Occurrence and Levels of Fecal Indicators and Pathogenic Bacteria in Market-Ready Recycled Organic Matter Composts

Abstract

Landfill diversion of organic wastes through composting is making compost products available for agricultural and horticultural crops. On certified organic farms, nonsludge green waste and manure composts are widely used because the use of these products removes harvest date restrictions imposed by the U.S. Department of Agriculture when raw manure is applied. We quantified several pathogens in point-of-sale composts from 94 nonsludge facilities processing 2.2 million m3 year(-1) of recycled green waste. Only one compost contained Salmonella (1.8 most probable number [MPN]/4 g), 28% had fecal coliforms exceeding the Environmental Protection Agency 503 sludge hygiene limits (1000 MPN g(-1)), and 6% had detectable Escherichia coli O157:H7. In 22 of 47 samples, very low levels of Listeria spp. were found. However, in one sample the Listeria level was very high, coinciding with the highest overall level of all pathogen indicators. Seventy percent of the compost samples were positive for Clostridium perfringens, but only 20% of the samples had levels >1000 CFU/g. All samples were positive for fecal streptococci, and 47% had >1000 MPN g(-1). Statistical analyses conducted using documented site characteristics revealed that factors contributing to elevated pathogen levels were large facility size, large pile size, and immaturity of compost. Application of the California Compost Maturity Index distinguished compost products that had very low levels of E. coli from those with high levels. Products produced with windrow methods were of higher microbiological quality than were those produced with static pile methods, and point-of-sale bagged composts scored very high. These data indicate that compost that is hygienic by common standards can be produced, but more effort is required to improve hygiene consistency in relation to management practices.

Organic Cultivation of Tomato in India with Recycled Slaughterhouse Wastes: Evaluation of Fertilizer and Fruit Safety

“…One compost sample contained Salmonella, 28% presented fecal coliforms exceeding the EPA 503 sludge hygiene limit and 6% had detectable E. coli O157:H7. Similar to our observations bulk compost products that were processed in the open had significantly higher fecal coliforms than bagged products [8]. Salmonella has a very high probability of proliferation in the environment by animal slurry and may survive from 6 to 47 °C for more than 77 days [26].…”

“…Fecal coliforms may be considered as useful indicators of organic fertilizer hygiene [8]. Furthermore, the number is within the EPA 503 limit (1000 MPN g −1 fecal coliforms) for organic fertilizers [8]. Alike our results, non-pathogenic E. coli in mature composts were reported in situations where the composting process employed was not carried out for an adequate time period at a high enough temperature [11].…”

“…The number decreased to 1.26 ± 0.18 log CFU mL −1 after processing, while 1.16 ± 0.08 log CFU mL [11] and not regarded as pathogens [24]. Fecal coliforms may be considered as useful indicators of organic fertilizer hygiene [8]. Furthermore, the number is within the EPA 503 limit (1000 MPN g −1 fecal coliforms) for organic fertilizers [8].…”

“…E. coli O157:H7 cells subjected to heat-shock may show increased thermo-tolerance and virulence, thus emphasizing the importance of re-growth within heat-treated substrates [13]. Brinton et al (2009) [8] quantified microorganisms in point-of-sale composts from 94 non-sludge facilities. One compost sample contained Salmonella, 28% presented fecal coliforms exceeding the EPA 503 sludge hygiene limit and 6% had detectable E. coli O157:H7.…”

“…In the United States, Salmonella and E. coli O157:H7 have been implicated in fresh produce-related outbreaks since 2005. Increased concern about E. coli O157:H7 from manures and green composts entering the food chain and its potential presence on vegetable products have been raised [8]. Application of untreated contaminated waste to land may aggravate the environmental spread of E. coli O157:H7 [9] and thus application methods of organic wastes play an important role in spread and survival of this pathogen [10].…”