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The Effects of Time and Temperature on the Fate of Pathogens and Indicator Bacteria During Municipal Wastewater Sludge - Mesophilic Anaerobic Digestion, Air-Drying, and CompostingBy Baltazar Lucero-Ramirez and Joseph Malina, Jr. ABSTRACT The fate of indicator bacteria and Salmonella and ova was investigated in field and laboratory-scale studies. The results of the field-scale studies indicated that the densities of fecal coliforms, fecal streptococci, and Salmonella were reduced by 6.1, 4.6, and 2.4 orders of magnitude, respectively, after mesophilic anaerobic digestion, air-drying and composting. Mesophilic anaerobic digestion produced EPA Part 503 Class B biosolids, i.e. fecal coliforms < 2x106 MPN/g. The majority of samples of air-dried anaerobically digested sludge were Class A biosolids, i.e. fecal coliform < 1,000 MPN/g, or Salmonella < 3MPN/4g), and viable helminth ova < 1 ovum/4g. All samples of composted biosolids were Class A biosolids. Laboratory-scale anaerobic digesters were operated at temperatures of 25°C and 35°C; hydraulic detention times of 7, 15, 30; and 45 days, and organic loadings of 0.9, 1.80, and 2.7 kg/m3-d. Anaerobic digestion at minimum detention times of 30 days at 25°C or 15 days at 35°C produced EPA Part 503 Class B biosolids fecal coliform densities < 2x106 MPN/g TS and 38% destruction of volatile solids. Analysis of variance (ANOVA) tests indicated that the individual effects of temperature, detention time, and organic loading and the interactions between time and temperature and between time and organic loading on the densities of fecal coliforms and Salmonella were statistically significant at the 95% confidence level. Temperature was the principal mechanism in reducing the densities of indicator bacteria in mesophilic anaerobic digestion. Class A biosolids (Salmonella < 3 MPN/4 g TS) were produced by anaerobic digestion at 35°C, detention times of 30 and 45 days and organic loadings of 1.80 and 2.70 kg/m3-d. Densities of fecal coliforms were 2.69x104 MPN/g at 25°C and 6.61x104 MPN/g at 35°C that are < 2x106 MPN/g required for Class B biosolids. The highlighted links that follow are connected to Adobe pdf files of the corresponding material. To view them you must have the Adobe Acrobat Reader 3.0. View the Report...(0.7 MB)
These materials may be used for study, research, and education, but please credit the authors and the Center for Research in Water Resources, The University of Texas at Austin. All commercial rights reserved. Copyright 2000 Center for Research in Water Resources.
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