Survey of Wastewater Indicators and Human Pathogen Genomes in Biosolids Produced by Class A and Class B Stabilization Treatments

Abstract

Domestic sewage sludges that have been stabilized to reduce pathogen content are termed biosolids; their beneficial reuse for agricultural applications constitutes approximately 60% of the 7 million dry tons generated each year in the United States (6). Driven by health complaints from residents living near application sites, concern has been expressed that a hazardous exposure is created when biosolid aerosols are spread onto fields, incorporated into soils, and released during high-wind events (23,36). Research in the last 5 years has made significant progress in estimating the human exposure to total biosolid aerosols and biosolid indicator microorganisms. Advances include both the development and calibration of theoretical and empirically based microbial aerosol models to assess off-site exposure during land application operations (8,16,31,54) and the application of culture and DNA-based microbial-source tracking methods to these aerosols (5, 14). However, the paucity of information on the viral and bacterial pathogen content of biosolids has limited model use and effectiveness.The U.S. Environmental Protection Agency (EPA) classifies end-product biosolids as class A (pathogen free) or class B (contains pathogens) based on indicator content and/or technologies used for stabilization (48). It is therefore important to distinguish between regulatory classes and treatment classes when describing the pathogen load in biosolids. In large U.S. municipalities, biosolids are most commonly stabilized with mesophilic anaerobic digestion (MAD) to produce a class B product, but current trends show that U.S. utilities have or are considering options for upgrading stabilization technology to produce class A biosolids. This includes the conversion to temperature-phased anaerobic digestion (TPAD) operations and/or composting the biosolids after anaerobic digestion (COM) (20). Meeting class A status requires the monitoring of fecal coliforms for estimating pathogen content, while the monitoring of enteric viruses, helminth ova, and Salmonella spp. is not required as long as "time and temperature" requirements are met. The majority of U.S. class A operations choose to meet class A status with time and temperature treatmentbased alternatives. Based on these regulatory monitoring targets, most culture-or PCR-based biosolid studies have focused on these microorganisms and similar enteric pathogens (i.e., Listeria monocytogenes, enterovirus, and Clostridium perfringens) but have not diversified to other relevant airborne pathogens, like Legionella pneumophila, that may proliferate during stabilization where enteric pathogens cannot (1,9,22,28,34,40,41,53). Only recently, and in limited sample sizes, have researchers begun to directly compare the diverse sludge stabilization methods available, including MAD, liming, and composting, to understand how selected enteric pathogens and indicators are removed (18, 22, 32, 34).

Quantification of Enteric Viruses, Pathogen Indicators, and Salmonella Bacteria in Class B Anaerobically Digested Biosolids by Culture and Molecular Methods

“…Several studies have reported the occurrence of enteric viruses in biosolids (18,35,47); however, information on the quantity and infectivity of enteric viruses in biosolids is still limited, and most studies focused solely on enteroviruses (41). Few studies have reported the levels of human adenoviruses (HAdV) in biosolids (6,47), and no quantitative results have yet been reported on some of the emerging viruses, such as hepatitis A virus (HAV) and noroviruses (NV).…”

Removal of pathogenic bacteria from sewage-treated effluent and biosolids for agricultural purposes

“…However, Viau and Peccia (2009) detected Legionella pneumophila, S. aureus and C. difficile in biosolids generated from 29 STPs in USA which was treated with mesophilic, temperaturephase anaerobic digestion and composting process, which Table 4 Processes to significantly reduce pathogens (PSRPs). Source; US EPA (2003) Treatment process Procedure of the treatment process Composting Using either the within-vessel, static aerated pile, or windrow composting methods, the temperature of the sewage sludge is raised to 40 °C (104 °F) or higher and remains at 40 °C or higher for 5 days.…”

“…In the light of the aforementioned, Enerhall and Stenmark (2012) also reported that TC and enterococci were 5.8 and 5.08 log 10 CFU/100 mL, respectively in treated sewage generated from STP in Sweden, which used filtration system during the disinfection process. Viau and Peccia (2009) stated that the concentrations of FC in biosolids generated from 29 STPs in USA, which use mesophilic anaerobic digestion (MAD), temperature-phased anaerobic digestion (TPAD), composting the biosolids after anaerobic digestion (COM) corresponded to US EPA regulatory limits for each biosolids Class A and Class B.…”

Polioviruses and other Enteroviruses

“…For example, viruses can survive the composting process when certain zones of the heap are not exposed or exposed for too short times to the temperatures required for viral inactivation. Average concentrations and reductions of a variety of enteric pathogens in biosolids by composting (COM) and temperature-phased anaerobic digestion (TPAD) for Class A and mesophilic anaerobic digestion (MAD) for Class B biosolids as well as the annual log probability of viral infections associated with land applications and aerosols were examined in detailed reviews by Viau et al (Viau et al, 2011;Viau and Peccia, 2009). Values for viability and molecular-based determinations were compared.…”