Persistence of salmonella during dairy manure compost at different sampling events and thermal conditions

Application of animal manure to agricultural land is considered as a viable option in exchange of commercial fertilizer application considering the environmental impacts. However, animal manure can be a source of several pathogenic bacteria such as Salmonella which can survive in manure or manure-amended soil for extended period of time. Considering the economic and environmental significance associated with animal manure application into cropland, a laboratory scale bench top study was conducted to determine the inactivation trend in dairy manure compost. Composted solid samples were collected at various sampling frequencies and different thermal conditions for two weeks to get a holistic understanding about the inactivation of Salmonella in initial phase of composting process. Collected samples were analyzed according the Bacteriological Analytical Manual (BAM) suggested by USFDA. Results from the analysis found almost 5 orders of magnitude reductions from initial Salmonella concentration of 1.6 x 109 cfu/ gm in compost at 37°C over the period of the experiment. While evaluating the effects of sampling time (between morning and evening) during the first three days of experiment, there was significant interaction between day and time of sampling in the compost samples. In addition to 37°C composting study, an intensive heat stress study was carried out at 48 and 58°C by collecting samples at 30 mins interval for 2 hrs (0, 30, 60, 90, and 120 mins) to observe the effect of elevated temperatures on inactivation of Salmonella during the 10th day of the experiment and the results showed that the change in Salmonella levels was inconsistent in composted material. We anticipate that the results will help in improving dairy manure management, and also provide scientific insight to the policy makers and farm owners, while using composting as a method of animal manure treatment.