Summary of Awards to Date

Developing and validating practical strategies to improve microbial safety in composting process control and handling practices.

Date

Jan. 1, 2011 - Feb. 28, 2013

Award Number

2011-147

Amount Awarded

$296,368.00

Investigator

Xiuping Jiang, Ph.D.
Clemson University

Resources
Summary

Compost as soil amendment and organic fertilizer is a major source of nutrients for plant growth. Although the high temperatures generated by microbial activities during active composting can inactivate pathogens, the survival or regrowth of foodborne pathogens during composting process or in the finished compost can be problematic for vegetable production. This proposed study uses a systems approach to address pathogen control during composting process and subsequent storage and handling of finished products, develop and validate some practical strategies, which can be readily adopted by composting operators or growers. In this proposed study, we'll validate the thermal inactivation data of E. coli O157:H7 and Salmonella in compost using naturally occurring isolates; optimize and validate the finished compost as physical covering and straw as the base of passive static compost heaps and windrow compost piles; apply the pathogen growth model to determine the potential of finished composts to support the pathogen growth, and investigate the growth, survival, and control of food borne pathogens in the finished compost. The results from this study will provide practical methods or practices on compost production and handling to eliminate or reduce pathogen contamination of compost, thereby helping produce industry to grow safe products for human consumption.

Technical Abstract

As a major source of nutrients for crop production, the safety of composts as soil amendment and organic fertilizer is critical for ensuring produce safety. Although the high temperature generated by microbial activities during active composting can inactivate human pathogens, the survival or regrowth of these pathogens during composting process or in the finished compost can be problematic for the vegetable production. This proposed study uses a systems approach to address this biological hazard control during composting process and subsequent storage and handling of finished products, develop and validate some practical strategies, which can be used by growers. In this proposed study, first we will use naturally occurring Escherichia coli O157:H7 and Salmonella strains isolated from compost to validate those thermal inactivation data acquired from outbreak strains, which will be conducted inside an environmental chamber to mimic early phase of composting process (Objective I). Since the compost surface is where the pathogens survive the longest due to lower temperature being exposed to, our strategies are to apply the finished compost as covering material and the straw
as the base of compost heaps to minimize the heat loss, and optimize the depth of covering over the freshly formed passive static compost heaps commonly found on small or medium farms (Objective II). Furthermore, we’ll validate this practical pathogen control method in a windrow composting system, and also evaluate the feasibility of weed seed germination as a composting temperature indicator which can be easily adopted by farmers. For Objective III, we’ll apply the pathogen growth model to predict the potential of finished composts (n=30) to support the growth of human pathogens. By comparing with currently required microbiological and maturity tests, we’ll identify the correlation of certain species or population level of background microorganisms with the safety of compost. Finally, we’ll determine the growth and survival of pathogens in the finished compost with different particle sizes, and apply the competitive exclusion (CE) microorganisms isolated and characterized from the previous project to some finished composts with potential for supporting pathogen growth, which will be conducted under greenhouse condition to simulate the storage condition on farm (Objective IV). The results from this study will provide the practical methods or practices on compost production and handling to eliminate or reduce pathogen contamination of compost, thereby helping produce industry to grow safe products for human consumption. This proposal will address the identified research area (1.1) of “Compost, Soil Amendment Fertilizer Use and Cultivation Practices”.