1. Microbiological Aspects Why is Treatment Necessary? 1.Infectious agents in sewage and able to grow on sewage 2.Infectious routes to man via food,water,crops, aerosols etc 3.Long survival times in water, plants, soil etc 4.Even major treatment processes (eg activated sludge) is insufficient to remove all infectious agents 5.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