Salmonella reduction in manure by the addition of urea and ammonia

Animal manure may contain pathogenic microorganisms and disinfection is suggested to avoid reinfection of animal herds and introduction of zoonotic disease into the food chain. Ammonia and urea were tested for disinfection of bovine manure and Salmonella was found to be rapidly eliminated by the addition of 0.5% aqueous ammonia or 2% w/w urea (s). Treatments (2% urea and 0.5% ammonia), temperature (4 °C or 14 °C) and combinations of these factors significantly affected the inactivation rate. Decimal values (T90) were reduced from 8.3 days in the control to 2.0 days and 0.4 days at 14 °C after the addition of urea and ammonia, respectively. At 4 °C, the decimal values were reduced from 34 to 4.8 and 1.1 days, respectively. Recommended treatments of bovine manure based on Monte Carlo simulations are 0.5% ammonia followed by storage for one week or 2% urea followed by storage for two weeks at 14 °C, one month at 4 °C. Storage without additives should include at least one summer in temperate regions. Enterococci were evaluated as indicators for Salmonella but significantly slower decay rate and different behaviour in the material made them unsuitable as indicators for Salmonella in manure disinfected by ammonia or urea. Free ammonia treatment of Salmonella-contaminated manure disinfects the material and raises its fertilizer value.