I would like to know the proper procedure for maintaining a seed source. Our current practice is to use a settled sewage (our test sample) as a seed source. This seed is only for our G-Ga Check as we do not need to seed our sewage sample. However, our assessor wants us to prepare an acclimated seed source by aerating a settled sewage and adding new sewage  daily.  We have a problem with this procedure because we only collect sewage  once every 2 months. So my question is, how are we going to feed and maintain this seed source? Can we use some nutrient like glucose? Is it really necessary, in our case, to maintain an acclimated seed source? Thank you very much for your help.

The trite answer is that if your assessor says you have to do it then you have to do it. I won't say how I feel about assessors and auditors with regard to understanding what they are saying.  

The purpose of the seed source is to provide bacteria that will decompose the sample and give you an oxygen demand. According to Standard Methods "The glucose-glutamic acid check is the primary basis for establishing accuracy and precision of the BOD test and is the principal measure of seed quality and set-up procedure." The purpose of keeping an acclimated seed source is so that you have bacteria that you know are fully capable of digesting your sample. I would argue that the sewage system does a much better job than you can of keeping the seed acclimated. The proof that it works is that the GGA standard passes. If you were to keep your own seed going somehow you would have to feed it sewage to 'acclimate' it. Feeding it anything else would just get it used to eating the other food source and you would possibly lose performance when used with the sewage.

Dear Mr David S,

Thanks for your reply. That's true. I guess we have no choice but to follow our assessor.
I agree that the way to have "acclimated seed" is to feed it with that particular sewage that you are analyzing. However, our problem is we don't have daily source of that sewage since we only collect sewage every 2 months. So basically, by feeding it with "some nutrients", we are not really maintaining an "acclimated seed " but just a seed source that hopefully should work on the day of analysis. As the assessor implied, this is better than what we are doing right now--which is using the actual sewage for testing as the seed for our G-Ga check, since we really don't know the actual characteristics of that sewage on that particular month. If it happens to be toxic, then we won't get any good result. He also suggested that we should actually seed our sample although we argued that we have been analyzing this particular sewage since 1995, and we have no problem so far.  As a seed source, it gives satisfactory G-Ga check and the BOD result of the sample itself is correct when compare with what get from our COD analysis. Thanks again for your reply.