WEF Discussion Forums
Laboratory Management and Technical Issues
GGA, results not consistent
Is there anyone that is not having issues with GGAs. On setup comes out in the low 200s and I do the same procedure the next time and get a 124 and 160. Frustrated. Yes the dilution blanks are perfect, the seed factor right on the money.
Pleased to say that we're not having issues. We use bottled distilled, Hach EZ GGA ampuoles and primary effluent for seed. Our range for nine tests last month was 192 to 212. Tell us what you're using and how long your values have been inconsistent.
I have some e-z gga on the way and I am going to use our supernanant from either our influent or effluent. I was using the biosystems seed with the glucose from a 50ml bottle. Hope my new way will be the answer. Inconsistent in that it would come out 200 one time and 150 the next. I'm convinced that the seed is part of the problem and tranfering GGA from one bottle to another clean bottle to a pipet then in the bod bottle. Crazy
By supernatant do you mean settled sewage? By no means use effluent as you will be seeding with nitrifiers for most waste streams. Nitrifiers will bias your GGA results high and give you a false appearence getting good results.
To get any good analytical results you have to be able to accurately and repeatedly pipet a known solution into the analysis container. You can check this by setting up 7 or so individual bottles for analysis using the same GGA and seed material and get repeated results. You need to know your precision with all else the same. If you then get 150 to 200 mg/L results then the seed material is not the problem.
By supernatant I mean 1 liter of influent settled at least 1 hour and then decant the supernanant and use that as seed. I realize that if i get 2 inches of rain, that will change things, but if my tests works, my big question is, how long can I freeze the supernanant and use it. A month, three months, 6 months??? I dont plan on using effluent because we are a lagoon system and we deal with nitrification a couple times a year.
When I last used frozen seed we settled fresh raw sewage, that we had collected during normal flows, and dispensed it in 60 ml plastic bottles. We froze the seed material. We thawed it in luke warm water and setup a series of GGA to evaluate the seed correction and GGA value. We would use this same seed material from 1 to 2 months without haveing any problems or running out of seed. We would collect another batch to settle, freeze, and check before running out of previous seed material.