WEF Discussion Forums
Laboratory Management and Technical Issues
SM 21st ed. BOD
I was reading a report by Young, Clesceri, and Kamhawy explaining changes in the BOD method in the 21st ed. of Standard Methods. Under Testing Procedure e. Add nitrification inhibitor: It states that "All samples receiving nitrification inhibitors should be seeded".
I have read the BOD method in the 21st ed. of Standard Methods and do not see that it makes this request for seeding. It just states different types of samples that should be seeded. I do not think that effluent samples requiring nitrification inhibitor that is not disinfected would require any additional seed material.
Does anyone else have a thought on this request? Did Standard Methods personnel really think it necessary to seed all CBOD samples?
<<I have read the BOD
method in the 21st ed. of Standard Methods and do not see that it makes
this request for seeding.>>
Are you saying that you don't see the sentence that Young, et. al., quote, or are you saying you don't understand why one must seed? The quoted sentence is there...the next-to-last sentence in section 5210B5e, 21st Ed.
As to why you must seed a sample to which the inhibitor has been added, I can understand that requirement for an effluent, GGA, or any other sample where one does not know for sure there are sufficient bacteria to naturally seed the sample, those being "non-nitrifying" or "carbonaceous" bacteria in the case of CBOD. Most plants are required to test their "final" effluent, which is after disinfection, a process that would prevent virtually all bacteria...carbonaceous as well is nitrogenous...from oxidizing degradable material and thereby depleting oxygen. The requirement to seed effluent samples really has nothing to do with whether or not you include the nitrification inhibitor...it's just something you must do to effluent samples. Same with GGA.
I don't understand why one would have to seed a domestic influent when doing CBOD (as the method seems to require)...generally an influent is known to contain sufficient carbonaceous bacteria without seeding...but perhaps their thought is that addition of the nitrification inhibitor ALSO inhibits the carbonaceous bacteria. I don't think that was their thought...I don't think they meant to say what they said...kind of like the "do all samples in a minimum of three diltutions" thing...they didn't really mean to say that in the 21st Ed.
I have read Standard Methods and do not see any reference to "seeding all samples with nitrification inhibitor". I do not think that all sample need to be seeded if for CBOD, only samples that have been disinfected, knowns, neutralized, ect or that we are unfamililar with as to suffecient bacteria.
In a publication where the authors explain the changes in BOD procedure in the 21st edition it states" all samples receiving nitrification inhibitor should be seeded". I do not necessarily agree with that statement as to being needed or that Standard Methods even states this.
We disinfect seasonally and so we seed the effluent 6 months during chlorination season and then we do not seed during the 6 months when we have the disinfection exemption. We do analyze for CBOD all 12 months. Seeding the 6 months without chlorination is not needed as there are plenty of bacteria in the effluent to utilize the organics in our effluent.
I think maybe the authors missstated the change in the 21st ed Standard Methods.
The sentence is there in the 21st edition.
5210 B. 5-Day BOD Test
5. Testing Procedure
e. Addition of nitrification inhibitor:Samples that may require nitrification inhibition1 Samples include, but are not limited to, biologically treated effluents, samples treated with biologically treated effluents, and river waters. Note the use of nitrogen inhibition and the chemical used when reporting results. (Note:TCMP is the preferred nitrification inhibitor but requires handling and transfer in a solid form. Allylthiourea is not always effective in inhibiting nitrification within the 5-d incubation period and concentrations above 2 mg/L may cause increases in carbonaceous BOD measurements. ATU concentrations above 2 mg/L also can adversely affect the azide modification of the iodometric method). Seed all samples to which nitrification inhibitor has been added. The amount of seed should be consistent with that required to achieve GGA test results in the range of 198 ± 30.5 mg/L (¶ 6b)
Bold added for emphasis of the sentence in question.
I can't begin to fathom the reasoning behind why this requirement is there. Perry's suggestions are probably close to what may have been on their minds, but it doesn't make too much sense to me. I agree with you that unchlorinated (or other disinfection treatment) samples shouldn't need any extra seed. Unfortunately, it is in there and should be followed.
I stopped reading when they went to ATU inhibitor. I should have read more closely.
I hope that this can be changed in 22nd ed as it is unnecessary. Past editions have stated " seed only when required or when the sample is unknown as to bacteria" but this has been eliminated.
Wastewater plant effluents, that are not disinfected, are never in need of seeding. If there is a need for seed or nutrient addition then the quality of the effluent is probably very good. A discharge from a membrane unit might qualify as needing seed and nutrients just to ensure the utilization of what organics are present.