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Determining pathogen and indicator levels in Class B municipal organic residuals used for land application
Citation:
Rhodes, E., L. Boczek, M. Ware, M. McKay, J. Hoelle, M. Schoen, AND E. Villegas. Determining pathogen and indicator levels in Class B municipal organic residuals used for land application. JOURNAL OF ENVIRONMENTAL QUALITY. American Society of Agronomy, MADISON, WI, 44(1):265-274, (2015).
Impact/Purpose:
As we move towards more sustainable practices to capture and reuse nutrient rich organic residuals (e.g., biosolids) that can be used to amend soils for food production worldwide, the human health effects associated with direct or indirect exposure to land applied biosolids needs to be addressed. The overall goal of this study is to assess the levels of microbial contaminants (bacteria, viruses, and protozoa) in biosolids throughout the United States.
Description:
Biosolids are nutrient rich organic residuals that are currently in use to amend soils for food production. Treatment requirements to inactivate pathogens for production of Class A biosolids are energy intensive. One less energy intensive alternative is to treat biosolids to Class B standards, but could result in higher pathogen loads. Quantitative microbial risk assessments (QMRA) have been conducted on land application of Class B biosolids, but current models developed contain many uncertainties because of limited data on specific pathogen densities and the use of fecal indicator organisms as accurate surrogates of pathogen loads. To address this gap, a 12-month comprehensive survey of the levels and relationships between Cryptosporidium, Giardia, and human adenovirus [HAdV]) with fecal coliform, somatic and F-RNA coliphage levels in Class B biosolids from nine wastewater treatment plants throughout the United States was conducted. Results revealed that fecal coliform, somatic, and F-RNA coliphage densities were relatively stable throughout the year. Further, results revealed that HAdV (1.5x105 viral particles/dry g) and Giardia (4.14 x103 cysts/dry g) were in all biosolids samples regardless of treatment processes, location, or season. Results also showed that Cryptosporidium spp. oocysts were also detected (38 % positive; range: 0 -1.9 x 103 oocysts/dry g), albeit sporadically. A positive correlation among three fecal indicator organisms and HAdV, but not protozoa levels, were detected. This study provides a comprehensive survey of the levels of pathogens present in biosolids throughout the US, which can further assist risk management and policy makers to establish more accurate human exposure risks levels associated with land application of partially treated municipal biosolids.
