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Commerical Seed or Supernantant??????
dmclaug
Posted: Thursday, April 8, 2010 7:50 AM
Joined: 12/23/2009
Posts: 5


I was wondering if anyone has any insight. The more I read the more I do not know what the real answer is. I am learning that for the most part, commercial seed will usually give your problems. Yes I understand some do not have issues. I just cannot get consistent results doing my GGAs and I am using commerical seed. So, this leads to my question, I know i can use supernatant from my influent, and i'm gona try some, but, my question is, if you get a batch that will work, you can freeze it and use it next time, but how long can it be frozen until its time for new?


James Royer
Posted: Thursday, April 8, 2010 8:12 AM
Joined: 9/21/2009
Posts: 98


I am not sure what you mean by "supernatant" from your influent. Settled fresh settled influent, such as from a primary clarifier, will work if there are not too many nitrifiers to cause interference.

Frozen seed material works well also. We used frozen settled sewage from a wastewater plant in the 70's and had no problems. You just have to meet the proper GGA values as you would with a commercial seed material. You would need a written procedure for all analysts to follow so as the results would be consistent. The thawing needs to be the same as not to encourage ntirification after freezing has stopped the nitrifiers. I would check results with a KHP standard also to demonstrate that nitrification is not being included in the BOD test.


Perry Brake
Posted: Thursday, April 8, 2010 12:50 PM
Joined: 12/16/2009
Posts: 69


The supernatant from settled influent works for some, dmclaq, but one problem with influent is that it is often inconsistent because it is affected by what is being dumped in the sewer system on any given day.

 

Your idea of freezing influent is perhaps to find an influent that works well (which you won't know for five days) and then freeze it so you can continue to use it.  I don't think anybody can give you a good estimate of how long it might retain its strength, but if you control chart your GGA results, you should see a downward trend as it starts to weaken.

 

Somewhere in your plant there is a consistent source of viable, hungry bacteria and I think finding that source would be well worth your while in the long run.  Usually, the supernatant from settled primary effluent (if your plant is running well, there might not be much settling necessary) is a good source.

 

My personal opinion is that freezing either influent or primary effluent (or any other seed source in your plant) is only asking for trouble.  Somewhat t like using a commercial seed, results depend on your ability to wake the bacteria up...sometimes it works, and sometimes it doesn't.   Why not just walk out to your chosen source (clarifier, oxidation ditch, or whatever), and grab a sample every day you do BOD, keeping in mind that if you choose the influent as your seed source, you might see a lot of unwanted variance in your GGA results.  Standard Methods recommends use of primary effluent.

 

Good luck!


Anonymous
Posted: Wednesday, January 26, 2011 2:09 PM

The more I read on GGA testing, the more confused i am. Is this test to test the effectiveness of seed you would use in your samples? In other words add  a certain amount of seed to a effluent CBOD?


Perry Brake
Posted: Thursday, January 27, 2011 9:55 AM
Joined: 12/17/2010
Posts: 23


Earlier editions of Standard Methods said that the purpose of the GGA test was to check the effectiveness of the seed, whether doing BOD or CBOD.  As used in practice, however, the majority of labs also used it to check the entire BOD/CBOD procedure.  The 21st Edition of SM finally (and properly, in my opinion) says that the GGA test is also used to check analytical performance for the entire test.

 

If a lab has good precision...that is, if the standard deviation of repeated GGA tests is small...the average (mean) GGA result is a good indicator of seed effectiveness.  But if a lab has bad precision (e.g., the standard deviation of repeated GGAs is 15 mg/L or more), it indicates there are several things adversely affecting test performance, several of which could also affect the average GGA result whether you have a good seed or not.

 

Don't feel like the Lone Stranger because you think the BOD/CBOD test is confusing!  It is...but it can be mastered.


Anonymous
Posted: Wednesday, February 9, 2011 8:28 AM

We don't seed any samples between 1 October and 14 May (seasonal chlorination), are we wasting our time doing GGA twice a week?


Perry Brake
Posted: Wednesday, February 9, 2011 11:27 AM
Joined: 12/17/2010
Posts: 23


If you are not adding seed, regardless of the reason, you are relying on the sample having enough natural seed (bacteria) to make the test work.  The primary purpose of the GGA test is check the effectiveness of the seed, whether it be natural or added.  If lab/plant inspectors find you are not seeding and also not checking the effectiveness of the natural seed, I would think they would throw the book at you.  The plant may be dumping tons of "BOD" into receiving waters and not even know it. 

 

So the answer to your question is, "No...you are not wasting your time doing the GGA twice a week", assuming that the frequency of you BOD test is 2/week.


James Royer
Posted: Wednesday, February 9, 2011 4:05 PM
Joined: 9/21/2009
Posts: 98


The 21st ed Standard Methods states taht certain samples need nitrification inhibitor such as "biologically treated effluents, samples seeded with biologically treated effluents and river water". It also states that all samples that are inhibited be seeded. Thus any G-GA sample that is not seeded with commercial seed material or fresh raw sewage without nitrifiers only CBOD can be analyzed. Frozen settled sewage should not have nitrifiers so it should work provided the correct volume of seed material is used.


Anonymous
Posted: Thursday, February 17, 2011 7:42 AM
Perry Brake wrote:

"If you are not adding seed, regardless of the reason, you are relying on the sample having enough natural seed (bacteria) to make the test work.  The primary purpose of the GGA test is check the effectiveness of the seed, whether it be natural or added.  If lab/plant inspectors find you are not seeding and also not checking the effectiveness of the natural seed, I would think they would throw the book at you.  The plant may be dumping tons of "BOD" into receiving waters and not even know it. 

 

So the answer to your question is, "No...you are not wasting your time doing the GGA twice a week", assuming that the frequency of you BOD test is 2/week."

