Preparation and Use: PolyTox®
1. How important is the cleanliness of the BOD bottles?
Although the cleanliness of the BOD bottles using POLYTOX is not as important as in BOD testing, it is still important. We recommend the following:
- Allow to soak (around an hour) in mild soapy water (we suggest Alconox), scrub with bottlebrush (designated for BOD5 bottles only).
- Allow bottles to soak in 9% Nitric acid solution or 1:1 HCl solution for about 1 hour.
- Rinse bottles by allowing tap water to flow into bottles while shaking. When you notice no more bubbles appearing while you shake the bottle, rinse 2 more times.
- Finally, 3 rinses with DI or sample water.
2. When I run baseline samples with POLYTOX I get different DOUR numbers. Is there something wrong with the product?
Probably not. As long as you are using POLYTOX from the same batch number there is a very high degree of consistency from vial to vial. We find that this issue occurs mostly with new POLYTOX users. Technique is everything. Once you get your technique perfected you will find that both baseline and live sample results will be repetitive and accurate.
3. Must I run the baseline and background samples every time?
No. We recommend running baseline samples on every new batch of POLYTOX that you use. Since this is simply determining the effect of the base POLYTOX product on the DOUR we find that it remains very consistent for every batch.
Once you achieve a data history for the background TW sample this test can also be run on a “spot-check” basis in order to determine the microbial effect of the TW sample. In tap water this background should be almost zero.
4. Do you have a spreadsheet that will automatically calculate DOUR’s?
Yes. To download the Excel file, please click here .
5. I ran a Baseline POLYTOX test that depleted in 21 minutes. What does this mean?
The POLYTOX test is designed for the baseline test (with DI water) to deplete in approximately 30 minutes. The time normally falls between 28 and 32 minutes. If your Baseline test is depleting in 21 minutes do the following:
- Re-clean the BOD bottles, DO probe and associated glassware
- Check the DO meter for malfunction
- Check the DI water to make sure the pH is about 7.0 and the conductivity is low
- Make sure the water temperature is +- 20°C
- Re-run the test
6. What does it mean when the initial dissolved oxygen level is at least 8.0 mg/I, but the background rate of respiration (DOURB) is greater than 0.05 mg/I/min.?
If this should occur, a DOUR-B that is greater than 0.05 mg/I/min. is likely to be caused by a combination of biological and chemical oxygen demand (i.e., sample composition and microscopic examination could verify biological activity). This will be normalized in the final equations.
7. What do I do when the dissolved oxygen has been completely depleted prior to the 19 minute reading?
If this should occur, record the pertinent times in which dissolved oxygen of at least 1.0 mg/L remains for the baseline (DOURs) and tests (DOURT). Using those times (i.e., 15 and 17 minute readings) calculate the various activity rates.
8. What does it mean when the dissolved oxygen rate of the test (DOURT) is greater than the baseline rate of respiration (DOURs)?
Depending upon the homogeneity of the contaminants within the sample, areas of low organic levels may even experience some enhancement of biological oxygen uptake activity. At concentration of samples where there is no toxic effect upon the microbial oxygen uptake rate, uptake rates greater than the baseline rate (DOURs) are sometimes experienced. These enhanced rates are represented as negative inhibition values and usually indicate the presence of certain readily degradable compounds which the “POLYTOX” bacteria can immediately utilize as a good source, thereby increasing cellular metabolic activity and the uptake of dissolved oxygen.