Microbiological Aspects

1
Microbiological Aspects

• Why is Treatment Necessary?
• Infectious agents in sewage and able to grow on
  sewage
• Infectious routes to man via food,water,crops ,
  aerosols etc
• Long survival times in water, plants, soil etc
• Even major treatment processes (eg activated
  sludge) is insufficient to remove all infectious
  agents
• Filtration and chlorine addition is necessary to
  complete treatment.

2
Microbiological Aspects

• Pathogen infection requires an infection dose and
  this will vary from pathogen to pathogen.
• Pathogens will also vary in their ability to
  cause sickness or death.
• Infectious pathogens may lead to health effects
  such as hepatitis (possibly leading to liver
  cancer), dysentry, poisoning, fever (eg typhoid),
  gastroenteritis etc
• Effects may be direct or indirect (eg
  enteroviruses via infected shellfish

3
Microbiological Aspects

• Infants, the elderly and the immune suppressed
  are especially vulnerable to dehydration and
  fatal health effects
• Pathogens may originate in human and animal
  feces, soil, water, aerosols etc

4
Microbiological Aspects

• With filtration and sterilisation of treated
  water, outbreaks of illness are significantly
  reduced
• Excreted pathogens can survive for long times in
  feces, sewage, soil and crops

5
Microbiological Aspects

• Wastewater treatment processes are designed to
  meet defined health criteria (e.g. (a) Freedom
  from gross solids, significant removal of
  parasite eggs (a) significant removal of
  bacteria (a) more effective removal of
  bacteria Not more than 100 coliform organisms
  per 100 ml in 80 of samples No faecal coliform
  in 1000 ml no toxic effect on man other
  drinking water criteria No chemicals that lead
  to undesirable residues in crops and fish no
  chemicals that lead to irritation of mucous
  membranes and skin) AND defined water use (e.g.
  Municpal Reuse, Industrial Resuse, Recreation,
  Irrigation etc)

6
Microbiological Aspects

• Waste Water Treatment Plants involve a number of
  standard processes, viz Primary Settling (or
  Enhanced Primary Settling), Biotreatment,
  Sedimentation, Sludge Stabilisation, Disinfection
• Some pathogens can survive some of these
  processes and sterilisation is increasing being
  consdered as an essential element in the
  treatment (eg chlorine, UV, ozone). Each of these
  processes have different problems and costs,

7
Microbiological Aspects

• Infants, the elderly and the immune suppressed
  are especially vulnerable to dehydration and
  fatal health effects
• Pathogens may originate in human and animal
  feces, soil, water, aerosols etc