1a. Objectives (from AD-416):
ARS is participating with Clemson University on strategies to improve microbial safety in the composting process. ARS is interested in the role of physical covering on survival of bacteria in composting process systems; static and windrow pile. The Cooperator is interested in laboratory scale studies and alternative compost covering for static pile system.
1b. Approach (from AD-416):
ARS proposes to evaluate finished compost as a physical covering for controlling bacterial pathogens in compost. A comparative set of triplicate static piles and windrow piles will be constructed. The ‘toes’ of the pile at both ends of each windrow will be focal points for microbial sentry samples, continuous temperature dataloggers, and weed seed indicator packets. Microbial sentry samples will be prepared and inoculated with the same strains as used in the Clemson studies and placed in the pile toes, the interface between the new feedstock, and the cover. Compost samples will be collected periodically for quality analyses and target bacteria. Weed seed viability as evidenced by germination following composting for different periods of time/temperature exposure will be described.
3. Progress Report:
The increased number of E. coli O157:H7 and Salmonella outbreaks associated with consumption of fresh produce has led the researchers to investigate the mechanisms of produce contamination at the farm level. Raw or inadequately composted manure can be a potential source of contamination. This study investigated the effect of using finished compost (FC) as covering (10-30 cm deep) on survival of E. coli O157:H12 and Salmonella in static and windrow composting systems. Feedstock inoculated with E. coli O157:H12 and Salmonella were placed in biosentry tubes and placed at approximately 10, 20, and 30 cm depths beneath the surface at three locations in compost piles. Compost samples were analyzed periodically for surviving populations of E. coli O157:H12 and Salmonella. Weed seed germination was investigated as a potential indicator of efficacy of the composting process. Salmonella populations were reduced significantly within 24 h in windrow piles and were below the detection limit after 3 and 7 days in the upper part of windrow and static piles covered with FC, respectively. Likewise, E. coli O157:H12 were undetectable after 1 day in windrow piles with FC. Use of finished compost as a covering significantly increased the number of days that temperatures above 55°C were maintained in windrow piles at all locations and in static piles in the upper part. This resulted in the rapid reduction of inoculated pathogens at these locations. Weed seeds placed in non-covered piles and static piles germinated after 28 days in locations with lower temperatures, concurrent with E. coli O157:H12 survival. These studies confirm that finished compost used as a covering aids in reduction of pathogens during the composting process. Seed germination may be a useful indicator of ineffective composting, hence pathogen survival.