4. (20) A backpacking water filter that I purchased has a minimum absolute pore

Question

4. (20) A backpacking water filter that I purchased has a minimum absolute pore size (i.e., a pore diameter) of 2.0 um. a. Will this filter trap the hepatitis A virus, which has a total molecular weight (including protein envelope) of about 32,000 kDa? (Calculate the virus diameter assuming it is spherical and using a reasonable estimate of its density.) If it is not trapped, how could you kill the virus in the water when backpacking? [ans: D 40 nm, so it is not trapped ] b. Will this filter trap the giardia cyst? If not, how could you kill giardia in the water when backpacking? (Note: you may find it useful to search the internet or reference books for the answers to parts b and c of this problem. Attach reference information for full credit) c. Is the E. coli 0157:H7 bacterium a "good" bacterium, or a "bad" bacterium? What effects does it have on the body? Will this filter trap the E. coli 0157:H7 bacteria? If not, how could you kill these bacteria in the water when backpacking?

Explanation / Answer

a. The virus can be killed by adequate chlorination of the water. After chlorination, the water is to be boiled continuously for 3 mnutes, but more advisable is for 20 minutes. Then cool and keep safely tightly closed.

b. Giardia cysts are large compared to bacteria and viruses. The size is 7-10 microns in diameter, a size that can easily be removed physically by filtration through a fine media. They are resistant to dysinfection procedures like chlorination. Thus its removal requires filtration process. Finally boiling water continuously for 1 minute kills the cysts, thus water can be used safely.

Since the fiter pore size is 2micrometer, the cysts are unlikely to enter the water through the filter.

C. E.coli 0157:H7 is a bad bacterium responsible for food poisoning causing contamination of raw milk and undercooked ground beef. It causes haemorrhagic diarrhoea and kidney failure. It can be fatal in children under 5 years of age, elderly patients and those with weak immunity. The bacterial size is less than the pore size of the filter, it can enter the water through the filter pore. Hence it should be removed by the disinfection procedure like chlorination. Finally boiling water for rolling 3 minuteskill the bacteria.

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