Pathogens and Indicators in United States Class B Biosolids: National and Historic Distributions

Abstract

This paper reports on a major study of the incidence of indicator organisms and pathogens found within Class B biosolids within 21 samplings from 18 wastewater treatment plants across the United States. This is the first major study of its kind since the promulgation of the USEPA Part 503 Rule in 1993, and includes samples before and after the Part 503 Rule was promulgated. National distributions collected between 2005 and 2008 show that the incidence of bacterial and viral pathogens in Class B mesophilic, anaerobically digested biosolids were generally low with the exception of adenoviruses, which were more prevalent than enteric viruses. No Ascaris ova were detected in any sample. In contrast, indicator organism numbers were uniformly high, regardless of whether they were bacteria (fecal coliforms) or viruses (phage). Indicators were not correlated with pathogen loads. Historic distributions were collected between 1988 and 2006 at one location in Tucson, AZ. By comparing data collected before and after 1993, the influence of the USEPA Part 503 Rule on indicator and pathogen levels within Class B biosolids can be inferred. In general, the bacterial indicators total and fecal coliforms decreased from the 1980s to present. Enteric virus concentrations after 1993 are much lower than those reported in other studies in the 1980s, although our values from 1988 to 1993 are not significantly different from our values obtained from 1994 to 2006. Presumably this is due to better and more consistent treatment of the wastewater, illustrating that the Part 503 Rule has been effective in reducing public exposure to pathogens relative to 17 yr ago. The percent reduction of both indicators and pathogens during anaerobic mesophilic digestion was between 94 and 99% for all organisms, illustrating that such treatment is effective in reducing pathogen loads.

Impact of Fertilizing with Raw or Anaerobically Digested Sewage Sludge on the Abundance of Antibiotic-Resistant Coliforms, Antibiotic Resistance Genes, and Pathogenic Bacteria in Soil and on Vegetables at Harvest

“…Waste can variously be delivered in the form of untreated raw sewage (i.e., waste handled by a municipal sewer system) or septage (i.e., waste handled by a residential septic system), untreated sewage sludge (i.e., the solid material recovered from wastewater treatment), or treated sewage sludge (also called biosolids) (12,13). In North America, human waste used in agriculture is typically in the form of biosolids, material that has a lower abundance of pathogens than found in untreated material (14). Biosolids are produced by treating (e.g., anaerobic or aerobic digestion) raw sewage sludge to effect modest pathogen reduction (in U.S. parlance, producing class B biosolids) or, more rigorously (e.g., thermal treatment and lime stabilization), to effect significant pathogen reduction (producing class A biosolids).…”

Efficiency of ASTM Method D4994-89 for Recovery of Enteric Viruses from Biosolids

“…Anaerobically digested (mesophilic) Class B biosolids were collected from the Ina Road sewage treatment plant in Tucson, AZ on several different occasions (USEPA 1993). These biosolids average 2.2 enteric viruses per four grams, but were undetectable in any of the samples used in this study (Pepper et al 2010). The percent total dry solids ranged from 6.01 to 8.23% (APHA 2005).…”

Anaerobic Membrane Bioreactor Effluent Reuse: A Review of Microbial Safety Concerns

“…A recent study that investigated the occurrence of indicator organisms in mesophilic anaerobically digested Class B biosolids at 18 different locations across the United states revealed that fecal coliform levels were between 1 × 10 4 and 6 × 10 5 CFU per g at a 95% confidence interval [100], which is reasonably below the maximum allowable level of 2 × 10 6 CFU/g. This range of digested sludge concentrations however is considerably broader than what was observed in associated undigested sludge (1.5 × 10 8 to 4.5 × 10 8 CFU/g), implying that there are other factors also contributing to the variability of mesophilic digester effluents than their respective influent concentrations.…”