Case example – analysis of energy consumption in iMBR

There are four major processes that consume energy in iMBR:

1) aeration for biological COD removal

2) aeration for membrane scouring

3) permeate suction

4) wastewater pumping and mixed liquor recycle

In this section, calculation of SED will be demonstrated for an imaginary iMBR treating municipal wastewater. Fig. 1 shows the flow diagram of the plant and the following are all the process parameters required for the energy demand estimation.


Q         : average wastewater flow rate (3,600 m3/d or 0.0417m3/s)

S0        : influent COD (350 mg/L or 0.35kg/m3)

STKN,0  : influent TKN (60 mg/L or 0.06kg/m3)

SNO3,0  : influent NO3-N (3 mg/L or 0.003kg/m3)


Se        : effluent COD (10 mg/L or 0.01kg/m3)

STKN,e   : influent TKN ( 1 mg/L or 0.001kg/m3)

SNO3,e  : influent NO3-N (10 mg/L or 0.01kg/m3)


SRT     : solids retention time (20 days)

Yobs    : observed biosolids yield (0.358 g MLSS/g COD based on Macomber’s equaion in Fig. 1 elsewhere)

iXB       : nitrogen content in biosolids (0.086 mgN/mgMLSS, Henze, 1987)

λ          : ration of COD to MLSS (1.1 g COD/g MLSS)

X0        : MLSS in aeration tank (10 g/L)

Process condition

Am       : membrane surface area (9,000 m2)

DO       : dissolved oxygen in aeration tank (2 mg/L)

HF        : average water head required to pump raw wastewater to anoxic tank (4 m H2O)

HS           : submergence of scouring air nozzle (2.5 m H2O)

HL,z       : head loss for scouring air (1.0 m H2O)

Hb        : submergence of fine bubble diffusers (4.5 m H2O)

HL,b      : head loss for biological air (0.5 m H2O)

Jnet       : net flux (25LMH or 6.94×10-6 m/s)

Qair,s   : scouring air flow (54 Nm3/min or 0.9 Nm3/s)

QIR       : internal recycle, 3Q (10,800 m3/d or 0.125 m3/s)

Qr         : flow rate to membrane tank, 5Q (18,000 m3/d or 0.208 m3/s)

T           : water temperature (25 oC)

eB         : blower efficiency (0.7)

eP            : pump efficiency (0.3 for permeate, 0.4 for mixed liquor recycle, 0.6 for wastewater pumping)

eM           : motor efficiency (0.7 for permeate, 0.9 for mixed liquor recycle and wastewater pumping)

recycleFig. 1. Flow diagram of typical iMBR with anoxic tank

© Seong Hoon Yoon