ENVR 890/296 Microbe/Pathogen Survival/Reduction in the Environment, Excreta and Excreta Treatment Processes. Mark D. Sobsey Dept. of Environmental Sciences and Engineering. Microbial Survival/Inactivation – A Kinetic Phenomenon. 100.
Mark D. Sobsey
Dept. of Environmental Sciences and Engineering
Microbes are most stable in the environment and will grow in some media (e.g., foods) in the mid pH range
Clumped: interior microbes protected
Adsorbed: partially protected
: Antimicrobial agent
Microbe type: Resistance to chemical disinfectants:
Solids association: microbes embedded in larger particles or aggregated are:
Temperature produces more microbial rapid inactivation:
Temperature elevation for some pathogens may promote growth:
Naegleria fowlerii and other amebas
Biological activity can decrease pathogens by:
Grazing, phagocytosis and other predation mechanisms
Increased enzymatic activity by bacteria and other treatment microbes:
proteases, amylases, nucleases, etc.
Increased adsorption to and accumulation in microbial biomass complexes:
floc particles, biofilms, etc.
Settle solids for 2‑3 hours in a static, unmixed tank or basin.
Aerobic microbes utililize carbon and other nutrients to form a healthy activated sludge AS biomass (floc)
The biomass floc is allowed to settle out in the next reactor;
some of the AS is recycled
(or burned if from anaerobic digestion: methane, hydrogen, etc.)
Class A sludge:
ORGANISM PROCESS % REMOVAL
Fecal indicators Primary sed. 0‑60%
E. coli Primary sed. 32 and 50%
Fecal indicators Trickling filt. 20‑80%
Fecal indicators Activated sludge 40‑95%
Fecal indicators Stab. ponds, 1 mo. >99.9999% @ high temp.
Salmonellae Primary sed. 79%, 6‑7 hrs.
Salmonellae " 73%, 6‑7 hrs.
Salmenellae Trickling filt. 92%
Salmonellae Activated sludge ca. 99%
ORGANISM PROCESS % REMOVAL
E. histolytica Primary Sed. 50%
E. histolytica Primary Sed., 2 hr. 64%
E. histolytica Primary sed., 1 hr. 27%
E. histolytica Primary sed. + Trickl. Filt. 25%
E. histolytica " 74%
E. histolytica " 91%
E. histolytica Primary sed. + Act. Sludge 83%
E. histolytica Oxidation ditch + Sedimentation 91%
E. histolytica Stabilization ponds + sedimentation 100%
E. histolytica " 100, 94, 87
E. histolytica " 100
E. histolytica Aerated lagoon (no settling) 84%
Details of these water treatment process will be presented in lectures on water treatment
(geom. mean values of 24 biweekly samples)
Sewage Treatment Rx: % Reduction Total % Reduction Sewage: Sewage Treatment Efficacy
Primary settling 50 50
2o biological treatment 99 99.5
Granular medium filtration 90 99.95
Disinfection 99 99.9995Estimated Pathogen Reductions by Sewage Treatment Processes: An Example