Abstract
Several screening methods at the so-called ready biodegradability level are suitable to test poorly soluble substances. Typical for these tests is that mineralization is evaluated from monitoring oxygen uptake or carbon dioxide production. Unfortunately, they suffer from a rather low precision in the calculated percentage of mineralization caused by subtracting a too high inoculum control measurement from the response in the test system. Criteria for blank oxygen consumption, due to the metabolic activity of the inoculum, are proposed from which maximum amounts of activated sludge or secondary effluent per litre test medium can be derived to be used as an appropriate inoculum. Both for current and future standardized tests the precision of the method can be kept within acceptable margins. Inoculum material was sampled from 40 communal biological waste water treatment plants. From endogenous respiration rates it was derived that the concentration of secondary effluent in the Closed Bottle Test can be increased up to 50 mL/L but that in respirometry tests inoculated with activated sludge the appropriate concentration is 10 mg/L dry matter or below, depending of the design of the test system.
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Abbreviations
- BOD:
-
biological oxygen demand
- CBT:
-
Closed Bottle Test
- C as :
-
inoculum concentration in mg dry solids of activated sludge per litre test medium
- C ef :
-
inoculum concentration in ml secondary effluent per litre test medium
- C ss :
-
dry weight content of activated sludge (g/L)
- CFU:
-
colony forming units
- DO7d :
-
dissolved oxygen concentration (mg/L) after 7 days
- ISO:
-
International Organization for Standardization
- NEN:
-
Dutch Organization for Standardization
- O c :
-
oxygen capacity in mg oxygen per litre vessel volume
- OECD:
-
Organisation for Economic Co-operation and Development
- Ox as :
-
oxygen consumption after one week in mg oxygen per mg dry weight activated sludge
- Ox ef :
-
oxygen consumption after one week in mg oxygen per mL secondary effluent
- Ox ef [n]:
-
oxygen consumption after one week in mg oxygen per n mL secondary effluent
- Ox flask :
-
oxygen uptake in mg per litre flask volume
- RBT:
-
Ready Biodegradability Test
- SLR:
-
sludge loading rate in kg O2/kg dry weight·d
- ThOD:
-
theoretical oxygen demand
- TPCBT:
-
Two Phase Closed Bottle Test
- V a :
-
volumes of air and water per litre vessel
- V w :
-
volume, respectively
- ρ a :
-
concentration of oxygen in air at 20° C and 101.5 kPa
- ρ s :
-
saturation oxygen concentration in te aqueous phase
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Struijs, J., Stoltenkamp-Wouterse, M.J. & Dekkers, A.L.M. A rationale for the appropriate amount of inoculum in ready biodegradability tests. Biodegradation 6, 319–327 (1995). https://doi.org/10.1007/BF00695262
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DOI: https://doi.org/10.1007/BF00695262