Pathogen and Chemical Concerns Associated with the Treatment and Land Application of Biosolids

The treatment and land application of sewage sludge is a standardized and regulated practice in the U.S., however there exist many concerns and challenges to the safe and economic feasibility of this activity. The three challenges which have been investigated in this thesis are: the relationship between energy costs and pathogen indicator inactivation performance of different digester configurations, the first-order behavior and changing composition of the fecal coliform indicator class during digestion, and the relative impacts of polybrominated diphenyl ether inhalation resultant from the emissions from land application fields.;Current and alternative configurations for anaerobic sludge digesters have been evaluated for net energy production and pathogen inactivation potential. Pathogen indicator inactivation performance is expected to be 1-2 log inactivation in mesophilic treatment, and 2-5 log inactivation in 50 to 55°C thermophilic and temperature-phased treatments. Incorporating a 60 or 70°C batch pretreatment phase resulted in dramatically higher potency. Due to shorter residence times in thermophilic reactors, the net energy production for all digesters was similar (less than 20% difference). Therefore incorporating a 60 or 70°C pretreatment phase can dramatically increase pathogen inactivation performance without decreasing net energy capture from anaerobic digestion.;The inactivation of fecal coliforms has been investigated in batch anaerobic sewage sludge digesters at temperatures of 50, 55 and 60°C. E. coli are the dominant fecal coliform across the inactivation process at each temperature. The total fecal coliform concentration was observed to inactivate at a constant first-order rate at each temperature, though less concentrated and less thermotolerant subpopulations were also identified. These results do not elucidate any specific disadvantages to the continued use of fecal coliforms as an indicator of pathogen inactivation.;U.S. inhalation exposures to polybrominated diphenyl ethers arising from the land application of biosolids have been estimated and incorporated into pharmacokinetic models to predict contributions to steady state-body burden. The maximum inhalation dosages from the biosolids field at a setback distance of 5 m, are found to be 4.1×102, 4.0×10 2, 3.8×101 and 1.2×103 fg/kg-day for significant congeners PBDE-47, 99, 153 and 209 respectively, which is 1-2 orders of magnitude less than the estimated exposure from time spent in the home. Though the health implications of low-level exposures are not well-understood, these biosolids-derived PBDE dosages are approximately 6 orders of magnitude below the oral reference doses established by the U.S. EPA and contribute less than a tenth of a percent to the estimated total body burden. The inhalation of PBDE's from biosolids fields do not represent a significant contribution compared to other exposure pathways.