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.

Impacts of different treatment methods for cattle manure on the spread of faecal indicator organisms from soil to lettuce in Nigeria.

AIM: This study investigated impacts of different organic waste treatment methods on reduction and spread of faecal indicator organisms to food crops in a developing country. METHODS AND RESULTS: Fresh cattle manure was subjected to three different treatments; anaerobic digestion, burning and composting. Escherichia coli, coliforms and nitrogen content of cattle manure were measured before and after treatment in the amended soil and harvested lettuce. All treatments significantly reduced E. coli and coliform counts but differed in the ratio of E. coli or coliforms to nitrogen. Application of the recommended nitrogen dose of 120 kg ha-1 as bioslurry resulted in significantly lower E. coli and coliform contamination of soil than the same nitrogen rate applied as compost or ash. The E. coli content of lettuces grown on soil amended with treated wastes at recommended rates did not differ between treatments but was significantly lower than in lettuces grown on soil amended with untreated manure. CONCLUSIONS: Treatment of manure before use as an organic fertilizer significantly reduces potential contamination of both soil and food crops with E. coli and coliforms. To best reduce the spread of E. coli from organic fertilizers, manures should be treated by anaerobic digestion. SIGNIFICANCE AND IMPACT OF THE STUDY: Information from this study quantifies potential risks associated with use of manures in growing food crops by determining the ratio between pathogen content and required nitrogen application rate.