Color me confused. During chlorination season we use well-mixed primary effluent as seed for our GGA and chlorinated effluent samples. When we are not chlorinating our unseeded effluent samples have adequate depletions so they do, in fact, have "enough natural seed to make the test work". 

 

What do you mean by "not checking the effectiveness of the natural seed"? Doesn't the fact that we have adequate depletions in the unseeded effluent BOD bottles prove its effectiveness? What's the point of running a GGA (seeded with primary effluent) with each set  when that seed is not being used in the effluent? Or are you saying effluent BOD samples should always be seeded? 


James Royer
Posted: Thursday, February 17, 2011 9:55 AM
Joined: 9/21/2009
Posts: 98


As I read 40 CFR 136 the approved method will be the latest edition of Standard Methods. As I read the 21 ed. Standard Methods it indicates that all effluents should be CBOD to eliminate nitrification. All inhibited samples should be seeded. Thus all effluents should be seeded.

 

This brings the point that seeding GGA will evaluate the seed material and procedure. But effluent samples also contain natural seed which also help oxidize the organics. This can not be separated unless we preserve the sample with acid or something.

 

My thoughts on evaluating the natural seed in the sample is to spike some GGA standard into some effluent and evaluate the recovery. GGA has been assigned a value of 198 mg/L. Thus if you analyze an effluent sample and an effluent sample spiked at 1.0% with GGA then the spiked effluent sample should have a result 2.0 mg/L higher than the effluent sample.

 

These should all be CBOD results as the effluent will have nitrifiers and then you can evaluate nitrification inhibition also. This is being added to our QA/QC as I rewrite the BOD/CBOD SOP's. Just analyzing the GGA standard only does not fully evaluate the procedure. The precision of this 2.0 mg/L spike can then be calculated.


Perry Brake
Posted: Thursday, February 17, 2011 11:56 AM
Joined: 12/17/2010
Posts: 23


Anonymous, you ask, "Doesn't the fact that we have adequate depletions in the unseeded effluent BOD bottles prove its effectiveness?".  The answer to that is "no."  The only way you can check bias in a test (i.e., whether results are too high, or too low) is to analyze a sample of known concentration.  For the BOD test, that sample is the GGA which has a known (or, in this case, accepted) value of 198 mg/L.  You may think you are getting good results for unseeded primary effluent, but how can you know since you don't know what the true value is?

 

The method doesn't come right out an say you HAVE TO run a GGA with each batch, but it implies such...the vast majority of labs do it, and inspectors will expect to see it done, in each batch.  If your primary effluent really is a good seed (consistently strong enough), you should WANT TO run a GGA in each batch, control chart the results, and hang the control chart on the wall so everyone can see you are doing a good job and reporting reliable results.  An oversimpfication?  Yes, but reading between the lines, I suspect your apparent reluctance to do a GGA in every batch might be an indication of a problem with the test.  If so, attack the problem...don't sidestep it by not doing GGAs.


 

And your second question, "Or are you saying effluent BOD samples should always be seeded?"  If here you are talking about primary effluent, the answer is "no".  If you have evidence that the primary effluent consistently contains a good seed, you don't have to seed.  The evidence would be using primary affluent for the GGA test, and getting good results.  If you are talking about final effluent (which I don't think you are), you MUST seed, just as James Royer says.

 

Also, James Royer is right that a better test for wastewater treatment plants is CBOD since, for one thing, it removes nitrifiers from the equation.  But unfortunately wastewater treatment labs aren't allowed to choose between BOD and CBOD...they must run the test specified in their discharge permit.

 

 

 

 


Brent Dickey
Posted: Thursday, February 17, 2011 2:03 PM
Joined: 9/28/2009
Posts: 18


Sorry for posting anonymous, having log-in issues.

 

Perry...James said all effluent BOD should be CBOD and all CBOD must be seeded...ergo all effluent must be seeded. You pointed out that we don't get a choice on CBOD. We run BOD and we do not seed unless we're chlorinating.

 

We run 2 sets of BOD per week and always run a GGA. We chart the results (25 tests) and our sd is typically in the 5 to 7 range and we show a positive bias. The reason for my post is a discussion in-house about why we were running a GGA and seed control when we were not seeding any samples. We haven't stopped running them..yet

 

 


Perry Brake
Posted: Thursday, February 17, 2011 4:38 PM
Joined: 12/17/2010
Posts: 23


Hi, Brent!  I'm not sure whether your "typically in the 5 to 7 range" means a depletion of 5 to 7, or a BOD of 5 - 7.  But it really doesn't matter as it doesn't say anything about the effectiveness of the seed.  If you said it gives "a depletion of 1.0 mg/L per milliliter of seed), that would be evidence of a good natural.  But I'll say again, the only way to check the effectiveness of the seed...natural or added...is to run a GGA.  5210-B has said that for many editions, except that they didn't mention the "natural or added" bit.

 

I don't know which side of the "discussion" you are on, but I know that I am right in the middle, a bad place to be with so much throwable sludge available in the plant!  shocked

 

Perry

 

 

 

 

 


James Royer
Posted: Friday, February 18, 2011 10:35 AM
Joined: 9/21/2009
Posts: 98


I know that we have to test for what is required by our permit. Standard Methods indicates that BOD results on samples with any significant nitrification is meaningless or needs a lot of interpretation. You should ask the permiting agency to set limits based on CBOD if there is nitrification. Chlorinated effluent would already have nitrifiers removed as they are sensitive to chlorine. When not disinfecting the nitrifiers would be significant in most effluent wastestreams. Thus the inhibitor would be needed so the nitrification does not effect results. This is where the 21st ed. Standard Methods requires seeding when there is probably plenty of organism already present. We just need to check that they are there.