Treating separated liquid dairy manure derived from mesophilic anaerobic digester effluent to reduce indicator pathogens and Salmonella concentrations for use as organic fertilizer

Abstract

Dairy manure has much potential for use as an organic fertilizer in the United States. However, the levels of indicator organisms and pathogens in dairy manure can be ten times higher than stipulated use guidelines by the National Organic Standards Board (NOSB) even after undergoing anaerobic digestion at mesophilic temperatures. The objective of this study was to identify pasteurization temperatures and treatment durations to reduce fecal coliforms, E. coli, and Salmonella concentrations in separated liquid dairy manure (SLDM) of a mesophilic anaerobic digester effluent to levels sufficient for use as an organic fertilizer. Samples of SLDM were pasteurized at 70, 75, and 80°C for durations of 0 to 120 min. Fecal coliforms, E. coli, and Salmonella concentrations were assessed via culture-based techniques. All of the tested pasteurization temperatures and duration combinations reduced microbial concentrations to levels below the NOSB guidelines. The fecal coliforms and E. coli reductions ranged 2from 0.76 to 1.34 logs, while Salmonella concentrations were reduced by more than 99% at all the pasteurization temperatures and active treatment durations.

Keywords:

• Anaerobic digestion
• dairy manure
• E. coli
• fecal coliform
• organic fertilizer
• pasteurization
• pathogens
• Salmonella

Acknowledgments

The authors thank Roy & Kathleen VanderHyde for their collaboration in the study. The authors also thank Sasha Howes, Nicholas Cook, Tamara Smith, and Catherine Colandro for their assistance with activities in the laboratory.