4+5. Microbiological analysis of drinking water. Purification of water. Disinfection.
Microbial analysis
-purpose of water treatment -> provide drinking water to the consumers which is free of waterborn pathogens
-ideally drinking water should not contain any microorganisms known to be pathogenic
-also should be free from any bacteria indicative of pollution with excreta
1) coliform organisms in drinking water
-include all aerobic and facultative anaerobic organisms, fecal and non-fecal
-E. coli provides conclusive evidence of recent fecal pollution and should not be present in drinking water
-coliform: gram-negative, NO spores, rod shape, oxidase negative, fermenting lactose at 35-37°C with production of acid and gas within 24-48 h (are easily detected by culture methods, normally present in intestine, greater resistance to forces of natural purification)
-oldest method: multiple tube fermentation method (MPN method or presumptive coliform test->broth with bromcresol purple, for 24h at 37°C)
-MPN (most probable number) -> 0 MPN/100ml in drinking water (E. Coli should not be detectable in drinking water!)
-for complete confirmation -> biochemical test of Hiss (lactose and oxidase)
-membrane filter method (with cellulose membrane, coliform bacteria can’t pass)
-MMO-MUG method (chromogenic enzyme substrate test) -> detects E. Coli in one day (colour change in media, yellow if positive)
-colilert test (100ml of water sample 35-37°C for 24-48h) -> if yellow colour change, it’s positive
2) enterococcus in drinking water
-mostly fecal origin -> human fecal pollution
-WHO and Bulgarian standard -> 0 indicators per 100ml water sample
-rapid test is Enterolert (in just 24h)
3) clostridium perfringens
-guidelines say: 0 indicators per 100ml water sample
-occur naturally in feces, but in lesser amount than E. Coli
-spore survive very long -> not eliminated with normal doses used in waterworks practice -> if spores are present and coliform group is absent in filtered water -> deficiency in filtration practice
4) pseudomonas aeruginosa
-commonly found in feces, soil, water and sewage
-it’s often associated with a rise in water temperature or low rates of flow
-detection is only in drinking water in bottles and should be 0 per 250ml water
5) colony count
-colony counts on nutrient agars at 37°C and 22°C (some bacteria growth better in 37°C or 22°C or in potable water)