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

Abstract

This study aimed to simulate deactivation of E. coli in soils amended with cattle manure after burning, anaerobic digestion, composting or without treatment. 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 was 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 fertiliser. 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. The results from this study suggest that the safest method for production of organic fertiliser would involve anaerobic digestion to reduce E. coli followed by composting to reduce its persistence.