Water and Wastewater.com Help Forums - Blower Design for MBBR

Gustavo Duarte

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Blower Design for MBBR
May 23^rd, 2012, 1:08pm

Friends,

I'm working on a basic worksheet for a MBBR design. As it's a "new" technology, many information in the books does not seem to match with the reality of the process, so it has been a challenging task.

As part of the work, I'm working on a correlation to determine the amount of air needed to achieve BOD removal and nitrification in a MBBR process, to size the needed blower to the job. I got some results, but I'd like to compare with the blower design flow rates used in real plants.

The basic input information are:
Q = 2000 m3/day
BOD = 500 mg/L (goal: 30 mg/L)
NTK = 15 mg/L (goal: 1 mg/L)
Dissolved O2 = 2 mg/L
O2 Dissolution Efficiency = 0,3 (is it a good value?)
T = 36ºC
F/M = 0,15 kg BOD/ kg VSS . d
Filling Ratio: 40%
Carrier Area: 600 m2/m3
Tank Volume: 1300 m3

If you need more information, let me know.

Regards!! Wink

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Regards,
Gustavo Duarte

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Jeff Naumann God Member Offline I love Water and Wastewater.com Posts: 1133 Torrance, California Gender: Company or Organization: Jeff Naumann & Associates	Re: Blower Design for MBBR Reply #1 - May 23^rd, 2012, 5:54pm How deep will the aeration tank(s) be? The blower output is greatly effected by water depth. This will also help choosing what type of blower will be needed.
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Liang 1957

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Re: Blower Design for MBBR
Reply #2 - May 23^rd, 2012, 8:02pm

The calculation of SOTR would be the same as activated sludge process. However the oxygen transfer efficiency depends on water depth, diffuse type and bubbles (coarse or fine), DO setpoint, type of media and media fill % etc. Please keep in mind that the air supply for MBBR process may not be determined by oxygen demand. It is quite often determined by providing sufficient mix of the media.

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Tom Keenan - nesa

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Re: Blower Design for MBBR
Reply #3 - May 24^th, 2012, 4:18am

The geometry of the tank, (particularly as it relates to water depth), will have a significant effect on the volume of air needed, particularly as air is to be used both for mixing and aeration. It is not unusual to find that more air is needed for mixing than is required for aeration.
When assessing the SOTR you should also be aware that temperature, (in you case 36ºC), is very high.

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Gustavo Duarte

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Re: Blower Design for MBBR
Reply #4 - May 24^th, 2012, 7:59am

Hey guys!

Thank you all for the feedback!

I was designing the blower by the Oxygen demand because I've read in an article that if you design this way, surely it will attend the media mixing. If it's not true, which design basis should I use? Can I calculate by the oxygen demand and insert a correction factor (x1.2 or x1.5...)?

Concerning the tank depth, I made this variable as an input. I was working with 10 meters (12,7 meters of diameter), I guess it's a good value. The media I'm assuming would have 600 m2/m3 (like AnoxKaldness K3, for example).

The temperature of 36ºC is just a conservative value, I agree that it's high (remember that I'm assuming the plant is in Brazil - very hot! Cool

). I've read that the limit for BOD removal and nitrification is something around 40ºC.

I just wanna have an idea of the blower flow rates that is generally used in MBBR systems similar to the one I'm working in.

Regards!

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Regards,
Gustavo Duarte

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Tom Keenan - nesa God Member Offline Environmental Consultant - contact info@nesa.ie Posts: 2103 Gender: Company or Organization: nesa environmental consultants	Re: Blower Design for MBBR Reply #5 - May 24^th, 2012, 8:03am There really is no "factor" that you can apply to ensure that air flow for Oxygen is converted to air flow for mixing, or vice versa. You simply have to do the calculations to ensure that the volume of air supplied is adequate for both.
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sherry250798

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Re: Blower Design for MBBR
Reply #6 - May 27^th, 2012, 5:57am

Though Higher depth of submergence will yield higher SOTE theoritically, but, you will have to choose the right depth where you get optimum SOTE.

Oftentimes, choice is between higher head for blower with lower air consumption versus medium head and slightly higher air flow. The call is to see what costs less and easy to maintian and also running cost.

I would not go for higher than 6 mSWD

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Liang 1957

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Re: Blower Design for MBBR
Reply #7 - May 29^th, 2012, 8:50pm

MBBR always requires a coarse bubble diffuser and uneven air distribution to make the carriers moving in the reactor. SOTE and air mixing is mainly impacted by the number and size of holes (orifices) on each diffuser, the number and layout of the diffusers when SOTR, water depth and temperature has determined.

As Tom said there is no “factor” you can apply. You have to get back to the diffuser supplier to find out typical figure of SOTE and air mixing from the specific diffusers used.

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