A National Survey of Pathogens, Indicators, and Aerosol Toxins in Class A and Class B Biosolids

Accurate aerosol modeling of infectious and respiratory health risk associated with land application of biosolids requires an in-depth knowledge of the magnitudes of pathogen and inflammatory agent concentrations for a variety of Class A and Class B stabilization methods. The following survey of 29 different utilities used quantitative PCR (qPCR) and culture assays to detect environmentally resistant bacterial and viral pathogens, lung inflammatory agents (e.g. endotoxins), and biosolids indicator organisms for biosolids from four stabilization processes, including Class B mesophilic anaerobic digestion (16 samples), and Class A temperature-phased anaerobic digestion (8 samples), MAD plus composting (10 samples), and MAD plus heat pelletization (2 samples). Indicator concentrations as well as pathogen genome concentrations for human adenovirus spp., Legionella pneumophila, Staphylococcus aureus, and Clostridium difficile were significantly lower in Class A biosolids, while lung inflammatory agents were comparable between the two classes. Pathogen genome and aerosol toxin concentrations in bulk biosolids were combined with previously described reconstruction methods and a biosolids aerosol transport model to predict pathogen and inflammatory agent dose at typical community setback distances.