All of the following statements about purificationof water are true except:
Presence of Clostridial spores indicate recent contamination of water Repeat from May 10 Presence of Clostridial spores indicate remote fecal contamination of water The spores of Clostridium perfringens survive in water for a longer time and usually resist chlorination at the doses normally used in water works. So, "The presence of spores of Cl. perfringens in a natural water suggest that fecal contamination has. occured and their presence, in the absence of the coliform group suggests that .fecal contamination occured at some remote time" -Park 20/e, p 630 Rest of the three options are true, as explained below Bacteriological quality of drinking water (WHO guidelines) Organism Guideline value All water intended for drinking . - E. coli or thermotolerant coliform bacteria * Must not be detectable in any 100 ml sample. * Treated water entering the distribution system - E. coli or thermotolerant coliform bacteria - Total coliform bacteria . - Must not be detectable in any 100 ml sample - Must not be detectable in any 100 ml sample. In case of large supplies, where sufficient samples are examined, must not be present in 95% of sample taken throughout any 12- month period. Note - Although E. coli is the more precise indicator of faecal pollution, the count of thermotolerant coliform bacteria is an acceptable alternative. If necessary, proper confirmatory test must be carried out. Total coliform bacteria are not acceptable indicators of the sanitary quality of rural water supplies, paicularly in tropical areas where many bacteria of no sanitary significance occur in almost all untreated supplies. So it is evident that colifonns should not be detectable in any 100 ml sample except for 5% of samples of large supplies taken over 12-month period. Surveillance of drinking water quality Sanitary survey - On-the-spot inspection and evaluation of the entire water supply system. Sampling - Collection of water samples has to be done with through aseptic precaution and according to guidelines. Bacteriological surveillance - A complete bacteriological examination consists of - (1) Presumptive coliform test (a) Multiple tube method - Estimation of the most probable number (MPN) of coliform organisms in 100 ml of water Confirmatory tests: In chlorinated water, presence of coliform organism is to be confirmed by Eijkman's test: Subculturing each presumptive positive tube in 2 tubes of brillian green bile broth. One tube is incubated at 37degC x 48 hrs to confirm coliform organism Other tube is incubated at 44degC x 6-24 hrs to confirm E. coli which produces gas from lactose at 44degC. - Fuher confirmation of E. coli can be obtained by testing for indole production at 44degC. (b) Membrane filtration technique (2) The detection of faecal streptococci and Cl. perfringens in doubtful cases of faecal pollutionof water. (3) Colony count - provides an estimate of the general bacterial purity of water. Counts from the same source at frequent intervals may be of considerable value in comparison to single count. A sudden increase in the colony count may give the earliest indication of contamination. Biological examination - The microscopic organisms such as algae, fungi, yeast, protozoa, rotifers, crustaceans, minute worms etc. are called as 'plankton'. They are an index of pollution of water. Chemical surveillance: Basic tests include test for pH, color, turbidity, chlorides, ammonia, chlorine demand and residual chlorine. Complete analysis will include analysis for toxic metals, pesticides, persistent organic chemical and radioactivity too. Sodium thiosulphate an antidote of cynanide poisoning is also used in water purification: - For dechlorination to reduce chlorinous taste after superchlorination of highly polluted waters, swimming pool or spas - To dechlorinate tap water for aquarium or treat effluent from waste water treatment prior to release into rivers.
Presence of Clostridial spores indicate recent contamination of water
Coliforms must not be detectable in any 100 ml sample of drinking water
Sodium thiosulphate is used to neutralize chlorine
Coliforms may be detected by multiple tube method & indole production