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BioSHA

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Temperature effects on MBBR design
Jun 12^th, 2012, 10:13am

Hello all.

I am currently designing an MBBR plant up north in Norway. It is cold here and it is not unusual that the influent untreated water is as cold as 5 degrees and even 4 degrees (Celcius).

The design basis for the case I am working with now, is:
Q_dim = 400 m3/day
BOD_dim = 70 kg/d.

We are to remove 70 % of the BOD.

According to Norwegian standards, the organic loading for 10 degrees Celcius is 8 g BOD/(m2 x day). Temperature correcting for 4 degrees Celcius, yields 5.04 g BOD/(m2 x day).

Hence, we need 13885 m2 with biofilm carrier area. With a specific area for our selected biofilm carrier media of 600 m2/m3, I get at total (two stages in series) reactor volume of 46 m3 with a fill ratio of 50 % with biofilm carriers.

However, my problem is: Our designing partner claims that due to the fact that we have as low temperatures as 4 degrees Celcius, the total reactor volume has to be doubled, i.e. 90 m3.

So, my problem leads to the following question: Which design is correct - mine with 46 m3 or our companies designing partner claiming 90 m3?

I would appreciate input from you guys.

WR,
S

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Descus

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Re: Temperature effects on MBBR design
Reply #1 - Jun 12^th, 2012, 11:31am

Hi,

If you are in Norway and you are designing according to Norwegian standards...you are probably off to a good start. Just be mindful of where and how exactly they derive the basis of 8 gBOD/m2d @ 10C.

Since your designing partner claims you should double your calculated total volume because of the low temperatures, perhaps they corrected for the loading rate differently than you did?

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BioSHA

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Re: Temperature effects on MBBR design
Reply #2 - Jun 12^th, 2012, 11:37am

Descus wrote on Jun 12^th, 2012, 11:31am:

Hi,

If you are in Norway and you are designing according to Norwegian standards...you are probably off to a good start. Just be mindful of where and how exactly they derive the basis of 8 gBOD/m2d @ 10C.

Since your designing partner claims you should double your calculated total volume because of the low temperatures, perhaps they corrected for the loading rate differently than you did?

I am in Norway and I am designing according to Norwegian standards. So, I am, as you are implying, off for a good start.
As for the correction of loading rate, it might be. Not sure, really (waiting for reply from them as well.. but wanted to explore the lower temperature validity of the 1.08^(T-20) correction for the organic loading rate).

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Descus

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Re: Temperature effects on MBBR design
Reply #3 - Jun 12^th, 2012, 2:59pm

Hi,

The van't Hoff-Arrhenius equation is the one typically used, so it is valid. What will vary is your temperature coefficient, in this case you chose 1.08. I've seen values lower and higher than that, and will change due to many factors.

Perhaps your partners like to be conservative...but with double the total volume...do they have the same fill fraction?

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BioSHA YaBB Newbies Offline I love Water and Wastewater.com Posts: 4 Gender: Company or Organization: WWTP company	Re: Temperature effects on MBBR design Reply #4 - Jun 12^th, 2012, 3:09pm Hello Descus. Even with small variations in the 1.08 factors, doubling the volume shouldn't happen. And, yes, we use the same fill ratio, 50 %.
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Ashoori

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Re: Temperature effects on MBBR design
Reply #5 - Jun 14^th, 2012, 1:11am

Hi BioSha
Is the Do in aeration tank the same? for example 6 mg/l?
The total HRT for your design is 2.76 hr and for your partnet total HRT is 5.4 hr.
According to increasing solubility of o2 in water in cold weather I think HRT 5.4 hr is too high.
(If you could find the right answer, please share it.)
Regards.
Ashoori

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BioSHA

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Re: Temperature effects on MBBR design
Reply #6 - Jun 14^th, 2012, 2:12am

Hello Ashoori.

Yes.
We also use the same DO level in the water.

I am now in a discussion with the group I am titling as our "designing partner". Everything seems to be due to thepossible lowest temperature of the influent wastewater of 4 degrees (they call it "extremely" low temperature) which is quite common in the northern countries.

The purpose with my opening post is nevertheless reached - a confirmation from you guys that my design is correct. Now the energy is focused on the convincing process towards our designing partner.

I have really appreciated your input, guys.

WR
S

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Bhagya

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Re: Temperature effects on MBBR design
Reply #7 - Jun 15^th, 2012, 7:12am

Hi Bioshah,

I assume that BOD_dim is the filtered BOD and NOT Total BOD. You will get double the reactor volume, if you design with the inlet total BOD.

Hope 600m2/m3 is the protected surface area and not the total area.

If 70 kg/d of BOD for a flow 400 m3/d will correspond to 175 mg/l and 70% removal means the outlet will have 52.5 mg/l BOD. Are you using this as a roughing reactor?

Rgds

Bhagya

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Ashoori Ex Member	Re: Temperature effects on MBBR design Reply #8 - Jun 15^th, 2012, 2:07pm Hi Biosha I`m so glad to see you`re in your way. I`ve learned so many things. thank all. Regards Ashoori
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JB

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Re: Temperature effects on MBBR design
Reply #9 - Jun 26^th, 2012, 2:08pm

Dear BioSHA

Following is the formula for determination of tank volume.

V=Y*Q*θ_c ((S_0-S))/([1+(k_d*θ_c ) ]*X)

Temperature is no way connected to determine MBBR basin volume, though it is one of the important factor that has to be considered 4to calculate SOR/ AOR/ surface saturation of dissolved Oxygen in clean water at the influent design temperature and basin elevation and temperature correction factor.

Hope that you got the solution to your problem.

JB

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