INACTIVATION REGROWTH DYNAMICS OF SALMONELLA AND FECAL COLIFORMS IN CLASS B BIOSOLIDS AND BIOSOLID-AMENDED SOIL
Ian Pepper1, Kathleen Zaleski2, Charles Gerba,2 and Karen Josephson2
1, The University of Arizona, Environmental Research Laboratory, USA
2, Department of Soil, Water and Environmental Science, Arizona, USA
(free)
Anaerobically (8% solid) and aerobically (2% solids) digested US Class B biosolids were pumped into field scale drying beds, and microbial populations were monitored during solar drying. Survival of fecal coliforms and Salmonella decreased as temperature and rate of dessication increased. After 3 to 4 weeks Class A requirements were achieved in both biosolids for the pathogens and the indicators. However, following rainfall events, significant regrowth was observed for both fecal coliforms and Salmonella. Laboratory studies subsequently showed regrowth of fecal coliforms in both biosolids and biosolid amended soil, but the regrowth of Salmonella observed in the concrete lined drying beds did not occur. These studies demonstrated that pathogens decreased in numbers when soil was amended with biosolids. Based on serotyping, regrowth of Salmonella seen in the drying beds was most likely due to contamination from fecal matter introduced by animals, and not from Salmonella indigenous to biosolids.
KEYWORDS Biosolid-amended Soil, Regrowth, Salmonella
