Input Data

[Cruz]

Just wondering if the measurement i have for BOd is for BOD5, can I use that BOD5 value because the data i have isn't CBOD. Can i still model my river? 

[Jihun Seo]

In the case of BOD5, as far as I know, it can be modeled by putting it in CBODfast.

or in other case, you can split the ratio. For example, if the BOD5 is 50mg/l, then the slow is 20mg/l, the fast is 30mg/l.

I hope my answer is helpful to you. 

2021년 5월 28일 금요일 오전 2시 9분 5초 UTC+9에 Cruz님이 작성:

[Cruz]

Oh so with my understanding, the value of my BOD5 from my water quality analysis on samples can be inputted in the CBODfast and it will work?

[joseph....@iehgrucon.com]

just to clarify,  you can model BOD5 with Q2k as fastBOD, but it needs to be converted to ultimate BOD with the relation presented on pg.40.

[Adam Rus Nugroho]

In the past, I used to input BOD5 data on CBODfast and assumed that CBODfast was BOD5 and CBODslow was BOD Ultimate.
Apparently, I was wrong.

Let alone the CBODfast and CBODslow, the carbonaceous BOD itself is different from the BOD5.

The explanation can be found on pages 40-43 of QUAL2Kw theory documentation which has been provided by Joseph above.

I quoted the last paragraph of the explanation here:

In some cases where available data are very limited and only 5-day BOD (BOD5) data are available to represent organic carbon, it may be reasonable to use a simplification of option 1 by assuming that BOD5 is approximately equivalent to CBODFN5. If the BOD decay rate constant is assumed to be a typical value of about -0.23 day-1 (Brown and Barnwell, 1985), then the fast CBOD could be approximated as about 1.46 × BOD5. A better simple alternative could be to estimate the carbonaceous fraction of the total BOD5 (CBOD5) from literature summaries or available data and then estimate the fast CBOD as 1.46 × CBOD5. 

tl dr: You can use BOD5 for CBODfast but only after converted it according to the guidelines explained in the theory and documentation of QUAL2K. Just as the previous reply by Joseph.

[Dr. Kyle Flynn]

Hi all - 

Good discussion and a couple of clarifications. 

1. The ability to use biochemical oxygen demand (BOD) and carbonaceous BOD (CBOD) interchangeably depends on the amount of ammonia in the system and its oxidation rate (nitrification). If nitrogenous BOD (NBOD) is low, BOD and CBOD can be used interchangeably. To correctly measure CBOD, an inhibitor is used in the laboratory analysis to suppress nitrification so that the BOD measurement is only reflecting oxidation of carbon. CBOD computations in the model are therefore only applied only to carbon in the system and NBOD computations are handled separately via the ammonia compartment. If you have a system with high NBOD, an assumption that BOD = CBOD will not be correct and you will overestimate deoxygenation of the system since the model is already accounting for oxygen losses due to nitrification elsewhere (i.e., conversion of ammonia to nitrate based on waterbody specific nitrification rate). 

2. The second comment is on the conversion of CBOD5 to CBOD ultimate, which has already been adequately described by Adam using equation 80 in the qual2kw manual (note: this is equation 75 in the updated manual on the qual2k.com website). The basis here is that a 5-day test does not reflect the overall ultimate oxygen demand exerted by material in the water and thus you use the 5-day to ultimate correction (because in a lab/bottle test you can't run the sample to 0). Alternatively, you could use 20-day BOD analysis (with nitrogen inhibition) to closely approximately CBOD ultimate, which we have done in past work.

3. Finally, the use of fast and slow CBOD in the model would conventionally be used to represent different types/sources of CBOD. A good example would be a river that has both a municipal sewage discharge (i.e., relatively labile or fast carbon oxidation) and another from a discharge like a paper/pulp mill that would have slow carbon oxidation (refractory/recalcitrant).

Hope that helps,

Kyle