Heat and lime-treatment as effective control methods for E. coli O157:H7 in organic wastes

Land-application of abattoir wastes is economically appealing and may provide an effective means of closing the nutrient cycling loop. This practise is constrained, however, by legislation which necessitates pre-treatment to remove pathogenic micro-organisms prior to land-spreading. Here we investigated whether heat-treatment or lime addition could eliminate Escherichia coli O157:H7 from three contrasting abattoir wastes. We found that treatment at 60 °C for 10 min effectively eradicated the organism while treatment for the same length of time at 50 °C led to 2–4 log reductions, but not a complete kill. Temperatures of 72 °C induced waste solidification rendering its use impractical. The potential for re-growth in heat-treated and untreated wastes was also investigated. Survival was significantly greater in heat-treated wastes, although the difference was less than half a log unit in magnitude. This effect of heat-treatment on pathogen survival appeared to be ameliorated when wastes were mixed with soil. No viable E. coli O157:H7 cells were recovered from any waste after application of lime (CaO) at a rate of 10 g l−1, even after enrichment. Our results indicate that pasteurisation-style or liming treatments may provide a suitable alternative method for reducing pathogen loads in abattoir wastes, so that they can be applied to land with minimal biological risk.