A city has recurring nitrification problems in their distribution system, in whi
ID: 54498 • Letter: A
Question
A city has recurring nitrification problems in their distribution system, in which ammonia-oxidizing bacteria oxidize ammonia to nitrite and nitrite-oxidizing bacteria oxidize nitrite to nitrate. The City is interested in estimating the size of the ammonia-oxidizing bacterial community in a part of the system with a long hydraulic residence time. The plant does a 5-tube MPN analysis for ammonia-oxidizing bacteria, using an ammonia-mineral medium inoculated with an aliquot of the sample from the distribution system. After 4 weeks of incubation, the nitrite concentration is measured in each tube. Each tube showing nitrite production is scored as a positive result, and the results are shown in the following table. Consulting the MPN handout, what is the MPN of ammonia-oxidizing bacteria and the associated 95% confidence limits?The plant is trying to avoid or minimize nitrification episodes. Why does the incubation time for the MPN tubes (4 weeks) pose a problem for plant?Explanation / Answer
1)
The oxidation of the ammonia to nitrate via nitrite is called nitrification and this process is conducted the autotrophic ammonia-oxidizing bacteria, like Nitrosomonas europaea. The MPN (most-probable-number) test is used for estimation of Number of ammonia-oxidizing bacteria in a sample.
The given data is:
The formula for calculation of MPN is:
Count of positive tubes begins with the highest dilution in which at least one negative results has occurred. Therefore,
Number of positive tubes 4+1 = 5, (neglect 10 mL inoculum)
Sample In the negative tubes = 1.4 mL
Sample in all tubes = 5 + 0.5 = 5.5
Thus, the MPN is 65.
The graph associated with 95% of confidence:
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