## 5 The immersed membrane bioreactor (iMBR) process

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Let's look at the components of an immersed membrane bioreactor, or iMBR; the immersed MBR is a type of MBR where the membrane is immersed in a tank, rather than sitting outside of it.

Watch Video 5 in which Simon describes the iMBR flowsheet − the sequence of individual unit operations which make up the complete iMBR wastewater treatment scheme. Then answer the questions that follow.

Video 5 The iMBR flowsheetVideo player: 5a%20iMBR.mp4

Transcript: https://www.open.edu/openlearncreate/mod/page/view.php?id=161928

Question 11:

Where is energy used in this flowsheet? [HINT: there are five places in total]

We need to calculate the SEC (E') in kWh/m3 for the individual energy-consuming operations in this flow sheet. Both the membrane tank and the biological tank use aeration, so there are equations for these two operations which determine the amount of air needed. Then there are equations which determined energy from liquid flow and pressure − exactly as in Section 4.

These equations are given below, and they are also listed in the Equation Sheet (314.8 KB) ('Ctrl click' to open in a new window) along with all symbols and appropriate guideline (or base) values for some of the parameters.

Specific aeration energy consumption for membrane scouring,  kWh/Nm3 air, E'a,m

0.011/ԑ

Specific aeration energy consumption for membrane scouring, kWh/m3 permeate, Ea,m

E'a,m Q'amԑ

Oxygen demand for biological processing, g/m3O2

0.67 COD, COD in mg/L

Specific aeration demand for biological processing, Nm3air/m3permeate, Q'a,b

0.0233 x O2

Specific aeration energy consumption for biological processing, kWh/Nm3 air, E'a,b

0.013/ԑ

Specific aeration energy consumption for biological processing, kWh/m3 permeate, Ea,b

E'a,b Q'ab

Specific energy consumption for sludge pumping & stirring, kWh/mpermeate, Es

0.032/ԑ

Specific energy consumption for permeate pumping, kWh/m3 permeate, Ep

(P + Ploss,filt)/(36 ԑ)

Total specific energy consumption of MBR, kWh/m3 permeate, EMBR

(Ea,m + Ea,b + Es + Ep + Eci)/R

Question 12:

Based on the calculated data from Section 4, determine the specific energy consumption Ea,m for the membrane air scour.

Question 13:

Calculate the oxygen demand and so the specific aeration demand (Q'a,b) and then the specific aeration energy consumption Ea,b for the process (biological) tank aeration.

Question 14:

Calculate the energy for (a) pumping and stirring the sludge, and for (b) pumping the permeate through the membrane.

Question 15:

Determine the total SEC for the MBR, based on the feed flow (NB: the feed flow is the retentate flow/recovery).

Now you've calculated the specific energy consumption of an iMBR, it's time to do the same thing for the reverse osmosis (RO) process.

You can now move to Section 6 Components of the reverse osmosis process