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Applied and Environmental Microbiology, July 2005, p. 3701-3708, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3701-3708.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Potential Regrowth and Recolonization of Salmonellae and Indicators in Biosolids and Biosolid-Amended Soil

Kathleen J. Zaleski, Karen L. Josephson, Charles P. Gerba, and Ian L. Pepper*

Department of Soil, Water, and Environmental Science, The University of Arizona, Tucson, Arizona 85721

Received 8 October 2004/ Accepted 8 February 2005

This study evaluated the potential for conversion of Class B to Class A biosolids with respect to salmonellae and fecal coliforms during solar drying in concrete lined drying beds. Anaerobically (8% solids) and aerobically (2% solids) digested Class B biosolids were pumped into field-scale drying beds, and microbial populations and environmental conditions were monitored. Numbers of fecal coliforms and salmonellae decreased as temperature and rate of desiccation 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 increase in numbers was observed for both fecal coliforms and salmonellae. In laboratory studies, regrowth of fecal coliforms was observed in both biosolids and biosolid-amended soil, but the regrowth of salmonellae observed in the concrete-lined drying beds did not occur. These laboratory studies demonstrated that pathogens decreased in numbers when soil was amended with biosolids. Based on serotyping, the increased numbers of salmonellae seen in the concrete lined drying beds following rainfall events was most likely due to recolonization due to contamination from fecal matter introduced by animals and not from regrowth of salmonellae indigenous to biosolids. Overall, we conclude that the use of concrete-lined beds created a situation in which moisture added as rainfall accumulated in the beds, promoting the growth of fecal coliforms and salmonellae added from external sources.

* Corresponding author. Mailing address: The University of Arizona, Environmental Research Lab, 2601 E. Airport Drive, Tucson, AZ 85706. Phone: (520) 626-3328. Fax: (520) 573-0852. E-mail: ipepper{at}ag.arizona.edu.

Applied and Environmental Microbiology, July 2005, p. 3701-3708, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3701-3708.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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