application rates. A statistically significant correlation and high coincidence between the simulated and measured values were obtained. The simulations revealed that although anaerobic digestion or burning of cattle manure effectively reduced the E. coli loads to background levels, burning retained very little nitrogen, so the ash residue was ineffective as an organic fertilizer. Anaerobic digestion was most effective at reducing E. coli levels while retaining a high proportion of N in the bioslurry residue, but the persistence of E. coli was higher than in compost. CONCLUSION: The results from this study suggest that the safest method for production of organic fertilizer would involve anaerobic digestion to reduce E. coli, followed by composting to reduce its persistence.